Main classification and application scope of DC resistance tester

The DC resistance tester (also known as an ohmmeter or transformer DC resistance tester) is mainly used to measure the DC resistance of equipment such as transformers, motors, and reactors. It is an important equipment for preventive testing in the power industry.
1, Classification of DC Resistance Testers
According to different measurement principles, core components, and output currents, they are mainly divided into the following categories:
1. Classified by core components and measurement principles
Traditional type (using bridge method):
Single arm bridge: measure median resistance (above 1 Ω).
Double arm bridge: measure low resistance (below 1 Ω).
Characteristics: Manual balancing, cumbersome operation, accuracy affected by human factors, currently gradually phased out.
Digital (using constant current source method/four wire measurement method):
Current mainstream products. Using large-scale integrated circuits and constant current source technology, automatic testing and direct display of resistance values.
Features: High measurement accuracy, good stability, strong anti-interference ability, with data storage and printing functions.
2. Classify by output current size
This is the most intuitive indicator when selecting, usually determining the scope of application of the instrument:
Micro ohmmeter/milliohmmeter: Used for measuring contact resistance at switch contacts and bus connections with low current (usually less than 1A).
Medium current tester: The current range is usually 3A, 5A, 10A, suitable for small and medium-sized distribution transformers.
High current tester: The current range is usually above 20A, 40A, 50A, or even 100A, suitable for large power transformers (due to the large inductance of the transformer, a high current is required to quickly establish a stable magnetic field and complete the test).
3. Classify by function and usage scenario
Portable: Small in size and lightweight, suitable for on-site carrying and outdoor high-altitude operations.
Desktop/high-precision type: usually used in laboratories or maintenance workshops, with higher accuracy.
Three channel/six channel frequency tester: specifically designed for three-phase transformers, it can simultaneously measure the resistance of three-phase windings, greatly reducing testing time, and has the function of magnetic assist method, used to measure transformers with neutral point leads.
Main application scenarios
DC resistance testing is mainly used to check the winding quality and conductive circuit connection of electrical equipment.
Transformer winding test: Check the welding quality of the internal wire joints of the winding, whether the connection between the lead and the bushing is good, and whether the contact of the tap changer (gear switch) is reliable.
Transformer testing: Measure the primary and secondary winding resistance of current transformers (CT) and voltage transformers (PT).
Motor/generator testing: Measure the DC resistance of the stator winding and rotor winding of the motor to determine whether there is a turn to turn short circuit or disconnection.
Switch/Circuit Breaker Testing: Measure the resistance of the conductive circuit of the circuit breaker and the contact resistance of the isolating switch contacts.
Cable/busbar testing: Check the conductivity of cable conductors or the connection quality of busbars.