The Three-Phase Winding Ohmmeter DV Power TWA25A

The three phase winding ohmmeter, DV Power TWA25A, finds typical applications in measuring the resistance of inductive test objects and analyzing on-load tap changers in the electric power industry and similar sectors. It is particularly well-suited for testing the windings of various transformers such as power transformers, distribution transformers, and autotransformers. Additionally, it serves as a valuable tool for verifying on-load tap changers and performing transformer demagnetization.
The DV Power TWA25A three phase transformer winding ohmmeter is employed in various scenarios including resistance measurement during manufacturing, commissioning, and testing of:

• Transformers 
• On-load tap changers 
• De-energized tap changers 
• Generators and electrical motors 
• High current busbar joints 
• Cable splices 

How to Use TWA25A?

The TWA25A is primarily designed for measuring the resistance of transformer windings, and it provides three options for testing: NONE, DETC, and OLTC. When testing the winding resistance of a transformer without a tap changer in the current path, it is recommended to select the NONE option. However, when testing the winding resistance of a transformer with a tap changer in the current path, either DETC or OLTC should be chosen. After that user needs to choose what type  the test object three-phase or single-phase transformer and which side of the transformer will be tested HV side, LV side, or Both sides.   TWA25A automatically regulates the injection and sets the path of current and after the tests finish discharges energy from the test object.
The winding-ohmmeter TWA25A is a precise measuring tool that generates a true DC ripple-free current. Another useful feature is the delta R function, which indicates the stability of the measurement readings and helps in obtaining accurate results.

TWA25A Three Phase Winding-Ohmeter Design 

The TWA25A is a reliable test device that can store up to 500 measurements in internal memory. 6 independent channels enable the testing of three phase transformers with one time connection. Free  DV-TR software is included in the purchasing price and communicates with the TWA25A three phase winding-ohmmeter via USB or RS232 interface. It allows you to run the test remotely from a PC, as well as to download test results, analyze them, and generate fully configurable test reports. A high output voltage (up to 55 V) enables the measurement of a wide resistance range and the use of long and thinner test cables, which is a benefit. As a digital three phase winding-ohmmeter is the ideal choice for industries that require precise and consistent measurement of electrical resistance.

Connecting TWA25A to a Test Object 

The TWA25A device follows Kelvin's (four-point) measurement principle for its connection principle and one-time connection. This principle ensures accurate measurements for all phases by using separate "Voltage Sense" terminals attached to one side of the measuring clamps and "Current Cables" attached to the other side of the measuring clamps. The resistance of the current cables and clamps is effectively eliminated from the resistance measurement. This configuration helps to provide precise reliable and fast resistance readings by minimizing the impact of any additional resistance in the measurement setup and much less time for measuring because of the one-time connection principle.