Digital Testing of High Voltage Circuit Breakers

Digital Testing of High voltage Circuit Breakers

Definition of Circuit Breaker Basically a circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to immediately discontinue electrical flow.

Purpose of Circuit Breakers in Power Systems > Minimize losses in closed position > Open and close on command > Open or close a circuit to connect the power to/from the transmission line (O - break, C - make) > Open a circuit for planned maintenance (O - break) > Open a circuit at system fault to protect the system behind the circuit breaker (O break, O-C reclose, O-CO, auto-reclose)

> Isolate between poles, open contacts and earth

CIRCUIT BREAKER COMPONENTS

CIRCUIT BREAKER COMPONENTS

A:

interrupter chamber

B:

insulated support column

C:

support structure

D:

central cubical

E:

wiring

F:

operating mechanism

IEC - timing definition

Circuit Breaker Testing

Circuit Breakers – Design and standards > Tests on Circuit Breakers CIBANO 500.

What is usually needed to test breakers

> Rewiring for each test > Individual µΩ-Measurement for each interrupter > Collect data for test report

Typical tests on circuit breakers 1. Minimum pick-up test 2. Static resistance or contact resistance test (µOhm) 3. Timing of main and auxiliary contacts a. different operations (O, C, OC, CO, OCO, COCO, OCOCO,...)

b. undervoltage test c. coil currents 4. Motor current 5. Contact travel (motion) of main contacts 6. Dynamic contact resistance (DRM)

Minimum Pick-up Test

Minimum Pick-up Test > Indicates the lowest voltage to operate the trip or close coil > Start at a certain voltage level > Try to operate > If not working increase voltage and try again > Ramp the voltage pulse until minimum voltage is reached with which the circuit breaker switches > Everybody has a „selfmade“ solution for this test

Contact Resistance Test

Contact Resistance Test

> Test is performed with a µOhm-Meter > A lot of different test devices on the market (weight, handling, output current and accuracy) > Inject a high current > Measurement of a small voltage in a noisy environment > Use 4-wire technique to connect

Timing Test > Connect to all main contacts > Connect to trip & close coil > Voltage supply required

Time-consuming and error-prone

Timing Test - Measured Values

Open Time, Close Time, Contact Spread, Phase Spread, Trip-Free Time, Reclose Time

Timing under voltage condition

> Coils are normally driven by station battery > What happens if battery condition is not the best > Perform a test with reduced supply voltage (e.g. 80 %) > Check times for under voltage > does it work anyhow > are there any delays compared to nominal voltage? > Measure the overall times and compare to manufacturer values

Coil Current > Important tool in circuit breaker analysis > Detect potential problems in actuating coils > Reveal information on power supply > Comparison is best method of analysis

Motor Current > Connect source to charging motor or use current clamp > Check charging times and charging currents > Compare with previous measurements

Contact Travel

Contact Travel - Travel Measurement to find out:  Mechanical defects of the cinematic chain  Overall mechanical performance  Slow operation due to jammed mechanism  Deterioration of mechanical damping  Contact wear  Arcing contact length (in combination with DRM)

Dynamic Resistance Measurement (DRM)  Recording the contact resistance during breaker operation (resistance over time)  Combination of contact resistance, timing and travel measurements 1. Inject high current 2. Start recording A & V 3. Operate Circuit Breaker 4. Calculate Resistance

Use DRM to find out > Problems with contact fingers > Lubrication problems > The arcing contact length

DRM Diagnosis: arcing contact length

Conventional Setup for Circuit Breaker Testing > Rewiring between micro-ohm measurement and timing tests > Lots of cables > Time-consuming and error-prone > Long test cables create inductive loops which catch interferences > External supply or station battery required

CONCLUSION:

Almost all people have experienced the effects of protective devices operating properly. When an overload or a short circuit occurs in the home, the usual result is a blown fuse or a trippedcircuit breaker. Fortunately few have the misfortune to see the results of a defective device, which may include burned wiring, fires, explosions, and electrical shock.

It is often assumed that the fuses and circuit breakers in the home or industry are infallible, and will operate safely when called upon to do so ten, twenty, or more years after their installation. In the case of fuses, this may be a safe assumption, because a defective fuse usually blows too quickly, causing premature opening of the circuit, and forcing replacement of the faulty component. Circuit breakers, however, are mechanical devices, which are subject to deterioration due to wear, corrosion and environmental contamination, any of which could cause the device to remain closed during a fault condition. At the very least, the specified time delay may have shifted so much that proper protection is no longer afforded to devices on the circuit, or improper coordination causes a main circuit breaker or fuse to open in an inconvenient location.