Auto-Configuration
745
Transformer Management Relay
Se
tpoints
http://www.GEindustrial.com/multilin
5–7
GE Multilin
The “zero position” terminal and the “wiper” terminal of the tap position circuit are
connected to the positive and negative 745 tap position terminals. Polarity is not
consequential. The following setpoints configure the 745 to determine tap position.
In the
S2 SYSTEM SETUP
!"
ONLOAD TAP CHANGER
setpoint menu, make the following
settings:
WINIDNG WITH TAP CHANGER
: “Winding 2”
NUMBER OF TAP POSITIONS
: “33”
MINIMUM TAP POSITION VOLTAGE
: “61.0 kV”
VOLTAGE INCREMENT PER TAP
: “0.50 kV”
RESISTANCE INCREMENT PER TAP
: “33
Ω
”
The maximum value resistance on the top tap is 5 k
Ω
.
Phase Shifts on Three-
Phase Transformers
Power transformers that are built in accordance with ANSI and IEC standards are
required to identify winding terminals and phase relationships among the windings
of the transformer.
ANSI standard C.37.12.70 requires that the labels of the terminals include the
characters 1, 2, and 3 to represent the names of the individual phases. The phase
relationship among the windings must be shown as a phasor diagram on the
nameplate, with the winding terminals clearly labeled. This standard specifically
states that the phase relationships are established for a condition where the source
phase sequence of 1-2-3 is connected to transformer windings labeled 1, 2 and 3
respectively.
IEC standard 60076-1 (1993) states that the terminal markings of the three phases
follow national practice. The phase relationship among the windings is shown as a
specified notation on the nameplate, and there may be a phasor diagram. In this
standard the arbitrary labeling of the windings is shown as I, II, and III. This
standard specifically states that the phase relationships are established for a
condition where a source phase sequence of I - II - III is connected to transformer
windings labeled I, II and III respectively.
The source phase sequence must be stated when describing the winding phase
relationships since these relationships change when the phase sequence changes.
The example below shows why this happens, using a transformer described in IEC
nomenclature as “Yd1” or in GE Multilin nomenclature as “Y/d30.”
FIGURE 5–2: Example Transformer
The above figure shows the physical connections within the transformer that
produce a phase angle in the delta winding that lags the respective wye winding by
30°. The winding currents are also identified. Note that the total current out of the
delta winding is described by an equation. Now assume that a source, with a
sequence of ABC, is connected to transformer terminals ABC, respectively. The
currents that would be present for a balanced load are shown below.
A
I
I
I
I
I
I
I
I
I
I
I
I
I
-
-
-
=
=
=
I
I
A
a
b
c
a
l
b
l
c
l
a
l
b
l
c
l
c
l
a
l
b
l
B
C
B
C
N
a
b
c
Summary of Contents for Multilin 745
Page 2: ......
