For a Delta transformer, the Vanguard TRM-403 Transformer Resistance Meter can measure the phase resistance readings and provide the individual Delta winding resistance values. The Vanguard TRM-403 can also provide the individual winding resistance values for a Wye transformer without the neutral terminal.
If the transformer winding resistance temperature is available at the time of testing, the TRM-403 can calculate the equivalent resistance value at any temperature value. This useful feature can be used to compare the field readings against the factory test resistance values.
The TRM-403 can perform a special test to collect data automatically for up to 90 minutes (at 60-second sampling intervals) or 45 minutes (at 30 second sampling intervals). The test data is recorded with a time stamp. All test results can be printed on the unit’s builtin 2.5” wide thermal printer.
Test record header information including the Company, substation name, transformer information, and operator information can also be entered using the rugged, 44–key “QWERTY”-style membrane keypad. The TRM-403 can automatically demagnetize the inductive device under test, eliminating the manual task of demagnetizing the transformer core after a resistance test.
The TRM-403 also has a “make-before-break” test mode that can be used to test the Load Tap Changer (LTC) or Voltage Regulator contact test sequence. The TRM-403 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 conveniently change the LTC/voltage regulator tap position from the TRM-403 front panel.