Fundamentals of Circuit Breaker Maintenance · • The circuit breaker must first detect a fault condition. • In small mains and low voltage circuit breakers, this is usually done

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Fundamentals of Circuit Breaker Maintenance

© AVO Training Institute, Inc. 2018

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Moderator

n  Ron Spataro AVO Training Institute Marketing Manager

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Q&A

n  Send us your questions and comments during the presentation

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Today’s Presenter

Mike Carter AVO Training Institute, Senior Instructor and Curriculum Advisor

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•  Definition •  A circuit breaker is an automatically operated electrical

switch designed to protect an electrical circuit from damage caused by excess current from an overload or short circuit. Its basic function is to interrupt current flow after a fault is detected.

•  Unlike a fuse, which operates once and then must be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation.

Definition and Purpose of Circuit Breakers

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•  Definition •  Circuit breakers are made in varying sizes, from small

devices that protect low-current circuits or individual household appliance, up to large switchgear designed to protect high voltage circuits feeding an entire city.

•  The generic function of a circuit breaker, RCD or a fuse, as an automatic means of removing power from a faulty system is often abbreviated as OCPD (Over Current Protection Device).


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•  Purpose •  Interconnection of multiple generator sources into an

electrical grid required development of circuit breakers with increasing voltage ratings and increased ability to safely interrupt the increasing short-circuit currents produced by networks.

•  Simple air-break manual switches produced hazardous arcs when interrupting high voltages; these gave way to oil-enclosed contacts, and various forms using directed flow of pressurized air, or of pressurized oil, to cool and interrupt the arc.


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•  Purpose •  All circuit breaker systems have common features in their

operation, but details vary substantially depending on the voltage class, current rating and type of the circuit breaker.

•  The circuit breaker must first detect a fault condition. •  In small mains and low voltage circuit breakers, this is

usually done within the device itself. •  Circuit breakers for large currents or high voltages are

usually arranged with protective relay pilot devices to sense a fault condition and to operate the opening mechanism.


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•  Purpose •  These typically require a separate power source, such as a

battery, although some high-voltage circuit breakers are self-contained with current transformers, protective relays, and an internal control power source.

•  Once a fault is detected, the circuit breaker contacts must open to interrupt the circuit; this is commonly done using mechanically stored energy contained within the breaker, such as a spring or compressed air to separate the contacts.


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•  Purpose •  Circuit breakers may also use the higher current caused by

the fault to separate the contacts, such as thermal expansion or a magnetic field.

•  Small circuit breakers typically have a manual control lever to switch off the load or reset a tripped breaker, while larger units use solenoids to trip the mechanism, and electric motors to restore energy to the springs.


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•  Purpose •  The circuit breaker contacts must carry the load current

without excessive heating, and must also withstand the heat of the arc produced when interrupting (opening) the circuit.

•  Contacts are made of copper or copper alloys, silver alloys and other highly conductive materials.

•  Service life of the contacts is limited by the erosion of contact material due to arcing while interrupting the current.


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Air, Low- Voltage Power Circuit Breakers

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•  Visual and Mechanical Inspection •  Inspect physical and mechanical condition. •  Inspect anchorage, alignment, and grounding. •  Verify that all maintenance devices are available for

servicing and operating the breaker. •  Prior to cleaning the unit, perform as-found tests, if required. •  Clean the unit. •  Inspect arc chutes. •  Inspect moving and stationary contacts for condition, wear,

and alignment.


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•  Visual and Mechanical Inspection •  Verify that primary and secondary contact wipe and other

dimensions vital to satisfactory operation of the breaker are correct.

•  Perform all mechanical operator and contact alignment tests on both the breaker and its operating mechanism in accordance with manufacturer’s published data.


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•  Visual and Mechanical Inspection •  Inspect bolted electrical connections for high resistance

using one or more of the following methods: •  Use of a low-resistance ohmmeter •  Verify tightness of accessible bolted electrical connections

by calibrated torque-wrench method in accordance with manufacturer’s published data or Neta Table 100.12.

•  Perform a thermographic survey


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•  Visual and Mechanical Inspection •  Verify cell fit and element alignment. •  Verify racking mechanism operation. •  Use appropriate lubrication on moving current-carrying parts

and on moving and sliding surfaces. •  Perform adjustments for final protective device settings in

accordance with coordination study provided by end user. •  Perform as-left tests. •  Record as-found and as-left operation counter readings.


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•  Electrical Test •  Perform resistance measurements through bolted

connections with a low-resistance ohmmeter. •  Perform insulation-resistance tests for one minute on each

pole, phase-to-phase and phase-to-ground with the circuit breaker closed, and across each open pole. Apply voltage in accordance with manufacturer’s published data. In the absence of manufacturer’s published data, use Neta Table 100.1.


