Beckwith M-3311 Transformer Protection Relay Setting and Engineering Application

Beckwith M-3311 Transformer Protection Relay Comprehensive Application and Setting Technical Manual

In the field of power system relay protection, the selection and configuration of transformer protection devices directly affect the service life and power supply reliability of the main equipment. M-3311 Integrated Protection System launched by Beckwith Electric ® It is a comprehensive protection relay designed specifically for double winding and three winding transformers, and is also suitable for unit protection, busbar area protection, and circuit breaker failure backup in power plants. This model adopts a standard 19 inch 3U chassis, supports 1A or 5A CT input, and provides rich standard protection functions and optional single-phase voltage protection package. This article is based on the M-3311 product specification, systematically reviewing its protective components, hardware characteristics, logic programming, engineering wiring, and testing standards, providing detailed technical references for on-site engineers.

Device positioning and applicable scenarios

M-3311 is designed for transformers with 2 or 3 windings, covering various voltage levels for transmission and distribution. Its core applications include:

Transformer main protection (differential, overcurrent, grounding);

Unit protection for power plants (overall differential of generator transformer unit);

Bus rapid protection (combined with feeder relay logic);

System backup protection and load shedding (voltage pack optional);

Independent failure protection for each winding incoming circuit breaker.

Compared to the later upgraded model M-3311A, this model does not support a four winding configuration, and the voltage input is only a single channel (optional phase voltage or open delta voltage). The ground differential only supports two windings (W2, W3). But its compact design and mature logic are still widely used in small and medium-sized substations.

Detailed explanation of standard protection functions

M-3311 is equipped with complete current type protection, thermal protection, differential protection, and external logic functions. All settings can be adjusted through communication or local HMI.

1. Negative sequence overcurrent (46W2/46W3)

Provide negative sequence overcurrent protection for winding 2 and winding 3, which can be set as timed or inverse time limit.

Time limit: Start value of 0.10~20.00A (secondary value), delay of 1~8160 cycles, accuracy of ± 0.1A or ± 3%.

Inverse time limit: Start value of 0.50~5.00A, supports Definite Time, Inverse, Very Inverse, Extremely Inverse and IEC standard curves, time scale of 0.5~11.0 (or IEC 0.05~1.10), accuracy of ± 3 cycles or ± 5%.

This function is crucial for detecting asymmetric faults such as phase failure and turn to turn short circuit.

2. Winding thermal protection (49)

Simulating winding temperature rise based on current thermal effect requires setting a thermal time constant (1.0~999.9 minutes) and a maximum overload current (1.00~10.00A). You can choose to protect winding W1, W2, or W3. After the action, it will output an alarm or trip, effectively preventing insulation overheating and aging.

3. Instantaneous/inverse time overcurrent (50/51)

Instantaneous phase overcurrent (50W1/50W2/50W3): Each winding provides 2 independent components (# 1, # 2), with a starting value of 1.0~100.0A (secondary) and a delay of 1~8160 cycles, which can be applied to instantaneous or fixed time limit.

Inverse time overcurrent (51W1/51W2/51W3): starting value of 0.50~12.00A, supports Definite Time and multiple inverse time curves (IEC and Beco), time scale of 0.5~11.0 (or IEC 0.05~1.10), accuracy of ± 3 cycles or ± 3%.

Instantaneous grounding overcurrent (50GW2/50GW3): For windings 2 and 3, the starting value is 1.0~100.0A, with a delay of 1~8160 cycles.

Inverse time grounded overcurrent (51GW2/51GW3): starting value of 0.50~12.00A, with the same curve and time scale as above.

Instantaneous/inverse time residual overcurrent (50NW1/50NW2/50NW3, 51NW1/51NW2/51NW3): Based on three-phase current vector sum (zero sequence), it provides high-sensitivity grounding protection, especially suitable for ungrounded or arc suppression coil grounded systems.

4. Circuit breaker failure protection (50BF)

Each winding incoming circuit breaker is equipped with an independent failure component, which can use phase current (50BFW1~W3) or residual current (50BFNW1~W3) as the discrimination variable, with a starting value of 0.10~10.00A (phase) or 0.10~10.00A (residual), and a delay of 1~8160 cycles. Once the circuit breaker refuses to move, this function will extend to trip adjacent circuit breakers.

5. Differential protection (87T/87H)

The core of transformer main protection is the percentage braking differential element 87T and the high setting instantaneous element 87H.

87T setting item:

Differential starting value: 0.10~1.00PU, step size 0.01PU;

The slope of the first section is 5%~100%, and the slope of the second section is 5%~200%;

Turning point: 1.0~4.0PU;

Second harmonic braking (2nd, 4th): 5%~50%, used to suppress excitation inrush current;

Fifth harmonic braking: 5%~50%, used for overexcitation lockout;

Additional starting value under fifth harmonic braking: 0.10~2.00PU;

CT tap compensation: 1.00~10.00 per winding (or 0.20~2.00 corresponding to 1A rated).

87H: Start value 5.0~20.0PU, delay 1~8160 cycles (minimum action time<1.5 cycles at 1 cycle).

