3-8
745 Transformer Management Relay
GE Multilin
3.2 TYPICAL WIRING
3 INSTALLATION
3
3.2.4 PHASE SEQUENCE AND TRANSFORMER POLARITY
For the correct operation of many relay features, the phase sequence and instrument transformer polarities shown on the
typical wiring diagram must be followed. Note the markings shown with all instrument transformer connections. When the
connections adhere to this drawing, the relay will operate properly.
3.2.5 AC CURRENT TRANSFORMER INPUTS
The 745 has eight or eleven channels for AC current inputs, each with an isolating transformer and an automatic shorting
mechanism that acts when the relay is withdrawn from its case. There are no internal ground connections on the current
inputs. Current transformers with 1 to 50000 A primaries may be used.
The 745 contains either two or three groups of three phase inputs (specified at the time of ordering) for the corresponding
two or three transformer winding, as well as two ground current inputs, G1/2 and G2/3. Refer to the wiring diagrams on
pages 3–6 and 3–7 for details. Upon transformer type selection, the ground inputs are associated to one or another winding
under the following conditions:
1.
The ground input settings will not be shown in the winding configuration if the winding connection type is Delta.
2.
The G1/2 ground input is associated with the first Wye or Zig-Zag type winding from a two-winding transformer; it is
never associated with Winding 3 from a three-winding transformer setup.
3.
The G2/3 ground input is associated with the second Wye or Zig-Zag type winding from two- or three-winding setup; it
is never associated with Winding 1. The G2/3 ground input is associated with Winding 3 only if Winding 3 is the wind-
ing of the Wye or Zig-Zag connection type from the transformer setup.
The following table shows the ground inputs use for some typical transformer setups:
Verify that the relay’s nominal current of 1 A or 5 A matches the secondary rating of the connected CTs.
Unmatched CTs may result in equipment damage or inadequate protection.
The exact placement of a zero-sequence CT so that ground fault current will be detected is shown below. Twisted pair
cabling on the zero-sequence CT is recommended.
IMPORTANT: The relay will correctly measure up to 46 times the current input nominal rating. Time over-
current curves become horizontal lines for currents above the 46
×
CT rating.
Table 3–2: TYPICAL GROUND INPUT CONNECTIONS
TRANSFORMER WINDING CONNECTIONS
WINDING ASSOCIATED WITH
GROUND INPUT
WINDING 1
WINDING 2
WINDING 3
G1/2
G2/3
Wye
Delta
--
Winding 1
--
Wye
Wye
--
Winding 1
Winding 2
Delta
Wye
--
Winding 2
--
Wye
Delta
Delta
Winding 1
--
Wye
Wye
Delta
Winding 1
Winding 2
Wye
Delta
Wye
Winding 1
Winding 3
Delta
Wye
Wye
Winding 2
Winding 3
Delta
Delta
Wye
--
Winding 3
CAUTION
NOTE
