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Oune 10, 1992
Memorandum for Record
Subject: SOSUS SYSTEM - Surge Protectors
INTRODUCTION————^— _._.
High Voltage (H.V.) carbon block and gas discharge protectors are used throughoutthe SOSUS SYSTEM SB/SD-C/FDS Front-End cable shore equipment Theseprotectors are utilized in the various High Voltage Power Plants (HVPP), the PowerSeparation Filter (PSF) cabinets and in the Current Protection Panels (CPP) asdeployed since the 1960 time frame. Many of these protectors have now failed inplace, have operated as intended and been replaced or they have been declaredManufacturer Discontinued (M.D.) by WECO/AT&T over the years. Any protectorfailure or fault has always been considered a very serious event and was immediatelyinvestigated for resolution.
Under certain conditions, the possibility exists that very high potentials could occurbetween the various ground systems interconnected in the HVPP's, PSF's and CPP's.These conditions are:
1. Lightening discharges near the buried cable patch that couple into thesystem.
2. A sudden break in the Ocean Ground (O.G.) cable while the HVPP isoperational.
3. A sudden break in the ocean cable coaxial outer or inner conductor orreturn tape conductor.
4. Loss of current regulation and safety controls in the HVPP.
5. Failed components, particularly current shunts, and loose wire connections.
The purpose of the various protectors deployed is to minimize personnel andequipment damage when these faults occur.
This memo is part of a series, related to the SOSUS Front-End, that documentmodifications implemented over a 18 year time span. Many of the protectors deployedhave been replaced and/or are M.D. and will need to be addressed in the future. This
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memo is divided into six parts. In view of the fact that these parts are considerable, abrief listing could help the reader select topics of interest. Topics that are addressedin this historical memo include:
Part 1 Protector Deployment2 Protector Application3 G840324 CPP Design4 Gas Tube Protectors5 Carbon Block Protectors6 Long Term Maintenance Concerns
This technical information is intended to facilitate future repairs, provide additionalinsight and to support future M.D. studies. The information contained herein is basedupon numerous MER's, field reports, M.D. activity, problems resolution, and studiesby the author conducted over a long time period. The contents of this memo areintended to supplement the technical manuals but all AT&T CO manufacturingdrawings are still considered proprietary. This work was documented as part ofN00039-92-C-0003, the FY'92 Sea & Shore Contract, Task 4.08 Investigation of M.D.equipment.
PART 1 PROTECTOR DEPLOYMENT
All of the various protectors used in the SB/SD-C/FDS Front-End's are AT&T/WECOKS type or apparatus coded devices. These codes were not specifically designed andmanufactured for use in the SOSUS systems. They were designed for use in theformer BELL SYSTEM commercial telephone circuits and all manufacturing drawingsare considered as AT&T Proprietary Information. This memo does not address thenumerous semiconductor circuit protectors such as ZENERS, MOV's andTRANSORB's or fuses/circuit breakers, etc., used in the SB/SD-C/FDS andMULTIPAIR cable systems. This memo, through illustrative examples, functionaldescription, electrical characteristics, brief operating theory, and simplified block andpictorial schematics, is intended to address only the SPARK GAP (CARBONBLOCK) and GAS TUBE type of protectors used. The following devices arediscussed in detail:
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CODE
118A123A1A123A1B123A1EKS-16169L2458C204AF-52571125EW126A1G126A1J126A1M
TYPE VOLTAGE
CARBONCARBONCARBONCARBONCARBONGAS (ARGON)GAS (ARGON)GAS (ARGON)GAS (ARGON)CARBONCARBONCARBON
3500V500V800V
1250V500V60V60V70V
500V3000V5500V8500V
NOTES
OLD 99A TYPE2B2A INSERT (2)2B2B INSERT (2)2B2E INSERT (2)
*RADIUM BROMIDE*AMERICIUM (AM241)*BARIUM BROMIDE331RL INSERT (2)
*RADIO ACTIVE GAS ADDED TO INITIATE IONIZATION
These devices are utilized in the following HVPP, PSF and CPP application:
SB SYSTEM (PSF is P/O HVPP)
A. GA11628AHVPPVI F-52571
PI
P2
123A1B
123A1A
Shunt protector across CR1, CR2, SHI,SH3 and SH4 from Ocean Ground (G3)to -H.V. BUS
PSF return tape enclosure to BuildingGround (G2)
Ocean Ground to Building Ground
It should be noted that some older HVPP's may utilize the F-51107 tubein place of the F-52571 and the 11 IB Protector in place of the 123A1B.The former devices were M.D.
B. KS19856 CPP
P3 118A Cable armor to Building Ground
PI & P2 KS-16169L2 Building Ground to Ocean Ground
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C. KS-20806
PI
P2 to P8
CPP (Sites 2100, 3100)
123A1A Building Ground to Ocean Ground
118A
SD-C SYSTEM
A. GF44812 HVPP
SGI
SG2
SG3.1&3.2
SG4
SG5
SGI
SG2
B. GS71802
FlF2F3
126A1M
126A1M
126A1G126A1J126A1M
123A1A
123A1A
123A1A
123A1E
PSF
123A1A123A1A123A1A
Cable armor to Building Ground (sixcable systems and one G3 cable)
P/O GF44814 Converter, 8500 VCurrent Regulator 1 protector
P/O GF44814 Converter, 8500 VCurrent Regulator 2 protector
X Option, 3000 VY Option, 5500 VZ Option, 8500 VConverter output protector shutdown
Converter cabinet, across shunts R63,R64 protection
Converter cabinet +H.V. BUS to FrameGround
P/O GF44815 Load Transfer, OceanGround to Frame Ground
P/O GF44815, Resistor Load BankProtection to Frame Ground
PSF shield to Frame GroundOcean Ground to Frame GroundCFLTS to Frame Ground
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C. KS20405 CPP (G644096 at sites 6300, 1600)
PI 123A1ASGI to 7 118A
Ocean Ground to Frame GroundCable armor to Frame Ground
FDS/UWS
A. G840324
PISGI to 7
B. J86929A
SG801
SG801
CPP
125EW118A
FDS/UWS HVPP
123
123
Ocean Ground to Frame GroundCable armor to Frame Ground
+H.V. to Frame Ground123 fuseless station protector with 365type inserts. Til Industries, Inc.Same as SG801
The 123 protector from Til Industries, Inc. is not addressed in this memo. as it is a commercial item.
PART 2 PROTECTOR APPLICATIONS
A. SD-C SYSTEMS
Under certain conditions, the possibility exists that high potentials couldoccur between the three ground systems in the HVPP, PSF and CPPcabinets. These conditions are (1) lightning discharges near the cable pathand (2) a sudden break in the Ocean Ground cable while the cable powerplant is in operation, and (3) a sudden break in the coaxial cable outerconductor or return tape conductor, and (4) component failure in the H.V.current path. Surges in G3 (Ocean Ground) may also occur with asudden, total loss of H.V. cable power. A break in the cable will alsocause the potential of the submarine cable return tape or O.G. to riserelative to Building Ground. To limit these voltages, 123AlA type carbonprotector blocks are connected between the three ground systems. Theseprotectors arc over at approximately 500 volts and immediately drop thevoltage to a much lower value. It should be noted that failed 123A typeprotectors may become permanently shorted and could cause artifacts.Others will partially fail due to oxidation or corrosion. Most will fail as ashort and others will only partially conduct. The 123 type protectors are
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unique from the other spark gaps in that they permanently become shortedupon firing one time. Slight arcing may not necessarily cause a permanentshort.
The H.V. Dummy Load has additional overvoltage protection in theGF44815 Load Transfer Cabinet. The SG2 protector is used to protect thecircuit should the TEST LOAD VOLTAGE ADJUST FINE potentiometer(R15) open. The SG2 (123A1E) protector is designed to fire atapproximately 1200 V dc, thus preventing a high direct current voltagefrom appearing at the Test Load Control leads. The SGI spark gap(123A1A) protector is used to prevent the (G3) Ocean Ground fromfloating too high above the (G2) Building Ground bus. The SGI isdesigned to fire at approximately 500 volts. Leakage in these devices willaffect the test load current and voltage readings, and fault resolution canbecome a challenge.
The Ocean (sea) Ground (G3) bus in the LOAD TRANSFER BAY alsohas a bank of low impedance R.F. coupling capacitors to Frame Ground.Ten Sprague .47 pF capacitors are connected in parallel to shunt all powerline, 20 kHz and R.F. frequencies to ground (G2) at this point. These tencapacitors C14.1 thru C14.10 or Sprague 196P474910S4 type capacitorsare rated at 600 V dc. They are of an extended paper foil construction,selected for extremely low direct current leakage. Also, located at thisjunction in the O.G. (G3) bus is an AT&T 123A1A Protector. Thisprotector (SG2) is rated for Ocean Ground (O.G.) to arc-over at 500 V dcto protect the HVPP from a sudden "OPEN" in the O.G. path to the PSF.It should be noted the CPP, PSF and each Converter also have the123A1A protector from O.G. (G3) to F.G. (G2).
Experience has shown that any differences in the ground return cablecurrent meter readings (130 mA dc) in the HVPP and the CPP (Ref. I)may be due to failure in these components. It is recommended to suspectin the following order:
1. Shunts in HVPP & CPP2. 123A1A Protector Leakage (HVPP/PSF/CPP)3. Capacitor (C14) Leakage (HVPP)4. Capacitor C7 & C8 Leakage (PSF)5. Current Meter Calibration or Faults6. Ocean Ground Connections
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Although theoretically close to earth potential, extreme caution should beexercised when working on any portion of the Ocean Ground (G3).Always short the G3 system to G2 with the shorting switch located in theCurrent Protection Panel prior to working on the Ocean Ground. Asuitable shorting strap connected from G2 to G3, installed in theimmediate fault area, would also be advised when working on the 123A1type protectors.
The 123A1A protectors have a small, fixed, gap set for the 500 V dcbreakdown level. Due to age and corrosion, this gap may only partiallyclose and units have also been replaced for current leakage problems. Thegap in the 123A1B protector is set at 800 V dc and the 123A1E is set at1200 V dc. Very abnormal CPP and HVPP meter readings will resultfrom a partially fired protector. Design and operational details of the123 A type protector will be discussed later in this memo.
Each Current Regulator 1 and 2 in the GF44814 Converter cabinet isprotected with 126A1M 8500 V spark gaps and its associated circuitry.Each output Current Regulator (CR) circuit is provided with a spark gaptype protector circuit comprised of spark gap, SGI, resistors R5.1, 5.2 andR6.1, 6.2, and high voltage relay PS1 for output CR1. Again, CR2 hasidentical circuitry. If the voltage developed across the regulator exceedsthe firing voltage of SGI (8500 to 8900 volts) the protector fires,developing the necessary voltage across the lower divider resistance, R6.1,6.2, to operate relay PS1. Resistors R5.1, 5.2 and R6.1, 6.2 also serve tolimit the maximum current through the spark gap protector. Operation ofrelay PS 1 actuates the protector alarm and shutdown circuits which will bedescribed in Appendix A and B.
\-SThe Converter cabinet protector network consists of two 126A1 type sparkgap type protectors SG3.1 and SG3.2 connected in parallel, resistorsR24.1, 24.2 and R25.1, 25.2, and high voltage relay PS3. Parallelconnection is for reliability reasons only. This circuit functions exactly asdoes the Current Regulator protector circuit, operating relay PS3 when aConverter overvoltage condition exists. Spark gaps SG3.1 and SG3.2 aswell as resistor R24.1, 24.2 are chosen according to options X, Y, Z onthe Converters output voltage. Spark gaps SG3.1 and SG3.2 areconnected in parallel to provide redundancy so that the PS 3 relay isoperated whenever the Converter output voltage exceeds the firingpotential of either protector. Operation of relay PS3 actuates protectoralarm and shutdown circuits which will be described separately in
Appendix A. Spark gaps SG3.1, SG3.2 will fire at the following voltagesdependent upon the option chosen:
OPTION FIRING VOLTAGE RANGE (VOLTS)
X 2900 - 3200Y 5700 - 6000Z 8500 - 8900
Spark gap SG4 (123A1A) prevents excessive voltage from beingdeveloped across the cable current ground return meter and recorder (itfires at approximately 500 volts). Spark gap SG5 (123A1A) prevents thepoint to which it is connected from rising more than 500 volts above theFrame Ground.
The one GAS TUBE protector used in the SD-C SYSTEM is circuitapplication VI in the GS71850 Impedance Matching Network of the PSFcabinet. This radioactive tube is designed for arcing at a low voltage(70 V dc), high current (1200 A) and a very fast reaction time (< 2 ps).The tube is intended to protect the 75 ohm R.F. transmission path fromthe PSF to the DEMUX system from any catastrophic fault. Designdetails of the GAS TUBE will be addressed later in this memo.
B. SB SYSTEM HVPP
In the SB system the PSF is an integral part of the HVPP. In the HVPPthree separate ground circuits are provided, namely Building Ground,Ocean Ground, and return tape conductor. The Building Ground isconnected to the frameworks, pullout units, shield cans of the pottedapparatus that are grounded on the circuit, the control battery positiveleads, and one side of each alternating current supply at the source. Thereturn tape is the outer conductor on the coaxial cable. The OceanGround is used for the negative (-H.V.) metallic ground return circuitcommon to the direct current cable supplies. The only 123A1A protectorused is to limit any surges in O.G. to F.G. to 500 V dc. If the 123A1Afires or fails in place, a permanent connection will result. Partial failureswill be very disruptive in the cable current return path readings andartifacts may result.
A gas tube, (VI) F-52571 is connected from the negative Regulator output(-HV BUS) directly to Ocean Ground. This tube is normallynonconducting but if an open occurs in the normal ground path through
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the various shunts the tube will fire at between 70 and 100 volts and willsustain at about 10 volts. Thus, preventing loss of cable current and theconsequent appearance on the low voltage apparatus and wiring up to3000 volts from the positive regulator supplies.
With the tube conducting, the (CABLE CURRENT METER) in theGround unit, and the (CABLE CURRENT) recorder will read either zeroor less than normal current. A minor audible alarm will occur togetherwith lighted lamps (CABLE ALARM CURRENT) and (RELAY TBL ORALT FUSE ALM). If this occurs, the circuits should be repaired withoutdelay. The first step should be to ground the (NEGATIVE) bus with atemporary jumper lead to the framework. This should extinguish the glowdischarge in the gas tube. After repairing the faulty wiring or apparatus,remove the jumper. If the gas tube does not fire again and the metersread properly, the trouble has been corrected.
PART 3 CPP DESIGN AND APPLICATION
Every SOSUS coaxial cable system shore station utilizes a Current Protection Panel.All of the panels are very similar in design and function. The various CPP's aredeployed as follows:
UNIT SITES CAPACITY
KS19856 SB SITES 1 CABLE, 285 mAKS20806 SB SITES 2100, 3100 6 CABLES, 285 mAKS20405 SD-C SITES 7100, 6200 6 CABLES, 160 mA
4400, 139WG644096 SD-C SITES 6300, 1600 6 CABLES, 160 mAG840324-l,2 FDS/UWS SITES 1, A, B -1, 6 CABLES, 300 mA
-2, 3 CABLES, 300 mA
All of the above units were originally designed for use with the BELL SYSTEM SB,SD, SF, SG and SL commercial ocean cable telephone systems. Design changesevolved due to M.D. components, shunts, meters, protectors and switches and tochanges in system cable current. A general description of the CPP's follows withexceptions noted for the G840324 unit used in the FDS/UWS system. Details of theFDS/UWS CPP are contained in drawing G840324 and in simplified form in Figures1, 2 and 3.
The purpose of the CPP panel is to detect faults in the Ocean Ground to power baycurrent path in the SB, SD, SF, SG and SL Ocean Cable Systems. It is intended for
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use in terminals employing a single Ocean Ground (G3) for returning system currentfrom a maximum of six communication systems, none of which has a system currentexceeding 300 milliamperes. The panel is housed in a metal cabinet and consists of ascaled system current meter, a Building Ground to Ocean Ground leakage meter,polarity and system selector switches, and seven detachable aluminum boxescontaining a 118A lightning protector. Six of the boxes, intended for use in groundinglightning surges on a similar number of armored communications cables, contain anoise suppression capacitor. The remaining box, used for grounding lightning surgeson the armored Ocean Ground cable, has no capacitor. The KS19856 CPP is intendedfor only one cable system and the G840324 CPP has no polarity switch. All unitshave a shorting interlock switch (O.G. to F.G.) that must be closed in order to exposethe O.G. BUS and SHUNT assemblies. The large cabinet is sealed, locked and wallshock mounted.
The CPP also provides the means for detecting a partial or complete diversion ofsystem return current from the intended Ocean Ground path. These conditions areindicated by a significant difference in reading between the ground return currentmeter in the HVPP and the system current meter in the CPP. A leakage current meterbetween the Ocean Ground and Building Ground provides the facility to check theexistence of faults in the Ocean Ground to HVPP path. The panel is intended for usein SB, SD, SF, SG and SL Ocean Cable Systems having terminals employing a singleOcean Ground (G3) for returning system current from a maximum of sixcommunication systems. None of these cables will have a system current exceeding300 milliamperes. The G840324 CPP also has a voltage meter to measure differencesof up to ±15 V dc between O.G. and F.G. The meter is protected with back-to-backZENER diodes rated at 15 V dc. Nominal O.G. to F.G. voltages should be in the 2-3volt range.
All systems contain a 1 ohm, 20 watt shunt in series with the Ocean Ground returnand its respective power supply. Connection from the shunt to the appropriate scaleon the system current meter is made through the proper deck and position on thesystem selector switch. A shorting switch which connects Building Ground to OceanGround is provided for use when shunt repair or replacement is necessary. A 123A1Aprotector is connected between Building Ground and Ocean Ground to provide aground path for lightning surges entering the cabinet on the Building Ground bus. TheG840324 CPP uses a 125EW protector in this application.
