The alarm for a 35kV busbar TV disconnection is triggered when abnormal voltage or current conditions are detected, typically with a short delay, to notify operators of potential transformer or busbar issues.

Function Overview

The TV (Voltage Transformer) disconnection alarm is designed to detect abnormal conditions in the busbar voltage measurement system, which may indicate a disconnection or fault in the voltage transformer circuit. This ensures that operators are promptly informed to prevent equipment damage or system instability .

Typical Alarm Criteria for 35kV Busbars

1. Voltage-Based Detection:
   • If the positive sequence voltage drops below a threshold (e.g., 30–33V) or the negative sequence voltage (3U2) exceeds a set value (e.g., 8V), an alarm is triggered .
   • For single-phase disconnection, if the residual voltage is below 44V and the bus voltage 3U2 is above 12V, a short delay alarm (around 1.25 seconds) is issued .
   • For three-phase disconnection, if all phase voltages fall below 18V and the bus-tie TA current exceeds 0.04In, a 1.25-second alarm is triggered .
2. Current-Based Detection:
   • The alarm may also be triggered if phase currents exceed specific thresholds, such as 0.04In for single-phase or 0.06In for any branch, or if three-phase balanced currents exceed set limits .
   • Negative sequence currents generated by disconnection faults are monitored to prevent motor overheating or system damage .
3. Delay and Reset:
   • Most alarms include a short time delay (typically 0.2–10 seconds depending on the relay type) to avoid false alarms from transient conditions .
   • The alarm resets automatically once the abnormal voltage or current condition clears, ensuring continuous monitoring without manual intervention .

Operational Purpose

• Early Fault Detection: Alerts operators to potential TV disconnections before they escalate into busbar faults or equipment damage.
• System Protection: Helps prevent negative sequence currents from causing motor overheating or transformer stress.
• Safety and Reliability: Ensures timely maintenance and reduces the risk of fire or ground faults in the 35kV distribution network . In summary, the 35kV busbar TV disconnection alarm monitors both voltage and current conditions, triggers a short-delay alarm when thresholds are exceeded, and automatically resets after the fault clears, providing critical protection and operational awareness for high-voltage busbar systems .