Megger TTR310 - Connections and Vector Voltage Diagrams

M
AVTMTTR310 Rev 8 May 2016
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Connections and Vector Voltage Diagrams
When testing three-phase transformers, it is necessary to understand the phase
relationships, vector diagrams, and winding connection diagrams for these
transformers. A detailed description of phase relationships, vector diagrams, and
terminal markings is contained in specification ANSI C57.12.70 – 2011 American
National Standard Terminal Markings and Connections for Distribution and Power
Transformers.
Refer to specification CEI/IEC 76-1:2011 and Publication 616:1978 for
International Standard terminal and tapping markings for power transformers.
Refer to specification AS-2374, Part 4-2003 for Australian standard tappings and
connections for power transformers.
Table 5-4 shows winding diagrams for standard transformers and nonstandard
transformers for power and distribution transformers marked in accordance with
the ANSI standard. Table 5-5 shows winding diagrams for power transformers
marked in accordance with the CEI/IEC standard, and Table 5-6 shows winding
diagrams for power transformers marked in accordance with the Australian
standard.
To make a measurement on a three-phase power transformer, match the vector
diagram from the transformer nameplate to the corresponding winding
connection diagram from Table 5-4 through 5-6, then enter the corresponding
diagram number (column 1 of table) in the appropriate setup menu of the
instrument.
The tables show the windings tested for each of the three-phases. The tables also
show the relationship between the measured turn ratio and the actual line-to-line
voltage ratio. For the ANSI specification, the rated voltage on the high-voltage
winding is represented by V
H
; V
X
represents rated voltage on the low-voltage
winding.
The TTR310 is also capable of measuring the turn ratio on three-phase
transformers with an inaccessible neutral point. In this case, the TTR310
automatically shorts an appropriate transformer winding, listed in the winding
shorted column of the table. An inaccessible neutral point on the high-voltage or
low-voltage transformer winding is designated by the symbol *.
For many utilities, different manufacturer nameplate diagrams make it impossible
to always find a corresponding diagram on Tables 5-4 to 5-6. To help determine
the correct connection and to test any transformer, the following explanation will
help self-check your work.
Figure 5-10 (a) shows the relationship in a typical delta-wye connected
transformer with accessible neutral connection point. The delta winding is the
high-voltage winding and the terminals are marked H
1
, H
2
, and H
3
. The wye
winding is the low-voltage winding and the terminals are marked X
0
, X
1
, X
2
, and