The G840324 CPP has a special bracket mounted on each of the six shunts. Thisbracket enables replacement of a faulty shunt without shutting the system down.
The G840324 CPP is a FDS/UWS non-developmental item that provides voltage andcurrent metering of the Ocean Ground cables and transient protection of the Ocean
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Ground cables and power/signal cables. It has the following operational interfaces andfunctions. (REF. 2).
Number ofOperational Interfaces Interfaces
AWG #6 stranded copper wire to the armor of the system cables. 6Wire shall be less than 50 feet long.
AWG #6 stranded copper wire to the armor of the Ocean Ground cable. 1Wire shall be less than 50 feet long.
AWG #6 stranded copper wire of appropriate coaxial cableto the Ocean Ground (G3).
Appropriate coaxial cable to the HVPS. 6#2 AWG stranded copper wire to Building Ground (G2). 1Wall connection brackets1.37-1.39 inch openings for conduit connections and cable entry of all cables exceptthe Ocean Ground cables which have a single 2.5 inch opening.
Functions
The CPP provides transient protection to the armor wires of the Ocean Ground cableand the power/signal cables as follows:
3500 volt breakdown devices between armor wire connections and G2 ground.
A 500 volt breakdown device connected between G2 and G3 grounds.
The CPP provides metering on the ground cables as follows:
DC leakage current between G2 and G3 grounds.±200 mA and ±2 A scales.The DC leakage current is measured by shorting the G3 ground to the G2Building Ground and measuring the resulting current
DC voltage between G2 and G3 grounds.±15 volt scale.Push to test meter.
DC system current on each system.200-300 mA scale.The current is selectively metered on individual Ocean Ground cables.
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PART 4 GAS PROTECTORS
The excellent reliability of the BELL SYSTEM sealed gas surge limiter (SGSL)devices has been long demonstrated by results of millions of devices deployed since1960. Gas protectors are used in the SOSUS system to protect personnel andequipment from high energy surges. The cables are charged normally in the 2000 to4000 V dc range. When a fault occurs a high energy ringing transient is initiated.Because of the high energy and high reliability required, SGSL devices are utilized.
The transient caused by a fault consists initially of a rapid rise in voltage V'=dv/dt.The gas protector is required to limit the voltage rise to limiting value VL. Theprotector then turns on to a low impedance. The voltage drops abruptly from VL to alow arc voltage VA. While in the arc mode a high current surge passes through theprotector. Calculated current discharge waveforms for the Bell System SB Cable,from (REF. 3), are given in Figure 4A. With V'^xlO'v/s, VL should not exceed2000 V.
For the SD-C LUSC application the objective is a maximum VL of 2100 V atV1=3Kl09v/s. The expected SD-C LUSC surge current waveform is given in Figure4B. Similar conditions were predicted for the older SB cable system (FIG 4A). Inthose portions of any cable system operating at more than about 2000 volts to ground,a fault resulting in the grounding of the center conductor produces sever electricaltransients. These transients propagate through several repeaters to either side of thefault before being attenuated to a safe level. If no protection was provided, damage toshore station components would be probable, and HVPP failure would be possible.
Two types of gas tubes were developed to provide the desired protection. Both typesare electrically symmetrical diode type gas tubes, designed to conduct current in eitherdirection. Both are of the cold cathode variety, requiring no power in the standbycondition. Cutaway views of the two tubes follow along with detailed technicaldescriptions.
A. 458C TUBE (SD-C/LUSC SYSTEM)
The 458C tube is bridged across the 75 to 46 ohm Z match transformer in theGS71850 unit of the SD-C/LUSC PSF. The 458C tube has two functions. These are:(1) in the event of a fault on the cable causing an abnormal current to flow throughthe PSF, the tube will fire and conduct the current, preventing damage to the DEMUXand to other parallel low-voltage components; and (2) if an PSF power path opens, therising voltage will fire the gas tube, holding the DEMUX circuit voltage at a safelevel. The cable voltage is then turned down by the HVPP sensing circuitry. The
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minimum firing voltage of the gas tube is set slightly above the maximum voltagerequired by the DEMUX circuitry for this operation so that the tube does not refire.
For surge protection service, the tube is designed to pass a charge of 0.6 coulomb at apeak current of 75 amperes in either direction. This provides a reasonable margin forthe maximum reverse surge which would occur in a near-shore repeater with a fault onthe shore side. It is also reasonable for the maximum forward surge which wouldoccur at the one-half voltage to ground point with a fault on the seaward side of thatrepeater. For a SD-C system of maximum length, the charge passed in either case isapproximately 0.5 coulomb (the charge stored in a 100 mF capacitor at 5 kV). Themagnitude of the peak surge current in the PSF circuit is less than 50 amperes undereither condition and well within the capability of the tube.
The tube has a nominal breakdown voltage of 60 volts, and being located inside thepower separation filters where the rate of rise of the transient voltage is relativelyslow, the voltage rises only a few tens of volts above breakdown before the tube fires.Glow condition is established within five microseconds at a tube drop of about 70volts. In less than 500 ms the cathode is heated sufficiently by ion bombardment tocause a transition to arc condition, giving a tube voltage drop of about 10 volts. Inthis mode, as an ionically heated cathode device, the tube can conduct the large surgetransient or the normal cable current as required. The power dissipation in the tube atnormal cable current is approximately 5 watts. Tube life in this condition is morethan 1000 hours, providing ample margin over the estimated maximum time requiredto replace a tube. As a surge protection device the tube can conduct more than 50maximum-energy surges without going out of firing voltage limits.
The fundamental characteristics and ratings are given in Table I.
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TABLE I
458C COLD CATHODE, GAS-FILLED ELECTRON TUBE (REF. 4)
Maximum ratings
average cathode current 5 mAsurge cathode current 1500 Acoulombic charge 1.5 millicoulombssurges 50 max.shelf life 20 years (min.)conducting life at 5 mA 200 hours (min.)ambient temperature -10 to +50°Cshock - 5 ms 50 g
Electrical data
breakdown voltage 60 Vsustaining voltage 10 Vbreakdown time -500 V 5 us max.breakdown time -4 kV/us 0.7 ps max.
The structural details of the 458A are shown in Fig. 5. The two identical cathanodesare mounted on a high-alumina ceramic disk, one on either side, with the cathanodesfacing each other through an aperture in the support disk.
Each cathanode is a square nickel cup with integral mounting tabs. The facingsurfaces are coated with a thin layer of emissive oxides of barium and strontium,activated during tube processing by means of a high-frequency discharge to developsuper-emissive cold cathodes. The "nutmeg grater" shaped perforations perform twofunctions: (1) the hollow cathode effect of the small depressions increases the emissionefficiency and life; and (2) they allow a visual observation, during testing, of the glowover the cathode surface to determine the uniformity of emission and cathodecoverage. A small boss is provided at each corner of the cathanode to limit andposition the contact area on the ceramic disk. This provides a leakage path of greaterthan 1000 megohms between the elements, even after the sputtering of the cathodematerial due to high-current arcs. A barium getter is used in all 458C tubes.
The gas filling in the 458C tube is 1 per cent argon and 99 per cent neon at 60 torrpressure. The plane-parallel electrode geometry at a 0.030-inch spacing gives a
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nominal breakdown voltage of 60 V and a sustaining voltage at 5 mA of 10 V. Onemicrocurie of radium bromide is used as a priming to insure sufficient initialionization for high-speed operation in the absence of light. The 204A tubes used inthe PSF's at sites 1600 and 6300 contains 1.1 microcuries of Americium (AM^j)isotope. The 204A tubes are very similar electrically and perform the same function.The radioactivity is required to ensure fast turn on when a fault occurs.
The 458A tube is bridged across the transmission path at the output of the PSF, justinside the power separation filters. The most severe voltage surge the tube is requiredto handle is that caused by a short circuit fault in the adjacent cable power path. Inthe higher voltage portions of the system this surge voltage may rise to a value ofmore than four kV in approximately one us. Since it is desirable to limit the voltageon many of the transmission path DEMUX components to less than 500 V, a very fasttube is required. The signal path tube is designed to fire in from 0.2 to 0.3 us on a4 kV per us transient, limiting the surge to the transmission path to a theoreticalmaximum of 800 V.
The charge shunted by the gas tube is a substantial portion of the charge stored in thehigh voltage capacitors of the PSF, and may be as much as 1.5 millicoulombs. Thedischarge is oscillatory in nature and lasts about 10 ps. The peak current through thetube on the first swing may be as high as 1200 A. These high currents are carried bythe tube in the metallic arc mode of conduction at a tube drop in the order of 10 V.
The ability of the tube to pass such surges is tested in a circuit equivalent to that in aPSF. The size of the capacitors is doubled, however, to insure an adequate testingmargin. In this test each tube is surged ten times in each direction with a totalintegrated charge of 4.5 millicoulombs and a peak current of 1800 A. The tube isconservatively rated to pass 50 maximum cable surges. In use in the PSF the tube isnot required to carry continuous current.
B. F-52571 TUBE (SB SYSTEM)
The F-52571 Gas Tube is referred to as a power bypass gas tube device (Fig. 6). Thetube application, previously described, requires that the SB cable return current(-H.V.) be continuous if any one of the 5 shunts should fail.
