ABB high voltage bus systems monitor phase sequence using positive and negative sequence voltage detection to ensure proper operation, protection, and safe bus transfer.

Phase Sequence Monitoring

ABB protection relays, such as the REU610 and REU615, continuously measure the positive and negative phase-sequence voltages of a three-phase bus to detect any imbalance or reversal in phase sequence . The positive sequence represents the normal phase rotation (A-B-C), while the negative sequence indicates a reversed or abnormal rotation (C-B-A). Monitoring these sequences is critical for:

• Motor and generator protection: Prevents damage due to reverse rotation or unbalanced voltages .
• Busbar and feeder supervision: Ensures correct operation of circuit breakers and load distribution .
• Automatic bus transfer (ABT): Synchronizes sources during bus transfer to avoid phase mismatch, which could cause faults or equipment damage .

Applications in ABB Relays

• REU610: Calculates positive and negative sequence voltages from phase-to-phase measurements, providing undervoltage, overvoltage, and residual voltage protection. It can trip feeders or busbars if phase sequence deviations are detected .
• REU615: Offers advanced protection including positive phase sequence undervoltage and negative phase sequence detection, supporting load shedding, generator rejection, and network stability enhancement .

Bus Transfer Considerations

During bus transfer operations, phase sequence monitoring ensures that the incoming source is synchronized with the bus. ABB recommends:

• Parallel (hot) transfer: Requires synchronism check to confirm matching phase sequence and voltage before connecting the new source .
• Open-circuit transfer: Phase sequence monitoring ensures safe reconnection without causing reverse rotation or transient faults .

Summary

ABB high voltage bus systems rely on phase sequence detection to maintain safe and reliable operation. Positive and negative sequence voltages are continuously monitored by protection relays like REU610 and REU615, which provide automatic tripping, load shedding, and bus transfer synchronization. Proper phase sequence monitoring prevents equipment damage, ensures correct motor rotation, and supports stable network operation .