Working Principle

Loop Resistance Tester Album

Loop Resistance Tester Album (3)

In the power system, many high-current electrical equipment need to accurately measure the resistance value of the circuit during preventive tests and handover tests. Circuit breakers are important electrical equipment in the power system. According to the latest standard "JJG1052-2009 Loop Resistance Verification Regulation", national standards GB763, GB50150, and power industry standard DL/T596, the measurement of the conductive circuit resistance of circuit breakers is specified: it should be measured using the DC voltage drop method, with a current not less than 100A.



The resistance of the conductive circuit of a circuit breaker mainly depends on the contact resistance between its moving and static contacts. The existence of contact resistance increases the loss when the conductor is energized, raises the temperature at the contact point, and 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 of each phase of the circuit breaker is an important data for the installation, maintenance, and quality acceptance of circuit breakers.



There are many methods for measuring contact resistance. Japanese scholar Isao Minowa proposed using superconducting quantum devices to measure contact resistance, H.Archi proposed using the electrolytic cell method, and Polish scholar Jerzy Kaczarek proposed using the third harmonic method. These methods are generally used for electrical contact research under laboratory conditions. In engineering, the four-terminal method is usually used to measure the contact resistance of actual contacts.



Previously, a DC double-arm bridge was commonly used to measure the contact resistance of circuit breakers. However, when using a double-arm bridge to measure the conductive circuit resistance of a circuit breaker, because the measuring circuit of the double-arm bridge passes a weak current, it is difficult to eliminate the oxide film with large resistance, and the measured resistance value is too large. However, the oxide film is easily broken down under a large current and does not hinder the normal current flow. Therefore, when testing using the DC voltage drop method, the current should not be too small.



The resistance of the conductive circuit of a high-voltage circuit breaker mainly depends on the contact resistance between its moving and static contacts. The existence of contact resistance increases the loss when the conductor is energized, raises the temperature at the contact point, and 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 of each phase of the circuit breaker is an important data for the installation, maintenance, and quality acceptance of circuit breakers.



Since there is an oxide film between the switch contacts, if a small 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 a large current. Theoretically, as long as the test current does not exceed the rated current, the larger the better. However, when the regulation was formulated, considering the production level of relevant domestic instruments at that time, the provision that the current should not be less than 100A was made. Power Equipment and Ground Grid Conduction 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 affected by factors such as humidity for a long time, resulting in 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 operate disconnected from the ground grid. It can be used for accurate measurement of the conduction resistance between the grounding down conductor of power equipment and the grounding grid or adjacent equipment.



The ground grid conduction resistance tester is used to measure the conduction resistance value of the grounding down conductor, and determine the fault point by comparing historical test values and adjacent point test values. The working power of the ground grid conduction 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 contact resistance of circuit breakers is very small, only a high current can ensure certain accuracy and stronger anti-interference ability.



It is used for high-precision measurement of circuit breaker contact resistance and current-carrying conductor resistance, 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".