What precautions should be taken when configuring REX 521 protective relays?

What precautions should be taken when configuring REX 521 protective relays?

Basic configuration preparation

Clarify application scenarios and requirements

Determine the protected objects: lines, transformers, motors, etc. Different objects require corresponding protection functions to be enabled (such as motors requiring startup monitoring and thermal overload protection).

System grounding method: neutral point directly grounded, grounded through arc suppression coil, or ungrounded system, affecting the configuration of grounding fault protection (such as high resistance grounding requiring REF1A function to be enabled).

Short circuit current calculation: Calculate the maximum/minimum short-circuit current based on the system impedance, which is used to set the overcurrent protection threshold.

Hardware configuration verification

Confirm model and version: Check if the hardware version (Basic/Medium/High/Sensor) matches the requirements, such as the need to configure an additional adapter for IEC 61850 communication.

I/O interface allocation: Reasonably plan digital inputs (DI) for status acquisition (such as circuit breaker position), digital outputs (DO) for tripping/alarm, and reserve backup interfaces.

Power compatibility: Ensure that the power supply voltage (DC 18-265V/AC 85-240V) is consistent with the site to avoid misoperation caused by undervoltage.

Key points for setting protection functions

Current protection parameter setting

Overcurrent protection (3I>):

Action current: Set according to the normal load current, usually 1.2-1.5 times the rated current.

Time characteristics: Choose definite time (DT) or inverse time (IDMT) according to system selectivity requirements, and the inverse time curve can be selected according to IEC or ANSI standards.

Differential protection (if any):

Balance coefficient: automatically calculated based on transformer ratio and wiring group to ensure zero differential current during normal operation.

Braking coefficient: usually set to 0.3-0.5 to prevent misoperation in case of faults outside the area.

Voltage and frequency protection

Overvoltage/undervoltage protection (3U>, 3U<<):

Action value: Overvoltage is generally 1.1-1.3 times the rated voltage, and undervoltage is 0.7-0.9 times the rated voltage.

Delay: Set according to the allowed voltage fluctuation time of the system, such as the need for motor restart.

Frequency protection (f1/f2):

Action value: Under frequency is generally 47-49Hz, over frequency is 51-52Hz.

Special function: Enable df/dt change rate detection to suppress system oscillation triggering errors.

Earth fault protection

Neutral point grounding method:

Direct grounding system: adopting zero sequence current protection (Io>), the operating current is set to avoid the maximum unbalanced current.

Non directly grounded system: adopting zero sequence voltage protection (Uo>) or directional zero sequence current protection (67N).

High resistance grounding fault: Enable REF1A function to detect high resistance grounding by comparing the sum of neutral point current and three-phase current.

Special function configuration

Automatic reclosing (O ->I):

Overlap frequency: generally 1-3 times, permanent faults require locking of overlap.

Dead time: adjustable from 0.2-300s seconds, which should be greater than the detachment time of the fault point (usually 0.5-1 seconds).

Circuit Breaker Failure Protection (CBFP):

Starting condition: After the tripping command is issued, there is no feedback change in the position of the circuit breaker.

Action delay: 100-1000ms, which should be greater than the inherent opening time of the circuit breaker.

Communication and System Integration

Protocol selection and parameter configuration

Communication protocol:

Traditional system: Choose Modbus RTU/ASCII or DNP 3.0, configure baud rate (9600-115200bps), parity check.

IEC 61850 system: Define GOOSE dataset (such as trip commands, alarm information) and SMV subscription relationship through SPA-ZC 400 adapter configuration.

IP address management:

Manually assign static IP addresses to ensure no conflicts with other devices in the network.

The subnet mask and gateway settings must be consistent with the upper computer, and support ping testing to verify connectivity.

Time synchronization configuration

IEEE 1588 v2：

Mode selection: PTP transparent clock or boundary clock, with the main clock priority (Priority 1/2) set to high.

Synchronization accuracy: Ensure ≤± 1 µ s to meet the requirements of distributed protection collaboration.

NTP synchronization: As a backup solution, configure the NTP server address with a synchronization period of 1-60s.

Data Mapping and Monitoring Point Configuration

Telemetry data: Map measured values such as current, voltage, and power to corresponding data points, and set an update cycle (such as 1 second).

Remote signaling data: configure status variables such as circuit breaker position and protection action signals, and define SOE resolution (≥ 1ms).

Remote control point: Set circuit breaker opening and closing control permissions, password verification is required to prevent misoperation.