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•  Electrical Test •  Perform a contact/pole-resistance test. •  (Optional) Perform insulation-resistance tests on all control

wiring with respect to ground. The applied potential shall be 500 volts dc for 300-volt rated cable and 1000 volts dc for 600-volt rated cable. Test duration shall be one minute

•  Determine long-time pickup and delay, short-time pickup and delay, ground-fault pickup and delay and instantaneous pickup current by primary current injection.


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•  Electrical Test •  (Optional)Test functions of the trip unit by means of

secondary injection. •  Perform minimum pickup voltage test on shunt trip and close

coils in accordance with Neta Table 100.20. •  Verify correct operation of auxiliary features such as trip and

pickup indicators, zone interlocking, electrical close and trip operation, trip-free, antipump function, and trip unit battery condition.


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•  Electrical Test •  Reset all trip logs and indicators. •  Verify operation of charging mechanism.

•  Test Values – Visual and Mechanical •  Compare bolted connection resistance values to values of

similar connections. Investigate values which deviate from those of similar bolted connections by more than 50 percent of the lowest value.


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•  Test Values – Visual and Mechanical •  Bolt-torque levels should be in accordance with

manufacturer’s published data. In the absence of manufacturer’s published data, use Neta Table 100.12.

•  Results of the thermographic survey. •  Settings shall comply with coordination study

recommendations. •  Operations counter should advance one digit per close-open

cycle.


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•  Test Values – Electrical •  Compare bolted connection resistance values to values of


•  Insulation-resistance values of breakers should be in accordance with manufacturer’s published data. In the absence of manufacturer’s published data, use Neta Table 100.1. Values of insulation resistance less than this table or manufacturer’s recommendations should be investigated.


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•  Test Values – Electrical •  Microhm or dc millivolt drop values should not exceed the

high levels of the normal range as indicated in the manufacturer’s published data. If manufacturer’s data is not available, investigate values that deviate from adjacent poles or similar breakers by more than 50 percent of the lowest value.

•  Insulation-resistance values of control wiring should be comparable to previously obtained results but not less than two megohms.


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•  Test Values – Electrical •  Pickup values and trip characteristic should be as specified

and within manufacturer’s published tolerances. •  Minimum pickup voltage on shunt trip and close coils should

be in accordance with manufacturer’s published data. In the absence of manufacturer’s published data, refer to Neta Table 100.20.

•  Auxiliary features should operate in accordance with manufacturer’s published data.


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Circuit Breakers, Air, Medium-Voltage

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•  Visual and Mechanical Inspection •  Inspect physical and mechanical condition. •  Verify that all maintenance devices are available for

servicing and operating the breaker. •  Perform operator analysis (first-trip) test. •  Prior to cleaning the unit, perform as-found tests, if required. •  Inspect arc chutes. •  Inspect moving and stationary contacts for condition, wear,

and alignment.


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•  Visual and Mechanical Inspection •  If recommended by manufacturer, slow close/open breaker

and check for binding, friction, contact alignment, contact sequence, and penetration.

•  Verify that contact sequence is in accordance with manufacturer’s published data.

•  Perform all mechanical operation tests on the operating mechanism in accordance with manufacturer’s published data.


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using one or more of the following methods: •  Use of a low-resistance ohmmeter, verify tightness of

accessible bolted electrical connections by calibrated torque-wrench or perform a thermographic survey.

•  Verify cell fit and element alignment. •  Verify racking mechanism operation.


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•  Visual and Mechanical Inspection •  Inspect puffer operation. •  Use appropriate lubrication on moving current-carrying parts

and on moving and sliding surfaces. •  (Optional) Perform time-travel analysis. •  Perform as-left tests. •  Record as-found and as-left operation-counter readings.


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•  Electrical Tests •  Perform resistance measurements through bolted


pole, phase-to-phase and phase-to-ground with the circuit breaker closed, and across each open pole. Apply voltage in accordance with manufacturer’s published data. In the absence of manufacturer’s published data, use Table 100.1.


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•  Electrical Tests •  Perform a contact/pole-resistance test. •  With the breaker in a test position, perform the following

tests: •  Trip and close breaker with the control switch. •  Trip breaker by operating each of its protective relays. •  Verify mechanism charge, trip-free, and antipump functions. •  (Optional)Perform minimum pickup voltage tests on trip and

close coils


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•  Electrical Tests •  (Optional) Perform power-factor or dissipation-factor tests

with breaker in both the open and closed positions and each bushing equipped with a power-factor/capacitance tap. In the absence of a power-factor/ capacitance tap, perform hot-collar tests.

