Beckwith M-0359 Syncrocloser ®  Application Guide for Check Plus Grid Connection Synchronization Check Relay Engineering

The voltage, frequency, and phase angle conditions at the moment of circuit breaker closing are directly related to system stability and equipment safety in key operations such as transmission line reclosing, substation busbar paralleling, and islanding system recovery. M-0359 Syncrocloser launched by Beckwith Electric ®  Check Plus is an all solid state synchronous inspection relay designed specifically for power transmission and primary distribution systems. It can detect the static phase angle on both sides of the fracture within 0.5 seconds, while monitoring voltage amplitude and frequency difference. It also supports dead wire/dead bus closing, remote phase angle setting offset, and SCADA analog output. This article is based on the official M-0359 application guide, providing a complete technical implementation manual for relay engineers from working principles, setting methods, external wiring, analog output configuration to on-site debugging and maintenance.

Product positioning and core features

M-0359 is a direct upgraded substitute for traditional electromechanical synchronous inspection relays (i.e. "synchronous inspection" relays), but its functionality far exceeds the latter. It not only has independently adjustable voltage upper and lower limits, voltage difference, frequency difference, and phase angle windows, but also adds dead line/dead bus closure and SCADA compatible analog output (phase angle, frequency difference, voltage and voltage difference on each side), allowing the dispatch center to monitor the status of both sides of the circuit breaker in real time and assist in decision-making.

Typical application scenarios:

Substation interconnection line circuit breaker - synchronously closes when there is static or rotating phase angle.

Operator's backup device - indicates the reason for lockout (voltage, frequency, or phase angle exceeding the limit) through status contacts, making it easy for the operator to adjust system parameters.

Backup of automatic synchronization device - such as in conjunction with Beckwith M-0193 Syncrocloser, M-0193 is responsible for rotating phase angle (island) closing, M-0359 is responsible for static phase angle (networking) or dead line/dead bus closing, complementing each other.

Core advantages:

All setting knobs are independent of each other and can be adjusted on-site without the need for additional instruments.

The power supply is taken from the higher voltage input of Line or Bus (automatically turned off when below 65V), with a power consumption of only 11VA (main input)+1VA (other side).

Fully sealed semiconductor devices, instrument grade resistive capacitive components, operating temperature range of -40~+80 ℃, suitable for harsh outdoor environments.

Both input and output have passed the ANSI/IEEE C37.90.1-1989 transient immunity test, with a ground withstand voltage of 1500V AC/1min. The Line/Bus voltage input transformer is isolated, and the grounding scheme is flexible.

Definition of Input, Output, and Terminal

M-0359 adopts a standard 19 inch chassis (2U height), and all external connections are completed through the rear terminal block (mainly TB1). The key terminal functions are as follows (see Figure 2 in the manual):

Terminal Function Description

TB1-1 Bus voltage input (hot end) 120V AC nominal, maximum continuous 145V, withstand 240V/1s

TB1-2 Bus Voltage Input (Neutral) -

TB1-3 Line Voltage Input (Neutral) -

TB1-4 Line voltage input (hot end) as above

TB1-5/6 Bus Voltage Analog Output 0~7.5V DC corresponds to 0~150V rms (Option 1) or Current Output (Option 2)

TB1-7/8 Line voltage analog output is the same as above

TB1-9/10 Delta V analog output 0~10V DC corresponding to 0~20V rms (standard range)

TB1-1/12 phase angle analog output 0~10V DC corresponds to 0~± 180 ° (absolute value output)

TB1-13 Analog Common Terminal (0V) All analog signals share ground

TB1-14/16 Dead Line/Dead Bus Enable Input Close Contact Enable Dead Line Close or Dead Bus Close respectively

TB1-15/21 phase angle limit offset input external contact point can reduce or expand phase angle setting value (choose variable ratio when ordering)

TB1-17/18/19 closing relay contact normally open dry contact, connected at 25A/250V DC, disconnected at 0.9A/120V DC (inductive)

TB1-20 status contact common terminal -

TB1-22/23 phase angle OK status relay closed indicates that the phase angle meets the requirements (light load, 1A/125V DC resistive)

TB1-24/26 synchronous check enable input high level (or contact) enable synchronous check function

TB3-c/D Delta F analog output 20V/Hz, 10V corresponds to 0.5Hz

Important notice: Both Line and Bus inputs need to pass through the PT secondary side (120V line voltage or phase voltage), and the two voltages are isolated from each other and can be connected to different grounding systems. All control inputs (dead line, dead bus, phase angle offset, synchronization enable) are external dry contacts or level signals (0V common terminal).

Simultaneous condition detection logic

M-0359 monitors the following four types of conditions internally, and only closes the closing relay when all conditions are met (except for dead wire/dead bus mode):

Voltage amplitude condition:

The voltage of Line and Bus must be ≥ Lower Voltage Limit and ≤ Upper Voltage Limit (two independent checks).

