Many high-current power supply system equipment, preventive tests and trial handover require accurate loop resistance measurement. Circuit breaker is an important equipment in the power system. National standards GB763, GB50150, and power industry DL/T596 specify the following conditions for circuit breaker resistance measurement: the voltage drop should be measured with a DC current not less than 100A. 

      Circuit breaker conductivity depends on the contact resistance between the dynamic and static contacts of the circuit breaker. The existence of contact resistance increases the loss when the conductor is energized, causing the temperature at the contact to rise. Its value directly affects the current-carrying capacity during normal operation and, to a certain extent, affects the ability to interrupt short-circuit current. Therefore, the resistance value of the conductive circuit in each phase of the circuit breaker is an important data for installation, maintenance, and quality acceptance of the circuit breaker. 

There are multiple ways to measure contact resistance. Japanese scholars proposed using a superconducting quantum device to measure contact resistance, while others used an electrolytic cell method. Polish scholar Jerzy Kaczarek proposed measuring contact resistance using the third harmonic. These methods are usually conducted under laboratory conditions. In practice, the four-terminal method is often used to measure the actual contact resistance. 

       Previously, the DC double bridge method was commonly used to measure the contact resistance of circuit breakers. However, when using the double bridge to measure the resistance of the circuit breaker, due to the weak current passing through the bridge measurement circuit arms, it is more difficult to remove the oxide film resistance, and the measured resistance value may be too large. But the oxide film can be easily punctured by large current, which does not hinder the normal passage of current. Therefore, the test method adopts the DC voltage drop test, and the current should not be too small.

       High-voltagecircuit breaker The resistance of the conductive circuit mainly depends on the contact resistance between the dynamic and static contacts of the circuit breaker. The existence of contact resistance increases the loss when the conductor is energized, causing the temperature at the contact to rise. Its value directly affects the current-carrying capacity during normal operation and, to a certain extent, affects the ability to interrupt short-circuit current. Therefore, the resistance value of the conductive circuit in each phase of the circuit breaker is an important data for installation, maintenance, and quality acceptance of the circuit breaker.  

Since there is an oxide film between the switch contacts, if a smaller current is used for detection, the test result is generally much larger due to the influence of the oxide film. However, the oxide film can be broken down under large current. Theoretically, as long as the test current does not exceed the rated current, the larger the better. But when formulating the regulations, considering the production level of relevant domestic instruments at that time, a provision was made that the current should not be less than 100A.   Power equipment and ground grid continuity resistance tester 

      The reliable and effective connection between the grounding down conductor of power equipment and the ground grid is the fundamental guarantee for the safe operation of power equipment and the personal safety of operators. Although necessary anti-corrosion treatment has been done at the connection of the grounding down conductor during the production of the grounding device, the connection point in the soil is still subject to long-term effects of moisture and other factors, leading to corrosion, disconnection, loosening, etc., which increases the resistance value at the contact point between the grounding down conductor and the ground grid, failing to meet the requirements of power regulations, causing potential safety hazards in the operation of the equipment, and in severe cases, causing the equipment to be disconnected from the ground grid. It can be used for precise measurement of the continuity resistance between the grounding down conductor of power equipment and the grounding grid or adjacent equipment. 

The ground grid continuity resistance tester is used to measure the continuity resistance value of the grounding down conductor, and to determine the fault point by comparing the historical test values and the test values of adjacent points. The working power of the ground grid continuity resistance tester is provided by an internal lithium battery, no external AC power supply is needed. The test process is controlled by a microcontroller, with the characteristics of simple operation, fast test speed, stable test data, and easy portability.  

    Since the circuit breaker contact resistance is very small, only by using a very high current for detection can a certain accuracy be guaranteed, and the anti-interference ability is also stronger.  

    It is used for high-precision measurement of circuit breaker contact resistance and current-carrying conductor resistance. It can output large current stably for a long time, and complies with the relevant provisions of DLT845.4-2004 "General Technical Conditions for Resistance Measuring Devices Part 4: Loop Resistance Tester".