Beckwith M-3520 Interconnection Protection Relay

Function Analysis and Application Guide of Beckwith M-3520 Interconnected Protection Relay

With the large-scale integration of distributed energy (DER) into the distribution network, the protection requirements for interconnected lines are becoming increasingly complex. The distributed power grid interface not only needs to have conventional overcurrent and grounding protection, but also must be able to detect special working conditions such as islanding operation, abnormal power flow, frequency fluctuations, etc., and automatically reconnect to the grid when conditions are met. M-3520 Integrated Protection System launched by Beckwith Electric ® The digital interconnection protection relay designed specifically for this requirement integrates 21 protection functions, synchronization check, reclosing enable, and waveform capture capabilities, providing a complete integrated solution for DER interconnection. Based on the technical specifications, this article systematically analyzes the protection function system, key parameter tuning, and engineering application points of M-3520, providing reference for engineers engaged in distributed energy grid connection and distribution protection.

Product positioning and design philosophy

M-3520 is an interconnection protection relay based on microprocessor and digital signal processing technology, specifically designed for the point of interconnection between distributed generation (DER) and the power grid. Its protection functions cover three dimensions: network loss protection (detecting islanding operation), abnormal power flow protection (reverse power/over power direction discrimination), and fault backup protection (phase to phase and ground faults). Simultaneously integrating synchronous inspection, reclosing, and frequency change rate monitoring to meet the requirements of interconnection protection in grid standards such as IEEE 1547 and UL 1741.

The core design features include:

Comprehensive features: Standard configuration includes 18 protection functions, with optional options of 21 (phase to phase distance), 78 (out of step), and 81R (frequency change rate) to expand to 21 types.

Flexible configuration: Supports two configurations: standard protection system or basic system, and users can choose functional modules according to their needs.

High precision measurement: Voltage accuracy ± 0.5% or ± 0.5V, current accuracy ± 3% or ± 0.1A (5A CT), frequency accuracy ± 0.02Hz.

Powerful data management: 170 cycle oscilloscope recording, 32 target storage, event sequence recording, supports COMTRADE format waveform export.

Open communication: Supports MODBUS and BECO 2200 protocols, equipped with two RS-232 ports and one RS-485 port.

Detailed explanation of standard protection functions

2.1 Synchronization check and dead bus/dead line closing (25)

M-3520 is equipped with high-precision synchronous inspection function, which is used to monitor the closing conditions of circuit breakers. Its core parameters include:

Phase angle limit: 0 °~90 °, accuracy ± 1 °

Voltage upper and lower limits: upper limit 60~140V, lower limit 40~120V

Δ V limit: 1.0~50.0V, accuracy ± 0.5V

Δ F limit: 0.001~0.500Hz, accuracy ± 0.0007Hz or 5%

Synchronization check delay: 1~8160 cycles

Dead bus/dead line voltage limit: 0~60V, dead zone delay 1~8160 cycles

Synchronization check can operate as an independent function or be supervised by the 79 (reclosing) function. Support multiple "hot/dead" bus/line combination closing schemes, suitable for various scenarios such as conventional grid connection, black start, and system recovery. The extremely high Δ F resolution (0.001Hz) ensures reliable discrimination even under extremely low slip, avoiding false closing.

2.2 Voltage Protection

27- Phase Undervoltage

Two independent settings, each adjustable between 5-180V, with a delay of 1-8160 cycles. Used to detect system voltage drops, lock protection or initiate tripping under undervoltage conditions. When the VT wiring is line to place and needs to be converted to line to line voltage, the accuracy is ± 0.8V or ± 0.75%.

59- Phase Overvoltage

Two independent settings, adjustable from 5 to 180V. Used to detect system overvoltage and prevent distributed power sources from injecting excessive voltage into the grid, which may cause equipment damage or power quality exceeding standards.

59G/27G - Neutral point overvoltage/undervoltage

Detecting neutral point voltage offset for ground fault detection and system grounding status monitoring. The setting range is 5-180V, with a delay of 1-8160 cycles.

59I - Peak Overvoltage

The setting range is 1.05~1.50PU, specifically designed for ferromagnetic resonance detection. This function is based on instantaneous voltage peak response and can quickly identify overvoltage caused by ferromagnetic resonance, with a delay of 1~8160 cycles. For signals with severe harmonic distortion, the accuracy will decrease as the harmonic order increases (applicable to voltages below 180V).

2.3 Direction power protection (32)

Provide active power direction detection with dual setting values, with a setting range of -3.000~+3.000PU and an accuracy of ± 0.002PU or 2%. Can be configured as: