Beckwith M-0388/M-0389 Synchronous Inspection Relay Application Guide

M-0193B is responsible for precise zero phase angle closing of rotating phase angles (with frequency differences).

M-0388 is responsible for supervising the static phase angle (without frequency difference or extremely low frequency difference) to ensure that the static angle does not exceed the limit.

The complementary functions of the two greatly reduce the probability of false closing caused by a single device failure. In the system recovery scenario, the two can also be used in parallel, allowing the circuit breaker to close when either the rotation phase angle or the static phase angle is met.

3.2 Enable/Lock Logic

M-0388 provides "Sync Check Enable" input (TB2-4 to TB2-5), which can be controlled through external dry contacts. When the contact is closed, M-0388 works normally; When disconnected, the output relay is disabled. For situations that require permanent activation, a short jumper can be used to directly connect these two terminals.

Users can choose two timer logic options as needed:

Option 1: The enable signal does not affect the timer. The timer starts timing when the phase angle is met, and the enable signal is only used for the final "allow" output.

Option 2: Enable the signal to keep the timer reset until the contacts are closed before starting the timer.

3.3 Dead Line/Dead Bus Closing Logic (M-0389)

M-0389 provides two independent enable inputs, "Enable Dead Line Closure" and "Enable Dead Bus Closure". When the corresponding terminal is short circuited, if the Line or Bus voltage is lower than the DEAD LINE/BUS LIMITED setting value, the output relay will operate within about 0.5 seconds, ignoring the phase angle condition.

This function is particularly critical during black start or line charging operations, but it should be used with caution to avoid accidentally closing the circuit to the faulty one. It is recommended to selectively enable through external dry contacts only after clarifying the system status.

Analog output and SCADA integration

M-0388 and M-0389 both provide analog output for remote monitoring and data collection:

Phase angle analog (M-0388): 0~10Vdc corresponds to 0~180 ° (accuracy ± 1 °), or 0~1.0mA corresponds to 0~180 ° (accuracy ± 3 °).

Voltage analog quantity (M-0389): 0~7.5Vdc corresponds to 0~150Vrms (accuracy ± 5% of full scale), or 0~1.0mA corresponds to 0~150Vrms.

These outputs can drive remote terminal units (RTUs) or SCADA systems, enabling the dispatch center to monitor the phase difference and voltage on both sides of the circuit breaker in real time, assisting in determining the timing of closing, especially suitable for remote operations during system recovery.

Users can adjust the range through external precision resistors to meet the requirements of different acquisition devices.

On site testing and maintenance

5.1 Front panel testing function

The front panel of M-0388 is equipped with two OPERATE/TEST switches:

When both switches are placed in the TEST position, the output relay is internally disabled, and the Line and Bus VT inputs are separated from the external wiring, isolating external wiring influences.

Users can connect 120Vac voltage and simulate Line and Bus inputs through the front panel test sockets.

If the phase angle is within the set range, the TEST CLOSE LED lights up, indicating that the closing condition is met (but the output relay will not actually operate).

This design makes on-site functional verification simple and safe, and all checks can be completed without disconnecting external wiring.

5.2 Modular maintenance

M-0388/M-0389 adopts a modular structure:

Power Supply Board integrated with panel

The Phase Validator Board is an independent plugin

M-0389 Voltage Validator Board is an independent plugin

The output relay and backplane are both replaceable components

All plug-in boards can be hot plugged and unplugged while powered on (but the OPEROTE/TEST switch needs to be placed in the TEST position first), greatly simplifying the on-site replacement process and reducing power outage time.

5.3 Key points for troubleshooting

Possible causes and solutions for the fault phenomenon

OUTPUT CLOSED LED is not on, phase angle has not entered the window, timer has not expired, and enable has not been closed. Check the Phase Limit and TIME Limit settings and confirm that the enable terminal is short circuited

The output relay does not operate, the output contacts are stuck, and the relay coil is damaged. Check the relay contacts and replace the output relay module if necessary

The PHASE OK LED flashes unpredictably, the input voltage is unstable, and there is poor PT contact. Check the tightness of the Line/Bus voltage input circuit and wiring terminals

Confirm the status of the Enable Dead Line/Bus terminal if the dead wire closing does not respond and the enable terminal is not short circuited and the voltage is not lower than the set value. Check the DEAD LIMITED setting

Analog output deviation, large load impedance mismatch, external noise interference. Confirm that the load meets ≥ 5K Ω (voltage output) or ≤ 10K Ω (current output), and use shielded wires