Beckwith M-3520 Interconnection Protection Relay

Positive Overpower (Positive Setting): Detect forward power exceeding the limit.

Reverse power (negative value setting): detects reverse power (suitable for anti islanding and anti backflow).

Underpower: The detected power is lower than the set value.

Single phase detection mode is optional (applicable to line ground VT wiring). In the application of distributed power grid connection, reverse power detection is one of the important means of anti islanding protection.

2.4 Negative sequence protection

46- Negative sequence overcurrent

Provide two modes of time limit and inverse time limit:

Time limit: Set to 0.10~20.00A (5A CT) or 0.02~4.00A (1A CT), with a delay of 1~8160 cycles.

Inverse Time: Supports Definite Time, Inverse, Very Inverse, Extremely Inverse, and IEC standard curves, with a time dial of 0.5-11.0 (or 0.05-11.0 IEC).

Negative sequence overcurrent is used to detect asymmetric faults and system imbalances, and is particularly important for rotor protection of rotating motors.

47- Negative sequence overvoltage

Two independent settings, adjustable from 5 to 180V, with a delay of 1 to 8160 cycles. Used to monitor system voltage imbalance and assist in distinguishing PT disconnection or system asymmetric operation.

2.5 Overcurrent protection

50- Instantaneous phase overcurrent

Set 1.0~240.0A (5A CT) or 0.2~48.0A (1A CT) with a fixed delay of 2 cycles. Used for quickly cutting off phase to phase short circuit faults.

50G - Instantaneous Neutral Overcurrent

Set 0.5~2400A (5A CT) or 0.1~48.0A (1A CT). Can be supervised by 67N (directional grounding) components to achieve directional instantaneous grounding protection.

51V - Voltage control/voltage suppression inverse time overcurrent

Inverse time overcurrent protection with voltage control (VC) or voltage suppression (VR) function. Set to 0.50~12.00A (5A CT), supporting multiple sets of inverse time curves. In voltage control mode, the lock is only released when the voltage is lower than the set value; In voltage suppression mode, the action value decreases linearly with the decrease of voltage. Suitable for load feeder protection in distribution networks, improving protection sensitivity when system voltage drops.

51G - Inverse time neutral point overcurrent

Set to 0.25~12.00A (5A CT) or 0.05~2.40A (1A CT), supporting Define Time, Inverse, Very Inverse, Extremely Inverse, and IEC curves. Can be supervised by 67N directional components.

2.6 Direction overcurrent protection (67/67N)

67- Directional phase overcurrent

Provide two modes: fixed time limit and inverse time limit. The directional component adopts positive sequence voltage polarization, with a maximum sensitivity angle (MSA) adjustable from 0 ° to 359 °, and has an 8-cycle fault memory function. The sensitivity at MSA is 0.5VA. Direction sensing can be independently disabled and is suitable for situations where direction discrimination is not required. When operating at high speed, the delay is set to 1 cycle and the response time is less than 1.5 cycles.

67N - Directional neutral overcurrent

Supports multiple polarization modes:

Zero sequence voltage polarization

Negative sequence voltage polarization

Current polarization (requires external current source)

Dual polarization (zero sequence+negative sequence combination)

Polarization methods 1, 3, and 5 are not applicable to line to line and line to ground to line VT configurations. When using polarization modes 4 or 5, MSA is not applicable and should be set to zero. Direction sensing can also be disabled.

2.7 Frequency Protection (81)

Four independently set over/under frequency protection, each segment can be independently selected as over frequency or under frequency. Setting range:

60Hz model: 50.00~67.00Hz

50Hz model: 40.00~57.00Hz

Accuracy: ± 0.02Hz within the range of 57~63Hz (60Hz model)/47~53Hz (50Hz model), ± 0.1Hz beyond the range

Delay: 2~65500 cycles

Distributed power sources must be disconnected within the specified time limit when the system frequency is abnormal, and the 81 function is a key protective component to achieve this requirement.

2.8 VT fuse breakage detection (60FL)

Detecting VT secondary circuit disconnection or fuse melting by comparing the positive and negative sequence components of voltage and current. After detecting VT disconnection, programmable locking of relevant voltage protection functions (such as 27, 59, 21, etc.) can be implemented to prevent misoperation. Wire breakage detection can come from internal logic or external input contacts, with a delay of 1~8160 cycles.

2.9 Re closing Enable (79)

Provide programmable reclosing delay function. When all contacts designated as trip outputs have dropped out, the reclosing timer starts and can issue a reclosing permission signal after a delay of 2-65500 cycles. This function works in conjunction with 25 (synchronous check) to achieve "checking synchronous reclosing" or "checking no pressure reclosing".

Optional protection function

For more complex application scenarios, M-3520 offers three optional protection functions:

21- Dual zone interphase distance protection

Suitable for backup protection of interconnected lines, providing two segments of M-O characteristic impedance protection. Each segment can independently set the circle diameter (0.1~100 Ω), offset (-100~+100 Ω), and impedance angle (0 °~90 °), with a delay of 1~8160 cycles.