Correct Power Off and Power On Sequence for Distribution Rooms and Step-by-Step Energizing Procedure

Power Off and Power On Sequence in the Distribution Room

Power-off sequence:
When de-energizing, first disconnect the low-voltage (LV) side, then the high-voltage (HV) side.

• When de-energizing the LV side:
  First open all LV branch circuit breakers, then open the LV main breaker. Additionally, disconnect the control circuits before de-energizing the main power circuits.

• When de-energizing the HV side:
  First open the circuit breaker, then open the isolating switch (disconnector).
  If the HV incoming line has two isolating switches, first open the load-side isolating switch, then the source-side isolating switch.

Power-on sequence: Reverse the above order.

Never operate an isolating switch under load.

Power-On Operation Procedure for the Distribution Room

The power-on procedure is as follows:

• Confirm that no personnel are working on any electrical equipment in the entire distribution room. Remove temporary grounding wires and warning signs. When removing grounding wires, disconnect the line end first, then the grounding end.

• Verify that the incoming line switches for both circuits WL1 and WL2 are in the open position. Then close the bus-tie isolating switch between the two HV busbars WB1 and WB2 to allow them to operate in parallel.

• Sequentially close all isolating switches on WL1, then close the incoming circuit breaker. If the closing is successful, it indicates that WB1 and WB2 are in good condition.

• Close the isolating switches for the voltage transformer (VT) circuits connected to WB1 and WB2, and verify that the supply voltage is normal.

• Close all HV outgoing isolating switches, then close all HV outgoing circuit breakers to energize the main transformers of the distribution room.

• Close the LV-side knife switch of the main transformer in Distribution Room No. 2, followed by the LV circuit breaker. Successful closing indicates that the LV busbar is intact.

• Use voltmeters connected to both LV busbar sections to verify normal LV voltage.

• Close all LV outgoing knife switches in Distribution Room No. 2, then close the LV circuit breakers (or close LV fuse-switch disconnectors) to energize all LV outgoing circuits. At this point, the entire HV distribution substation and its associated workshop substations are fully operational.

Restoring Power After Fault Clearance:

If power is being restored after a fault-related outage, the procedure depends on the type of switching device installed at the incoming line:

• If the incoming line uses a high-voltage circuit breaker:
  In the event of a short-circuit fault on the HV busbar, the circuit breaker will trip automatically. After the fault is cleared, power can be restored simply by reclosing the circuit breaker.

• If the incoming line uses a high-voltage load-break switch:
  After fault clearance, first replace the fuse cartridge, then close the load-break switch to restore power.

• If the incoming line uses a high-voltage isolating switch with fuses (fuse-disconnector combination):
  After fault clearance, first replace the fuse tube, then open all outgoing circuit breakers. Only then may the isolating switch be closed, followed by reclosing all outgoing breakers to restore power.

• If the incoming line uses a drop-out fuse (expulsion fuse):
  The same procedure applies—replace the fuse tube, ensure all outgoing switches are open, close the fuse, then re-energize the outgoing circuits.