According to the requirements of DL/T 596- 1996, the test current of conductive loop resistance of various switchgear should be no less than 100A. Contact resistance increases due to contact surface oxidation, poor contact fastening and other reasons. When a large current flows, the temperature of the contact point increases, which accelerates the oxidation of the contact surface and further increases the contact resistance. If it continues, there will be a serious accident. Therefore, it is necessary to measure the contact resistance frequently or regularly.
The Loop Resistance Tester is also called contact resistance tester, and its English name is loop resistance tester. According to the requirements of the new specification for handover and preventive test of power equipment, this paper introduces in detail the measurement of conductive loop resistance of various switchgear, and the test current should not be less than 100A. In this regard, according to the requirements of the new regulations, our factory has designed and developed a new generation of intelligent loop resistance tester, which is suitable for testing the contact resistance of the main contacts of high and low voltage switches and the DC resistance of high and low voltage cable lines.
principle of operation
Many high-current electrical equipment in power system need to accurately measure the resistance value of the loop in preventive test and handover test. Circuit breaker is an important electrical equipment in power system. According to the latest standard JJG 1052-2009 "Verification Regulation of Circuit Resistance", national standards GB763, GB50 150 and electric power industry standard DL/T596, it is stipulated that DC voltage drop method should be used to measure the resistance of circuit breakers, and the current should not be less than 100A.
The resistance of the conductive circuit of the circuit breaker mainly depends on the contact resistance between the dynamic and static contacts of the circuit breaker. There are many ways to measure contact resistance. Japanese scholar Aesop Minowa proposed to measure the contact resistance with superconducting quantum devices, H Archie proposed to measure the contact resistance with electrolytic cell method, and Polish scholar Jerzy Kaczarek proposed to measure the contact resistance with third harmonic method. These methods are usually 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.
In the past, DC double-arm bridge was usually used to measure the contact resistance of circuit breakers. However, when using the double-arm bridge to measure the resistance of the conductive circuit of the circuit breaker, because the measuring circuit of the double-arm bridge passes through a weak current, the measured resistance value is too large, so it is difficult to eliminate the oxide film with large resistance, but the oxide film is easy to be broken down under a large current, which does not hinder the normal current. Therefore, the current should not be too small when DC voltage drop method is used for testing.
The resistance of the conductive circuit of high voltage circuit breaker mainly depends on the contact resistance between the dynamic and static contacts of the circuit breaker. The existence of contact resistance increases the loss of the conductor when it is electrified, and makes the temperature of the contact point rise. Its value directly affects the current carrying capacity in normal operation and the ability to cut off short-circuit current to some extent. Therefore, the resistance value of each phase of the circuit breaker is an important data for the installation, maintenance and quality acceptance of the circuit breaker.
Because there is an oxide film between the switch contacts, if it is detected by a small current, the test result is generally much larger 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, it should be as large as possible. However, when formulating the regulations, considering the production level of domestic related instruments at that time, the specified current should not be lower than 100A. On-resistance tester for power equipment and grounding grid
The reliable and effective connection between the down lead of power equipment and the ground network is the fundamental guarantee for the safe operation of power equipment and the personal safety of operators. Although the connection of grounding downlead was treated with necessary anti-corrosion treatment when making grounding device, the connection point in soil will still be affected by moisture and other factors for a long time, resulting in corrosion, disconnection and looseness of the connection point, which will lead to the increase of the resistance value of the contact point between grounding downlead and grounding grid, which can not meet the requirements of power regulations, and make the equipment have unsafe hidden dangers in operation, which will lead to the equipment leaving the grounding grid in serious cases. It can be used to accurately measure the on-resistance between the grounding down lead of power equipment and the grounding grid or adjacent equipment.
The on-resistance tester of grounding grid is used to measure the on-resistance value of grounding down conductor, and the fault point can be determined by comparing the test values of previous years with those of adjacent points. The working power supply of the on-resistance tester for grounding grid is provided by internal lithium battery, and external AC power supply is not needed. The test process is controlled by single chip microcomputer, which has the characteristics of simple operation, fast test speed, stable test data and easy carrying.
Because the contact resistance of the circuit breaker is very small, only high current detection can ensure a certain accuracy and stronger anti-interference ability.
It is used to measure the contact resistance of circuit breaker and the resistance of current-carrying conductor with high precision, and can output large current stably for a long time, which conforms to the relevant provisions of DL\T845.4-2004 General Technical Conditions for Resistance Measuring Devices Part 4: Circuit Resistance Tester.