Beckwith M-3310 Transformer Protection Relay Complete Guide

Full analysis of engineering application of Beckwith M-3310 transformer comprehensive protection relay

In the field of transformer protection in power systems, traditional electromagnetic relays and early microcomputer devices face dual challenges of flexibility and reliability. The M-3310 transformer protection relay launched by Beckwith Electric is a fully digital multifunctional integrated protection system designed for various capacity dual winding transformers and some three winding applications. This device not only provides comprehensive differential, overcurrent, grounding fault and backup protection, but also has programmable input/output, multi fixed value group switching, waveform recording and multiple communication protocols, providing a one-stop protection solution for power plant step-up transformers, substation main transformers and industrial distribution transformers. This article is based on the M-3310 specification book, systematically sorting out its protection functions, hardware configuration, wiring definitions, parameter settings, and engineering application points, providing in-depth technical references for relay protection engineers.

Product positioning and system architecture

M-3310 is a standard 19 inch rack mounted (3U high) digital relay with a modular design that includes a motherboard, power board, optional M-3931 human-machine interface module (HMI), and M-3910 target indication module. Its core design concept is "highly integrated and flexible configuration", suitable for the following scenarios:

Main and backup protection for double winding power transformers (of any capacity);

Partial three winding transformer (configured with two sets of winding CT inputs);

Optional three-phase voltage protection package, realizing overexcitation, undervoltage, neutral point overvoltage and low-frequency protection;

Through external I/O expansion, achieve logic such as load shedding, rapid isolation of bus faults, and backup tripping of feeder switches.

The standard protected function library (corresponding to ANSI number) includes:

Negative sequence inverse time overcurrent (46)

Double winding double segment instantaneous phase overcurrent (50W1 # 1/# 2, 50W2 # 1/# 2)

Circuit breaker failure (50BF)

Transformer neutral point instantaneous/inverse time overcurrent (50G/51G)

Double winding inverse time overcurrent (51W1/51W2)

Residual inverse time overcurrent (51NW1/51NW2)

Dual winding phase to phase differential (87T) and high-value instantaneous differential (87H)

Grounding differential (87GD)

Six external functions (programmable delay exit)

Optional voltage protection package (to be ordered) added:

Overexcitation (24) V/Hz

Undervoltage (27) is used for load shedding

Neutral point overvoltage (59G)

Low frequency (81U)

Hardware structure and external wiring

2.1 Chassis and Power Supply

Physical dimensions: 19 "wide x 5.21" high x 10.20 "deep (approximately 48.3 x 13.2 x 25.9 cm), 3U high, can be installed horizontally or vertically.

Power input: You can choose 110/120/230/240V AC or 110/125/220/250V DC (UL range 85~265V AC/80~288V DC), or choose the 24/48V DC low voltage version. Power consumption is about 20VA. Optional redundant power supply (dual power module).

Power status indication: The PS1/PS2 LED on the front panel indicates that the power supply is normal, and the self-test status relay (normally closed) is closed after the device self-test is passed.

2.2 Analog input (see Figure 1 for terminal definitions)

Voltage input: 4-channel voltage (Va, Vb, Vc, Vn), rated at 60-140V AC, used for voltage protection package and differential voltage reference (such as V/Hz). Can be connected to phase voltage or line voltage.

Current input: 7 current inputs, corresponding to:

Winding 1 three-phase current (IA1, IB1, IC1)

Winding 2 three-phase current (IA2, IB2, IC2)

Neutral point/ground current (IG)

The CT rating can be selected as 5A or 1A (specified when ordering). Tolerance: 2 x In continuously, 100 x In for 1 second.

2.3 Control inputs and outputs

6 programmable digital inputs (terminals 5-10, common terminal 11): with 24V wet contacts inside, only dry contacts are allowed to be connected (external voltage is strictly prohibited). Can be configured as:

Block any protective function;

Trigger waveform recording;

Switch between fixed value groups (Profile 1-4);

Drive output relay;

Circuit breaker status (used to indicate the position of the circuit breaker).

8 programmable output relays: 1~6 are type A normally open contacts, and 7~8 are type C conversion contacts. Output 1-4 with high-speed drive circuit (about 4ms faster than 5-8). All contact ratings comply with IEEE C37.90, UL certification: 8A current carrying, 6A disconnect (120V AC), 0.1A disconnect (125V DC).

Self check alarm output: a normally closed contact (opens in case of power failure or self check failure).