Each braking component can be independently enabled/disabled or set to cross phase averaging to increase flexibility.

6. Grounding differential (87GDW2/87GDW3)

Used to detect grounding faults in winding 2 or winding 3, as a directional differential element, the directional element automatically exits when the zero sequence current is extremely small. The startup value is 0.2~10.00A, and the recommended delay is not less than 2 cycles. The CT transformation ratio correction coefficient is 0.1~7.99.

7. External functions (EXT # 1~# 6)

Provide 6 external input/output logic functions, which can trigger specified outputs after delay (1-65500 cycles) for any input contact (IN1-IN6) or output contact (OUT1-OUT8), and can be combined with BECO Logic to form complex interlocks. This function facilitates the integration of non electricity protection (such as gas, temperature) and the unified recording of target information.

Optional single-phase voltage protection package

For applications that require voltage, M-3311 provides an optional single-phase voltage input (only one channel), which can be connected to either phase voltage (for frequency, undervoltage, overexcitation) or open delta voltage (for ground overvoltage), but the two cannot be used simultaneously. Specific functions include:

Overexcitation protection (24 V/Hz): Based on the rated secondary voltage and frequency, provide 2 timed limit elements (starting value 100%~200%, delay 30~8160 cycles) and 1 inverse time limit element (starting value 100%~150%, multiple curves to choose from). The accuracy is suitable for the range of 10~80Hz and 0~180V.

Undervoltage (27): Used for load shedding, with a starting value of 5-140V, a delay of 1-8160 cycles, and a suppression voltage (to prevent PT disconnection and misoperation).

Grounding overvoltage (59G): Only available when the voltage input is connected to the open delta VT, providing 2 components with a starting value of 5-180V and a delay of 1-8160 cycles.

Frequency protection (81O/U): 4 components each for overclocking and low-frequency, with a setting range of 45-65Hz (45-55Hz for 50Hz models), a delay of 2-65500 cycles, and an accuracy of ± 0.1Hz (57-63Hz for 60Hz models).

Attention: When selecting phase voltage input, 59G is not available; When selecting an open triangle, 24, 27, and 81 are not available and need to be balanced based on the actual main wiring.

Standard hardware and communication interface

1. Input/output configuration

Control/status inputs: 6 (INPUT1~6), internal wet connection 24Vdc, minimum excitation current>25mA. INPUT1 is dedicated to connecting the auxiliary contacts of circuit breaker 56a to provide circuit breaker status LED indication. There is also an independent input used to monitor the integrity of the trip circuit (expected to be supported in the future).

Programmable outputs: 8 (OUTPUT1~8), of which 1-6 are A-type normally open contacts and 7-8 are C-type conversion contacts; There is also a power failure alarm output (type B) and a self-test alarm output (type C). All output contacts are rated in accordance with IEEE C37.90 (specific parameters see below).

Output contacts 1-4 have high-speed operation characteristics, about 4ms faster than 5-8, suitable for fast tripping circuits.

2. Communication port

Three serial ports: two RS-232 (one front and one back) and one RS-485;

One IRIG-B port (BNC) for time synchronization (supporting modulation or demodulation);

Supports MODBUS, BECO 2200, and DNP 3.0 protocols, and with M-3820B IPScom software, it can achieve constant value reading and writing, real-time measurement, event extraction, and waveform download.

3. Measurement and recording

Real time measurement: voltage, three-phase current, neutral point current, frequency, and positive/negative/zero sequence components; Can record the required current and maximum value (with time stamp) for 15/30/60 minutes.

Accuracy: Voltage ± 0.5V or ± 0.5%; Current (5A rated) ± 0.1A or ± 3%; Frequency ± 0.1Hz.

Oscillatory recording: The sampling rate is 16 times the system frequency, and the total recording length can be configured with 1-4 partitions, with a maximum storage capacity of 152 cycles of data. The triggering methods include status input, trip output, or communication command. The recorded data can be analyzed or exported as COMTRADE using IPSlot Plus.

Target storage: It can store 32 recent tripping events, including action components, current values, time scales, and I/O states.

Circuit breaker monitoring: Estimate the wear of each phase contact by integrating I ² t or It, and trigger an alarm or trip when the cumulative value exceeds the user threshold. The timing needs to be triggered by an external starting contact.

4. Optional hardware modules

M-3931 HMI module: Provides a 2-line x 24 character LCD and a 6-key keyboard, supporting on-site fixed value viewing, modification, event retrieval, and measurement display, with three-level password protection.

M-3911 Target Module: Provides 24 target LEDs and 8 output LEDs to visually display protection actions and output status.

Redundant power supply: Optional dual power modules improve power supply reliability.

Programmable Logic (BECO Logic)

M-3311 has built-in BECO Logic function, which can generate new output control signals by Boolean logic combination (OR, AND, NOR, NAND) of input status, output status, and protection element action flags through IPScom software. For example, the temperature controller alarm contacts can be combined with overcurrent signals to achieve air cooling interlocking or lockout pressure regulation. This feature greatly enhances the flexibility of the device and adapts to various special secondary circuit requirements.

