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ISO 9001 and 17025 Certified



Transformer Resistance Meter


The TRM-403 is a  three phase transformer winding resistance meter that allow the user to connect all test cables to the transformer bushings. The unit will then measure the transformer resistance value for each of the phases without the need to disconnect and reconnect cables for each phase. The TRM-403 can provide a fast and stable reading of very large transformers by utilizing a 60Vdc power supply. It is capable of outputting a selectable test current from 1A to 40A. Since the TRM-403 can accurately measure resistance from 1 micro-ohm to 500 Ohms, it can be used as a micro-ohm meter to measure EHV circuit breaker contact resistance, or for any low resistance measuring application.

  • Perform three phase test on a transformer without the need to switch cables
  • Can provide individual Delta winding resistance values
  • Can provide individual Wye (with no neutral) winding resistance values
  • Demagnetize transformer after test
  • Selectable test current from 1A to 40A
  • Computer control via RS-232C, USB, or Bluetooth interface
  • Built-in 2.5" wide thermal printer





Technical Specifications

TYPE Portable transformer winding resistance meter
PHYSICAL SPECIFICATIONS 21” W x 17” H x 9” D (53 cm x 43 cm x 24 cm); Weight: 35 lbs (15.8Kg)
OPERATING VOLTAGE 100 – 240 Vac, 50/60 Hz
RESISTANCE READING RANGE 1 micro-ohm to 500 Ohms
ACCURACY 1 – 19,999 micro-ohms: ±0.5% reading, ±1 count
20 – 999 milliohms: ±1% reading, ±1 count
1 – 500 Ohms: ±1.5% reading, ±1 count
TEST CURRENT 1-40A in 1A increments
TEST VOLTAGE 60 Vdc charging, 18V DC max during measurement
INPUT CHANNELS 4 input channels for measuring resistance
DISPLAY Back-lit LCD (128 x 64 pixels), viewable in direct sunlight and low light levels
PRINTER Built-in 2.5" wide thermal printer
INTERNAL DATA STORAGE 256 static test records (each can contain up to 111 readings) and 120 dynamic test records
EXTERNAL DATA STORAGE Up to 999 test records on external USB Flash drive.
SAFETY Designed to meet UL 61010A-1 and Can/CSA C22.2 No 1010.1092 standards
ENVIRONMENT Operating: -10ºC to 50ºC (15ºF to +122ºF)
Storage: (-30ºC to 70ºC (-22ºF to +158ºF)
HUMIDITY (MAX) 90% RH @ 40˚ C (104˚ F) non-condensing
ALTITUDE (MAX) 2000m (6562 ft) to full safety specifications
CABLES Four 50-foot test cables, one LTC control cable, one ground cable, one power cord, one USB cable
OPTIONS Shipping Case
WARRANTY One year on parts and labor
Specifications are valid at nominal voltage and ambient temperature of +25˚C (+77˚F).



Field Pictures

TRM-203 in Malaysia
TRM-203 Testing on 200MVA Transformer
TRM-403 Testing at Elecktromak, Turkey
TRM-403 Testing in Malaysia
TRM-403 at CFE Tizayuca Substation - Mexico
TRM-403 at CFE Tizayuca Substation - Mexico
TRM-203 Demag Test at Oncor, Texas
Winding Resistance Test with TRM-203 at Xcel Energy, Lubbock, Texas
TRM-203 Testing at TBEA Energy, Vadodara, India