Beckwith M-3310 Transformer Protection Relay Complete Guide

3.1 Differential protection (87T and 87H)

87T percentage differential: with dual slope characteristics (Slope # 1 and # 2), the inflection point can be set to 1.0~4.0 PU. The minimum operating current is 0.10~1.00 PU (step size 0.01 PU).

Second/fourth harmonic blocking: can be set to 5%~50% respectively, used to prevent excitation inrush current misoperation; Fifth harmonic blocking (5%~50%) is used for overexcitation suppression.

87H high-value instantaneous differential: action current of 5.0~20.0 PU, delay of 1~8160 cycles (minimum action time of 1.5 cycles), used for quickly cutting off serious faults in the area.

CT ratio compensation: Two sets of windings are each equipped with CT ratio coefficients (1.00~10.00/0.20~2.00) to automatically balance the currents on both sides.

Setting suggestion: Calculate the minimum differential operating current based on the rated capacity of the transformer, CT ratio, and short-circuit impedance, generally taking 0.3~0.5 PU; Slope # 1 is usually set to 20%~30%, and Slope # 2 is set to 50%~80%; The typical value of harmonic blocking is 15%~20%.

3.2 Phase Overcurrent and Grounding Overcurrent

51W1/51W2 inverse time overcurrent: Each winding is independently set, and options include Define Time, Inverse, Very Inverse, Extremely Inverse, and IEC standard curves (SIT, VIT, EIT, LTI). Current setting of 0.50~12.00 A (under 5A CT), time dial of 0.5~11.0.

50W1/50W2 instantaneous phase overcurrent (dual stage): two independent constant values (1.0~100.0 A), fixed action time of 2 cycles, used for rapid fault removal in the near area.

51G neutral point inverse time overcurrent: used for grounding protection of transformer neutral point grounding system, with the same setting and curve as above.

50G instantaneous overcurrent at neutral point: fixed value 1.0~100.0 A, fixed 2-cycle action.

3.3 Negative sequence overcurrent (46)

It can be set with a fixed time limit or inverse time limit (multiple curves), with a constant value of 0.10~20.00 A (secondary side), used to detect asymmetric faults (such as turn to turn short circuits, wire breaks), prevent rotor overheating (especially important for generator side transformers).

3.4 Circuit breaker failure (50BF)

The starting criterion can be selected as phase current or residual current, with a fixed value of 0.10~10.00 A and a delay of 1~8160 cycles. Usually, the delay is set to be greater than the inherent opening time of the circuit breaker plus the protection action time, such as 10-20 cycles.

3.5 Grounding Differential (87GD)

Grounding fault protection for transformer neutral point direct grounding system, which achieves directional differential by comparing the neutral point CT with the residual current of the winding. Fixed value 0.2~10.00 A (secondary), delay 1~8160 cycles. Built in CT ratio correction (0.1~7.99). Note: If 3I0 or I is extremely small, the directional component will be disabled.

3.6 External Functions (EXIT # 1~# 6)

Six programmable external input triggers, each of which can select any input (IN # 1~# 6) or output (OUT # 1~# 8) as the starting condition, and drive the selected output after adjustable delay. Used to implement user-defined logic such as interlocking tripping and load shedding.

Voltage protection package (optional)

When ordering a voltage pack, the following additional protections can be enabled:

4.1 Overexcitation (24) V/Hz

Time limit: Two stages, fixed value of 100%~200% (rated V/Hz), delay of 30~8160 cycles.

Inverse time limit: There are four curves to choose from, with a time dial of 0-9.0 (curve 2-4) or 1-100 (curve 1), and a reset rate setting (1-999 seconds). The accuracy is effective within the range of 10~80Hz, 0~180V, and 100%~150% V/Hz.

4.2 Undervoltage (27)

Using positive sequence voltage measurement, with a fixed value of 5-140V, and a prohibition value can be set (for load shedding locking). Delay of 1~8160 cycles.

4.3 Neutral point overvoltage (59G)

Fixed value of 5.0~140.0V, can be configured to measure open delta zero sequence voltage (external VN input), with adjustable delay.

4.4 Low frequency (81U)

Three independent fixed values (48.00~59.99 Hz or 38~49.99 Hz for the 50Hz model) with a delay of 2~65500 cycles. Accuracy ± 0.02Hz (within the operating frequency band).

Set up groups and flexible configurations

M-3310 supports 4 independent constant value groups (profiles), which can be switched through HMI, communication, or external input contacts. This function is very suitable for quickly switching protection settings under different operating modes (such as parallel/split, winter/summer load changes), avoiding manual reset errors.

Each fixed value group can independently store the action values, delays, curve selection, and output mapping relationships of all protection functions.

Wave recording, event recording, and measurement

6.1 Oscillographic Recorder

Sampling rate: 16 times the power frequency (50/60Hz corresponds to 800/960Hz), with a maximum total recording length of 170 cycles, and can be partitioned (1-4 recording blocks).

Trigger source: Optional digital input, output contacts, or serial commands. Support pre triggering and delayed triggering, facilitating the capture of transient fault waveforms.