Handheld Ratio & Winding Resistance Tester DV Power TWR-H

The TWR-H device is DV Power handheld single-phase turns ratio & winding resistance tester. It can test power & distribution transformers, instrument transformers, rotating machines, as well as non-inductive test objects.

• Handheld, battery powered device
• Maximum test voltage 40 V AC
• Maximum test current 10 A DC

Ratio & Winding Resistance Tester Intended Use 

The turns ratio & winding resistance tester, DV Power TWR-H, is designed for measuring transformers turns ratio, winding resistance of both inductive and non-inductive test objects, and demagnetization of transformers and rotating machines. The device also detects phase shift and excitation current in addition to turns ratio. This makes it possible to notice transformer core or winding turn faults that are invisible when just measuring turns ratio.
The following is a list of instrument applications:

• Distribution and instrument transformers, motors, and generators winding resistance measurements
• Distribution transformer turns ratio measurement
• Verification of instrument transformer turns ratio
• Calculating the turns ratio deviation
• Transformer excitation current measurement
• Transformer phase angles measurement
• Checking the polarity of instrument transformers
• Distribution and instrument transformers, motors, and generators demagnetization

How to use Ratio & Winding Resistance Tester?

The instrument can test both single phase and three phase transformer. When three phase transformer is tested, TWR-H advises user to properly connect instrument for each phase and each test. Transformer ratio and winding resistance measurement can be performed in multiple tap positions. All results are saved in one record, for easier analysis.

TWR-H turns ratio & winding resistance tester design

The device has two output DC sources that it uses to measure the resistance of the transformer windings. The high voltage winding of the transformer is injected with current using the first DC source, which has a maximum output of 2 A DC. The low voltage winding of the transformer is tested using the second DC source, which has a maximum output of 10 A DC. When testing the winding resistance of distribution transformers, this is extremely helpful. Due to the high turns ratio, there is a significant difference in resistance between the high voltage and low voltage windings. It is additionally feasible to demagnetize the transformer core during the winding resistance test. Demagnetization is a completely automated and secure process.The instrument can provide a test voltage of up to 40 V AC for this test, but it can also produce a very low test voltage of just 1 V AC, which is required for the majority of current transformers' turns ratio verification.An integrated Li-Ion battery powers TWR-H. The battery can run up to 100 tests when fully charged.

Connecting TWR-H device to a test object

The instrument comes with two sets of cables, one for connecting to high voltage transformer winding, and another for connecting to low voltage transformer winding. Jumper cable is also provided for shorting one phase on transformer high voltage side, which may be necessary for turns ratio testing of three phase transformers with certain vector groups.The connection principle used by original test cables is based on Kelvin's (four-point) measurement principle. By using distinct "Voltage Sense" terminals attached to one side of the measuring clamps and "Current Cables" attached to the other side, this approach provides reliable measurements. The resistance measurement is effectively free of the resistance of the current wires and clamps. By reducing the impact of any additional resistance in the measuring setup, this design aids in the provision of accurate and trustworthy resistance data.