3–12 745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
TYPICAL WIRING CHAPTER 3: INSTALLATION
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 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transformer and an automatic shorting mechanism that acts when the relay is withdrawn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 Relay has inputs for either two or three transformer windings (specified at the time
of ordering) and for two ground current inputs, G1/2 and G2/3. Refer to the wiring
diagrams below 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 be shown in the winding configuration for the
transformer type selections associated with a ground input.
2. When a 2-winding transformer is selected, ground inputs are enabled, on both, and
are pre-assigned. G1/2 is assigned to winding 1, and G2/3 is assigned to winding 2.
3. When a 3-winding transformer is selected, both ground inputs are enabled, and are
associated with the windings via the following rules (see table 3-2):
• The 50G function is enabled for all connection scenarios (ie: delta and wye).
• Flexibility is provided to the user in the case of a 3-winding transformer, so the user
can assign G1/2 and G2/3 Ground inputs to any two of the three available
windings.
4. Robustness, built into the relay, will not allow the user to assign a ground input to
more than one winding. In the EnerVista 745 software, a flag informs the user with the
text: "Ground CT Input ’G#/#’ has already been selected for another winding". On the
relay firmware, "Input Function is Already Assigned" text is displayed.
The following table shows the ground inputs use for typical transformer setups:
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 Wye -- Winding 1 Winding 2
Delta Delta -- Winding 1 Winding 2
Delta Wye -- Winding 1 Winding 2
Delta Delta -- Winding 1 Winding 2
Wye Zig-Zag -- Winding 1 Winding 2
Delta Zig-Zag -- Winding 1 Winding 2
Wye Wye Wye Winding 1 Winding 2
Wye Wye Wye Winding 2 Winding 3
Wye Wye Wye Winding 3 Winding 1
Wye Wye Wye Winding 2 Winding 1
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