Friday, 07 August 2015 14:46 Written by 
Rate this item
(0 votes)



winding resistance meter, specially designed for field testing as well as factory testing of large transformers up to 500MVA. Winding resistance value of transformer and rotating machine are directly displayed on 5.7” TFT display. TRM25 is designed to work in live EHV switchyard conditions, ensuring operator’s safety and repeatability of results. Maintenance time saving is ensured by one time connection to transformer with simultaneous resistance measurement of three / six windings , measurement of resistances of all taps with automated tap change and demagnetisation facility. The meter is protected against the back-EMF offered by large inductive windings.


  • Can measure DC winding resistance of large rotating machines, highly inductive test objects like Transformer, Generators and Motors etc.
  • 25 A DC current makes it possible to measure low resistances with high accuracy.
  • One time connection to either all windings of primary and / or secondary. Simultaneous measurement reduces connection and measurement time.
  • Change in winding resistance, short or open windings can be detected from measured values.
  • Automatic temperature measurement and temperature corrected value calculation.
  • Measurements of winding resistance of all taps of phases in one go. Recoding, printing and storage of results.
  • OLTC contact opening and compete OLTC performance test facility. Testing of either single or three phases in one test. Single report generation.
  • To know condition of OLTC contacts, OLTC mechanism, transition resistor.
  • Discharges and demagnetizes the object after test
  • Uses Kelvin’s 4 wire method for resistance measurement.
  • Designed to measure DC winding resistance of highly inductive objects like transformers, generators, motor etc.
  • 30V / 50V* DC open circuit voltage.
  • Simultaneous measurement of 1 / 2 / 3* windings.
  • Quick stabilization of test results
  • Direct readings of all channels on backlit LCD
  • Automatic back-emf discharge with indication
  • Simple setup and use.
  • OLTC discontinuity indication

*- Features available only in TRM25

Features only in TRM 25

  • Displays, prints and stores test reports in the form of text header and tabulated test results.
  • Stand-alone & PC control mode
  • Managed by powerful CTrans software to configure setup, conduct test, view & analyse results, generate test report.
  • Current range selection, enable / disable of channels, printing, downloading etc.
  • 25A / 10A / 5A / 1A / 0.1A / 0.01A DC current injection range. Resistance auto-ranging.
  • Inbuilt thermal printer for test results.
  • Temperature measurement channel and automatic temperature correction for winding resistance for copper & aluminum windings. Supplied with RTD temperature sensor.
  • OLTC dynamic test facility available optionally.

OLTC Feature

Tap changer failures account for more than 40 % of all failures on power transformers. OLTC failures are caused by degradation of OLTC contacts. SCOPE offers dynamic OLTC test facility with TRM 25 to identify weaknesses in OLTC assembly. The test is conducted in PC control mode at higher sampling speed of 10 KHz.

  • This test records variation in current flowing through the OLTC against time during tap change.
  • Gives % drop in current and transition time
  • The drop in current during OLTC transition indicates change in transition resistance.
  • I t is also possible to calculate transition time which shows healthiness of mechanism.
  • The test is very useful for assessing health of OLTC.

This optional feature extends the capability of the basic instrument making it complete test equipment for testing transformers.


Parameter TRM14 TRM104 TRM25
Resistance Channels Two Two Three
Temperature Channel Not Available Yes
Current Ranges 1A, 0.1A, 0.01A 10A, 1A, 0.1A, 0.01A 25A, 10A, 5A, 1A, 0.1A, 0.01A
Maximum Resistance Range 2000Ω 2000Ω 2000Ω
Best Resolution 1μΩ 1μΩ 1μΩ
Accuracy Value ± 0.5% ± 2 digits
O/C Voltage 30V DC 50V DC
Protection Back EMF, Over Temperature, Accidental Disconnection of Lead
Discharge Automatic
OLTC Discontinuity indication Yes
 Temperature Correction No Yes
Display 4 Line 20 character backlit LCD for Resistance & Test Current  256 X 128 pixel, backlit graphic LCD for Resistance & Test Current
 Memory No  5000 results
 Inbuilt Printer No  Yes
 PC Connectivity No  Yes
Dimension 475 x 405 x 175 mm 475 x 405 x 230 mm 585 x 480 x 195 mm
Instrument Weight 10 kg 15 kg 20 kg
OLTC Dynamic Test No Yes (Optional)
Read 12224 times Last modified on Friday, 28 October 2016 06:47

Latest from Super User

More in this category: TRM 50+ »