1. Sudden Power Outage

When a sudden power outage occurs in the substation, the first step is to disconnect the relevant power switches. Following this, a thorough inspection of the electrical equipment and power supply lines should be conducted. If the outage is confirmed not to have originated from the substation, the following measures can be taken:

• If the power supply is through a dual-circuit system, switch to the backup power supply in accordance with switching operation regulations. In the case of a single power supply, contact the power supply department and wait for power restoration.

• If there are signs of electrical equipment failure in the substation, promptly disconnect the relevant circuit breakers and disconnectors. Investigate the cause of switch refusal and report to the power supply department. If the faulty equipment is not disconnected or cannot be disconnected, do not start the backup power supply.

• If the substation has a generator unit, it is permissible to start a small generator. However, it is strictly forbidden to back-feed power into the system.

2. Switch Overtripping

If the protective device of a branch switch does not trip while the main transformer or power switch does, disconnect all branch switches. Attempt to reclose the main transformer or power switch, followed by closing the unaffected branch switches. Before attempting to close the faulty branch switch, identify and resolve the fault.

In cases where both the branch switch and the main transformer or power switch trip simultaneously, disconnect the unaffected branch switches. Attempt to close the main transformer or power switch, followed by closing each branch switch. Before closing the faulty branch switch, ensure that the coordination between the two-level relay protection devices is intact.

3. Single-Phase Grounding in 35kV and Below Systems

Typically, substations operating at 35kV and below feature ungrounded neutral points or use arc suppression coils for grounding, forming a small current grounding system. If single-phase grounding occurs, the system may continue operation for a short period, during which alarm signals will sound, and grounding indicator lights will illuminate.

In the event of complete single-phase grounding, the insulation monitoring voltmeter will display inconsistent phase readings, with the grounded phase voltage at or near zero and non-fault phase voltage elevated to √3 times the nominal voltage. Monitor the heating of voltage transformers to prevent overheating and proceed with fault location and rectification.

In cases of intermittent grounding, where grounded phase voltage fluctuates and non-fault phase voltage varies, investigate and eliminate the grounding fault.

If an arc-grounding fault occurs, the non-fault phase voltage may reach 2.5 to 3 times the rated voltage, posing a threat to system safety. Locate the cause of arc grounding or adjust the arc suppression coil turns.

Generally, it is not permissible to disconnect the grounding point using an isolating switch. However, if disconnection is necessary (e.g., when the grounding point lies between the incoming line isolator and the circuit breaker), first ground the fault phase via the circuit breaker before using the isolating switch.

For selective short-term disconnection of tie or looped lines, isolate both side circuit breakers, ensuring no overload occurs on other lines after disconnection.

4. Grounding of DC Systems

If a grounding fault occurs in the DC circuit of the substation, suspend all operations under the DC loop and perform a meticulous inspection. During troubleshooting, avoid peak load periods. Follow this sequence for inspection: emergency lighting, signal circuit, charging circuit, outdoor closing circuit, indoor closing circuit, carrier backup power supply, control circuits for 6~10kV, major control circuits for 35kV and above, DC busbar, and battery. Adjust the order flexibly according to the situation.

When identifying the faulty circuit, operate breakers or disconnect wires to gradually narrow down the fault range.

Utilize a high-resistance voltmeter (20,000 Ω/V) instead of a low-resistance test lamp to detect grounding faults.

5. DC System Voltage Drop

When the voltage of a DC system supplied by a battery pack drops, check the contact quality of the adjustment switch, internal short circuits, sulfation of battery plates, sediment buildup, container damage, and insulation level.

If the voltage drop is due to silicon rectifier supply, examine the AC voltage input and regulate it if necessary. Inspect silicon rectifier elements for damage and check AC power fuses for blown elements.

Should the DC power source suddenly vanish during operation, inspect fuses and replace them if blown. If new fuses also blow, check for short circuits and report to the relevant department for resolution.

6. Relay Protection and Secondary Circuit Faults

Upon encountering faults in relay protection or secondary circuits, immediately reset alarms and thoroughly check instrument indications and relay protection signal responses. Record the action times and detected issues before resetting the relays.

Inconsistent instrument indications, such as current surges or voltage drops, warrant quick inspection of the signal devices for potential faults.

If an instrument shows no indication or abnormal readings, examine other instruments in the same loop to ascertain whether the issue lies within the instrument or secondary circuit.

7. Arc Suppression Coil Faults

Unusual sounds from the coil, cracked bushings, significant oil leakage, or a marked increase in temperature require immediate reporting and cessation of coil use.

During single-phase grounding, the upper oil temperature should not exceed the prescribed value while operating under load. If the temperature rises or exceeds the rating, halt the use of the arc suppression coil.

If the coil emits smoke or sparks and the ammeter fluctuates, cease operation immediately, first disconnecting the transformer side circuit breaker before isolating the arc suppression coil.