To protect against an open circuit in the return path, such as shunt failure, anadditional device is required to bypass the line H.V. current. This bypass must be ahigh resistance under normal operating conditions since any current taken by thisdevice will introduce meter errors. If an open circuit occurs, the bypass must carrythe full cable current. At full current, the voltage drop should be small to avoidexcessive localized power dissipation in the device. The device should recover when
16.
power is removed so that false operation by a transient condition will not permanentlybypass the shunts.
A gas diode, using an ionically heated cathode, has been used since the late 1950's tomeet these requirements. By making the breakdown voltage safely greater than thedrop across the shunt string, no power is taken by the tube under normal HVPPoperation. In the event of an open circuit in any shunt, the voltage across the tuberises and breakdown occurs. Full cable current is then passed through the gasdischarge. Removal of power from the cable allows the tube to deionize and recoverin the event of false triggering by transients. The cathode is a coil of tungsten wirecoated with a mixture of barium and strontium oxide. A cold cathode glow dischargeforms when the tube is first broken down. This discharge has a sustaining voltage ofthe order of 70 volts. The glow discharge initially covers the entire cathode area.Local heating occurs and some parts of the oxide coating begin to emit electronsthermionically. This local emission causes increased current density and furtherincreases the local heating. The discharge thus concentrates to a thermionic arccovering only a portion of the coil. The sustaining voltage is then on the order of 10volts.
Mechanically the tube was designed to minimize the possibility of a short circuitresulting from structural failure of tube parts. Fig. 6 shows the construction of thetube. The glass envelope and stem structure which had previously been developed forthe hot cathode repeater tubes were used as a starting point for the design. The anodeis a circular disk of nickel attached to two of the stem lead wires. To provide shockresistance the supporting stem leads are crossed and welded in the center. To protectagainst weld failure, a nickel sleeve is used at each end of the cathode coil. It iscrimped to hold the coil mechanically in place and then welded at the end forelectrical connection. At the end of the coil, as well as in all other places where it ispossible, a mechanical wrap is made in addition to spot welding. An additionalprecaution is taken by inserting an insulated molybdenum support rod through thecenter of the cathode coil. The filling gas is argon at a pressure of 10 mm Hg. Toprovide initial ionization, 1 microgram of radium in the form of radium bromide wasplaced on the inside of the tube envelope. All materials were procured in batches ofsufficient size to make the entire lot of tubes and carefully tested before beingapproved for use. The tubes were fabricated in small groups and a complete historywas kept of the processing of each lot. For detailed study of tube performance, anumber of electrical tests were made. These involved measurements of breakdownvoltage, operating voltage as a glow discharge at low current, current required to causethe transition to a thermionic arc, the time required at the cable current to causetransition to the low voltage arc, and the sustaining voltage at the full current.
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All tubes were aged by operating at 250 milliamperes on a schedule which included asequence of short on-off periods (2 min. on, 2 min. off) followed by periods ofcontinuous operation. A total of 150 starts and 300 hours of continuous operationwere used. Following this aging schedule the tubes were allowed to stabilize for afew days and then subjected to a 2-hour thermal treatment or pulse at 125°C. Special,close tolerance F-52571 tubes were used in SB cable repeaters. It was required thatno more than a few volts change in breakdown voltage occur during this thermal pulsebefore a tube was considered as a candidate for use in repeaters as a heater bypassprotector.
After aging and selection as candidates for repeaters, tubes were stored in a light-tightcan at 0°C. Measurements were made to assure stability of breakdown voltage andbreakdown time.
The quality of each group of 12 tubes was further checked by continuous and on-offcycling life tests. The fact that none of these tubes has failed on the cycling tests atless than 3,500 hours and 1,500 starts and no tube on continuous operation has failedat less than 4,200 hours gives assurance that system tubes will start once and operatefor the few hours necessary to repair a defective shunt. Long-term shelf tests ofrepresentative samples at 70°C and at 0°C give assurance of satisfactory behavior inthe system (Ref. 5).
C. 125EW GAS TUBE (FDS/UWS CPP)
The 123EW gas tube type protector is used in the G840324 FDS/USS CPP. Thisdevice functions as a replacement for the M.D. 123A1A protector previously used toprotect OG to FG surges above 500 V dc. Physically the unit is depicted in Fig. 12and consists of two 331RL gas tube devices.
A 331RL gas tube consists basically of a discharge gap between two metal electrodessealed in a ceramic or glass envelope containing an inert (Argon) gas or combinationof gases at reduced pressure. A discharge gap of given spacing will spark over in agas at reduced pressure on a considerably lower potential than at normal atmosphericpressure. The large gap spacing typically used in this gas tube greatly reduces thepossibility of the electrodes becoming permanently short circuited, or partiallyconducting as a major mode of failure in the 123A1A. When the gas tube is subjectedto a surge voltage exceeding its static breakdown voltage, (500 V) the gas will ionizeand form a conducting path across the discharge gap. The path will sustain at avoltage considerably lower than the static breakdown voltage. Removal of the voltagerestores the discharge gap to an open circuit condition. Two 331RL inserts compriseone 125EW unit as depicted in Fig. 12.
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The characteristics of this gas tube plus its higher price as compared to the old123A1A protector blocks indicate that gas tube application to HVPP facilities, shouldnot be done indiscriminately. Based on favorable reports of field experience with gastubes, it is strongly recommended that future cost studies be undertaken, especially inheavy lightning areas, to determine if substantial savings would accrue through use of125EW gas tubes to replace 123A1A carbon blocks. Studies have confirmed thatsubstantial savings have resulted from their use, especially in high lightning areas(Ref. 6). Specification of 125EW gas tubes may be considered in the following HVPPsituations:
(a) As substitutes for carbon block protectors at remote HVPP terminalswhere frequent interruptions caused by permanent grounding of the blockson lightning discharges create a maintenance problem.
(b) On long cable systems where requirements for low overall noise andcontinuity preclude use of carbon block protectors, and the large numberand remote location of protectors would create a maintenance problem ifcarbon blocks were used.
(c) At applications where frequent interruptions caused by permanentgrounding of carbon blocks on lightning discharges would create anexpensive maintenance problem.
(d) At existing (or planned) NAVFAC's where lightning exposure and/orintermittent power induction surges have caused (or are expected to cause)maintenance problems if carbon blocks were used.
(e) The 123A type protector housings are M.D. If the 2A2 type inserts(carbon) are M.D. in the future all 123A carbon protectors should bereplaced with 125EW type units.
Each 125EW protector used two AT&T 331RL type gas tubes permanently sealed intothe plastic protector block. Repairs or replacements of the 331RL type inserts are notpossible. Failed units of the 125EW requires an entire new protector.
The AT&T Technologies, Inc. 331RL gas tube protector provides substantially longerservice lifetime than 3-mil carbon block or earlier gas tube designs. The 331RL gastube will provide surge protection at voltage levels comparable to carbon blocks evenif the gas envelope should vent to the atmosphere. In addition, at the end of itsservice life, the mode of ultimate failure for the 331RL is a short circuit. The fail-safefeatures of the 331RL (when incorporated in its protector unit) make it unnecessary toplace carbon blocks or back-up gaps in parallel with the protector unit in the CPP.
19.
The 331RL gas tube is incorporated in the AT&T Technologies 125EW protector unitsto fit the appropriate protector wells. The operating characteristics of the 331RL gastube are shown as listed below:
OPERATING CHARACTERISTICSFOR 331RL ELECTRON (GAS) TUBE
CHARACTERISTIC VALUE
Direct Current Breakdown 315 Volts MeanVoltage 275 Volts Minimum
Time for Current Turn-Off* 150 Milliseconds Maximum
Surge Limiting Voltage t 550 Volts Typical
Insulation Resistance 100 Megohms Minimum
Time for device to clear momentary transient when device is exposed to150 volt, one ampere source capability (1 ohm/volt supply with 1 uFcapacitor across the tube).
tRate of rise: 100 volts/microsecond
The 321RL gas tube protector units are UL listed for use in UL listed customerterminal protectors manufactured by AT&T Technologies, Inc. The 123EW can beused as direct replacement for the 2A2A and 2B2A carbon block protector units,respectively. The 123EW contains the 331RL gas tube surge protectors and fusiblediscs and provides lightning and ac fault protection in the CPP. The gas tube ismounted in a drawn brass cap, threaded for insertion into 7/16-inch wells of all AT&TTechnologies multi-pair protectors, terminal blocks, and cable terminals. Typicalapplications for the 331RL units are the 125EW type single pair fused protector andother AT&T configurations.