Power status relay: normally open, closed when the power supply is normal.

Wiring precautions: Terminal blocks require # 22~12 AWG copper wire with a torque of 12 in lbs (terminals 1~34), and other terminals require 8~9 in lbs.

Detailed description and setting of core protection functions

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.

Data can be accessed through a dedicated IPSlot ®  PLUS software analysis, or conversion to COMTRADE standard format through ComVert tool for easy interaction with third-party tools.

6.2 Event Recording

It can store 32 recent events (targets), including action functions, picking, input/output status, timestamps, and current values of each phase during tripping.

6.3 Real time measurement

Measurement parameters include voltage, current, power factor, active/reactive/apparent power, frequency, demand (15/30/60 minute sliding), and maximum value (with time stamp).

Accuracy: Current ± 0.1A or ± 3% (5A rated), voltage ± 0.5V or ± 0.5%, power ± 0.01PU or ± 2%, frequency ± 0.02Hz.

Communication and time synchronization

Communication ports: Front panel RS-232 (for local debugging), rear panel RS-232 and RS-485 (can connect 2 or 4 wires), supporting Modbus RTU and BECO 2200 proprietary protocols.

PC software: M-3820A IPScom ®  Used for parameter reading and writing, real-time monitoring, and firmware upgrades.

IRIG-B synchronization: accepts modulated or demodulated IRIG-B signals, providing high-precision time labels for events and recording.

Key points for installation and debugging

Rack installation: Standard 19 inch cabinet can be installed horizontally or vertically (optional mounting rack is required). The opening size is shown in Figure 4/5.

CT polarity: Differential protection requires that the CT polarity directions on both sides be consistent (both pointing towards the transformer), and must be confirmed according to the typical wiring diagram in Figure 2/3.

CT ratio compensation: By adjusting the CT Tap parameters, the balanced current of the differential circuit is made to approach zero at rated load.

Harmonic blocking test: Before powering on, a relay protection tester can be used to apply a current containing second harmonic to verify whether the differential is reliably blocked.

Circuit breaker status input: INPUT1 needs to be connected to contact 52b (closed when the circuit breaker is open) to ensure that the BRKR CLOSED LED and logic on the front panel are correct.

Output contact testing: Verify the mapping relationship between the protection functions corresponding to each output, ensuring that the tripping matrix is correct (for example, tripping both the high and low voltage side circuit breakers simultaneously after the 87T action).

Fixed value group switching verification: If multiple fixed values are used, external contacts or communication should be used to switch and verify the current activated group.

Environment and Certification

Working temperature: -20 ℃~+70 ℃ (storage -40 ℃~+70 ℃), humidity 93% RH@40 ℃.

Electromagnetic compatibility: through IEC 1000-4-2 electrostatic discharge (8kV), IEC 1000-4-4 fast transient (4kV), IEEE C37.90.1 oscillating wave/fast transient (2.5kV/5kV) and radiation immunity (35V/m).

Insulation withstand voltage: All circuits to ground 3500V DC/1min, RS-485/RIG-B to ground 1500V DC.

Certification: cULus Listed (UL 508 and CSA C22.2), suitable for industrial control equipment and control cabinets.

Common engineering application extensions

Load Shedding: Utilizing the undervoltage (27) function in the voltage protection package, in conjunction with external output contacts, to quickly cut off secondary loads when the bus voltage drops, preventing transformer overload.

Bus Fault Protection: Combining the logic of M-3310 and feeder digital relays, it receives feeder protection action signals through external inputs to achieve rapid isolation of faults within the bus area.

LTC fault lockout: When an internal fault is detected, the on load tap changer operation is locked to prevent the fault from expanding.

Cooperate with automatic backup power input (BZT): Utilize circuit breaker failure and low-frequency protection to quickly activate the backup power input logic after the transformer trips.

Maintenance and fault diagnosis

Self check function: The device continuously performs software and hardware self checks. If any abnormalities are found, the SELF-TEST ALARM contact will activate and the RELAY OK LED on the front panel will turn off.

Target reset: Press the TARGET RESET key to reset the target LED (if the fault has disappeared); Long press to view the protective components currently in the picking state.

Wave recording analysis: For tripping accidents, the wave recording file should be downloaded and IPSpot should be used to analyze the differential current waveform, distinguishing between faults within the area and non fault disturbances such as excitation inrush current and CT saturation.

Firmware upgrade: Use IPScom software to upgrade through the RS-232 port on the front panel, and be sure to save the original settings file.