Key points of tuning and configuration

1. Setpoint Groups

The relay supports 4 independent constant values, which can be switched through HMI, communication, or external input to adapt to different operating modes (such as parallel/split, summer/winter load levels). The switching process does not affect the normal operation of the protection.

2. CT and VT wiring

CT input: There are a total of 11 current inputs, covering three-phase winding current and neutral/ground current. Rated 5A or 1A optional, continuously withstand 3 times the rated value, and withstand 100 times the rated value in 1 second.

VT input: single voltage, rated at 60-140Vac, can be connected to phase voltage (L-G or L-L) or open delta. The wiring method needs to be configured with VT Config (VA, VB, VC, VAB, VBC, VCA, VG) in the Nominal Settings.

Phase rotation: ABC or ACB can be selected to ensure correct differential phase correction.

3. Differential protection CT tap compensation

The CT tap value (CT Tap) of each winding needs to be calculated and set based on the actual CT transformation ratio and transformer voltage ratio to ensure minimal differential current during external faults. Tap range 1.00~10.00 (5A rated) or 0.20~2.00 (1A rated).

4. Precautions for grounding differential

The time delay of 87GD should not be less than 2 cycles to avoid transient unbalanced misoperation. When the zero sequence current is extremely small, the directional component automatically exits and becomes non directional, requiring coordination with the system grounding method.

5. Temperature controller monitoring

BECO Logic can be connected to the alarm contacts of the transformer temperature controller (such as oil temperature, winding temperature) to start the fan, issue an alarm or lock the on load voltage regulation according to the temperature level. Figure 1 (original manual Figure 1) is a typical application example.

Example of Engineering Application Wiring

The manual provides various typical wiring diagrams (Figure 3-Figure 8):

Typical single line diagram of dual winding/triple winding transformer (Figure 3): Clearly display the signal flow of CT layout, differential, overcurrent, grounding, and voltage input.

Dual power plant unit protection (Figure 4): Integrating the generator and transformer into the same differential zone to expand the protection range.

Integrated unit protection for power plants (Figure 5): applicable to generator transformer units.

Three winding transformer with parallel reactor and ground fault protection (Figure 6): shows the coordination of ground differential and zero sequence overcurrent.

Main backup bus coupled radiation substation (Figure 7): Combined with bus protection logic.

Figure 8 is a typical three wire connection diagram, with detailed labeling of the external terminal arrangement (Figure 2). Attention should be paid to the high-speed characteristics of output contacts 1-4, torque requirements for wiring terminals (12 in lbs for terminals 1-34, 8-9 in lbs for terminals 35-63), and only dry contacts are allowed for input terminals (internal wet connections, external pressure may damage the device).

Testing standards and reliability

M-3311 complies with multiple international and industry standards:

Insulation withstand voltage: IEC 60255-5, 3500Vdc (1 minute) for each independent circuit to ground and between circuits, 1500Vdc for IRIG-B and RS-485 circuits.

Impulse voltage: 5000V peak to peak value, 1.2/50 μ s waveform, 500 Ω impedance.

Electromagnetic compatibility: electrostatic discharge IEC 61000-4-2 Class 4 (8kV contact); Fast transient IEC 61000-4-4 Class 4 (± 4kV, 2.5kHz); Radiation immunity IEEE C37.90.2 (25~1000MHz, 35V/m).

Output contact: IEEE C37.90 (30A closed for 0.2 seconds at 250Vdc); UL 508 (8A current carrying, 6A disconnection at 120Vac).

Environment: Working temperature -20 ℃~+70 ℃, humidity 93% (40 ℃), vibration response 0.5g, vibration resistance 1.0g.

Certification: cULus Listed (NRGU/E128716), compliant with CAN/CSA C22.2 No.14.

Physical parameters and storage requirements

Size: 19 "wide x 5.21" high x 10.20 "deep (3U), weight approximately 20.4 pounds (excluding options), shipping weight 28 pounds.

Power supply: Wide range AC/DC universal (85~265Vac or 80~288Vdc), or low-voltage DC (18~56Vdc), with a power consumption of 20VA. Optional redundant power supply.

Storage: It is recommended to maintain a temperature of 5-40 ℃, humidity of ≤ 80% (below 31 ℃), and avoid dust, corrosive gases, rainwater, and sunlight.

Maintenance and spare parts recommendations

Considering that M-3311 is an early model that has now been replaced by M-3311A, it is important to note during on-site operation that:

If replacement is required, refer to the compatibility of M-3311A, but confirm the differences in CT quantity, voltage input channels, and winding number (M-3311A supports four windings and more voltages).

Regularly download waveform and event records through IPScom software, as data loss occurs after the device loses power (oscillation waveform and event records are stored in RAM).

Check that only dry contacts are allowed on the input terminals to avoid damage caused by accidental connection to external power sources.

For external logic such as temperature controller monitoring, it is necessary to regularly verify the correctness of the BECO Logic program.