Meanwhile, | Vbus - Vline | ≤ Delta V Limit.

Three voltage related LEDs (BUS UPPER/OWER OK, LINE UPPER/OWER OK, DELTA V OK) are all illuminated.

Delta F Limit condition:

Measure the frequency difference (slip) on both sides, and when it is ≤ the set value (0.01~0.5Hz continuously adjustable), the DELTA F OK LED will light up.

Phase Angle Limit:

Measure the phase angle difference (absolute value) of the voltage on both sides. When it is ≤ the set value (0~± 30 °, other ranges can be customized), the ANGLE OK LED lights up.

Phase angle detection is static and does not consider the direction of slip (i.e. sign). As long as the absolute value is less than the limit, it is allowed.

Dead line/dead bus mode (enabled through external contacts):

If Dead Line Close is enabled, when the Line voltage is lower than DEAD LINE LIMIT (10~60V), the phase angle and frequency difference are ignored, and closing is allowed (but at least one side voltage is greater than 100V to ensure relay action).

Similarly, Dead Bus Close takes effect when the Bus voltage is below DEAD BUS LIMITED.

Attention: When both are activated simultaneously, dead wires and dead busbars will not occur simultaneously (the system will not close when there is no power on both sides).

When all allowable conditions are met and the synchronization check enable (TB1-24/26) is valid, the closing relay (TB1-17~19) closes and outputs a closing command.

Setting values and tuning methods

All settings are completed through the front panel knob, without the need for auxiliary power or instruments. The calibration accuracy of the scale is as follows:

UPPER VOLTAGE LIMITED (110~140V): ± 2% of full scale.

LOWER VOLTAGE LIMITED (90~120V): ± 2% of full range.

DELTA V LIMITED (1-5V, other ranges optional): ± 5% full range.

DEAD LINE/BUS LIMITED (10~60V): ± 7% of full scale.

Phase Angle Limit (0~± 30 °, other ranges optional): ± 5% full range.

DELTA F Limit (0.01~0.5Hz): ± 5% of full scale.

Setting steps (recommended):

Set the Upper/Lower limits based on the rated voltage of the system, for example, if 125V ± 10%, set Upper=137V and Lower=112V.

According to the allowed steady-state pressure difference, Delta V is usually set at 2-3V (corresponding to approximately 2-3kV on the primary side).

Set the phase angle limit (e.g. 15 °) based on the maximum allowable impulse power when the system is parallel, taking into account the system impedance and circuit breaker capacity.

Set a frequency difference limit (e.g. 0.1Hz) based on the system's frequency modulation capability to ensure that the circuit breaker does not close frequently during low-frequency oscillations.

If dead line/dead bus is required, set the Dead Line/Bus threshold (usually 30-40V, indicating that the line has significantly lost voltage).

Phase angle offset function: The phase angle limit can be changed through external contacts (TB1-15/21). For example, if the switch needs to be closed at 15 ° during normal operation and relaxed to 30 ° during emergency, select a 1/2 ratio for ordering, set the panel knob to 30 °, and close the contacts normally (making the limit value 15 °), and open the contacts in emergency (restoring 30 °). On the contrary, if a normal angle of 15 ° is required and a special working condition is narrowed to 3 °, then a 1/5 transformation ratio is selected, the panel is set to 15 °, and the contact is closed in emergency situations (the limit is changed to 3 °).

Analog output and SCADA interface

M-0359 provides 5 analog outputs (Bus voltage, Line voltage Delta V、 Phase angle Delta F）， The output type can be voltage type (0~10V DC) or current type (0~5mA DC), please specify the option when ordering. The voltage type can be directly connected to the AI module of RTU or PLC, while the current type is suitable for long-distance transmission.

Output characteristics (voltage type standard):

Phase angle: 0.0556 V/°, 10V corresponds to ± 180 ° (absolute value, i.e. 0~180 ° corresponds to 0~10V).

Voltage: 0.05 V/V, 7.5V corresponds to 150V rms.

Delta V: 0.5 V/V, 10V corresponds to 20V rms (if other ranges are selected, please consult the factory).

Delta F: 20 V/Hz, 10V corresponds to 0.5Hz.

Current type modification: Users can connect resistor R3 in series at the output terminal of the internal operational amplifier to achieve voltage current conversion. The manual provides the calculation formula for R3 (see Equations 2-4 and Table 1). For example, if 1mA is required for phase angle output corresponding to 180 °, then R3=(1V/1mA) * 1000=1k Ω. It should be noted that the maximum output current is 5mA, and the output voltage of the operational amplifier is limited to 12V. It is necessary to verify that I × (R1+RS+R3) ≤ 12V.

