• Auto-discharge circuit for operator safety
• Demagnetizes transformer after test
• Selectable test current from 1A to 20A
• RS-232C, USB, and Bluetooth computer interfaces
• Built-in thermal printer

The TRM-20 is Vanguard Instruments’ third generation transformer winding resistance meter. The TRM-20 is designed specifically to measure DC resistance values of transformer windings, rotating machine windings, or any dc resistance of an inductive device.

The TRM-20 features dual resistance-reading input channels that can measure two winding resistances simultaneously (primary and secondary windings of a transformer). It 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.

Since the TRM-20 can accurately measure resistance values from 1 micro-ohm to 2,000 Ohms, it can be used as micro-ohm meters to measure EHV circuit breaker contact resistance, or for any low resistance measuring application. The TRM-20 can automatically demagnetize the inductive device under test, eliminating the manual task of demagnetizing the transformer core after a resistance test.

Since the TRM-20 and TRM-40 can accurately measure

resistance values from 1 micro-ohm to 500 Ohms (up

to 2,000 Ohms for the TRM-20), 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

fi eld readings against the factory test resistance values.

A special test mode allows the TRM to collect data automatically

for up to 90 minutes (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 automatically demagnetize

the inductive device under test, eliminating the

manual task of demagnetizing the transformer core after

a resistance test.

The TRM can also be computer-controlled via the unit's

RS-232C, USB, or Bluetooth interface.

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.

Part number TRM-20 TRM-20, cables, software

Part number TRM-40 TRM-40, cables, software

Part number TP3 2.5-inch wide thermal printer paper