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PART 5 CARBON BLOCK PROTECTORS
The carbon block protectors used in the SOSUS system are divided into three maingroups. They are:
1. ARC-OVER - One Time Operation (123A, KS16169L2)2. ARC-OVER - Multiple Firing (118A)3. ARC-OVER - Multiple Firing (Relay protector shutdown)(126A)
A. 123A TYPE PROTECTOR
The 123A type carbon block protectors are used throughout the SB/SD-C HVPP andPSF. Their circuit application and functions have been previously described. The123A types are as follows:
UNIT VOLTAGE INSERT (2) GAP
123A1A 500 V 2B2A .003 IN123A1B 800V 2B2B .006 IN123A1E 1250V 2B2E .010 IN
It should be noted that some older SB HVPP's may utilize a 111A protector in placeof the 123A1A. Each 123A protector consists of a base of insulating materialequipped with threaded studs and two protector inserts as listed above. When the123A1A protector is mounted in the PSF, special covers (No. 150B) must be ordered.The 123A is unique in that when arc-over occurs the protector insert element meltsand permanent closure occurs, i.e. a short circuit results. The insert must then bereplaced with a new unit.
In the SB and SD-C HVPP's, discharge devices called protector blocks (123A type)are essentially gaps which discharge in air. They are open circuit devices that pass nosignificant current at normal operating potentials. Protector blocks are normallyconnected to or closely associated with the protection of communication circuits,equipment, plant, and personnel. The devices consist of two small carbon electrodes(inserts) which provide a small air gap between a conductor and ground. Thearrangement consists of one block entirely of carbon and the other a carbon insert in aporcelain block. The carbon insert is held in place by a lead borate cement and isrecessed slightly below the bearing surface of the porcelain to provide the appropriategap spacing. The gap is formed when the larger carbon block is held against theporcelain bearing surface.
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Rectangular protector blocks have been in use much longer than the cylindrical type.Presently, all protection devices are designed to accommodate cylindrical blocks;consequently, rectangular blocks are obsolete. Since both types of protector blocksemploy flat surface carbon electrodes, their arc-over characteristics are similar. (Ref.6) If the potential between the conductors and ground across the carbon electrodesshould rise to the point where the arc-over rating of the gap is exceeded, an arc willbe established, grounding the line conductor (see Fig. 7 and Fig. 8). If the potentialrise is short-lived (such as is caused by a lightning strike), the arc-over will bequenched when the current in the conductor is reduced below approximately 50 mA,allowing the protector to return to its open circuit condition.
On longer steady-state discharges of considerable duration (cable faults), the leadborate cement will melt from heat produced by the arc, allowing the spring-loadedcarbon block to be moved into contact with the larger carbon block. This results inpermanent grounding of the conductor and provides a lower impedance path to ground.When the fault on the conductor is cleared, the carbon block insert must be replaced.In areas of heavy exposure, permanent grounding of blocks can present a maintenanceproblem of such proportions that special attention is required.
The IB-type cylindrical protector insert unit shown in Fig. 8 is now in common use.The cylindrical block assembly is inserted in a threaded metal cap which is screwedinto a well under spring loading. The well-type mounting provides moistureprotection. Figure 8 shows this type protector insert unit installed in fused andfuseless station protector mountings, respectively.
The 2B-type cylindrical protector block thermal shorting feature employs a fusible leadalloy pellet to provide metal-to-metal short-circuiting around the protector blocksunder conditions of high, continuous fault current flow. When the pellet melts, itallows the spring-loaded metal platform or metal cage (as applicable) to push bothcarbon blocks forward until the platform or cage contacts the metal shell or base(ground). This action forms a path capable of carrying steady state current in theorder of 30 amperes rms per protector unit.
Figure 8 shows the operating sequence for the 2B-type protector insert units,respectively. The thermal shorting feature prevents overheating damage to theprotector mountings and hastens operation of fusible elements if provided elsewhere inthe line (i.e., fuses, bridle wire, fuse cable). These fusible elements protect plant,personnel and avoid fire hazards. The different codes of each type of protector unitmay be identified by differences in cap shape or by letter marking on the cap. The 2Bprotector insert units are interchangeable. The 2B insert is 1/2 inch thread diameter.
22.
If melt down does not occur, the 123A1A units have a very long, proven operatinglife. The ability of a protector to discharge current without developing a permanentshort improves very rapidly with an increase in gap spacing, as may be noted from thecurve in Fig. 9. For example, widening the gap from 0.003 inch to 0.006 inch willincrease its duty life 4 to 5 times. For a given gap spacing, protector shorting isroughly a function of current magnitude and length of discharge time. Protectors willhandle relatively large lightning surge currents without permanent short circuitingbecause of the short discharge time, but on abnormal steady-state discharges, such asmay occur during a power fault, they become permanently shorted at rather lowdischarge values. This does not materially affect maintenance, however, becauseprotectors are not frequently exposed to abnormal steady-state potentials. When theyare, it is an indication of an abnormal plant condition that requires investigation.
A
For the protection of SOSUS terminal and switching center equipment where dischargecurrents are generally limited by considerable impedance, protector gaps have anominal spacing of 0.003 inch. This gap does not introduce excessive corrosion ormaintenance except in cases of exceptionally high exposure to humidity. For theprotection of other HVPP circuit, it is generally preferable from the protector blockmaintenance standpoint to employ 0.006 inch or 0.010 inch gaps which are capable ofdischarging much higher currents without becoming permanently short circuited. Mostpartial failures involve the 123A1A because of its smaller air gap (.003 IN.). Faultdiagnosis is very difficult with a partially failed insert as discussed previously. Somefailed units have exhibited a "holdover" characteristic to sustain arcing at a very lowvoltage.
When a discharge is once initiated in a protector gap, the discharge will sustain untilthe magnitude of the discharge voltage and current drops below the critical sustainingvalue of the protector. The signal potentials and currents in a communication circuitare normally well below the critical value; therefore, after the abnormal potential thatinitially operated the protectors dissipates, arcing in the gap will be extinguished.However, the protectors may not clear after the initiating surge has attenuated if asteady-state potential of appreciable magnitude is present. Such steady-state potentialsare characteristic for certain types of carrier systems where power for remote repeatersis transmitted over the communication conductors. Failure of a protector to clear, orto "hold over" as it is frequently called, ultimately results in permanent short-circuitingof the gap and operation of power fuses. Holdover is the continuing discharge ofcurrent across the air gap of a protector block after the initiating surge has passed andis dependent on the steady-state voltage, current, and air gap spacing.
Studies of the holdover characteristics of the commonly used 2B2-type cylindricalprotector blocks with 3-mil and 6-mil gaps, where current is limited by seriesresistance, have revealed the voltage-current relationship as shown in Fig. 10. Voltage
23.
is the open circuit voltage across the terminals of the protector; current is the shortcircuit current available at the protector terminals. The circuit design trend toward useof steady-state voltages in excess of 48 V dc has increased emphasis on theunderstanding and control of holdover. Since steady-state voltages and currents onOcean Ground must be held within certain limits for numerous design reasons, theinformation presented in Fig. 10 is of greater interest. Where steady-state voltages andcurrents exceed the critical value, the power source should include circuitry intendedto prevent holdover of the associated protector blocks.
B. KS16169L2 PROTECTOR
The KS16169L2 Spark Gap protector is used in the SB SYSTEM KS-19856 CPP.These low voltage (-50 V dc) protectors consist of a molded round phenol-plastic capincorporating a metal shell equipped with a pair of protector blocks. The KS16169L2unit consists of two inserts: a WECO 32A protector and a 33B protector. Thecompleted assembly is shown in Fig. 11. Upon failure these units should be replacedwith 125EW units.
These protectors are designed for use only with the KS-16170 protector mounting.The LIST 2 unit was designed for use in the commercial BELL SYSTEM SB and SDsubmarine cable shore stations. They provide for a high voltage and abnormal surgecurrent protection between Ocean Ground (G3) and Building Ground (G2) fields.
C. 126A1 PROTECTOR
The 126A1 Type spark gap protectors are used only in the SD-C HVPP. Each unitconsists of two large, curved carbon electrodes mounted on special electrodes. Theelectrodes are feed-though insulators assembled on a porcelain disc in a metal base.The unit is equipped with a glass dust cover which is threaded into a plastic base.The entire assembled unit is shown in Fig. 13. Terminals are arranged for H.V. leadsolder connections. In order to maintain the specified corona free levels of10,000 V dc, from terminal to terminal, threaded chrome metal caps are provided tocover the solder connections. Also, chrome corona dome nuts are used to cover thethreaded rods holding the carbon blocks in place.
The following factory settings are made:
UNIT GAP VOLTAGE
126A1G .025 2500-2800 V dc126A1J .055 5700-6000 V dc126A1M .085 3500-8900 V dc
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Special H.V. test equipment is required to properly set this gap in the factory. It is notpossible to repair a faulty 126A1 type protector in the field. The only known mode offailure has been crushed or broken glass covers or loose carbon blocks. Thermal changeswill cause the carbon blocks to become loose over a long time period. Arcing in the gapis a function primarily of the adjusted spacing. The temperature, pressure and humiditywill also have a minor affect.
