When a 20 kV Vacuum Circuit Breaker (VCB) fails to close, it can interrupt operations and even pose safety risks if not handled correctly. To avoid confusion, it is important to follow a structured troubleshooting process. Each step—from checking control power to verifying mechanical and electrical interlocks—helps identify the root cause in a safe and systematic way. By learning these checks, maintenance teams can reduce downtime and ensure reliable operation of the electrical system.
1️⃣ Check Control Power Supply
Verify the control voltage (e.g., 110 VDC or as per specification) is present at the closing coil.
Check if the control fuse or MCB has tripped or blown.
For DC supply, ensure the voltage is above 90% of its nominal value.
Confirm that any emergency stop circuit is reset.
2️⃣ Check Mechanical Interlocks
Panel door interlock: The breaker will not close if the panel door is not fully latched.
Spring charging: Verify that the closing spring is fully charged (indicator should show "charged"). If not, charge manually or using the motor.
Position interlock: The VCB must be in the service position. In the test/isolation position, closing is not possible.
3️⃣ Check Electrical Interlocks
Refer to the interlock scheme drawing to trace the logic.
Confirm that no protection relays are still in the trip condition (e.g., transformer protection, OCR/GFR). Reset if necessary.
Check interlocks from incoming feeder, outgoing feeder, bus-tie, transformer, or SCADA logic.
Ensure the remote/local selector switch is in the correct mode for closing.
Test the close button circuit with a multimeter for continuity.
4️⃣ Check Closing Mechanism
Press the manual close button and listen for the closing coil sound.
If the coil does not operate, it may be damaged or not receiving voltage.
If the coil operates but the breaker does not close, the mechanism may be jammed or the spring too weak.
If possible, test the mechanism with a manual operating lever.
5️⃣ Advanced Checks
Measure the resistance of the close and open coils and compare with manufacturer specifications.
Inspect auxiliary contacts and wiring for loose connections or carbonization.
6️⃣ If Still Not Closing
Stop further attempts. Contact an experienced technician or the manufacturer.
Internal mechanism failure or damage to the main components may require specialized repair.
Always follow safety regulations and never attempt unsafe bypassing of interlocks.
Troubleshooting a VCB that does not close is not just about fixing the breaker—it is about understanding how all supporting systems work together. From control voltage and protection relays to interlocks and mechanical components, every part plays a role. By following this step-by-step method, engineers can quickly isolate faults while keeping safety as the top priority. This knowledge ensures not only a faster recovery but also more reliable and safer operation of power equipment in the long run.
Other Related Articles:
Why Does the Contact Resistance Testing Need 100A or Higher?
Hazards and Treatment of Excessive Contact Resistance of Circuit Breakers or HV Switches
How to measure the contact resistance without changing the circuit?
How to Correctly Test the Contact Resistance of HV Switchgear or Circuit Breaker?
Why Does Excessive Contact Resistance Occur In Electrical Secondary Circuits?
What is the Testing Checklist for 110kV/220kV Substation Acceptance and Maintenance Testing?
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