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8/14/2019 HV Equipment File 1 of 5
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High voltage equipment
Prepared by
Dr.-Ing. Thanapong Suwanasri
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Contents1. Power transformer
2. Instrument transformer
3. Disconnecting switch
4. Power circuit breaker
5. Surge arrester
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History 1831 discovery of induction law by Faraday and Henry. 1856 First transformer construction in iron core.
1889-1891 Invention of AC transformer in 3 legs form by M.Dolivo Dobrowolsky
Power Transformer (ANSI Std. C 57.12.00)
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Transformer Outline (Courtesy of Mitsubishi)
1,4) Oil filter valve2) Conservator3) Buchholz relay5) Pressure-relief vent6,7) HV, LV bushing
10) Tank 11) Off-load tap changer17) Oil drain valve
21) Grounding terminal23) Coil29) Radiator32) Oil level gauge
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1) Magnetic Core Core form for small transformer in KVA rating. Shell form for large transformer > 50 MVA.
Material is thin flat laminations of soft iron (0.3mm thick) mixedwith low carbon silicon alloyed to reduce friction loss orhysteresis loss. Eddy current loss is reduced by insulate betweenlaminated or thin sheet with oil - proof coating or vanish.Nowadays we mix phosphate or magnesium during productionprocess.
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Winding arrangement
Core Form Transformer
Shell-Form Transformer
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2) Winding Copper Coil
good mechanical strength and electrical conductivity. Aluminium Coil
Cheap, good thermal dissipation and light weight.
Insulation uses craft paper and pressboard paper with enamelseparate between turn and layer of winding (dry in oven with 120-130C for 3-4days)
Thermal problem!!
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Winding configurations
1) Core form transformer- Cylindrical (Layer - Wound , Helical , Spiral) winding
Cylindrical, Helical, Squared circle cylindrical winding(Courtesy of Mitsubishi)
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Disk (Single and double - wound) winding
2) Shell form transformer uses interleaved rectangularpancake coil for furnace transformer with high mechanicalstress.
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3. Tank Enclosure3.1) Free breathing or open type
air can go in or out depending on temperature andpressure via dehydrating breather to filter moisture
3.2) Conservator or expansion Tank Type consists of expansion
tank on the top with 3 - 10% of tank volume and filled with oiluntil half of conservator tank
air can go in or out of conservatortank via dehydrating breather
( Courtesy of Factory Mutual )
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Dehydrating Beather(Courtesy of Mitsubishi power transformer)
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3.3) Sealed - Tank TypeOn top of oil is filled with inertgas under pressure. Top coveris welded to prevent leakageand pressure-vacuum relief
device to control pressurebetween -8 to +8 psi
( Courtesy of Factory Mutual )
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4. BUSHING INSULATOR
Solid Type Bushing To 25KV Oil Filled to Tally Enclosed Type Bushing 69-92 KV Condenser Type Bushing
Capacitor - type oil - filledbushing for V > 69kV uses oil -
impregnated paper withaluminium foil separated intolayer inside porcelain cylinder
for equal voltage distributionbetween each layers.
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Off load tap ChangerTransformer must be disconnected from system on both side
before changing tap. It can be changed both from inside oroutside tank. Disadvantage is service interruption therefore it is
suitable to use with seasonal load. On load tap changer1) as impedance to prevent short circuit on tap
2) 2 circuits for load current flow and tap changing
2 Types of on load tap changer
High Speed Resistor Type2 compartments, first part is selector switch working while noload current, second part is switch and resistor which causes arcduring operation.
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1
2
3
4
5
R2 R1
Installation inside tank
outside tank Long life because of
short arcing duration
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Reactor type usingdiverter switches
Reactor type usingvacuum switches
1
2
3
4
5
Diverter switch
Selector switch #1 Selector switch #2
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Rating Data
Rated KVA and Phasepower output that transformer can supply within specifictime at rated voltage and frequency and temperature rise< 65 oC (by resistance)IEEE Std. C57.12.00 single phase transformer rated inKVA from 5KVA - 33MVA and 3 Phase from 15KVA- 100MVA
Cooling Classes
Liquid-Immersed, Air-CooledOA, OA/FA, OA/FA/FA means liquid-immersed, self-cooled/ forced air- cooled/ forced air- cooled
frequency
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Voltage Ratings and Taps Nominal System Voltage Maximum System VoltageRated voltage specified under no load condition and based on
turn ratio. ConnectionDepends on transformer type according to ANSI C57.12.70
ImpedanceStandard impedance depends on transformer type based on
average winding temperature rise (by resistance) plus 20C.
Total LossesNo-load loss (T REF 85 oC) plus load loss (T REF 20oC)without losses by ventilation & cooling system, heater, pumpand auxiliary device.
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Insulation Level
It depends on system voltage1) Class1 V < 69kV2) Class2 for 115kV and above
Temperature Rise1) Winding Rise average temperature rise from
ambient should be less than 65o
C by resistancemeasurement and < 80 oC by winding hot spot.2) Temperature rise of liquid insulation < 65 oC
when measures at the top of main tank.