This specification is applicable to conducting on-site contact resistance tests on high-voltage circuit breakers, disconnectors, GIS combined electrical equipment, etc., using contact resistance testers. The aim is to standardize the test operation procedures, clarify safety requirements and judgment criteria, ensure accurate test data and controllable operation safety, provide reliable basis for equipment condition assessment and maintenance, and be applicable to power maintenance teams and construction units for on-site operations.
I. Test Objectives
Based on the contact resistance tester, accurately measure the contact resistance value of the conductive circuit of high-voltage switchgear, and core determine the contact state of the contacts. Timely identify potential contact failure hazards such as contact oxidation, loosening, burning, insufficient contact pressure, and surface oil contamination, avoid overheating problems caused by excessive contact resistance during equipment operation, and prevent accidents such as insulation damage and equipment failure.
Verify the conduction performance of the conductive circuit of high-voltage switchgear in the closed state, combine the factory parameters and historical test data to analyze the operating conditions of the equipment, and provide precise and scientific data support for preventive maintenance, condition assessment, and fault detection of the equipment.
Ensure that high-voltage switchgear complies with the safety operation standards of the power system, maintain the stability and reliability of the power grid supply, and prevent power safety accidents caused by poor contact.
II. Test Basis
This test strictly follows national and industry standard specifications to ensure the compliance of the test process and the validity of the test results. The specific basis is as follows:
DL/T 845.4-2019 “General Technical Conditions for Resistance Measurement Devices – Part 4: Loop Resistance Testers”, which is the core technical basis for contact resistance testers;
GB/T 11022-2020 “Common Technical Requirements for High-Voltage Switchgear and Control Equipment”, which is the general technical specification for high-voltage switchgear;
DL/T 596-2021 “Preventive Test Procedures for Electrical Equipment”, which is the core execution standard for preventive tests of high-voltage equipment;
GB 50150-2016 “Standard for Electrical Equipment Commissioning Test”, which is the core basis for the commissioning test stage;
The factory manual and technical parameters of the tested high-voltage switchgear, which should be given priority to follow the specific technical requirements of the equipment;
The user manual of the contact resistance tester, which standardizes the instrument operation and ensures measurement accuracy.
III. Test Preparation
3.1 Safety Preparation
The contact resistance test of high-voltage switchgear is a power-off-related test, and it is necessary to strictly follow the power safety operation procedures and implement a complete set of safety protection measures to prevent personal and equipment safety accidents. The specific requirements are as follows:
Power-off operation: Confirm that the tested equipment is completely de-energized, open the disconnectors on both sides of the equipment, form an obvious disconnection point, and hang the “Do Not Close, Equipment is Under Test” warning sign. Do not allow irrelevant personnel to enter the operation area.
Electrical testing and discharge: Strictly follow the “Power-off – Electrical Testing – Discharge – Hang Ground Wire” operation process. Use a qualified electrical tester to detect the connection terminals of the equipment, confirm that there is no electricity, then fully discharge the conductive circuit, release residual charges, and eliminate the risk of electric shock.
Grounding protection: Install a qualified grounding wire with a cross-sectional area of no less than 25mm² at the conductive terminals of the tested equipment to ensure a firm grounding; reliably ground the casing of the contact resistance tester, with a grounding resistance not greater than 4Ω, to prevent the instrument from leaking electricity and causing safety hazards.
Safety protection: Workers should wear qualified insulating gloves, insulating shoes, and safety helmets; a dedicated supervisor should be on site to monitor throughout, and prohibit workers from leaving their posts or operating illegally; set up a safety fence in the operation area and mark a warning zone.
Environmental restrictions: Outdoor operations are prohibited when there is thunderstorm weather, wind force of 6 or above, or environmental humidity greater than 80%. Indoor operations should ensure good ventilation to avoid adverse environmental influences such as moisture, dust, and corrosive gases. Procedure: Prepare the work ticket in advance, complete the safety technical briefing, clarify the division of labor, risk points and control measures. All the workers must be familiar with the briefing content and sign to confirm before starting the work.
3.2 Instruments and Tools Preparation
All the instruments and tools must be qualified and within the validity period of verification to ensure stable performance and measurement accuracy. The specific requirements are as follows:
Core Instruments: Contact Resistance Tester, with a DC current output of no less than 100A, capable of breaking through the oxide film on the contacts; using the four-wire Kelvin connection method, the measurement accuracy shall not exceed ±1%, the display resolution shall not be less than 0.1μΩ, equipped with a qualified power adapter, and within the validity period of verification.
Test Cables: The large current test cables have no damage, broken strands, or aging issues, with a cross-sectional area of no less than 16mm², sufficient clamping force for the wire clamps, and the recommended cable length shall not exceed 5m; the voltage measurement cables use shielded wires, with clean terminals without oxidation or loosening, intact wire cores, and capable of shielding electromagnetic interference.
