GE745-W2-P5-G5-HI-ASR745 Transformer Management Relay, 2-Winding, 5 A Phase and Ground CTs, Analog I/O, Drawout Case, Modbus RTU / DNP 3.0

Product Description

The SR745 is GE Multilin’s dedicated transformer management relay. This build — 745-W2-P5-G5-HI-A — is the two-winding version with 5 A CT secondaries on both the phase and ground inputs, universal-range control power, and the analog input/output option fitted.

Decoding the order code

This is where most listings for the 745 go wrong, so here is the whole code from GE’s own ordering table:

745 — base relay.W2 — two windings per phase. It is not a hardware revision and it does not mean “withdrawable”. W3 is the three-winding build.P5 — phase CT inputs rated 5 A secondary, all windings.G5 — ground CT inputs rated 5 A secondary, both windings.HI — control power range, high: 90–300 V DC or 70–265 V AC, 48–62 Hz. It does not mean harmonics or high impedance. LO is the low-range alternative.A — analog inputs and outputs fitted.The absent trailing letters are just as informative: no B/E/T display-and-Ethernet option, so this relay has the basic display and no Ethernet port; no H, so no harsh-environment conformal coating; no L, so no loss-of-life option; no R, so no restricted ground fault.

Protection and metering

Percent differential with harmonic restraint adjustable 0.1–65.0%, plus instantaneous differential. Per-winding phase and neutral overcurrent (50P1, 50P2, 51P, 50N1, 50N2, 51N), ground overcurrent (50G1, 50G2, 51G) and negative-sequence overcurrent. V/Hz overexcitation, two elements, 1.00–4.00 V/Hz. Underfrequency (two elements), overfrequency, four rate-of-change-of-frequency elements, and a fifth-harmonic element. Metering and monitoring include THD, current demand, insulation aging / loss-of-life estimation and tap-changer monitoring.

Inputs and outputs on this build

Eight current channels: six phase CT inputs plus two ground CT inputs. One voltage input, 60–120 V, burden under 0.025 VA. Sixteen logic inputs. Because the A option is fitted, you also get one analog mA input and seven analog outputs — which is how you get transformer loading, winding temperature proxies and demand values out to a SCADA or chart recorder without polling. RTD input and IRIG-B time synchronisation are provided. CT burden is under 0.2 VA with 80x for one second and 3x continuous withstand.

Communications — serial only

Three serial ports: a front 9-pin RS-232C for local setup, rear COM1 selectable RS-485 or RS-422, and rear COM2 RS-485. Protocols are Modbus RTU and DNP 3.0 Level 2 at 300–19200 baud. There is no Ethernet on this order code — Ethernet was the “T” option. If your integration plan assumes an Ethernet relay, this is not it; you will need a serial-to-Ethernet gateway.

The drawout case, and what “SR745-CASE” means

The 745 is a fully drawout relay with automatic CT shorting — pull the relay out and the CT secondaries are shorted for you, so you are not opening a live CT circuit. There are no electronic components in the case itself; all the intelligence is in the withdrawable unit. The case has a dust-tight door with provision for a seal and mounts in a panel or a 19-inch rack. Combined weight is 8.4 kg (18 lb 6 oz).

The string “SR745-CASE” appears in the trade but is not a GE catalogue number, and because the case is a genuinely separate electronics-free assembly, that phrase is ambiguous on a surplus listing — it can mean case only. The photographs resolve it: this is a complete relay. The withdrawable unit is present and seated in its case, with the faceplate, LED target panel, alphanumeric display and keypad all fitted, and the drawout handle visible at the right-hand side. You are buying a whole relay, not an empty case.

Environment and approvals

Operating −40 to +60 °C, storage −40 to +80 °C, 90% relative humidity non-condensing, up to 2000 m. UL listed for USA and Canada under file E83849, CE marked, FCC Part 15 and ACA. Control power draw is 30 VA nominal, 40 VA maximum, behind an internal 3.15 A fuse.

Lifecycle: discontinued, replaced by the 845
GE has discontinued manufacture of the 745 and directs users to the 845 relay as the alternative. A retrofit kit (document 1601-0726-C430) lets an 845 reuse the existing 745 panel cutout and wiring — useful to know, but a retrofit is still an engineering exercise with new settings, new comms and new commissioning tests. For a substation with a proven 745 settings file and a spares policy built around it, a matching new-old-stock 745 keeps the fleet identical and avoids re-approving a protection scheme.

Two internal inconsistencies in GE’s own documentation

In fairness to anyone specifying from this page: GE’s SR745 manual disagrees with itself in two places. The ordering table gives the HI control-power range as 90–300 V DC while section 3.2.8 of the same document says 88–300 V DC. And the enclosure rating is given as IP40 front / IP20 back in one place and “IP class X0” in another. We have quoted the ordering-table values above. Confirm against your own copy of the manual if either figure is critical.

Interchange and searching

Also written 745W2P5G5HIA, 745 W2 P5 G5 HI A and SR745. Part of GE Multilin’s SR (Second Generation Relay) family alongside the 750/760 feeder relays and the 469 motor relay. Now GE Vernova Grid Solutions. Commonly searched as “SR745 transformer differential relay”, “GE 745 transformer protection relay” and “Multilin 745”.