Handheld Turns Ratio & Winding Resistance Tester TWR-H

Handheld Turns Ratio & Winding Resistance Tester TWR-H


TWR-H is a handheld, battery operated, fully automatic test set specially designed for turns ratio, phase shift, excitation current and winding resistance measurements of transformers. It can also perform demagnetization of these transformers. Transformer turns ratio is determined by applying AC voltage across high voltage winding, accurately measuring AC voltage across the corresponding unloaded transformer winding, and then displaying the ratio of these voltages. User can enter a transformer’s nameplate voltages, so that turns ratio deviation can be calculated. This feature eliminates any error otherwise caused by an operator’s manual calculation. TWR-H compares measured turns ratio with the nameplate ratio and prints out the % of error for each test. Transformer winding resistance is determined by injecting DC current through a winding, accurately measuring DC voltage across the winding, and then calculating resistance as the ratio of voltage and current. The device generates true DC ripple-free currents. Both the injection of the current and the discharge of energy from transformer magnetic circuit are automatically regulated.

  • Unique handheld instrument on the market.
  • Performs 3 different tests – turns ratio, winding resistance, and demagnetization.
  • Single-phase test voltage up to 40 V AC
  • Two DC current sources.
  • Test current up to 2 A DC for transformer HV side.
  • Test current up to 10 A DC for transformer LV side.
  • Extremely lightweight – only 1.4 kg / 3.1 lbs
  • Battery-powered

Connecting TWR-H to Test Object

Using two sets of cables, TWR-H can be can be connected to one phase at transformer HV side, and one phase at transformer LV side, simultaneously. Connecting to both sides is necessary for turns ratio measurement. For winding resistance measurement, TWR-H can be connected to either transformer HV side or LV side, or to both of them in case when HV and LV winding resistances are going to be measured simultaneously.

Benefits and Features

Two Output DC Sources

A common issue when testing winding resistance of distribution transformers is the selection of test current. Distribution transformers have high turns ratio, and therefore high difference between rated HV and LV currents. Testing HV and LV winding simultaneously with the same current source can be challenging – test current must be less than or equal to 10% of the HV rated current, which is very often too low for LV winding. For this reason, TWR-H has two output DC sources – one for transformer HV side, and the other for transformer LV side. This way, transformer HV and LV windings can be tested simultaneously using different test currents.

Multiple Tests

Built-in AC and two output DC sources enable performing multiple tests on a same transformer – winding resistance, demagnetization, turns ratio, excitation current, and phase angle – with a single cable and test setup.

Internal Battery

TWR-H is powered by internal Li-Ion battery. Up to 100 tests can be performed with fully charged battery. Memory

TWR-H has internal SD card of 8 GB memory space. This enables saving tens of thousands of results.

DV-Win Software

All results from TWR-H internal memory can be easily transferred to a DV-Win software via Bluetooth communication. This allows user to analyze results in the office, to print them, or to create customized test reports. The software is included in the purchase price.

The list of instrument application includes:

  • Winding resistance measurement
  • Turns ratio measurement
  • Turns ratio deviation calculation
  • Excitation current measurement
  • Phase angle measurement
  • Demagnetization

  • Type: Li-Ion, 14.8 V, 2.9 Ah
  • Rechargeable
  • User replaceable

Power Supply Adapter

  • Input voltage: 90 – 264 V AC, 50/60 Hz
  • Output voltage: 12-19 V DC
  • Output current: 2 A DC

Output AC Source

  • Voltage: Up to 40 V AC

Output DC Source 1

  • Current: up to 2 A DC
  • Voltage: up to 18 V DC

Output DC Source 2

  • Current: up to 10 A DC
  • Voltage: up to 18 V DC

Turns Ratio Measurement

  • Measurement range: 0.8 – 20 000
  • Resolution: 5 digits
  • Typical accuracy:

Excitation Current Measurement

  • Measurement range: 0 – 500 mA
  • Range / resolution:

0.0000 – 9.9999 mA 0.1 μA

  • Typical accuracy: ±(0.25% rdg + 0.5 mA)

Phase Angle Measurement

  • Measurement range: 0 – 360o
  • Resolution: 0.01o
  • Typical accuracy: ±0.05o

Winding Resistance Measurement

  • Measurement range: 0.1 µΩ – 3 kΩ
  • Range / resolution:

0.1 µΩ – 999.9 µΩ 0.1 µΩ
1.000 mΩ – 9.999 mΩ 1 µΩ
10.00 mΩ – 99.99 mΩ 10 µΩ
100.0 mΩ – 999.9 mΩ 0.1 mΩ
1.000 Ω – 9.999 Ω 1 mΩ
10.00 Ω – 99.99 Ω 10 mΩ
100.0 Ω – 999.9 Ω 0.1 Ω
1.000 kΩ – 3.000 kΩ 1 Ω

  • Typical accuracy: ±(0.1% rdg + 0.1% FS)


  • LCD 4.8” display, 240 x 128 pixels Interface
  • Bluetooth Internal Memory
  • SD card 8 GB Warranty
  • 3 years

Environmental Conditions

  • Operating temperature:

-10 ºC – +55 ºC / +14 ºF – +131 ºF

  • Storage & transportation:

-40 ºC – +70ºC / -40 ºF – +158 ºF

  • Humidity: 5% – 95% relative humidity,

non condensing
Dimensions and Weight

  • Dimensions (W x H x D):

170 x 310 x 58 mm / 6.69 x 12.21 x 2.28 in

  • Weight: 1.4 kg / 3.1 lbs
Download the catalogue: Handheld Turns Ratio & Winding Resistance Tester TWR-H.

Download the catalogue of Handheld Turns Ratio & Winding Resistance Tester TWR-H.

If you want to acquire Transformer ratio meters with quality, you can also consult prices of Transformer ratio meters.

If you have any doubts or need advice from our engineers, don't hesitate to contact us and we will be pleased to help you. You can also call us at (+34) 982 20 99 20.