Overview
Configured for differential and overcurrent protection in transformer monitoring networks, the GE Multilin SR745, also referenced as the SR745 Transformer Protection System Relay, provides direct physical and electrical execution of two-winding per phase protection logic with 5 A phase and ground current inputs, operating from 90 to 300 VDC or 70 to 265 VAC control power.
Hardware Specifications
| Parameter | Specification |
|---|---|
| Model Brand | GE Multilin |
| Origin | Canada |
| Weight | 16 lbs 9.6 oz (7.5 kg) |
| Dimensions | 8.5 in x 10.0 in x 9.5 in (21.6 cm x 25.4 cm x 24.1 cm) |
| Operating Temp | -40 degC to +70 degC |
| Power Consumption | < 30 W typical |
| Phase Current Input | 5 A rated per winding |
| Ground Current Input | 5 A rated |
| Control Power Range | 90–300 VDC / 70–265 VAC, 48–62 Hz |
Backplane Bus Communication Velocity & Firmware Flash Compatibility
The SR745 interfaces via the GE Multilin backplane bus, supporting deterministic peer-to-peer data exchange within compatible UR family relay platforms. Firmware flash compatibility is limited to certified Multilin UR series images; cross-flashing with non-UR firmware will disable hardware initialization routines and invalidate configuration CRC checksums. Ethernet communication supports IEC 61850 MMS and DNP3 protocol stacks, with firmware version dependencies enforced at the bootloader level.
Frequently Asked Questions
Q: Does the SR745 support hot-swap replacement on an energized backplane?
A: No. The relay must be installed and removed only with control power disconnected to prevent arcing on the backplane connectors and corruption of configuration data.
Q: What is the maximum burden on the 5 A current inputs?
A: Each current input circuit presents less than 0.04 VA at rated current, suitable for direct connection to CT secondary circuits without additional burden resistors.
Q: Can firmware be downgraded to earlier versions?
A: Downgrading is supported only within the same major release branch; switching between incompatible branches may require full configuration restore and recalibration.
Field Installation Guidelines
Mount the SR745 in a vertical orientation inside the enclosure to maintain convection cooling efficiency. Use separate conduit runs for control power and current transformer wiring to minimize inductive coupling. Shielded twisted-pair cabling is mandatory for all analog signal connections; terminate shield drains directly to the relay chassis ground terminal with no intermediate splices. Torque all power terminals to 1.2 N·m and verify tightness after initial energization cycle. Ensure rear connector seating by applying uniform pressure until locking clips engage fully.
