In the power system, many high-current electrical equipment require accurate measurement of circuit resistance during preventive tests and handover tests. Circuit breakers are important electrical equipment in the power system. According to the latest standard JJG1052-2009 Verification Regulation of Loop Resistance, national standard GB763, GB50150, and power industry standard DL/T596, the measurement of the conductive circuit resistance of circuit breakers is specified: the DC voltage drop method should be used, with a current not less than 100A.
The resistance of the conductive circuit of a circuit breaker mainly depends on the contact resistance between the moving and static contacts. 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 bridge was often used to measure the contact resistance of circuit breakers. However, when using a double bridge to measure the conductive circuit resistance of a circuit breaker, because the measuring circuit of the double bridge passes a weak current, it is difficult to eliminate the oxide film with high resistance, and the measured resistance value is too large. However, the oxide film is easily broken down under large currents and does not hinder the normal passage of current. Therefore, when using the DC voltage drop method for testing, 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 the 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, the ability to interrupt short-circuit currents. Therefore, the resistance value of the conductive circuit of each phase of a circuit breaker is an important data for installation, maintenance, and quality acceptance of circuit breakers.
Loop Resistance Tester Assembly (3 photos)
Due to the oxide film between 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 large currents. Theoretically, as long as the test current does not exceed the rated current, the larger the better. However, when formulating the regulation, 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 affected by moisture and other factors for a long time, resulting in 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, causing hidden dangers in equipment operation, and in severe cases, causing equipment to be disconnected from the ground
Loop Resistance Tester (3 photos)
grid operation. 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 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, 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 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".
Technical Parameters
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1. Measurement range: 0~4mΩ (50A gear) 0~2mΩ (100A gear) 0~1.33mΩ (150A gear) 0~1mΩ (200A gear)
2. Test current: DC50A, 100A, 150A, 200A fixed output
3. Measurement accuracy: ±(0.5% rd+2d)
4. Continuous working time: 5s~599s
5. Display mode: large screen Chinese LCD display
6. Communication method: RS232 serial port
7. Working power: AC220V±10% 50Hz
8. Total power: 1200W
