Megger TTR310 - Page 45

SETUP AND CONNECTIONS
AVTMTTR310 Rev 8 May 2016
33
X
3
. Determine which windings (lines) are parallel to each other. In the diagram,
winding H
1
– H
3
is parallel to X
1
– X
0
as illustrated by the two solid straight
arrows. Only H
1
– H
3
will ratio against X
1
– X
0
. Also H
2
– H
1
is parallel to X
2
–
X
0
, and H
3
– H
2
is parallel to X
3
– X
0
. All ratio measurements are made between
parallel windings. The phase polarity must also be observed and is designated by
the order of terminal mention, i.e., H
1
- H
3
is of the same phase polarity as X
1
–
X
0
.
Note that the phase displacement for Figure 5-10 (a) diagram is 30 and has an
IEC vector group coding of Dyn1. Refer to the notes to Tables 5-4 through 5-6
for an explanation of vector group coding. For phase displacement between
windings the vector relating to the HV winding is taken as the vector of origin
(dotted line on delta winding, H
1
on wye winding). The vector relating to the
low-voltage wye winding is taken as X
1
(dotted line on a delta winding) and is
expressed in counterclockwise rotation of low-voltage winding in 30 clock-hour
figure increments. The low-voltage winding lag may be from 0 to 330 in steps of
30 .
The TTR310 test set is capable of measuring the turn ratio of three-phase
transformers where the windings are rotated or are connected in various phase
displacements from standard. Figure 5-10 (b) vector diagram is an example of a
typical case where the phase is displaced 150 from that of Figure 5-10 (a)
diagram. Vector group coding for this diagram is Dyn5.
Figure 5-10 (c) is an example of a nameplate vector diagram drawn differently
from that of Figure 5-5 (a). Although a corresponding figure cannot be found in
Table 5-4, the transformer and its testing is identical to that for Figure 5-10 (a).
Figure 5-10 (d) vector diagram is an example of a typical wye-delta connected
transformer winding which has a phase displacement of 210 . H
1
is the high-
voltage winding vector of origin and the dotted line on the delta winding is the
low-voltage winding reference. Vector group coding for this diagram is YNd7.