•  (Optional) Perform a dielectric withstand voltage test on each phase with the circuit breaker closed and the poles not under test grounded. Test voltage should be in accordance with manufacturer’s published data or Neta Table 100.19.


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•  Electrical Tests •  Verify blowout coil circuit continuity. •  Verify operation of cubicle space heaters.

•  Test Values – Visual and Mechanical •  Compare first-trip operation time and trip-coil current

waveform to manufacturer’s published data. In the absence of manufacturer's published data, compare first-trip operation time and trip coil current waveform to previously obtained results.


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•  Test Values – Visual and Mechanical •  Compare bolted connection resistance values to values of


•  Bolt-torque levels should be in accordance with manufacturer’s published data.

•  Results of the thermographic survey. •  Compare travel and velocity values to manufacturer’s

published data and previous test data.


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•  Test Values – Visual and Mechanical •  Operations counter should advance one digit per close-open

cycle.




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•  Test Values – Electrical •  Insulation-resistance values of circuit breakers should be in

accordance with manufacturer’s published data. In the absence of manufacturer’s published data, use Neta Table 100.1. Values of insulation resistance less than this table or manufacturer’s recommendations should be investigated.

•  Microhm or dc millivolt drop values shall not exceed the high levels of the normal range as indicated in the manufacturer’s published data. If manufacturer’s data is not available, investigate values that deviate from adjacent poles or similar breakers by more than 50 percent of the lowest value.


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•  Test Values – Electrical •  Breaker mechanism charge, close, open, trip, trip-free, and

antipump features shall function as designed. •  Minimum pickup for trip and close coils shall be in

accordance with manufacturer’s published data. •  Power-factor or dissipation-factor values shall be compared

with previous test results of similar breakers or manufacturer’s published data.


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•  Test Values – Electrical •  Power-factor or dissipation-factor and capacitance values

should be within ten percent of nameplate rating for bushings. Hot collar tests are evaluated on a milliampere/milliwatt loss basis, and the results should be compared to values of similar bushings.

•  If no evidence of distress or insulation failure is observed by the end of the total time of voltage application during the dielectric withstand voltage test, the circuit breaker is considered to have passed the test.


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•  Test Values – Electrical •  The blowout coil circuit should exhibit continuity. •  Cubicle space heaters should be operational.


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Circuit Breakers, Vacuum, Medium-Voltage

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•  Visual and Mechanical Inspection •  Inspect physical and mechanical condition. •  Inspect anchorage, alignment, and grounding. •  Verify that all maintenance devices are available for

servicing and operating the breaker •  (Optional)Perform operator analysis (first-trip) test. •  Prior to cleaning the unit, perform as-found tests, if required. •  Clean the unit. •  Inspect vacuum bottle assemblies.


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•  Visual and Mechanical Inspection •  Measure critical distances such as contact gap as

recommended by the manufacturer. •  If recommended by the manufacturer, slow close/open the

breaker and check for binding, friction, contact alignment, contact sequence, and penetration.

•  Perform all mechanical operation tests on the operating mechanism in accordance with manufacturer’s published data.


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using one or more of the following methods: •  1. Use of a low-resistance ohmmeter. •  2. Verify tightness of accessible bolted electrical connections

by calibrated torque-wrench method in accordance with manufacturer’s published data. In the absence of manufacturer’s published data, use Neta Table 100.12.

•  3. Perform a thermographic survey


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•  Visual and Mechanical Inspection •  Verify cell fit and element alignment. •  Verify racking mechanism operation. •  Inspect vacuum bellows operation. •  Use appropriate lubrication on moving current-carrying parts

and on moving and sliding surfaces. •  Perform time-travel analysis. •  Perform as-left tests. •  Record as-found and as-left operation counter readings.


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•  Electrical Test •  Perform resistance measurements through bolted


pole, phase-to-phase and phase-to-ground with circuit breaker closed and across each pole with the breaker open. Apply voltage in accordance with manufacturer’s published data. In the absence of manufacturer’s published data, use Table 100.1.


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•  Electrical Test •  (Optional)Perform insulation-resistance tests on all control

wiring with respect to ground. •  Perform a contact/pole-resistance test. •  With breaker in a test position, perform the following tests: •  1. Trip and close breaker with the control switch. •  2. Trip breaker by operating each of its protective relays. •  3. Verify mechanism charge, trip-free, and antipump

functions.


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•  Electrical Test •  (Optional) Perform minimum pickup voltage tests on trip and

close coils. •  (Optional) Perform power-factor or dissipation-factor tests on

each pole with the breaker open and each phase with the breaker closed.

•  (Optional) Perform power-factor or dissipation-factor tests on each bushing equipped with a power-factor/capacitance tap. In the absence of a power-factor/ capacitance tap, perform hot-collar tests.


