Vt/Pt Excitation Current; Vt/Pt Continuity Test - AEMC 8500 User Manual

4.3.4

VT/PT Excitation Current

Excitation Current, displayed in milliamperes, is the RMS current in the H
winding due to test excitation, during negligible loading of the associated
X winding.
The DTR uses a maximum 44V excitation signal for testing, thus the
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displayed excitation current value will almost always be a small fraction
of the tested transformer's no-load excitation at full (rated) voltage. Most
transformers will require 100mA or less; some will require less than 1mA.
Note: If you are presently using a ratiometer that employs "X" side
"step-up" excitation (e.g. common hand-cranked instrument), exci-
tation currents displayed by the DTR
cantly lower. This is normal and results directly from the fact that in
most step-down transformers, the H winding exhibits much higher
impedance than its associated X winding.
4.3.5

VT/PT Continuity Test

The Continuity Test function of the DTR
means of identifying open primary and secondary windings, open circuit
breakers, and blown fuses. When selected, the DTR
for continuity between its X cables and between its H cables.
The Continuity Test is selected when the user depresses the TEST button
at the Press [TEST] to Check Continuity prompt. The DTR
the results of continuity checking, then enter a brief degaussing period.
During this time, the message Pre-Test Checks will be displayed.
• The DTR will indicate OPEN for tested circuits greater than 4kΩ, and
CONT for those less than 4kΩ. A small percentage of transformers
(e.g. those with extremely high inductance or high winding resistance)
may appear as open circuits to the DTR
• An OPEN indication will not cancel the test cycle in progress and the
results of ratio testing will still be displayed.
• Transformers whose winding arrangement involves multiple, parallel
paths (e.g. Delta-connected types) may read CONT, when in fact one
or more windings may be open.
Digital Transformer Ratiometer DTR
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Model 8500 serves as a useful
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Model 8500
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will, in most cases, be signifi-
alternately checks
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.
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will display
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