GE 745 TRANSFORMER MANAGEMENT RELAY User Manual

5-8 745 Transformer Management Relay GE Power Management
5.2 AUTO-CONFIGURATION 5 SETPOINTS
5
5.2.5 PHASE ANGLE CORRECTION
The following diagram shows the internal connections of the Y/d30
°
transformer of our example:
Figure 5–5: WYE / DELTA (30
°
LAG) TRANSFORMER
Under balanced conditions, the Winding 2 phase current phasors lag the corresponding phase current phasors
of Winding 1 by 30°. With CTs connected in a Wye arrangement (polarity markings pointing away from the
transformer), the corresponding phase currents cannot be summed directly to obtain a zero differential current,
since corresponding phasors will NOT be 180° out-of-phase.
Traditionally, this problem is solved by connecting the CTs on the WYE side of the transformer (Winding 1) in a
Delta arrangement. This compensates for the phase angle lag introduced in the Delta side (Winding 2).
The 745 performs this phase angle correction internally based on the following setpoint. Under
S2 SYSTEM
SETUP/TRANSFORMER
, set:
The 745 supports over 100 two and three-winding transformer types. Table 5–1: TRANSFORMER TYPES on
page 5–10 provides the following information about each transformer type:
TRANSFORMER TYPE:
Y/d30°
WINDING 1 (WYE)
WINDING 2 (DELTA)
abc
AB
C
N
TRANSFORM
ER TYPE
WDG
#
CONNECTIO
N
VOLTAGE
PHASORS
PHASE
SHIFT
Y/d30
°
1WYE
(gnd 1/2)
30
°
lag
2DELTA
30° lag
0
°
angle by which a winding lags Winding 1
winding connection (wye, delta, or zig-zag) and ground CT assignment
transformer type notation as it appears on the display
diagrams showing the phase rela-
tionship of voltage phasors, where
↑ (the arrow head) indicates the
reference phase
phase angle correction (or phase shift)
that is performed internally to calculate
differential currents

GE 745 TRANSFORMER MANAGEMENT RELAY Specifications

General

Brand	GE
Model	745 TRANSFORMER MANAGEMENT RELAY
Category	Relays
Language	English