Chapter 3 — Measuring with the DWR-10
Page 36
September 2004
If the substation is energized, choose a location that is on
the de-energized side of the transformer to reduce effects
on induction on the test cables and the test set. The test set
can tolerate up to 40 volts p-p (peak to peak) between
positive and negative terminals, and no more than 50 V
from any terminal to ground.
Testing One or Two Windings
Transformers may be tested one winding at a time or two
windings at a time, since the DWR-10 has two channels.
Two-winding testing is recommended when testing a low-
voltage winding on a large capacity transformer (i.e., over
100 MVA).
By connecting the primary and secondary windings in
series, the speed of saturation and stability of the readings
is increased because there are more amp-turns
contributing to the flux in the core. The resistance
measurement of both windings is made at the same time
on channels A and B.
The polarity of the windings to be connected in series
must be considered—the amp-turn effect must be
additive, otherwise, there is no advantage to the series
connection.
If the transformer is a single-phase unit with terminals
marked as H1, H2, X1, and X2, connect as follows:
•
Connect the jumper between H2 and X1 (rule of
thumb is to connect the jumper between opposite
polarities).
•
Connect the positive current to H1.
•
Connect the negative current to X2.
•
Ground one of the points for safety reasons.
This concept can also be applied to three-phase
transformers. The table below gives a few examples for
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