The 126A1 type were only manufactured in the WECO-KY and BU plants. Units arenow only available from the AT&T-GC Department 1120 Engineering Model Shops. Thefollowing protrietary items comprise one 126A1 type protector (Fig. 14):
ITEM QTY
A-581462 Type Protector AssemblyA-581465 Requirements, testingA-581276 Plugging Compound ARP-17E800 Brass Cap, Rod 2P-17E801 Cap, Dome 2P-17E802 Cap, Lead 2P-17E803 Plate 1P-17E804 Block, Carbon 2P-17E805 Washer 2P-17E807 Cap, Fixture Assembly 1P-17E808 Cap, Fixture 1P-420690 Washer 2P-205653 Screw 2P-480346 Nut, HEX 2RM-651956 Insulator 2RM-781071 Dome Globe 1RM-6L12624 Epoxy Compound ARP460847 Washer 2Cork Sealing Gasket 1
D. 118A LIGHTENING PROTECTOR
The 118A protector is designed specifically as a high current lightening protector. Theprotector assembly is depicted in Fig. 15. Each unit consists essentially of three curvedcarbon blocks, having a .030 in. gap. The blocks are mounted on a porcelain base andenclosed in a shield can. One electrode is intended to be connected to frame ground andthe other two connected to the coaxial cable outer shield. The 118A has No. 8 gaugeinsulated wire leads to properly conduct lightening surges. The device is rated and testedat a 3500 V dc sparkover rating.
25.
The ability of this protector to prevent a large rise of potential in the CPP, reduces thestress on associated smaller 123A1 type units. The carbon blocks serve as excellent R.F.insulators of the cable shield, can conduct up to 10,000 A of surge current and block dccurrent for corrosion control. Due to its rugged, simple design no failure of 118A unitshave ever been experienced by the author. The complete assembly of the 118A protectoris describe in AT&T drawing A-777058.
All 118A devices are used in the various CPP's deployed. In the CPP all USA's areindividually enclosed in a metal shield box. This shielding is required due to theunpredictable high voltages and current associated with a lightening strike to the outercable shield. The cables are vulnerable only on the land link that could be up to a mile inlength at some SOSUS sites. Repairs are not possible on damaged units, hence, the entireassembly must be replaced.
PART 6 PROTECTOR MAINTENANCE/TESTING
Protector devices used in the SOSUS System are inherently very reliable, long lasting andmaintenance free. Long term (20 years) reliability is realized through very rigorousmanufacturing controls, inspection and testing. Field testing is not practical for the H.V.carbon block devices due to the high voltages involved. Appendix B details an approachfor testing of the 126A1 TYPE protectors. This test is recommended to be conductedonly by personnel familiar with the SD-C HVPP, its capabilities and to be very familiarwith safe H.V. testing procedures.
Testing of the lower voltage GAS TUBES is much safer and practical. The F-52571 tubeused in the SB HVPP is relatively easy to test. The test should be conducted at leastevery year as normal PMS checks. This test is detailed in the GA11628A InstallationTest Specification T-150-957 paragraph 3.03 in., Steps 1 to 8.
This procedure consists of: Turning down all Regulators and Switching to (MAN)control. Throw the (EMERGENCY CABLE SHORTING) switch to (FINAL). Afterchecking that the cable current and voltage are zero, pull out the Ground Unit.Disconnect the (LOAD +) terminal lead on the Recorder, (SH3) shunt Leave the unitpulled out so the gas tube (VI) is visible.
Slowly turn up Regulator 1 by turning its handwheel manually while watching the gastube. Observe that at some point a glow discharge occurs in the tube. Initially thisshould be a blue glow throughout the tube, later changing to a violet glow concentrated onthe cathode (small coiled element). The glow may shift along the length of the cathode atrandom. Leave the (CONTROL) switch at (MAN) and raise the output until the (V1-V2VOLTS) meter reads 300. Using the (CABLE CURRENT ADJUST FINE) control set thecable current to 225 mA and check that the (CABLE CURRENT METER) in the Ground
26.
unit and the (CABLE CURRENT) Recorder read zero. Connect a KS-14510 or equivalentvoltmeter temporarily across the gas tube at its terminals. Check that the reading does notexceed 15 volts.
The tube should now be operating in the arc discharge region as depicted in Fig. 16. Inorder to understand the stages of gas ionization, consider a gas filled tube such as theF-52571 with a thermionic type cathode. At low anode potentials, kinetic energy acquiredby the electrons is insufficient to ionize gas molecules by collision. The electron-molecule collisions are elastic. A negative space charge now exists at the cathode, andthe plate characteristic of the gas filled tube is similar to that of the space-charge-limitedvacuum diode (see Fig. 16). Transition regions are:
Electron Avalanche Region
As the anode potential of the gas filled tube is increased, ion pairs begin to be producedby electron impact. Now more electrons reach the anode than leave the cathode. Cathodeand anode currents are related by
L, = I0e~d (REE 7)
where L, is plate current, I0 is cathode current, d is anode-cathode separation, and a is thenumber of new electrons formed by one electron traveling a distance of one meter througha gas. Electron multiplication is known here an electron avalanche. In the electronavalanche region anode current increases rapidly with increased voltage until the platecharacteristic develops a very steep slope.
Normal-glow Region (Blue)
At the point where the plate characteristic develops a steep slope, the gas breaks down(150 volts) and the gas in the tube begins to glow. Photo emission and ion bombardmentof tube elements supplement electron-molecule collision in the body of the gas as a meansfor increasing production of electrons. The current increases and the voltage droprequired to sustain a given level of current decreases. This is the normal-glow region (70volts) where most gas tubes operate. The fact that the firing (avalanche) potential ishigher than the sustaining (normal-glow) potential accounts for the 30 per cent over-voltage required to fire this gas-filled voltage regulator tube.
Abnormal-glow Region (VIOLET)
27.
If the anode potential is increased far beyond even the electron avalanche region, the tubeenters the abnormal-glow region. This region (200 volts) is an unstable region ofrelatively high voltage drop and relatively low anode current. The abnormal-glow effecthas not been adequately explained. Perhaps photoionization at tube surfaces is a majorsource of electrons. This photoionization results in a great deal of ionization throughoutthe tube with much photon activity, although the resulting electrons add little to the anodecurrent
Arc Discharge Region
If the anode potential of a gas tube is increased above that which causes the abnormal-glow region, the gas-tube anode current concentrates itself in a single path, usually theshortest distance from cathode to anode, although existence of a sharp point may tend toconcentrate the current path elsewhere. The gas discharge is now very intense andcharacterized by low voltage (10 volts) and very high current. This is the arc dischargeregion of Fig. 16.
An arc can be struck by moving step by step through all the intermediate stages of anodevoltage, but it need not be struck in this manner. As anyone knows who has watchedlightning or laid his screwdriver across H.V. hot wires, an arc is provided across thefilaments. In the filamentary kind of arc, heavy current is forced to flow across afilamentary conducting path. The filament is consumed by the intense heat, but thecurrent continues as an arc if the conditions of gas pressure, temperature, and appliedanode voltage are all favorable. The filamentary arc seems to be the way a defectiveceramic tube socket breaks down. Gas leaks due to cracked glass seals are the onlyknown mode of failure in these tubes.
As mentioned previously, these BELL SYSTEM protectors are very rugged and reliable.No failure of the 118A devices have ever been experienced by the author. The 126A1TYPE protectors are prone to the following long term problems (Fig. 14):
1. Loose H.V. wires and connectors2. Loose corona dome nuts3. Loose carbon blocks4. Cracked glass domes
All of these problems are related to long-term thermal changes and stress. Repairs,obviously, should only be conducted with the HVPP turned off.
The most common protector failures are in the 123A1 type units as discussed previously.Continuity measurement across the 2B inserts should be conducted with much thought.Many protectors of this type are used in the SD-C HVPP and PSF from F.G. to O.G., sothat it is hard to find a faulty unit. These inserts should be replaced every ten years or
28.
when abnormal failures occur. It should be noted that replacement of these units ispossible with the HVPP operational but care must be exercised. Removing a failed insert,while the HVPP is operational, will suddenly divert the established current flow. Thismay result in a sudden surge voltage across the insert. A suitable strap wire should beconnected across the protector from O.G. to F.G. whenever an insert is removed. The123A1A unit inserts (500 V) can be tested using an AT&T CO A4H402L1 protector testset using the A4H402L5 (MOD) adaptor.
All devices are now listed as manufacture discontinued by AT&T except for thefollowing: (All AT&T CO manufacturing drawings are protrietary)
118A AT&T OMAHA2B Inserts AT&T OMAHA125EW AT&T MEXICO
The 126A spark gaps can be manufactured in the AT&T-GC, Department 1121,Engineering Model Shops. The last F-52571 tubes available are retained by the author.Some old residual assets are available in the Cheatham Annex Depot. No spare 458Ctubes are known to exist. Caution should be considered whenever old residual assets aredeployed.
CONCLUSION
All spark gap and surge protector devices used in the SOSUS Front-End equipment arevital for personnel and equipment safety. While large in scope this memorandum isintended to cover all devices, along with CPP design, in one publication. While manyprotectors are M.D. by AT&T CO they still are repairable and/or maintainable. Theinformation contained herein is intended to facilitate long-term life cycle support andM.D. activities in the future. All of the SOSUS protectors, while simple and utilitarian inapplication, remain gratifingly complex in details, materials and in manufacturing.
