Beckwith M-3425A Generator Protection Relay Debugging Guide

3.2 Directional power (32)

Provide three independent components, each of which can be set as forward over-power, reverse reverse power, or low forward power. Component 3 can also choose reactive power. For steam turbines, the reverse power setting is usually set at 0.5% to 3% of the rated power, with a delay of 20-30 seconds; Diesel engines can reach 10% to 25%. Low forward power protection is commonly used to monitor the remaining steam power after the main steam valve is closed, and it needs to be coordinated with the locking of the circuit breaker position.

3.3 Negative sequence overcurrent (46)

Divided into timed and inverse timed. The inverse time limit is based on the characteristic of I ₂ ² · t=K, and the K value is provided by the generator manufacturer (usually 10~95). The fixed value is set to 3%~5% of the rated current (alarm), and the reverse time starting value is usually equal to the continuous negative sequence capability (such as 5%). The maximum delay time can limit long-term imbalance. The reset time is set to simulate the cooling characteristics of the generator.

3.4 Out of Step Protection (78)

Using the "blind barrier+impedance circle" criterion, detect the crossing time of power swing. Set the circle diameter, offset, blind barrier position, and impedance angle, with a typical action delay of 3-6 cycles. The "trip when exiting the circle" option can be enabled to improve the breaking conditions of the circuit breaker. The polar sliding counter can be set to 1-20 times to avoid instantaneous oscillation and misoperation.

3.5 Frequency and Frequency Accumulation (81/81A)

81 provides four independent frequency components, which can be set as overclocking or underflocking at will. The underfrequency setting needs to consider the resonance zone of the turbine blades. Usually, the first stage 57.5Hz delay can be short (5-10 seconds), while the second stage 56Hz delay is longer. The 81A frequency accumulation function can monitor the cumulative operating time of the unit in hazardous frequency bands (such as 56-58.5Hz). If it exceeds the set value, an alarm will be triggered to prevent blade fatigue damage.

3.6 100% stator grounding (64S) - optional

Adopting the external 20Hz low-frequency injection method requires the use of an external signal generator, bandpass filter, and dedicated CT. During normal operation, the 20Hz current is very small, but it significantly increases in the event of a ground fault. Set two thresholds for total current and real current, and set a delay (usually 5-10 cycles). Simultaneously enable voltage suppression (to prevent misoperation during shutdown) and frequency suppression (lockout below 40Hz).

On site debugging and functional testing

4.1 Power on self-test and status indication

After power on, the panel LED lights up sequentially, and then "RELAY OK" stays on or flashes (adjustable). If an error occurs, the LED will flash a specific number of times to indicate the type of fault (such as 3 times indicating loss of ExSync signal, 5 times indicating failure to save fixed value, etc.). All measured values such as voltage, current, power, frequency, impedance, etc. can be viewed through the "Status" menu on the HMI to verify CT/VT polarity.

4.2 Polarity check (key)

After connecting to the actual system, read through HMI:

The positive sequence voltage should be ≈ Vnom, the negative sequence should be ≈ 0, and the zero sequence should be ≈ 0 (star connection).

Positive sequence current should ≈ load current, negative sequence and zero sequence should ≈ 0.

The active power symbol should be correct (positive indicates that the generator is supplying power to the system). If it is negative, the CT polarity may be reversed and the terminal wiring needs to be adjusted.

The differential current (87) should be close to 0. If there is a large differential current, check the CT ratio or polarity.

4.3 Functional testing (using relay protection tester)

Chapter 6 of the manual provides detailed testing procedures. Taking directional power (32) as an example:

Apply rated three-phase voltage and current according to the calculated value (e.g. 0.5 pu, corresponding to Inom × 0.5), adjust the current angle to make the power factor=1, slowly increase the current until 32 components act, record the action value, and the error should be ≤ ± 2% or 0.002 pu.

For the timed limit, apply 1.1 times the action value, measure the action time, with a tolerance of ± 16 cycles or 1%.

Other functions (21, 24, 27, 59, 87, etc.) can be verified with the assistance of the tester. Attention: Other unrelated functions should be disabled during testing to avoid accidental operation.

Common fault phenomena and troubleshooting

Possible causes and solutions for the phenomenon

Differential (87) misoperation CT polarity reversal, inconsistent transformation ratio, external fault CT saturation check CT terminal polarity (marked with "·" for inflow direction), check whether the CT transformation ratio setting is consistent with the neutral side; If there is an external malfunction causing misoperation, the slope can be appropriately increased or the delay can be extended