• 10 Critical Tests for New Power Circuit Breakers

    Advertisement

    There are many things can happen to a circuit breaker on its journey from the factory to facility, and while they are always tested by a manufacturer prior to shipping, the following checks and tests should be performed at a minimum to ensure that a new low voltage circuit breaker is ready to be placed into service.

    Warning: Failure to perform these tests before energizing equipment may result in a serious hazard to equipment and/or personnel.

    Testing should always be performed by qualified workers using test instruments that have been calibrated within the past 12 months.

    Visual and Mechanical Inspection

    1.) Compare all nameplate data with jobsite drawings and specifications

    Pay special attention to the circuit breaker frame size, ampacity and interrupting ratings.

    Verify that the correct catalog number to be sure that the proper accessories are installed and that the control voltage is correct.

    Ensure that all of the manufacturer supplied maintenance devices for the circuit breaker are available, including charging/racking handles and lifts.

    Note: Some circuit breakers may require special interlock keys or secondary blocks for testing outside of its cell. Consult manufacturers literature.

    2.) Inspect the physical and mechanical condition of the circuit breaker

    The breaker should be clean and arc chutes intact. Inspect the main contacts and finger clusters for abnormalities. Check that lubrication is in accordance with manufacturers specifications and mechanically charge, close and trip the circuit breaker multiple times.

    3.) Verify that the circuit breaker fits inside of its cell and is properly aligned.

    Look inside the cell for any obvious signs of bent guides or other components. Check that the circuit breaker racking mechanism operates smoothly. Do not rack the circuit breaker onto live bus until all other testing is completed!

    Inspect the physical and mechanical condition of the circuit breaker

    Verify that the circuit breaker fits inside of its cell and is properly aligned. PHOTO: EATON.

    4.) Record as found and as left operations counter readings

    The operations counter should advance one digit per close-open cycle operation. Verify settings comply with coordination study recommendations and document as found protective device settings. Make sure the trip unit battery is in good working condition.

    Electrical Tests

    5.) Inspect bolted connections, fuses, and contact/pole resistance using a low-resistance ohm meter

    Microhm or dc millivolt drop values should not exceed levels of the normal range as indicated in the manufacturer's published data.

    If no manufacturer's literature can be found, investigate values that deviate from adjacent poles or similar breakers by more than 50 percent of the lowest value.

    6.) Insulation Resistance

    Perform insulation resistance tests on each pole, phase-to-phase, and phase-to-ground with the circuit breaker closed, and across each open pole. Test duration should be one minute using a voltage in accordance with manufacturers published data. If no literature is available, apply 1000 volts DC for equipment with a nominal rating of 600 volts.

    Apply 500 volts DC for equipment with a nominal rating of 250 volts. Values should typically be no less than 100 Megohms for equipment with a rating of 600V, and 25 Megohms for equipment rated 250 volts or less.

    Important: Units with solid-state components could be damaged if not properly isolated (via removal of plugs and/or fuses) before applying test voltage. Be sure to follow all manufacturers' recommendations when performing dielectric tests on solid state components.
    Solid-state components could be damaged if not properly isolated before applying test voltage

    Solid-state components could be damaged if not properly isolated before applying test voltage. PHOTO: SQUARE D.

    7.) Control Wiring Tests

    Perform insulation-resistance tests on all control wiring with respect to ground. Apply 500 volts DC for 300-volt rated cable and 1000 volts DC for 600-volt rated cable for the duration of one minute. Insulation-resistance values of control wiring should not be less than two Megohms.

    8.) Test all basic trip unit functions via primary injection testing

    Verify and document the long time pickup, long time delay, short time pickup, short time delay, instantaneous pickup, ground fault pickup and ground fault delay using a high current test set.

    Primary injection should always be performed on new breakers prior to being placed into service to ensure proper CT ratio and polarity. Secondary injection may only be used after primary injection testing has first been completed.

    Note: Ground fault protection will most likely need to be disabled by either rewiring or using the manufacturers recommended device. Saving ground fault tests for last will ensure the function is working properly before placing the circuit breaker into service.
    High current test sets verify that the circuit breaker ratio and polarity is correct

    High current test sets verify that the circuit breaker ratio and polarity is correct. PHOTO: ETI.

    9.) Verify the correct operation of any auxiliary features

    Check trip and pickup indicators, zone interlocking, electrical close, shunt trip, trip-free, and anti-pump functions. Perform each test multiple times to ensure consistency.

    Most of these tests, such as electrical charge and close operations can be performed while primary injection testing using the proper voltage listed on the circuit breaker nameplate. Other devices may require special equipment and procedures.

    10.) Reset all trip logs and indicators after testing is completed

    Verify the breaker is discharged, racked out, and that any auxiliary plugs removed for testing have been re-installed.

    References

    • ANSI/NETA Acceptance Testing Standards

    Share this page

    Comments

    Be the first to comment.

Search TestGuy
   Tag Cloud   Advanced Search
Follow us


Explore TestGuy


NETA Certification Training


Help and Support