Beckwith M-3425A Relay Guide

Beckwith M-3425A Relay Guide

Product Overview and Functional Architecture

M-3425A is a microprocessor based digital generator protection relay that utilizes digital signal processing technology to provide the following protection functions:

1.1 Base Package

24 overexcitation (V/Hz)

27 phase undervoltage

32 directional power (reverse power, low forward power, or over power, can be tripped sequentially)

40 demagnetization (dual zone offset mO, capable of under voltage acceleration)

46 Negative sequence overcurrent and alarm

50 instantaneous phase overcurrent

50/27 accidental power on protection

50BF circuit breaker malfunction

50N instantaneous neutral overcurrent

51N inverse time neutral point overcurrent

51V voltage control/voltage braking phase overcurrent

59 phase overvoltage

59N neutral point overvoltage

59X Multipurpose Overvoltage (Interturn Fault or Bus Grounding)

60FL voltage transformer fuse loss detection and locking

67N zero sequence direction overcurrent

81 Four Step Over/Under Frequency

87 phase differential

87GD zero sequence differential

IPSigmic Programmable Logic

1.2 Comprehensive Package

Add the following features:

21 Three section inter phase distance protection (can be used as out of step locking, with load intrusion blind zone)

27TN third harmonic neutral point undervoltage (in conjunction with 59N to achieve 100% stator grounding)

49 stator overload (positive sequence overcurrent)

50DT timed overcurrent (for split phase differential)

59D Third Harmonic Voltage Ratio Differential

78 step loss protection (Mu Ou characteristic)

81A frequency accumulation

81R frequency change rate

1.3 Optional advanced features

25 Synchronous inspection (with dead busbar/dead line closing)

64F/64B rotor grounding and carbon brush lifting detection (requires external M-3921 coupler)

64S 100% stator grounding protection (20Hz low-frequency injection method, requiring external 20Hz signal source, bandpass filter, and CT)

Installation and wiring points

2.1 Mechanical Installation

M-3425A is a standard 19 inch rack mount, with optional heights of 3U (without expansion I/O) or 4U (with expansion I/O), and can also be installed vertically on a panel. Environmental temperature -20~+70 ℃, humidity ≤ 95%, no condensation. Good heat dissipation and ventilation should be ensured during installation.

2.2 Power Supply and Grounding

Power supply: Optional 24/48Vdc (18-56V) or 110/125/220/250Vdc/110/120/230/240Vac, with a power consumption of approximately 40VA. Optional redundant power supply.

Grounding: The equipment grounding terminal (protective ground) must be reliably connected to the power station grounding grid, and the grounding resistance should be less than 0.1 Ω.

2.3 Voltage Transformer (VT) Wiring

M-3425A provides 5 voltage input terminals, which can be flexibly configured as:

Single phase (line to line or line to ground)

Open Triangle (Two PT)

Three phase three wire star

Three phase four wire star

Dual bus (single-phase only)

Important: The transformation ratio and wiring method of the generator side VT and the bus side VT need to be accurately configured in the system settings. When using line to ground voltage but wanting to calculate internally according to line to line, the "Line Ground to Line" mode can be selected. At this time, the rated voltage should be set to the line to line value (approximately √ 3 times the line to ground value), and the secondary line to ground voltage should be 69V (not 120V).

2.4 Wiring of Current Transformer (CT)

Provide 7 current inputs, which can be connected to:

Three phase current (IA, IB, IC)

Three phase neutral point side current (Ia, Ib, Ic) - used for differential

Neutral point current (IN) or residual current

Cross flow compensation CT (ID+/-)

The CT secondary rating can be selected as 1A or 5A. Warning: The CT circuit must not be open circuited, and the CT secondary side must be short circuited before debugging.

2.5 Switching input/output

6 programmable control/status inputs (with expandable I/O up to 14), providing 24V wet contacts internally, only able to connect dry contacts.

8 programmable output relays (with expandable I/O up to 23), contact capacity: disconnect 6A/120Vac, 0.5A/48Vdc, 0.3A/125Vdc, etc.

The output relay can be configured as a pulse or self holding.

