Six AC and DC tests on a three-phase transformer, with a single connection
TWR250B is a fully automatic three-phase analyzer that combines winding resistance, the on-load tap changer dynamic test (DVtest), demagnetization, turns ratio, phase shift and excitation current. All 6 to 8 transformer terminals are connected at once and the tests run one after another without rewiring.
Benefits
One connection for every test
Three or four H cables and three or four X cables connect all HV and LV bushings, which greatly shortens field testing, especially on large transformers.
Winding resistance up to 25 A DC
True, ripple-free DC current with a dedicated algorithm for each transformer configuration. With all six windings connected, the instrument injects current simultaneously through the HV and LV windings on the same core limb, so the core saturates sooner.
Turns ratio up to 250 V AC under IEC 60076-1
Accurate ratio and magnetic balance measurements on large generation and transmission transformers, with automatic vector group detection and calculation of the deviation from the nameplate.
Tap changer under control
The built-in control unit operates the on-load tap changer remotely and automates testing across multiple positions with a single operator.
Applications
- Commissioning and maintenance of three-phase and single-phase power transformers and autotransformers.
- On-load tap changer diagnostics with DVtest across multiple positions.
- Ratio, polarity, winding resistance and demagnetization of current transformers.
- Winding resistance of motors, generators and other inductive objects.
About the product
Once the vector diagram is selected, the instrument runs the specific test for each connection -delta-wye, delta-delta, delta-zigzag, etc.- without changing the leads, and proprietary filtering cancels the interference of HV fields. The internal battery allows testing where no mains supply is available.
The 10.1" touch screen works with templates prepared in the office; the 32 GB SD card stores tens of thousands of results, which are printed on the 58 mm thermal printer or exported via USB. The PC software, included with free updates, exports results to Excel and generates PDF reports.
Technical specifications
| Test sources | 1 - 250 V AC; 5 mA - 25 A DC, up to 50 V |
| Turns ratio | 0.8 - 50,000; 5-digit resolution |
| Winding resistance | 0.1 µΩ - 100 kΩ |
| Phase angle and excitation current | 0 - 360° (0.01°); 0 - 2 A |
| DVtest and AC current channel | 1 ms resolution |
| Temperature | -50 to +180 °C; Pt100 class B |
| Display, memory and interface | 10.1" touch screen; 32 GB SD; Ethernet and USB |
| Power supply | 90 - 264 V AC, 50/60 Hz; 14.4 V, 6.8 Ah Li-ion battery |
| Dimensions and weight | 503 × 193 × 406 mm; 11.0 kg |
| Standards and warranty | EN 61010-1:2010; EN 61326-1:2013; 3 years |
Frequently asked questions
Which tests run without changing the leads?
All of them: resistance of all six windings, DVtest, demagnetization, turns ratio, phase shift and excitation current, with the same H and X cable connection.
Can it test single-phase transformers and CTs?
Yes. Single-phase units use two H and two X cables. On current transformers, the H cables go to the secondary and the X cables to the primary, or are slid through the core when there are no primary terminals.
Why demagnetize the core?
A DC test can leave residual magnetism that distorts other tests. The instrument removes it with a current of alternating polarity and decreasing magnitude down to zero.
How are results documented?
They are printed on the instrument, exported via USB or downloaded with the PC software, which generates customized PDF reports.