All protector failures should be viewed by engineering and by the customer as a veryserious fault. Techniques for fault insolation, testing and repairing are reviewed.Protector faults can manifest themselves in many strange ways. Problem resolutions canbe very perplexing, time consuming and dangerous. It is recommended that all siteresident engineering personnel review the contents of this memo and retain it for futurereference. Utilization of the AT&T CO A4H402L1 protector test set may expediteresolution of protector failures and return current anomalies.
29.
I wish to acknowledge the support and contribution of numerous AT&T engineeringpersonnel to the contents of this memo. They are too many to mention, retired or lost inmemory.
a. /:A. K. Wittmann
Attachments:Appendix A and BFigures 1 to 16ReferencesList of Figures
Copy to:S. M. Averyt - GC 1135N. J. Kuczmanski - GC 1135J. G. Peeples - GC 1135R. C. Zak - GC 1331J. J. McGough - GC 1135J. J. Dziadosz - GC 1135R. Dewey - GC 1135G. R. Mueller - GC 1135D. P. Jacobs - GC 1135J.Maxwell - GC 1135A. L. Skipper - GC 1135L. L. Berkowitch - GC 1135M. G. Binkley -GC1135E. R. Burns - GC 4936A. S. Burrows - GC 1 135I. Cruz - GC 1321L. L. Dimmick - GC 1320R. J. Granger - GC 1120J. R. Gregory - GC 1121E. Kiess - GC 4932J. L. Melzer - GC 1135J. J. Papa -GC1135D. B. Rhue - GC 1121D. C. Ross - GC 1324P. A. Sierk - GC 1135J. E. Swing - GC 4961
30.
Copy to: (continued). D. Tollison - GC 1135
R. C. Watts -GC1135W.E.Williams - GC 1131J. A. Workman - GC 4961S.L.Lucas -GC1100
31.
LIST OF FIGURES
1. FDS CPP APPLICATION
2. G840324 VIEW
3. G840324 INTERFACE
4. CALCULATED CABLE DISCHARGE WAVEFORM
5. 458C GAS TUBE
6. F-52571 GAS TUBE
7. 123A TYPE PROTECTOR
8. 2B TYPE INSERT
9. 123A1A LIFE TESTING
10. 2B INSERT HOLDOVER
11. KS-16169L2 PROTECTOR
12. 125EW GAS PROTECTOR
13. 126A1 TYPE PROTECTOR
14. 126A1 INTERNAL ASSEMBLY
15. 118A LIGHTENING PROTECTOR
16. GAS TUBE DISCHARGE CURVES
Al SD-C HVPP PROTECTOR SHUTDOWN CIRCUIT
A2 KS-15957L1 H.V. RELAY
32.
LIST OF REFERENCES
1. SD-C FRONT-END GROUNDING DEPT. 1121 GCA. K. WTTTMANN, SEPT 11, 1989
2. CURRENT PROTECTION PANEL INTERFACE DEPT. 46234L. H. STEINHURST, MAY 23, 1991
3. SG SUBMARINE CABLE SYSTEM, DESIGN INFORMATIONS. T. BREWER, FEB 20, 1975
4. BELL SYSTEM TECHNICAL JOURNAL, JULY 1964
5. BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1957
6. TELECOMMUNICATION ELECTRICAL PROTECTION - AT&TEDWARD P. CARTER, 1985
7. ELECTRON DEVICES AND CIRCUITS, MCGRAW HILL, 1962, J. M.CARROLL
A-l
APPENDIX A
126Al TYPE PROTECTOR SHUTDOWN CIRCUIT
Each Converter cabinet used in the SD-C GF44812 HVPP uses four 126A1 type spark gapprotectors. These units are used in association with selected H.V. resistors and theprotector shutdown (P.S.) H.V. relay (KS-15957) as depicted in Figure Al.
The KS-15957L1 vacuum relays are H.V. DC types (FIG 2A) with two double-throwcontacts. The contacts are sealed in a glass vacuum chamber and are activated by thearmature of a magnet mounted in the base of the vacuum chamber. The relay is designedfor "dead-circuit" switching but may be used for "live-circuit" switching at limited loadsand voltage. Solder type terminals are provided. Corona shields are provided on allcontact terminals, rated corona free up to 10,000 V dc. Typical specifications are:
PHYSICAL SPECIFICATION
CONTACT ARRANGEMENT: DPDTWEIGHT: 8 OZ. MAX.TERMINAL STRENGTH: 5 LBS. PULL IN ANY
DIRECTIONCONTACT MATERIAL: DEGASSED TUNGSTEN
OPERATING SPECIFICATIONS
NOMINAL OPERATING VOLTAGE 48.0 V dcPULL IN VOLTAGE @ 25°C: 25 V dc MAX.DROP OUT VOLTAGE: 1-20 V dcMAXIMUM OVER VOLTAGE @ 25°C 56 V dcOPERATE TIME:—(INCLUDES BOUNCE) 23 ms MAX. (AT RATED COIL
VOLTAGE)RELEASE TIME: 10 ms MAX.CONTACT BOUNCE: 2 ms MAX.LIFE: 500,000 MECHANICAL
OPERATIONSDIELECTRIC STRENGTH 17,500 V dcCORONA 10,000 V dcTEMPERATURE RANGE 0°C TO 85°CSHOCK 100 gPRESSURE 100 psigVIBRATION (5-1000 Hz) 3 g
The supplier is Lear Siegler Jennings Inc. and their part number is RB2A 48N199.
A-2
Figure Al depicts the Protector Shutdown (PS 1,2,3) circuit configuration. For the XOPTION calculations for the relay pull-in voltage, when the SG fires can be calculated asfollows:
V, = 3000 V\ 4.12JC//735[ (4.12K//735) + 14.0JT
= 3000V 624
14,624
= 3000V[.043]
= 128 VDC
This voltage will result in a real fast turn-on of the PS relay. The sequence of events are:
1. SPARK GAP fires with an over-voltage.2. PS relay turns ON.3. The Protector Alarm (PA) relay turns ON.4. The PA circuit latches until manually cleared.5. The Inverter Power Operate (IPO) relay turns OFF.6. The Inverter Power (IP) main contactor relay turns OFF.7. The -78 V dc powering the Inverter Power Stages A and B is disconnected
and the Converter shuts down.
Testing of this circuit is detailed in Appendix B.
B-l
APPENDIX BSD-C HVPP
126A1 PROTECTOR SHUTDOWN TESTING
CAUTION: THIS TEST FOR SPARK GAP (SG) ARCING IS NOT NORMALLYPERFORMED IN THE FIELD. EXTREME CARE AND CAUTION BYKNOWLEDGE PERSONNEL MUST BE FOLLOWED. LETHALVOLTAGES AND CURRENTS ARE AVAILABLE AT MANYTERMINALS IN THE HIGH VOLTAGE (H.V.) COMPARTMENTS THATARE EXPOSED.
NOTE: THIS TEST IS IN GENERALIZED FORM FOR TESTING SGI INCURRENT REGULATOR 1. SIMILAR STEPS SHOULD BE FOLLOWEDFOR SG2 IN CR2 AND FOR SG'S 3.1 AND 3.2 IN THE CONVERTEROUTPUT. A H.V. D.C. VOLT METER (Ml) WITH SUITABLE H.V.LEADS SHOULD BE AVAILABLE.
STEP 1. SHUT DOWN THE HVPP
STEP 2. STRAP METER Ml BETWEEN TERMINAL 1 OF MAGNETICAMPLIFIER AR3 AND TERMINAL E31 IN THE H.V. COMPARTMENT.TERMINAL AR3-1 IS -H.V. AND TERMINAL E31 IS +H.V.
STEP 3. IN THE CONVERTER H.V. COMPARTMENT REMOVE:
R24.1 & 24.2 DISABLES SG3.1 & 3.2R 14.1 & 14.2 DISABLES SG2R7.1 & 7.2 DISABLES SLOPE OF CR1R16.1 & 16.2 DISABLES SLOPE OF CR2R19.1 & 19.2 DISABLES CONVERTER DROOP 1R20.1 & 20.2 DISABLES CONVERTER DROOP 2R21.1 & 21.2 DISABLES ±8% VOLT ALARMR22.1 & 22.2 DISABLES ±15% VOLT ALARM
STEP 4 IN THE LOAD TRANSFER H.V. COMPARTMENT REMOVE:
Rl.l & 1.2 DISABLES TEST LOAD VOLTMETER
STEP 5 IN EACH CR1 AND 2 REMOVE DROOP AMPLIFIER 1 AND 2 ANDFSLI1 AND 2 CIRCUIT PACKS AND STRAP TERMINALS 35-36 OFDETECTOR 1 AND 3 CONNECTORS. REMOVE THE DETECTOR 8CIRCUIT PACK (+15% OVERVOLTAGE SHUTDOWN) FROM THECONVERTER MONITOR SLIDE. STRAP OUT THE RECTIFIEROUTPUT VOLTAGE METER ON EACH CR1 AND 2.
STEP 6 SET THE TEST LOAD COURSE ADJUST TO 8400 V POSITION.