2.6 Communication Interface

COM1: Front panel RS-232 (DTE)

COM2: Rear panel RS-232 (if Ethernet option is enabled, COM2 is not available, but IRIG-B is still available)

COM3: Rear panel RS-485

Optional RJ45 Ethernet (supports MODBUS TCP/IP, BECO2200 over TCP/IP, or IEC 61850)

IRIG-B: BNC interface (accepts modulated signals) or COM2 pin 6 (TTL level, requires jumper)

Software configuration and debugging

3.1 IPScom software installation and connection

The accompanying IPScom communication software runs on Windows 2000 and above systems. The first connection requires the use of a null modem cable to connect the RS-232 port and relay COM1 port of the PC, with a default baud rate of 9600, 8 data bits, 1 stop bit, and no verification. The default communication address is 1. If communication fails, COM1 settings can be viewed/modified through the front panel HMI.

3.2 System Setup

To select 'Relay/Setup/Setup System' in IPScom, the following system parameters must be entered correctly:

Rated voltage: VT secondary side rated line line voltage (50-140V)

Rated current: CT secondary side rated value (1A or 5A)

VT configuration: line to line/line to ground/line to ground conversion line to line

Delta-Y Transformer: If the generator is connected to the system through a Δ/Y transformer, Delta-AB or Delta-AC should be selected for the relay to automatically compensate for a 30 ° phase shift.

Phase sequence: ABC or ACB

59/27 amplitude calculation method: RMS (frequency range 10-80Hz, slightly lower accuracy) or DFT (only fundamental frequency, high accuracy)

CT/PT ratio: primary value/secondary value

3.3 Protection Function Configuration

In "Relay/Setup/Replay Setpoints", set them one by one according to the function number:

Enable/Disable: Check according to the purchasing options

Output contact allocation: Select the output relay (OUT1~OUT8/OUT9~OUT23) that closes when the function is activated

Locking input: Select which input contacts can lock the function (such as circuit breaker position, external locking signal)

Setting value: Input according to the generator nameplate, capacity curve, and system coordination requirements

Example of typical function settings:

87 phase differential

Minimum operating current: 0.2-3.0A (usually 0.3A)

Slope: 1-100% (usually 10%)

Time delay: 1-8160 cycles (usually 1 cycle)

40 demagnetization protection

Two M-O circles: circle 1 diameter=X'd (transient reactance), offset=- X'd/2; Circle 2 diameter=Xd (synchronous reactance), offset=- X'd/2

Delay: Short delay for circle 1 (e.g. 15 cycles), long delay for circle 2 (e.g. 3600 cycles), with the option to add undervoltage acceleration

78 step loss protection

Muo circle diameter, offset, impedance angle, blind plate impedance

Out of step delay, sliding pole count (usually once)

Optional 'trip when the M-O circle exits' to obtain a more favorable trip angle

64S 100% stator grounding (low-frequency injection)

An external 20Hz signal source, bandpass filter, and dedicated CT are required. Settings:

Total current starting value (2-75mA)

Real current starting value (2-75mA)

Delay (cycles)

Optional voltage braking and low-frequency locking

3.4 Fixed value group (Profile)

The relay supports 4 sets of fixed values, which can be switched manually, through input contacts, or through IPSigmic. The relay will temporarily lock for about 1 second when switching. During debugging, you can first configure a set of "online" settings, copy them to another set, and then modify them to "maintenance" settings.

Common troubleshooting

The following is a summary of common fault phenomena and countermeasures based on Chapter 7 of the manual.

4.1 Excitation Control Issues (FCR Mode)

Possible causes investigation and handling of phenomena

No excitation current output excitation not enabled, wiring error, PMG power supply missing inspection software excitation enabled and external excitation enabled input (EX-D+); Check the excitation output circuit; Measure PMG input voltage

If the excitation output is lower than the set value FCR and not selected, the gain is incorrect, and the magnetic field resistance is too high, confirm that AVR-FCR_Select=1; Check the gain; Disconnect the excitation output to measure the magnetic field resistance, which should be within the specification range

Unstable excitation, improper gain, wiring interference, and recalibration of PID; Check the shielding grounding

4.2 Voltage regulation issues (AVR mode)

Possible causes investigation and handling of phenomena

Non excited output is the same as FCR -

Voltage below set value AVR not selected, insufficient power supply voltage, generator speed not reaching rated, droop compensation driving voltage reduced, OEL limiter action confirmed AVR-FCR_Select=0; Check the PMG voltage; Increase the rotational speed; Check if the droop is mistakenly activated; View OEL-Active bit

Voltage above set value AVR not selected, gain too high, UEL limiter action check mode selected; Reduce AVR_Kg; View UEL_Active bit

Voltage instability, improper gain, unstable prime mover speed regulator, limiter oscillation, and recalibration of PID; Check the speed regulator; Adjust OEL/UEL gain