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•  Electrical Test •  Perform a vacuum bottle integrity (dielectric withstand

voltage) test across each vacuum bottle with the breaker in the open position in strict accordance with manufacturer’s published data.

•  (Optional) Perform a dielectric withstand voltage test on each phase with the circuit breaker closed and the poles not under test grounded. Test voltage should be in accordance with manufacturer’s published data. In the absence of manufacturer’s published data, use Neta Table 100.19.


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•  Test Values – Visual and Mechanical •  Compare first-trip operation time and trip-coil current

waveform to manufacturer’s published data. In the absence of manufacturer's published data, compare first-trip operation time and trip coil current waveform to previously obtained results.

•  Mechanical operation and contact alignment should be in accordance with manufacturer’s published data.

•  Compare bolted connection resistance values to values of similar connections. Investigate values which deviate from those of similar bolted connections by more than 50 percent of the lowest value.


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•  Test Values – Visual and Mechanical •  Bolt-torque levels should be in accordance with

manufacturer’s published data. In the absence of manufacturer’s published data, use Neta Table 100.12.

•  Results of the thermographic survey. •  Compare travel and velocity values to manufacturer’s

published data and previous test data. •  Operation counter should advance one digit per close-open

cycle.


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•  Insulation-resistance values of circuit breakers should be in accordance with manufacturer’s published data. In the absence of manufacturer’s published data, use Table 100.1.


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•  Test Values – Electrical •  Microhm or dc millivolt drop values shall not exceed the high

levels of the normal range as indicated in the manufacturer’s published data. If manufacturer’s data is not available, investigate values that deviate from adjacent poles or similar breakers by more than 50 percent of the lowest value.

•  Breaker mechanism charge, close, open, trip, trip-free, and antipump features shall function as designed.


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•  Test Values – Electrical •  Minimum pickup for trip and close coils shall be in

accordance with manufacturer’s published data. In the absence of data use NetaTable 100.20.

•  Power-factor or dissipation-factor values shall be compared to manufacturer’s published data. In the absence of manufacturer’s published data the comparison shall be made to similar breakers.


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•  Test Values – Electrical •  Power-factor or dissipation-factor and capacitance values

should be within ten percent of nameplate rating for bushings. Hot collar tests are evaluated on a milliampere/milliwatt loss basis, and the results should be compared to values of similar bushings.

•  If no evidence of distress or insulation failure is observed by the end of the total time of voltage application during the vacuum bottle integrity test, the test specimen is considered to have passed the test.


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•  Test Values – Electrical •  If no evidence of distress or insulation failure is observed by

the end of the total time of voltage application during the dielectric withstand voltage test, the test specimen is considered to have passed the test.

•  Heaters should be operational.


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•  We discussed the definition and history of circuit breakers. •  We addressed the Neta MTS maintenance standards for the

following circuit breaker types: •  Low voltage air circuit breakers. •  Medium voltage air circuit breakers. •  Medium voltage vacuum breakers. •  In future we will discuss oil circuit breakers of all voltage

classes as well as SF6 gas breakers.

Summary

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Save the Date for Our Next Webinar

Tuesday September 18, 2018 at 1pm – 2pm CDT Title: Vacuum Interrupter Technology

Presented by: Greg Richmond AVO Training Specialist - Instructor

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Megger®RecommendedEquipment

n  EGIL •  For substations 245kV and below •  Vacuum CBs, OCBs, and gang operated

SF6 CBs •  CBs with 1 break per phase and 1 operating

mechanism (gang op)

n  TM1800 •  765kV substations and below •  Can be used on all circuit breakers •  16 main and 16 Resistor contacts

per phase •  Gang operated or IPO •  OCBs, SF6, Vacuum, GIS,

Airblast… •  Dualground™ testing

n  CABA Win •  Interfaces with EGIL, TM1600,

TM1700, and TM1800 •  Detailed CB analysis and

comparison to historical tests •  Simple consistent testing •  Fully customizable testing with

Test Plan Editor (TPE)

n  DLRO 100 •  100A micro ohmmeter •  Smooth DC output •  Programmable ramp up, time on, ramp down,

and output current •  Battery and line operated

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Questions? After more than 50 years, AVO Training remains a global leader in safety and maintenance training for the electrical industry. We deliver an engaging, hands-on experience for our clients in a professional, real-world environment. We strive to provide industry relevant courses in a practical and flexible learning environment through an ongoing commitment to quality service, integrity, instruction, and client satisfaction. Our goal is to convey practical job skills and career development for our clients and students by saving lives through a world-class learning experience.

© AVO Training Institute, Inc. 2018

Documents

Fundamentals of Circuit Breaker Maintenance · • The circuit breaker must first detect a fault condition. • In small mains and low voltage circuit breakers, this is usually done