I. Test Principle
The switch circuit resistance tester is based on the classic Ohm’s Law as its core principle and adopts the four-wire measurement method for the detection work. This measurement method is equipped with two sets of independent test cable bundles, which can completely avoid the interference of lead resistance and contact resistance on the measurement data, ensuring the accuracy of the measurement results.
During the actual testing process, the instrument inputs high-stability direct current with large current into the conductive circuit of the tested switch in the closed state through the dedicated current output cable. The conventional test current specifications are 100A or 200A. The core function of the large current is to break the oxide film and surface dirt layer produced by the long-term operation of the switch contacts, eliminating the interference of surface impurities on the detection and truly restoring the actual conductive performance of the switch in the closed state.
At the same time, the independent voltage sampling cable provided by the equipment will closely adhere to the two ends of the tested resistance to collect the voltage drop data. Since the voltage sampling circuit has almost no current flow, the voltage loss on the sampling cable can be completely ignored, further ensuring the accuracy of the voltage sampling data. The instrument is equipped with an internal computing system, which can automatically and accurately calculate the circuit resistance value of the tested equipment based on the real-time collected current and voltage data.
This equipment solves the problem that traditional microcurrent detection cannot penetrate the oxide film on the contacts and the detection results show false high resistance values, significantly improving the authenticity and reliability of the switch circuit resistance detection.
II. Followed Standards and Procedures
The production and on-site detection operations of the switch circuit resistance tester are strictly carried out in accordance with relevant national and power industry standards and procedures to ensure that all test results are valid, uniform, and comparable, and to standardize the power equipment detection operation process.
(1) Equipment Manufacturing Standards
The power industry standard DL/T 845.4-2004 “General Technical Conditions for Resistance Measurement Devices – Part 4: Circuit Resistance Tester” is the core basis for equipment manufacturing. This standard clearly stipulates that the direct current test current used for the detection of the conductive circuit of the high-voltage switch shall not be lower than 100A. This technical requirement guarantees that the test current can effectively break through the oxide film on the contacts from the production source, avoid detection errors, and obtain accurate and true contact resistance data.
(2) Test Procedure and Result Determination
The core guiding document for power equipment test and result determination is DL/T 596-2021 “Power Equipment Preventive Test Procedures”. This procedure specifies the test cycle, standardized testing methods, and qualified determination standards for circuit resistance for various voltage levels of circuit breakers. The procedure requires that the detection work be carried out in the closed state of the switch and use a direct current test current of 100A or above; the test results need to be compared with the factory parameters and previous test data of the equipment, and in normal conditions, the resistance value fluctuation shall not exceed 20% of the factory value.
In addition, the relevant regulations for the state maintenance test of dedicated power transmission and transformation equipment in the power industry have made detailed requirements for on-site testing of circuit resistance, clarifying the details of environmental temperature, test current stability, and test line contact status, further refining and standardizing the operation standards for on-site detection.
For GIS gas-insulated fully enclosed combined electrical equipment, the relevant regulations also specify special measurement requirements for disconnectors and grounding switches. These equipment have a compact internal structure, and the contact state of the contacts cannot be inspected visually, so the circuit resistance test is the core detection method for determining their conductive performance and identifying internal hidden dangers.
III. Main Application Scope
The switch circuit resistance tester is widely applicable in power production, power transmission and distribution projects, and power equipment detection scenarios, covering equipment operation and maintenance, factory inspection, fault diagnosis, and maintenance verification, and is the core detection equipment for ensuring the safe and stable operation of power equipment.
(1) Power System Operation Maintenance In the daily operation and maintenance of power equipment, this device can conduct periodic inspections on various core power equipment, accurately identifying potential equipment operation hazards:
The high-voltage circuit breaker is the primary inspection target, covering SF6 circuit breakers, vacuum circuit breakers, oil circuit breakers, etc., and can measure the circuit resistance of each phase main contact of the equipment on a regular basis; for circuit breakers with multi-break structure, individual detection of each break can be achieved, comprehensively grasping the equipment’s conductive performance.
Isolating switches and grounding switches need to undergo periodic circuit resistance tests, especially for equipment that operates outdoors for a long time, affected by environmental erosion, the contact spring is prone to rust and elastic fatigue, which can lead to insufficient contact pressure and increased contact resistance. Through circuit resistance testing, such hidden hazards can be accurately detected.
The connection points of busbars and cable terminal joints are not part of the switch body equipment, but their connection status directly affects the overall power supply reliability. The tester can effectively detect problems such as loosening and oxidation of these connection parts after long-term operation, avoiding power supply failures caused by poor contact.
The drawer-type switches of the complete switch cabinet have their contacts hidden inside the cabinet and cannot be visually inspected for contact status. Circuit resistance testing is a key method to determine the assembly quality of insertion and connection and the contact performance of the equipment.
(II) Equipment Factory Inspection
In the production and manufacturing process of switch equipment, this device is the core equipment for factory quality inspection. Newly assembled switch equipment needs to conduct circuit resistance tests phase by phase to verify the quality of contact assembly and whether the equipment’s conductive path design complies with technical standards. All factory test data will be archived and retained as the core basis for the equipment’s factory qualification.
(III) Fault Diagnosis and Maintenance Verification
When switch equipment is subjected to short-circuit fault current impact or experiences abnormal conditions such as insufficient closing or contact burnout, the circuit resistance can be measured to determine the equipment’s fault condition, providing data support for contact replacement, mechanism adjustment, etc. for maintenance work. After equipment maintenance, circuit resistance testing needs to be conducted again to confirm that the resistance value returns to normal, verifying the maintenance effect, and ensuring the subsequent safe and stable operation of the equipment.
Post time: Jun-11-2026