SR750-P5-G5-S5-HI-A20-R-T GE Protection Relay

Description

Product Introduction & Engineering Value

The GE Multilin SR750-P5-G5-S5-HI-A20-R-T is a digital feeder management relay designed to provide primary protection, control, and monitoring for distribution feeders, transformers, and bus zones. Unlike the 4-series motor/generator relays (like the 469 or 489), the 750 series belongs to GE’s higher-tier 700 platform, offering faster processing, advanced waveform capture, flexible programmable logic blocks (FlexLogic™), and high-density protection elements.

This specific configuration is fully featured for high-reliability, harsh industrial environments:

• Triple 5A CT Inputs (P5-G5-S5): Covers phase overcurrent alongside both standard and sensitive ground fault detection.
• Redundant Power Supply (R): Dual power inputs protect against station DC battery bank or control transformer outages.
• Conformal Coating (T): UV-curable protective layer shields internal PCB traces from corrosive gases, high humidity, and dust.

Part Number Decoder & Hardware Specs

Order Code Breakdown: SR750 - P5 - G5 - S5 - HI - A20 - R - T

• SR750: Base Series (Multilin 750 Feeder Management Relay)
• P5: Phase Current Inputs — 5A CT Secondaries
• G5: Ground Current Input — 5A CT Secondary
• S5: Sensitive Ground Current Input — 5A CT Secondary
• HI: Control Power — 90–300 VDC / 70–265 VAC high-voltage bus
• A20: Analog Outputs — 4x 4–20 mA (or 0–20 mA / 0–1 mA) outputs
• R: Hardware Option — Redundant Power Supply Module
• T: Environmental Option — Test / Conformal Coated PCBs

Key Protection & Metering Elements

• Overcurrent Protection: Time Overcurrent (ANSI 51P/51G/51N), Instantaneous Overcurrent (ANSI 50P/50G/50N), Directional Overcurrent (ANSI 67P/67N)
• Voltage & Frequency Elements: Over/Undervoltage (ANSI 59/27), Over/Underfrequency (ANSI 81O/81U)
• Breaker Control & Monitoring: Breaker Failure (ANSI 50BF), Trip Circuit Monitoring (TCM), Breaker Arc (I^2t) Duty Accumulator
• Programmable Logic: FlexLogic™ equations for custom interlocks, scheme control, and auto-transfer logic
• Data Logging: Fault locator, event recorder (up to 256 events), and oscillography waveform capture (up to 128 cycles)

SR750-P5-G5-S5-HI-A20-R-T

SR750-P5-G5-S5-HI-A20-R-T

SR750-P5-G5-S5-HI-A20-R-T

Field Application & The “Trench” Experience

During a critical power distribution upgrade at a offshore petrochemical platform, electrical reliability was paramount. Process downtime meant massive financial losses, and salt spray combined with trace hydrogen sulfide (H_2S) degraded standard open-chassis electronics. Additionally, a single control power circuit breaker failure could drop a feeder relay off the SCADA network unnoticed.

The facility selected the SR750-P5-G5-S5-HI-A20-R-T. The conformal-coated internal boards (T) prevented airborne salt corrosion. By landing both the primary 125V DC station battery and a secondary 120V AC UPS feed onto the redundant power supply terminals (R), the relay stayed online during routine battery maintenance. The 5A sensitive ground input (S5) allowed sub-amp ground fault sensing on high-resistance grounded (HRG) feeder buses.

Niche Application Scenarios:

• Chemical & Refining Plants: Feeders operating in corrosive chemical atmospheres requiring redundant control power.
• High-Resistance Grounded (HRG) Systems: Utilizing the S5 5A sensitive ground CT input for low-level fault detection.
• Industrial Substation Bus Feeder Tie Breakers: Executing auto-transfer schemes via FlexLogic™ while streaming telemetry over 4–20 mA loops (A20).

Transparency SOP: QA & Testing

1. Dual Power Supply Bus Test (R Option): Independent voltage ramps are applied simultaneously to Power Supply Input 1 and Input 2 (70–265 VAC / 90–300 VDC). Either source is dynamically dropped while the relay is under full load to confirm zero-dip seamless rollover.
2. Conformal Coating & Physical Chassis UV Audit: Internal boards are UV-inspected to confirm unbroken protective coating across all microprocessors, resistors, and solder joints.
3. Triple CT Input Injection (P5, G5, S5): Secondary 5A currents are injected into Phase, Ground, and Sensitive Ground terminals simultaneously to verify metering accuracy within ±0.5%.
4. FlexLogic™ & Contact Output Verification: All Form-C and Form-A output contacts are toggled via programmed test logic to verify physical contact resistance and speed.
5. Analog Output Calibration (A20): Precision milliammeters are tied to the 4 analog output channels while forcing 0mA, 10mA, and 20mA test signals to verify output linearity.

The Veteran’s Tech Trap Guide

• ⚠️ Ground (G5) vs. Sensitive Ground (S5) Terminal Wiring: Do not confuse the standard Ground CT terminals with the Sensitive Ground CT terminals. The S5 input channels use high-accuracy internal toroidal transformers with a much lower threshold range. Wiring a main feeder ground CT into the S5 terminal instead of G5 will cause immediate nuisance trips on normal system unbalances.
• PRO TIP (Redundant Power Wiring): When wiring the R redundant supply option, feed Supply 1 from your primary DC battery bank and Supply 2 from an independent AC UPS. This provides true dual-path resilience against both AC blackout and DC fuse clearing.
• ⚠️ FlexLogic™ CPU Overhead: When building complex custom protection schemes using GE FlexLogic™, monitor the internal CPU usage metric in the EnerVista setup software. Pushing logic equations past recommended execution limits can lengthen protection processing loops.

Dynamic FAQ

Q: What does the R option add to the ?

A: The R suffix denotes a Redundant Power Supply, providing two independent control power input terminals so the relay remains fully operational if one power source fails.

Q: Why does this relay have both G5 and S5 in its part number?

A: G5 provides standard 5A ground overcurrent protection (typically for solid or low-resistance grounded systems), while S5 provides a dedicated 5A sensitive ground input tailored for high-resistance grounded (HRG) systems or sensitive earth-leakage detection.

Q: Is the GE interchangeable with the GE SR760?

A: Physical dimensions and draw-out cases are identical, but the SR760 includes additional auto-reclosing functionality (ANSI 79) for overhead line protection. The is designed primarily for bus and feeder protection without auto-reclosing.