B-2
STEP 7 RAISE THE VOLTAGE BY CONTROLLING THE CURRENT ADJUSTCOURSE POTENTIOMETER IN THE CR1 OR TEST LOAD FINECONTROL IN THE LOAD TRANSFER BAY.
When Meter Ml indicators between 8500 V and 8900 V, SGI should fire. The firing ofSGI may be detected by visual observation and by a reduction in the voltage indicated inMl. In addition, the firing of SGI may be accompanied by a protector shutdown of CR1.
Testing of SG's 3.1 and 3.2 will require moving the leads of Ml to Z3-1 (-H.V.) andZ3-3 (+H.V.). Also, the resistor R24.1 and 24.2 must be reinstalled to enable the turn onof the PS 3 relay. The following should also be noted:
OPTION TEST LOAD SETTING FIRING RANGE
X 2800 V 2900 - 3200 V dcY 5600 V 5700 - 6000 V dc
Firing of SG's 3.1 and 3.2 should enable PS3 to initiate a PROTECTOR SHUTDOWN ofthe entire Converter cabinet.
NEMA ENCLOSURE
SHORTINGSWITCH
INTERLOCK
M2SYSTEMCURRENT
METERM1
G3-G2LEAKAGECURRENT
METER
M3
G3-G2VOLTAGE
METER
SYSTEMSELECTOR
CABLEARMOR
PROTECTORS
G3PROTECTOR FIGURE 2
CURRENT PROTECTION PANELEXPLODED VIEW
G840324AKW
3/9/92
Ri ©
R2 ©
R3©
Al
A2©
A7 I
+ HV TO PFECABLE SYSTEM"4
1.2,3
TO CABLESYSTEM I ARMOR
TO CABLESYSTEM 3 ARMOR
TO CABLESYSTEM 3 ARMOR
TO 63 CABLEARMOR SHIELD
TO 33OCEAN GROUNDONE PER SITE
FDS-DWT
. +HV TO PFEFCABLE SYSTEM
4,3,6
TO CABLESYSTEM ZARMOR
TO CABLESYSTEM 4 ARMOR
TO CABLESYSTEM 6 ARMOR
TO G2BUILDING GROUND
©33OG
©R6
© R 5
©R4
)A6
DOOR NOT SHOWN
FIGURE 3CURRENT PROTECTION PANEL
INTERFACE WIRINGG840324
CURRENTAMPERESMAXIMUM CURRENT, AMPERES
CO
to
oCD
moc -n5 5m
COo
Qm
33m
-t COen ro
COCD
CO-<COHm
zm
COO
m
>< H
m o>
33maCOo
33Qm
ooCOO
m
oo
rooo
COoo
ootCO
CO
CO
o
COCOo0>o— LooCOooa>oo
o>mO
2.60"
SEALEDMETAL ENCLOSURE
LEADS
ELECTRON TUBE
,- CATHANODE NO. 1
„.PERFORATIONS
f, CATHAN0O6 NO, 2
/' ,-HIGM ALUMINA,' / CERAMIC
METALCLIP --
-•-_ EMISSIVECOATING
FIGURE 5458C GAS TUBE
AKW3 / o / Q r>
MOUNTING
GETTER
SLEEVE
SUPPORTING STEMS
LEADS
CERAMIC BASE
GLASS ENCLOSURE
CATHODE (TUNGSTEN)
ANODE(NICKEL)
FIGURE 6
F-52571 GAS TUBE
AKW3/9/92
CARBONBLOCKS
2B INSERT(FIG. 8)
TERMINALS
1.50'
2B INSERT
PHENOLICBASE
FIGURE 7123A1 PROTECTOR
AKW3/9/92
FROM LINETO PROTECTED
CIRCUIT
BEFOREOPERATION
FUSIBLE PELLET SPACER
32 BLOCK
CARBON INSERT OF33 PROTECTOR BLOCK
PORCELAIN RINGNORMALLY HOLDS ONE BLOCKSLIGHTLY A W A Y FROMTHE OTHER BLOCK AND THUSPROVIDES A DISCHARGE GAP
FROM LINETO PROTECTED
CIRCUIT
AFTEROPERATION
PELLET AND LEADBORATE HAVE MELTED
FIGURE 82B TYPE INSERT
AKW3/9/92
123A1B .006
GAP SPACING .004IN INCHES
123A1A
.003
.002DISCHARGE CURRENT 700 CREST AMPERES DURATIONOF IMPULSE TO HALF VALUE 500 MICROSECONDS
20 40 60 80 100 120 140 160 180
AVERAGE NUMBER OF OPERATIONS TO SHORT CIRCUIT
FIGURE 9
123A PROTECTORLIFE TESTING
AKW3/9/92
COLUCCUJex.2
Z111DCoc
HOLDOVER
100 200 300 400 500
STEADY-STATE POTENTIAL (VOLTS)
HOLDOVER CHARACTERISTICS OF CYLINDRICAL
2B2 TYPE PROTECTOR BLOCKS BELOW 500VDC
FIGURE 10
2B2 TYPE HOLDOVER
A K W3/9 /92
DESIGNATION PIN
WASHER
CARBONPROTECTOR BLOCK
PROTECTORBLOCK
CONNECTOR
SPRING ASSEMBLY
RING
CAP ASSEMBLY
SPACER
PROTECTOR ASSEMBLY
KS-16169
.719'
PROTECTOR MOUNTINGASSEMBLY
KS-16170
PANEL MOUNT
RING
FIGURE 1 1
PROTECTOR ASSEMBLYAND MOUNTING
AKW3/9/92
GROUNDMOUNTING
FLANGE
331RLWIDE GAPGAS TUBE
TERMINAL ASSEMBLY
SOLDER PELLET
HOUSING
COVER
POTTING COMPOUND
NUT
WASHERS
PROTECTOR CUPASSEMBLY
331RL
VOLUTE SPRING
GROUND TERMINAL
FIGURE 12
125EW PROTECTORAKW
3/9/92
r\
JVIEW
FIG. 14
5.68'
CARBON BLOCKS
n n GLASS DOME
PHENOLIC BASE
MOUNTING STUDS
SOLDER TERMINALS
FIGURE 13
126A1 TYPEPROTECTOR ASSEMBLY
AKW3/9/92
ADJUSTABLE GAPSEE TABLE A
A
NUT HEX
WASHER
INSULATOR
PORCELAININSULATOR
CORONA DOME
WASHER, SPRING LOCK
BLOCK CARBON
PLATE
CAPSECTION A-A
FIGURE 13
GASKET
CAPFIXTURE
ASSEMBLY
WASHER
TABLE A
ROD
CODE NO.
126A1F
126A1G
126A1J
126A1M
DIM A
.020
.025
.055
.085
FIGURE 14
126A TYPE PROTECTORWITH BULB REMOVED
CROSS SECTION (VIEW A-A)AKW
3/9 /92
TOP VIEW
CARBON ELECTRODES
GAP .030
3500VDC
PLASTIC COVER
MOUNTINGBRACKET
SLEEVE
0
2.5"
CARBON ELECTRODES
WIRE LEAD 2.75*
CERAMIC BASE
8 AWG LEADS (3)
FIGURE 15
118A LIGHTNING PROTECTOR
AKW3/9/92
zaicccc
01ooZ
O01
01ccccoo
10
10 -11
ARCDISCHARGE
ABNORMALGLOW
NORMAL GLOWDISCHARGE
TRANSITION
REGION
SPACE-CHARGEREGION
GASAMPLIFICATION
10V70V
150V 200V
ANODE POTENTIAL VOLTS
FIGURE 16
F-52571 GAS TUBE
DISCHARGE
AKW
4H.V.
-̂"- ^%-
SG ( g
R <(N<
i >
126A1(NOTE 1)
DTE 1)
L2 735 ohms 6 2
L1 PS ?1
KS-15957L1
-H.V.
H.V. COMPARTMENT
NOTE 1 H.V.
X OPTION
Y OPTION:
Z OPTION:
CURRENT REG's
1 * fc-> •••
P/O H.V.f\ f\ K 4 n A f™» T & j ̂ hCOMPARTMcf
PA
I
IPORELAY
P.P. OPTIONS
126A1G, 14.0 Kohm, 3000V
126A1J, 24.0 K ohm, 5500V
126A1M, 37.5 K ohm, 8500V
126A1N, 37. 5 K o h m , 8500V
-26V
FIGURE A1
PROTECTOR SHUTDOWNCIRCUIT '
AKW3/9/92
L2
L1
NO NC NO NC1 3 * 6
_1 - - - -
3.60"
KS-15957L1 RELAY
W
BASE
H.V. TERMINALS
VACUUM
ENCLOSURE(GLASS)
LEADS
LISTNO.
1
COIL RATING
VOLTS
44-52
FREQ
DC
DC RES
OHM±10%
735
CONTACT RATING
LINE SWITCHING
AMP
4
KV
8
KW
20
CLOSED
AMP
20
DC RES.OHMS
.01
CAP.
IPS
CONTACT
APR.
2 POT
TYPICAL RATING
FIGURE A2
KS-15957L1 H.V. RELAYAKW
3/8/92
