TWA Standard Series

TWA Standard Series


The TWA standard series instruments are designed to measure the resistance of six coils and simultaneously analyze the three-phase tap changer on load of the primary and secondary transformer coils (provided by model TWA40). This is done in a single cable configuration, with test currents up to 40A. Each transformer configuration has a special measurement algorithm that is optimized for rapid stabilization of test results. The TWA instruments generate a true DC current without ripple. Both current injection and magnetic circuit energy discharge are automatically regulated.


The list of the instrument application includes:

  • A six-coil transformer coil resistance measurement with a single cable connection

  • Fast YN mode, which allows you to measure the resistances of three transformer coils in the YN simultaneously (TWA40D)

  • Dynamic resistance measurement (DVtest) of on-load tap-changers, which can be performed simultaneously on all three phases, or in a single phase (TWA40D)

  • An evaluation of the synchronisation between the phases of the on-load tap changer (TWA40D)

  • An on-load tap changer motor current measurement using a dedicated channel (TWA40D)

  • An automatic three-phase or single-phase transformer demagnetization

Benefits and features

Resistance measurement of six coils

The TWA injects the current with a voltage as high as 55 V. This ensures that the magnetic core is quickly saturated and the duration of the test is as short as possible. All transformer coils, both primary and secondary, can be measured with only one cable configuration. The TWA has an internal memory that can store up to 500 measurements. All measurements are time and date stamped. The is equipped with thermal instruments and

overcurrent protection. The TWA has a very high capacity to cancel the electrostatic and electromagnetic interference that exists in HV electrical fields. This is achieved by means of a patented system solution applied to both the construction of hardware and the implementation of application software.

A special mode is provided for resistance measurement in de-energized multi-tap changer (DETC) positions.

Tap changers ... Simultaneous dynamic resistance The measurement (DRM) of all three phases.

The model TWA40D can be used to measure the resistance of individual taps of a power transformer without discharging between tests.

The unit also checks the load tap changer (OLTC) without an interruption. The moment the one touch position is changed from one tap to another, the device detects a sudden and very short drop of the current test. These drops called "Ripple" should be consistent, where any off-line drop should be investigated. Tap changer failures can be detected by analysis of the transition waveform measurements, the transition time and the DRM graphics display. The currents in all three phases are recorded simultaneously. The test currents can reach up to 40 A in total during the test.

The dynamic resistance graphs are recorded for all three phases simultaneously, so the synchronization is checked by means of the cursors provided in the DV-Win software. All three phase traces are plotted on the same graph. In addition, the motor current of the tap changer is recorded and displayed on the same graph. The built-in tap changer control unit allows remote control of the tap changer operation from the instrument keyboard.

DV-Win software

The Windows-based DV-Win software allows control and observation of the testing process, as well as saving and analyzing the results in a PC. Provides a test report, arranged in a selectable form as an Excel spreadsheet, PDF, Word, or ASCII format. The software provides an evaluation of the condition of the OLTC (tap changer) through analysis of graphs representing dynamic resistance values during tap changer transitions In addition, the DV-Win measures and calculates the OLTC transition time, ripple and winding resistance for each tap-changer operation. The interface is USB. RS232 is optional. The additional test mode, Quick YN, is enabled by the DV-Win software for the TWA40D model. In this mode, it is possible to simultaneously measure the resistances of three transformer coils in the YN configuration. It is also possible to test the resistances of all taps of the three phases in a single pass through the tap changer positions.

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