Status contacts (light load): There is a set of normally open/normally closed contacts for voltage status, phase angle status, and frequency difference status, which can be used for SCADA to query the reason for locking or access panel indicator lights.

Installation and mechanical dimensions

M-0359 is a 19 inch rack mount (2U height) and can also be installed horizontally or vertically on the panel. The external dimensions are 48.3cm x 8.9cm x 33.0cm (width x height x depth), with a weight of approximately 6.8kg. The panel opening dimensions are shown in Figure 6 (detailed drilling diagrams are provided in the manual). Optional M-0217 transparent protective cover accessory to prevent accidental contact with the knob.

Installation precautions:

Ensure that the chassis is grounded (through dedicated grounding terminals, not just by installing screws).

The voltage input circuit should be equipped with a fuse (recommended 1A or 2A slow melting) to prevent PT secondary short circuit.

The analog output line should use shielded twisted pair cables, with the shielding layer connected to the control room ground at one end.

On site debugging and verification

Check before powering on: Confirm that the Line/Bus voltage does not exceed 145V continuous value, the wiring is correct, and all external contacts are in the preset state (such as whether the dead wire/dead bus enable is connected as needed).

First power on: Observe the front panel LED. Except for undervoltage shutdown (<65V), each LED should light up accordingly. After about 0.5 seconds of power on, the voltage detection stabilizes.

Single function testing:

Use a single-phase voltage regulator to apply adjustable voltages to Line and Bus respectively, and verify the upper/lower limit action points (LED on/off matches the setting).

Apply an adjustable voltage difference (e.g. 0-10V) between Line and Bus to verify the Delta V LED flip point.

Apply two signals of different frequencies (such as 50.0Hz and 50.1Hz) and check the response of DELTA F OK at the set value.

Use a phase shifter to change the phase of Line relative to Bus, and observe the movement of ANGLE OK LED at the set angle boundary (with a hysteresis of approximately 0.2 °).

Dead line/dead bus verification: Reduce the voltage on one side to below the Dead Limit set value, while enabling the corresponding contact. The relay should be able to close immediately (ignoring phase angle/frequency difference), but note that the other side must be>100V to ensure that the relay coil is energized.

Closing relay test: Use a multimeter or circuit breaker to monitor TB1-17~19. When all OK conditions are met and the synchronization enable is effective, the contacts should be closed. Pay attention to the carrying capacity of the relay (consider arc extinguishing when disconnecting inductive loads).

Analog calibration: Use a standard meter to measure the analog output terminals and compare the ratios in Table 1. If the deviation exceeds the specifications, factory calibration may be required (on-site adjustment is not recommended).

Protection and transient immunity

The voltage input circuit is equipped with transient suppression devices, which can pass C37.90.1 oscillation wave and fast transient tests.

The power supply is taken from the higher side voltage. When both sides are below 65V, the internal low voltage detection will turn off the output to avoid relay misoperation.

The contact of the closing relay adopts a double break structure, which can withstand a voltage of 1500V to ground and has sufficient breaking capacity (inductive load 0.9A/120V DC). It is suitable for directly driving the closing coil of the circuit breaker or the intermediate relay.

All external control inputs (dead wires/dead busbars, etc.) are optically isolated to avoid ground circuit interference.

Maintenance and troubleshooting

On site maintenance is not recommended: due to the use of MOS circuits, non professional operations are prone to electrostatic damage. If a fault is suspected, the external power supply, fuse (if any), and wiring should be checked first.

Repair process: Prepay the shipping cost of the entire machine (with ownership reserved) and send it back to Beckwith, along with a detailed description of the malfunction. During the warranty period (5 years), free repairs will be provided for manufacturing defects, and reasonable fees will be charged for artificial or insurance circuit breakers.

common problem:

Closing without exit: Check if all LEDs are fully lit, especially if SYNC CHECK ENABLE is short circuited; Check if the dead line/dead bus is accidentally enabled (if enabled, the phase angle/frequency difference is bypassed).

Abnormal analog output: Check if the external load is too large (current type not exceeding 5mA, voltage type load impedance should be greater than 2k Ω); Confirm that the common terminal (TB1-13) is not short circuited with other circuits.

No response when powered on: Measure whether the Line or Bus voltage is below 65V; check the internal fuse (if any).

Coordination with automatic synchronization device (M-0193)

In a typical configuration, the M-0193 automatic synchronizer is responsible for fast synchronization (slip closing) of the generator or connecting line, while the M-0359 serves as the final hard contact verification that allows relays to be connected in series in the closing circuit, providing voltage, phase angle, and frequency difference. At this time, the phase angle limit of M-0359 is usually set to 5-10 °, and the frequency difference limit is set to 0.05Hz, as the last line of defense to prevent M-0193 from issuing premature closing commands due to faults. For specific wiring, please refer to Figure 1 in the manual (System Recovery Application).