Many high-current power supply system equipment, preventive tests and trial handover require accurate loop resistance measurement.Circuit breakers are important equipment in power systems. National standards GB763, GB50150, and power industry standard 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.
The conductivity of a circuit breaker depends on the contact resistance between the dynamic and static contacts. When the contact resistance increases, the power loss increases, causing the temperature at the contact to rise. Its value directly affects the normal current-carrying capacity and, to a certain extent, the ability to interrupt short-circuit currents. Therefore, the resistance of the conductive circuit in each phase of a circuit breaker is an important data for installation, maintenance, and quality acceptance.Loop resistance of circuit breakers is a crucial parameter for installation, maintenance, and quality acceptance.
There are various methods to measure contact resistance. Japanese scholars proposed using a superconducting quantum device to measure contact resistance, while others used electrolytic cells. Polish scholar Jerzy Kaczarek proposed measuring contact resistance using the third harmonic. These methods are typically conducted under laboratory conditions for electrical contacts. In practice, the four-terminal method is often used to measure the actual contact resistance.
Previously, a DC double bridge was commonly used to measure the contact resistance of circuit breakers. However, when using a double bridge to measure the resistance of a circuit breaker, the bridge measurement circuit passes a weak current, making it difficult to remove the oxide film resistance. The measured resistance value appears too high, but the oxide film can be easily punctured by a large current, which does not hinder the normal current flow. Therefore, in the test method, a DC voltage drop test is adopted, and the current should not be too small.
High-voltagecircuit breakers The resistance of the conductive circuit mainly depends on the contact resistance between the moving and static contacts. The presence of contact resistance increases the loss when current flows, raising the temperature at the contact. Its value directly affects the normal current-carrying capacity and, to a certain extent, the ability to interrupt short-circuit currents. Therefore, the resistance value of the conductive circuit in each phase of a circuit breaker is an important data for installation, maintenance, and quality acceptance.
Since there is an oxide film between the switch contacts, if a small current is used for testing, the test results are generally much larger due to the influence of the oxide film. However, the oxide film can be broken down under a large current. Theoretically, as long as the test current does not exceed the rated current, the larger the current, 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 andground 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 applied to the connection points of the grounding down conductor during the construction of the grounding device, the connection points in the soil are still affected by moisture and other factors for a long time, leading to corrosion, disconnection, loosening, and other phenomena, resulting in an increase in the resistance 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 during operation, and in severe cases, causing the equipment to operate disconnected from the ground grid. It can be used for accurate 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 of the grounding down conductor, and to determine the fault point by comparing historical test values and adjacent point test values. 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, featuring simple operation, fast test speed, stable test data, and portability.
Since thecircuit breaker contact resistance is very small, only by using a very high current for testing can a certain accuracy be ensured, and the anti-interference ability is also stronger.
Used forcircuit breaker contact resistance and current-carrying conductor resistance high-precision measurement, it can stably output large current for a long time, complying with the relevant provisions of DLT845.4-2004 "General Technical Conditions for Resistance Measuring Devices Part 4: Loop Resistance Tester".
