Loop Resistance Tester

The loop resistance tester adopts 100A constant current output. The maximum output voltage reaches 10V (2-3 times that of conventional instruments), allowing the use of thinner test leads, greatly reducing the labor intensity of field test personnel. The entire testing process is automatically controlled by a single-chip microcomputer, offering high accuracy, good repeatability, and simple one-button operation. Test data is displayed on an LCD. It is suitable for various working environments. This instrument has a built-in 100A/200A switching power supply, enabling constant 100A current with two sets of circuits for real-time tracking testing, ensuring correct test results. It is designed by combining digital circuit technology with switching power supply technology. It is applicable for measuring contact resistance and loop resistance of switch control equipment. The test current adopts the DC above 100A recommended by national standards.



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, raising the temperature at the contact point. Its value directly affects the current-carrying capacity during normal operation and, to a certain extent, the ability to interrupt short-circuit currents. Therefore, the loop resistance test value of each phase of the circuit breaker's conductive loop is an important parameter for installation, maintenance, and quality acceptance.



The loop resistance tester is designed by combining digital circuit technology with switching power supply technology. It is suitable for measuring contact resistance and loop resistance of switch control equipment. The test current adopts the DC 100A/200A recommended by national standards. It can directly measure loop resistance and contact resistance at currents of 100A/200A, with digital display. The switch loop resistance tester offers accurate measurement and stable performance, suitable for on-site high-voltage switch maintenance in power and power supply departments, as well as loop resistance testing in high-voltage switch factories. Alternative names for the loop resistance tester include: switch loop resistance tester, contact resistance tester, and contact loop resistance tester. This instrument features small size, light weight, strong anti-interference capability, high accuracy, easy operation, and comprehensive protection functions.

Working Principle

Loop Resistance Tester Album

Loop Resistance Tester Album (3)

In power systems, many high-current electrical devices require accurate measurement of loop resistance during preventive tests and acceptance tests. Circuit breakers are important electrical equipment in power systems. According to the latest standard "JJG1052-2009 Loop Resistance Verification Regulation", national standards GB763, GB50150, and power industry standard DL/T596, the measurement of conductive loop resistance in 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, raising the temperature at the contact point. Its value directly affects the current-carrying capacity during normal operation and, to a certain extent, the ability to interrupt short-circuit currents. Therefore, the loop resistance value of each phase of the circuit breaker's conductive loop is an important parameter for 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, and 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 commonly used to measure the contact resistance of actual contacts.



Previously, the DC double-arm bridge was often used to measure the contact resistance of circuit breakers. However, when using the double-arm bridge to measure the conductive loop resistance of circuit breakers, since the measurement circuit passes a weak current, it is difficult to eliminate the thicker oxide film, resulting in a higher resistance reading. But the oxide film is easily broken down under large currents and does not hinder normal current flow. 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, raising the temperature at the contact point. Its value directly affects the current-carrying capacity during normal operation and, to a certain extent, the ability to interrupt short-circuit currents. Therefore, the loop resistance value of each phase of the circuit breaker's conductive loop is an important parameter for installation, maintenance, and quality acceptance.



Due to the oxide film between switch contacts, if a small current is used for testing, the test results are generally much higher due to the influence of the oxide film. However, the oxide film can be broken down under large currents. Theoretically, as long as the test current does not exceed the rated current, the larger the better. But when the regulations were formulated, considering the production level of domestic instruments at that time, a requirement of not less than 100A current was stipulated. 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 points of grounding down conductors during the construction of grounding devices, 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, which increase the resistance value at the contact point between the grounding down conductor and the ground grid, failing to meet the requirements of power regulations, posing safety hazards during equipment operation, and in severe cases, causing equipment to be 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 grounding down conductors, and to determine fault points 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, requiring no external AC power supply. The testing process is controlled by a microcontroller, featuring simple operation, fast testing speed, stable test data, and portability.



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



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