Phase Relationships Of Three-Phase Transformers; Example Transformer - GE T60 Instruction Manual

5 SETTINGS
P [w] =
SETTINGS
rated
V [w] =
SETTINGS
nominal
Connection [w] =
SETTINGS
Grounding [w] =
SETTINGS
[w]
=
SETTINGS
CT primary [w] = the phase CT primary associated with Source [w]
Note that w = winding number, 1 to w
The following transformer setup rules must be observed:
1. The angle for the first winding from the transformer setup must be 0° and the angles for the following windings must be
entered as negative (lagging) with respect to (WRT) the winding 1 angle.
2. The "Within zone" and "Not within zone" setting values refer to whether the winding is grounded. Select "Within zone" if
a neutral of a wye type winding, or a corner of a delta winding, is grounded within the zone, or whenever a grounding
transformer falls into the zone of protection.
d) PHASE RELATIONSHIPS OF 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 terminal labels include the characters 1, 2, 3 to represent the names of the indi-
vidual 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 condi-
tion 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 rela-
tionship 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 rela-
tionships 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 reason the source phase sequence must be stated when describing the winding phase relationships is that these rela-
tionships change when the phase sequence changes. The example shown below shows why this happens, using a trans-
former described in IEC nomenclature as a type "Yd1" or in GE Multilin nomenclature as a "Y/d30."
The above diagram shows the physical connections within the transformer that produce a phase angle in the delta winding
that lag the respective wye winding by 30°. The currents in the windings 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 trans-
former terminals ABC respectively. The currents that would be present for a balanced load are shown the diagram below.
GE Multilin
 
SYSTEM SETUP TRANSFORMER
 
SYSTEM SETUP TRANSFORMER
 
SYSTEM SETUP TRANSFORMER
 
SYSTEM SETUP TRANSFORMER
 
SYSTEM SETUP TRANSFORMER
total
A B
I I
A B
I I
a l b l
I = I - I I =
a a l c l b
a b
Figure 5–28: EXAMPLE TRANSFORMER
T60 Transformer Protection System
 
WINDING w WINDING w RATED MVA
 
WINDING w NOM  VOLTAGE
WINDING w
 
WINDING w WINDING w CONNECTION
 
WINDING w WINDING w GROUNDING
 
WINDING w WINDING w ANGLE WRT WINDING 1
C N
I
C
I
c l
I - I I = I - I
b l a l c c l b l
c
828716A1.CDR
5.4 SYSTEM SETUP
5
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