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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

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

2. Equipment and Installation Inspection Items

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

3. Testing Requirements

Step Description of what you should do
3.1 Test insulation resistance of switchgear bus with a 1-minute test (phase to phase and phase to ground).
3.2 Test insulation resistance of all instrument transformers with a 1-minute test at applicable voltage.
3.3 Test insulation resistance of each circuit breaker (closed position) with a 1-minute test (phase to phase and phase to ground).
3.4 Test circuit breaker contact resistance with micro-ohmmeter.
3.5 Test 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.)
3.6 Test integrity of each vacuum interrupter on a vacuum circuit breaker in accordance with manufacturer’s instructions.
3.7 Calibrate and test each protective relay. Settings on devices shall be in accordance with the approved relay settings summary or coordination study.
3.8 Test 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.
3.9 Test each window-type ground CT and their circuits by applying current to conductor passed through the window.
3.10 Test 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.
3.11 Test voltmeter, ammeter, and related selector switches.
3.12 Test operation of all space heaters, including switching and indicating devices.
3.13 Perform circuit breaker minimum voltage trip test. Trip unit should be operable at 40 percent of nominal voltage.
3.14 Verify that each circuit breaker opening time meets the manufacturer’s specifications.
3.15 For double-ended switchgear, test phasing after energizing but before closing the tie breaker.

4. Function Test Items

Step Description of what you should do
4.1 Function-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.
4.2 Function-test circuit breaker in normal operating position before energization of bus.
4.3 When 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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