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Home / Technical Articles / Field Inspection of New Medium-Voltage Switchgear
DNF7 40.5kV Medium-voltage switchgear field inspection (In Schneider Electric factory)
DNF7 40.5kV Medium-voltage switchgear field inspection (In Schneider Electric factory)

1. Equipment and Installation Check Items

StepDescription of what you should do
1.1Check switchgear assembly for alignment, levelness, and tightness of all bolting.
1.2Check all equipment for the removal of blocking, supports, temporary ties, and temporary jumper wires.
1.3Check control power transformer and PT fuses for size, type, and circuit location.
1.4Check CT and PT ratios.
1.5Check CPT size.
1.6Check all components for proper identification per the drawings and specifications.

2. Equipment and Installation Inspection Items

StepDescription of what you should do
2.1Inspect switchgear bus bar connections for tightness by verifying that the torque meets manufacturer’s specifications. Verify that connection hardware is consistent with the Owner’s project specifications.
2.2Inspect switchgear bus supports for cleanliness and tightness.
2.3Inspect ground connections to switchgear ground bus.
2.4Inspect operation of the drawout mechanism including mechanical interlocks, position indicators, and safety features.
2.5Inspect operation of shutter devices.
2.6Inspect operation of PT disconnecting and grounding mechanisms.
2.7Inspect circuit breaker insulating parts for cleanliness and dryness.
2.8Inspect electrical contact surfaces of air circuit breaker for cleanliness and smoothness. Lubricate stationary contact surfaces per manufacturer’s
2.9Inspect contact wipe and alignment of air circuit breaker and verify that it is in accordance with manufacturer’s recommendations.
2.10Inspect vacuum breaker mechanical adjustments and critical dimensions in accordance with manufacturer’s recommendations.
2.11Inspect circuit breaker manual operation (maintenance closing procedure) to verify that all parts are free and that they work smoothly.
2.12Inspect operation of breaker mechanical trip function.
2.13Inspect lubrication of breaker-operating mechanism and all other breaker moving parts.

3. Testing Requirements

StepDescription of what you should do
3.1Test insulation resistance of switchgear bus with a 1-minute test (phase to phase and phase to ground).
3.2Test insulation resistance of all instrument transformers with a 1-minute test at applicable voltage.
3.3Test insulation resistance of each circuit breaker (closed position) with a 1-minute test (phase to phase and phase to ground).
3.4Test circuit breaker contact resistance with micro-ohmmeter.
3.5Test dielectric strength of each medium-voltage circuit breaker (closed position) with DC high-potential unit using the step voltage method and with final voltage value according to the table in paragraph 5.5, unless specified otherwise by the Owner. (Isolate and test each phase to ground with the other two-phase terminals connected together and to ground.)
3.6Test integrity of each vacuum interrupter on a vacuum circuit breaker in accordance with manufacturer’s instructions.
3.7Calibrate and test each protective relay. Settings on devices shall be in accordance with the approved relay settings summary or coordination study.
3.8Test each CT secondary circuit by applying current to CT secondary circuit with CTs disconnected and by verifying operation of all applicable relays and metering devices. Perform a ratio-verification test using the voltage or current method in accordance with ANSI C57.13.1.
3.9Test each window-type ground CT and their circuits by applying current to conductor passed through the window.
3.10Test each PT secondary circuit by applying voltage to PT secondary circuit, with the PTs disconnected, and then by verifying the operation of all applicable relays and meters.
3.11Test voltmeter, ammeter, and related selector switches.
3.12Test operation of all space heaters, including switching and indicating devices.
3.13Perform circuit breaker minimum voltage trip test. Trip unit should be operable at 40 percent of nominal voltage.
3.14Verify that each circuit breaker opening time meets the manufacturer’s specifications.
3.15For double-ended switchgear, test phasing after energizing but before closing the tie breaker.

4. Function Test Items

StepDescription of what you should do
4.1Function-test circuit breaker in test position:

  1. Close and trip circuit breaker from its local and remote control devices.
    Verify operation of all auxiliary devices by functional testing.
  2. Trip circuit breaker individually from each local protective device.
  3. Test any special circuits such as main-tie-main controls.
4.2Function-test circuit breaker in normal operating position before energization of bus.
4.3When resistance-grounding systems are installed, function test the equipment using the available protection/alarm test features.

Resource: Field Inspection and Testing of New Electrical Equipment – Process Industry Practices Electrical

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Edvard Csanyi

Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV/MV switchgears and LV high power busbar trunking (<6300A) in power substations, commercial buildings and industry facilities. Professional in AutoCAD programming.


  1. louie chow
    Mar 12, 2015


    good day, would like to check if all Schneider DNF7 switchgear have individual PT’s and CT’s installed.

    I heard that the OEM design comes with Common PT’s for all cubicle.

    is this correct?

    thanks for info.


  2. Altaf Ahmed Nizamani
    Nov 08, 2014

    Can you please give me some feedback in regard to Highest current in MV switchgear operation from 6.6 KV to 36 KV. Like
    Design Ampherage
    Short Circuit Level.

  3. Gary Burgess
    Aug 11, 2014

    Can you point me to a website for OSHA / NFPA and / or NEC required testing of switch gear in a manufacturing plant, please?

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