Tee Differential Protection (TEED) is a specialized type of differential protection scheme used to protect electrical systems with a tee connection, where a branch connects to a main line or busbar. It is particularly applicable in one-and-a-half breaker schemes, where a single circuit breaker is used to protect two lines connected to a common busbar.
Principle of Operation:
TEED protection relies on the principle of comparing the current entering and leaving a protected zone. In a tee connection, the protected zone encompasses the main line and the branch. Current transformers (CTs) are installed on both sides of the tee junction to measure the currents flowing in and out of the zone.
The CTs are connected to a differential relay, which continuously compares the magnitudes and phase angles of the currents. Under normal operating conditions, the currents entering and exiting the zone should be equal and opposite, resulting in a net zero differential current.
However, during a fault within the protected zone, the current balance is disrupted, and a significant differential current flows. The differential relay detects this imbalance and initiates the tripping of the associated circuit breakers to isolate the faulted section.
Advantages of TEED Protection:
- High Sensitivity: TEED protection is highly sensitive to faults within the protected zone, allowing for rapid fault clearance.
- Selectivity: It is selective, meaning it can distinguish between internal and external faults, preventing unnecessary tripping for faults outside the protected zone.
- Reliability: TEED protection is reliable and immune to external disturbances like load variations or power swings.
Diagram of TEED Protection:
In the diagram, CT1 and CT2 are connected to the main line, while CT3 is connected to the branch. The differential relay (DR) compares the currents from these CTs. If a fault occurs within the protected zone (shaded area), the relay detects the differential current and initiates tripping of the circuit breakers CB1 and CB2 to isolate the fault.
Applications of TEED Protection:
TEED protection is commonly used in:
- One-and-a-half breaker schemes for busbar protection
- Tee-offs from transmission lines
- Transformer feeders with tee connections
Conclusion:
TEED protection is an effective and reliable method for protecting electrical systems with tee connections. Its high sensitivity, selectivity, and immunity to external disturbances make it a valuable tool for ensuring the safety and reliability of power systems.