ALSTOM SCN804 Protection Relay

General Description

The SCN804 is part of ALSTOM’s MiCOM family of numerical protection relays, widely used in medium voltage (MV) distribution networks. It provides comprehensive protection for overhead lines, cables, and transformers. The relay combines high-speed protection with metering and control functions in a compact, drawout case suitable for switchgear mounting.

Key Features

• Protection Functions: Definite time or inverse time overcurrent (50/51), directional overcurrent (67), earth fault (50N/51N/67N), thermal overload (49), and breaker failure (50BF).

• Measurement: Phase currents, residual current, voltage (optional), frequency, power, energy.

• Inputs/Outputs: 4 current inputs (1 A or 5 A), 4 voltage inputs (optional), 8 digital inputs, 6 output relays.

• Communication: RS485 Modbus RTU (standard), optional Ethernet IEC 61850 or Profibus DP.

• Event Recording: Up to 256 events with time stamp; fault recorder (up to 20 faults).

• Display: Large graphical LCD with backlight, showing real-time values, settings, and alarm messages.

• Self-Monitoring: Continuous hardware and software watchdog with alarm contact.

Technical Specifications

• Auxiliary Supply: 48-250 V DC / 100-240 V AC,<10 W.

• Current Inputs: Rated 1 A or 5 A, dynamic range 0.1-40 A.

• Frequency Range: 50/60 Hz.

• Accuracy: ±1% for protection, ±0.5% for metering.

• Operating Temperature: -25°C to +70°C.

• Case Size: 4U height, 19" rack or flush mounting (177 x 266 x 210 mm).

• Protection Class: IP54 (front), IP20 (rear).

Functional Description

The SCN804 continuously samples currents and voltages (if voltage inputs present) to detect faults. It applies user-configurable curves (IEC, ANSI, or user-defined) to determine trip times. Directional elements use voltage polarizing for accurate fault direction discrimination. The relay also includes logic schemes like auto-reclose, cold load pickup, and setting groups for different network configurations. All settings are stored in non-volatile memory.

Applications

• Feeder protection in utility distribution substations.

• Industrial plant power distribution.

• Mining and heavy industry electrical networks.

• Protection of small power transformers (as primary protection).

• Backup protection for transmission lines.

Configuration and Software

The relay is configured via the front panel keypad or using MiCOM S1 software (PC-based). The software allows offline setting preparation, upload/download, and disturbance analysis. Communication protocols enable integration with SCADA and energy management systems. The relay supports time synchronization via IRIG-B or SNTP.

Certifications

• CE, UL, and CSA certifications.

• Complies with IEC 60255 series standards.

• Designed for use in substations according to IEC 61000-6-5 (EMC).

Note: This document is for technical reference only; for detailed application, refer to the ALSTOM SCN804 technical manual.