Vanguard TRM-20_40 - Manual (Page 6)

TRM-20 AND TRM-40 USER’S MANUAL REV 1
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1.0 INTRODUCTION
1.1 General Description and Features
The TRM-20 and TRM-40 are Vanguard Instruments’ third generation transformer winding
resistance meters. The TRM line is designed specifically to measure DC resistance values of
transformer windings, rotating machine windings, or any dc resistance of an inductive device.
The TRM line features dual resistance-reading input channels that can measure two winding
resistances simultaneously (primary and secondary windings of a transformer).
Both the TRM-20 and TRM-40 can provide a fast and stable reading of very large transformers
by utilizing a 60Vdc power supply. The TRM-20 is capable of outputting a selectable test current
from 1A to 20A while the TRM-40’s test current is selectable from 1A to 40A.
Since the TRM-20 and TRM-40 can accurately measure resistance values from 1 micro-ohm to
2,000 Ohms, they can be used as micro-ohm meters to measure EHV circuit breaker contact
resistance, or for any low resistance measuring application.
If the transformer winding resistance temperature is available at the time of testing, the TRM
can calculate the equivalent resistance value at any temperature value. This useful feature
allows the user to compare the field readings against the factory test resistance values.
A special test mode allows the TRM to collect data automatically for up to 90minutes (at 60-
second sampling interval) or 45 minutes (at 30 second sampling interval). Test data is recorded
with a time stamp.
All test results can be printed on a 2.5” wide thermal printer. Test record header information
including the company, substation name, transformer information can also be entered using
the 16-key key pad.
The TRM-20 and TRM-40 can also demagnetize the inductive device under test, eliminating the
manual task of demagnetizing the transformer core after a resistance test.
The TRM also has a “make-before-break” test mode that can be used to test the load tap
changer (LTC) or voltage regulator test sequence. The TRM produces a “Dynamic-Resistance”
graph of the LTC or voltage regulator contact under operation. An opened contact can be
detected visually from this resistance chart.
The TRM’s built-in LTC/Voltage regulator can be used to change the LTC/Voltage regulator tap
position from the TRM front panel.
Safety Features
The TRM automatically dissipates the energy stored in the transformer at the end of each test.
The discharge circuit will continue to work even if the TRM power supply is lost.
Test Record Storage
The TRM can store up to 100 test records internally. For external test record storage, the TRM
features a USB Flash drive interface port. Up to 999 test records can be stored on a connected
USB Flash drive.