4.3 Uneven distribution of reactive power in parallel (sagging or cross flow)

Possible causes investigation and handling of phenomena

The voltage does not sag with reactive power changes and is not enabled. The cross current mode is selected incorrectly. Check for V_DrooopEn=1 and Drooop_CCC_Select=0 (sag); If cross flow is required, check the ID CT wiring

Unequal distribution of reactive power, improper cross current gain, and increased cross current gain due to CT polarity reversal; Measure the polarity of ID+and ID - with a voltmeter, compare with the voltage of phase B, and switch the polarity of CT in reverse phase

Transfer of reactive power in the opposite direction with CT polarity error. Compare the CT polarity of each machine's cross flow to ensure consistency

4.4 Misoperation or non operation of demagnetization protection

No action: Check if the 40 function is enabled; Confirm that the diameter and offset of the M-O circle have been correctly set according to the generator parameters (Xd, X'd); Check if the CT/PT polarity is correct.

Erroneous movement: It may be due to the stable oscillation of the system entering the circle. The delay of circle 2 can be increased or the undervoltage control (VC) can be added to accelerate only at low voltage.

4.5 Out of step protection does not operate or malfunctions

Not moving: Check if the impedance circle and blind plate settings cover the out of step trajectory; Confirm if 'Trip on MHO Exit' is enabled as needed.

Erroneous movement: Stable oscillation may be misjudged as out of step, and delay or sliding pole counting can be increased.

4.6 100% stator grounding (64S) cannot operate correctly

Check external equipment: whether the 20Hz signal source is powered, whether the bandpass filter is connected correctly, and whether the 20Hz CT is connected correctly.

Set verification: The starting values of total current and real current should be greater than the capacitor current during normal operation (usually a few milliamps). When there is no fault, the 20Hz current value of IN can be monitored through IPScom and set to 2-3 times this value.

Voltage braking: If enabled, ensure that the neutral point 20Hz voltage is less than 25V under normal conditions, otherwise braking may reduce sensitivity.

4.7 Communication Failure

Possible causes and solutions for the phenomenon

Unable to establish connection serial port parameter mismatch, cable error, relay in local mode confirming COM1/COM2 baud rate, checksum, stop bit through HMI; Use null modem cable; Exit local mode

Read data errors after connection, address conflicts, noise interference, and check address uniqueness; Use shielded twisted pair cables and ground them; Add Dead Sync Time

Ethernet is not connected, IP address is set incorrectly, DHCP is not obtained. Check the IP/Netmask/Gateway in the "Ethernet Setup". If DHCP fails, manually set it

4.8 Circuit breaker failure (50BF) not triggered

Check whether the 50BF function is enabled; Is the starting value of phase current or neutral point current set too high; Is the input of the auxiliary contact (56a) of the circuit breaker wired correctly; Is the output contact configured with a circuit breaker failure tripping circuit.

Test: Simulate a fault to activate the protection, observe whether the 50BF timer starts, and if the current does not drop below the starting value and the circuit is still closed, output after a delay.

4.9 Loss of fuse (60FL) false alarm

Reason: When a phase to phase fault occurs in the system, the negative sequence voltage increases but the negative sequence current is not large, which may be mistaken as fuse loss.

Solution: Adjust the voltage/current threshold in the internal logic of 60FL (such as I2>0.167 I1 condition); Alternatively, an external fuse loss detection contact input can be used as a lockout.

Wave recording and event recording applications

M-3425A has a built-in recorder that can store up to 416 cycles of data, with partition numbers ranging from 1 to 16. Sampling rate of 16 points per cycle. Trigger method: input contact, output contact, functional action, serial command. The data can be stored in COMTRADE format and analyzed using IPSplot Plus.

Debugging technique: Before the first grid connection, IPScom can be used to manually trigger the waveform recording and observe whether the voltage and current waveforms are symmetrical and the phase sequence is correct. After the protection action, call the oscillograph file to analyze the fault type and action sequence.

Maintenance suggestions

Regular self check: Check the "Error Codes" and "Checksums" through HMI to confirm that there are no abnormalities.

Battery: The real-time clock uses a lithium battery. If it stops (displaying 80 seconds), it needs to be replaced (please contact the factory).

Firmware upgrade: Use IPScom's "Tools/Firmware Update" to perform the upgrade, and be sure to save the firmware file before upgrading.

Cleaning: Keep the panel and ventilation holes clean, and check the condition of the electrolytic capacitors every 5 years.

Calibration: It is recommended to verify the accuracy of voltage and current measurement with a standard source every year, and if necessary, perform "Auto Calibration" (to enter diagnostic mode).