The 35kV switch tripped causing the busbar to trip as well

The 35kV switch tripped due to a busbar insulation fault, which triggered protective relays to trip the busbar as a safety measure. Cause of the TripA common reason for a 35kV switch to trip and subsequently cause a busbar trip is insulation breakdown or a ground fault on the busbar. In one documented case, poor installation led to overheating and breakdown of the busbar insulation, resulting in a ground fault that activated the protective relays, causing both the switch and busbar to trip (installation errors and poor conductor contact were identified as root causes).

Busbar Protection Mechanism

Busbar protection is designed to detect faults on the busbar and isolate only the affected section to prevent damage and maintain system stability. High-voltage busbar protection typically uses differential relays that compare currents entering and leaving the busbar. If a fault occurs, the relay trips the associated breakers to clear the fault.

In multi-segment busbar systems, such as double or triple busbars, the protection system uses a dynamic bus replica to track which breakers are connected to each segment. This ensures that only the faulted segment trips, while healthy segments remain in service.

Relay Operation

When a busbar fault occurs, the tripping protection relay contacts operate in series with the circuit breakers. Separate tripping relays for each breaker are preferred to simplify wiring and improve reliability. In some configurations, the relay system uses a two-out-of-three voting scheme to reduce the risk of unnecessary trips while ensuring security against maloperation.

Preventive Measures

Proper Installation and Inspection: Ensure all conductors and connectors are installed according to manufacturer specifications to prevent overheating and insulation breakdown. Regular Insulation Testing: Measure insulation resistance periodically to detect early degradation, especially on high-voltage busbars. Relay Settings and Coordination: Configure differential relays and time delays correctly to isolate only the faulted section without affecting the entire busbar.

Professional Training: Operators and maintenance personnel should be trained in high-voltage switchgear operation and busbar protection principles to minimize human error.

Summary

The 35kV switch tripping and subsequent busbar trip is typically caused by busbar faults such as insulation breakdown or ground faults, which activate protective relays. Proper installation, regular testing, and correctly configured busbar protection relays are essential to prevent unnecessary trips and ensure safe, reliable operation of high-voltage systems.