Auxiliary Tools: Equipped with multimeters, fine sandpaper, anhydrous alcohol, cleaning cotton cloth, screwdrivers, and wrenches. The multimeter is used to detect the continuity and grounding status of the lines; sandpaper, alcohol, and cotton cloth are used to clean the oxide layer and oil stains on the equipment terminals; the hardware tools are used for tightening the connection terminals.
Safety Tools: Configured with a matching equipment voltage level test pen, compliant grounding wires, as well as qualified insulating protective equipment, safety barriers, and warning signs.
Recording Tools: Prepare a test record book, signature pen, thermometer, hygrometer, for recording the test data, environmental parameters, and equipment status, ensuring complete and traceable records.
3.3 Preparation of the Tested Equipment
Before the test, conduct a comprehensive inspection and pre-treatment of the tested equipment to avoid interference to the test data caused by the equipment’s own defects. The specific requirements are as follows:
Status Confirmation: Set the tested equipment such as high-voltage circuit breakers and disconnectors to the closed state to ensure the integrity of the conductive circuit; for drawer-type circuit breakers, place them in the working position and ensure they are fully closed.
Contact Cleaning: Control the equipment to open and close 2 to 3 times, relying on mechanical actions to remove dust and floating oxide films on the contact surfaces; use a cotton cloth dipped in anhydrous alcohol to wipe the connection terminals and contacts, removing oil stains and dust; when the oxidation of the terminals is severe, gently sand them with fine sandpaper, clean again after sanding, ensuring the contact surface is clean without impurities or looseness.
Appearance Inspection: Check that the equipment contacts have no burn marks, deformation, or looseness, the connection terminals have no damage, cracks, and the conductive circuit is firmly connected; for GIS equipment, there is no need to disassemble the grounding contact plates, and it is sufficient to confirm that the grounding contact plates are in good condition.
Parameter Verification: Verify the core parameters of the equipment such as model, voltage level, and rated current to ensure they match the test plan and the specifications of the testing instruments, preventing parameter mismatch from causing test failures or equipment damage.
VII. Test Principle and Wiring Method
4.1 Test Principle
This test adopts the DC voltage drop method, relying on the four-wire Kelvin connection method for detection. During the test, a stable DC current of no less than 100A is applied to the conductive circuit of the high-voltage switch, using the electromagnetic force and Joule heating effect to break through the oxide film on the contacts, truly reflecting the contact state of the contacts; through the independent voltage measurement circuit, the voltage drop between the two ends of the circuit is collected, combined with Ohm’s law to calculate the contact resistance value. The calculation formula is: R
=
U
/
I
R=U/I
(R is the contact resistance, U is the voltage drop, and I is the test current).
The four-wire measurement method can separate the current circuit from the voltage measurement circuit, effectively canceling out the interference of the test cables and the resistance of the terminals on the test results, achieving micro-ohm-level high-precision measurement and meeting the requirements of the high-voltage switch contact resistance testing standards.
4.2 Wiring Method
The wiring follows the core principle: the voltage connection terminals must be placed inside the current connection terminals, close to the measured contacts, with a spacing of no more than 50mm. Remember the “current surrounds the voltage” rule to avoid measurement errors.
4.2.1 Conventional Wiring Sequence (Single-phase High-Voltage Switch)
Connect the voltage wires: Connect the positive and negative terminals of the tester to the inner side of the contact terminals on both sides of the equipment through shielded voltage wires, ensuring that the wire clamps are tightened and the contacts are firmly connected. The voltage wires should be laid close to the contacts and should not be crossed or bundled with the current wires.
Connect the current wires: Connect the positive and negative terminals of the tester to the outer side of the voltage wire clamps through high-current test wires, tighten the wire clamps to avoid overheating or sparking during high-current operations.
Wiring verification: Confirm that the tester’s casing and the tested equipment are firmly grounded, that the test wires are not damaged or exposed, and repeatedly check the line markings to prevent reverse connections or looseness.
4.2.2 Special Equipment and Environmental Wiring Requirements
GIS Switchgear: Use a DC clamp current meter combined with wireless transmission technology, without the need to remove the grounding contact plate, directly complete the detection, retain the equipment grounding integrity, and improve work efficiency.
Strong interference environment: Conduct the test while maintaining the grounding state on both sides of the switch to eliminate induced current interference and ensure stable test data.
4.2.3 Wiring Prohibitions
Do not connect the voltage wires outside the current wires, do not cross or bundle the current wires and voltage wires, do not have poor contact of the wire clamps or exposed wires, to avoid measurement errors or damage to the test equipment.
V. Data Analysis and Judgment Criteria
5.1 Data Organization
After the test, summarize and organize the test data of each phase. Repeat the test 2 to 3 times for each phase, calculate the arithmetic average; standardize the filling of test records, clearly mark the equipment name, number, test date, environmental temperature and humidity, instrument information, single test data and average value, to ensure the completeness and traceability of the test data.
Post time: May-22-2026