Working Principle

Loop Resistance Tester Album

Loop Resistance Tester Album (3)

In the power system, many high-current electrical equipment require accurate measurement of loop resistance 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 loop 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 loop of a circuit breaker mainly depends on the contact resistance between its moving and static contacts. The presence 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 currents. Therefore, the resistance value of the conductive loop of each phase of a circuit breaker is an important data for its installation, maintenance, and quality acceptance.



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, Polish scholar Jerzy Kaczarek proposed using the third harmonic method. These methods are generally used in laboratory conditions for electrical contact research. In engineering, the four-terminal method is usually used to measure the contact resistance of actual contacts.



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



The resistance of the conductive loop of a high-voltage circuit breaker mainly depends on the contact resistance between its moving and static contacts. The presence 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 currents. Therefore, the resistance value of the conductive loop of each phase of a circuit breaker is an important data for its installation, maintenance, and quality acceptance.



Due to the oxide film between switch contacts, if a smaller current is used for detection, the test results are generally much higher due to the influence of the oxide film, but 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, a provision was made that the current should not be less than 100A. 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 applied to 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, leading to phenomena such as corrosion, disconnection, and loosening of the contact point, resulting in an increase in the resistance value at the contact point between the grounding down conductor and the ground grid, which cannot 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 precise measurement of the conduction resistance value 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 to 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 portability.



Since the contact resistance of circuit breakers is very small, only a high current can ensure certain accuracy, and the stronger the anti-interference ability.



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