High voltage cable testing

Test items

Electrical performance test:
Insulation resistance measurement: measure the resistance of the cable insulation layer to determine whether the insulation is damp, aged or defective.

Partial discharge test: detect whether there is partial discharge inside the cable, evaluate the insulation condition, and promptly find the weak points inside the insulation.

Withstand voltage test: including DC withstand voltage test and AC withstand voltage test, apply a voltage higher than the normal working voltage to the cable to test its tolerance and verify the insulation strength of the insulation layer.

Conductor DC resistance: check whether the physical cross-sectional area of ​​the cable core meets the standard, and its size directly affects the cable's electrical transmission performance and heating during operation.

Finished product voltage test and insulation core voltage test: examine the electrical insulation performance of the cable insulation layer and sheath layer to ensure good insulation between each insulation core and between the insulation core and the sheath.

Mechanical performance test:
Structural size inspection: check whether the material, structure, diameter, eccentricity, thickness, etc. of each part of the cable meet the standard, including conductor diameter, insulation thickness, sheath thickness, etc. These parameters affect the electrical performance and mechanical strength of the cable.

Bending test: Evaluate the performance and durability of the cable under bending, simulate the bending of the cable during laying and use, and test the flexibility and bending resistance of the cable.
Tensile strength and elongation at break test: Examine the tensile strength and elongation at break of the insulation and sheath plastic materials, which are the basic indicators for measuring the mechanical properties of the cable, ensuring that the cable will not easily break or be damaged when stretched by external force.

Physical performance testing:
Thermal stability test: Evaluate the performance and thermal resistance of the cable under high temperature conditions, detect the performance changes of the cable under rated operating temperature and overload temperature, and ensure that the cable can withstand the effects of thermal stress during long-term operation.

Flame retardant performance test: Check the flame retardant performance of the cable through vertical burning test, bundled flame retardant test, etc., evaluate its safety in emergency situations such as fire, and prevent the spread of cable combustion from causing greater accidents.

Chemical composition analysis: Analyze the chemical composition of the cable material to ensure that it meets the relevant standards, check whether it contains harmful substances, and whether the content of each component is within the specified range.

Testing method

Electrical performance testing method:
Insulation resistance measurement: Use a megohmmeter for measurement, and select the appropriate measuring voltage according to the voltage level of the cable. During measurement, measure each phase separately, and the non-test phase and metal shield and armor layer are grounded together.

Partial discharge test: Common methods include pulse current method, ultrasonic method, radio frequency detection method, etc. By detecting the partial discharge signal generated by the cable during operation, analyzing the amplitude, phase, frequency and other characteristics of the signal, the insulation condition inside the cable can be judged.

Withstand voltage test: DC withstand voltage test is applicable to paper insulated cables, and rubber-plastic insulated power cables are applicable to AC withstand voltage test. AC withstand voltage test can be carried out by power frequency withstand voltage test, variable frequency resonance withstand voltage test and other methods, applying the specified test voltage to the cable for a certain period of time to observe whether the cable breaks down or flashes over.

Mechanical performance test method:
Structural dimension inspection: Use measuring tools such as calipers and micrometers to measure the outer diameter, single wire diameter, insulation thickness, sheath thickness and other dimensions of the cable to ensure that the dimensional deviation is within the allowable range. For the detection of eccentricity, optical measuring instruments or imaging equipment can be used for measurement.

Bending test: Wrap the cable around a cylinder of specified diameter, bend it at a certain angle or number of times, and then check whether the appearance, insulation performance, etc. of the cable have changed, or measure the stress and strain of the cable during the bending process.

Tensile strength and elongation at break test: Use an electronic tensile testing machine to perform tensile tests on the insulation and sheath materials of the cable, and measure the tensile strength and elongation at break of the material during the stretching process.

Physical performance testing methods:
Thermal stability test: Place the cable in a high temperature environment, simulate the thermal stress conditions of the cable in actual operation through methods such as thermal aging tests and thermal cycle tests, and then detect changes in indicators such as the insulation resistance and mechanical properties of the cable.

Flame retardant performance test: Perform vertical burning tests or bundled flame retardant tests in accordance with relevant standards, hang the cable samples vertically or install them in bundles in the test device, ignite the lower end of the cable or apply an external fire source to the bundled cable, observe the burning of the cable, measure parameters such as burning time, carbonization length, and dripping, and evaluate the flame retardant performance of the cable.

Testing standards

GB/T 12706.2-2020: "Extruded insulated power cables and accessories with rated voltages of 1kV (Um=1.2kV) to 35kV (Um=40.5kV) Part 2: Cables with rated voltages of 6kV (Um=7.2kV) to 30kV (Um=36kV)", specifies the technical requirements, test methods and acceptance rules for extruded insulated power cables within this voltage level range.

GB/T 12706.3-2020: "Extruded insulated power cables and accessories with rated voltages of 1kV (Um=1.2kV) to 35kV (Um=40.5kV) Part 3: Cables with rated voltages of 35kV (Um=40.5kV)", gives detailed standard requirements for extruded insulated power cables with a voltage level of 35kV.

GB/T 28427-2012: "27.5kV single-phase AC cross-linked polyethylene insulated cable and accessories for electrified railways", applicable to the production, inspection and use of 27.5kV single-phase AC cross-linked polyethylene insulated cables and accessories for electrified railways.

GB/T 4909.2-2009: "Bare wire test method Part 2: Dimension measurement", specifies the method, measuring tools and measurement accuracy requirements for bare wire dimension measurement, which has guiding significance for the structural dimension inspection of high-voltage cables.

Detection significance

Ensure the safe and stable operation of the power system: Through comprehensive inspection of high-voltage cables, defects and hidden dangers in the manufacturing, installation and operation of cables, such as insulation aging, partial discharge, mechanical damage, etc., can be discovered in time to avoid breakdown, short circuit and other faults of cables during operation, thereby ensuring the safe and stable operation of the power system and reducing the occurrence of power outages.

Improve the service life of cables: Regular testing can evaluate the performance of cables, timely discover and deal with potential problems, take corresponding maintenance and repair measures, slow down the aging of cables, extend the service life of cables, and reduce the cost of cable replacement.

Ensure the safety of personnel and equipment: Testing can ensure that the insulation performance of cables is good, avoiding personal electric shock accidents and equipment damage accidents caused by cable leakage. At the same time, flame retardant performance testing can ensure that cables have a certain flame retardant ability when fire occurs, reducing the spread and harm of fire.

Maintain the economic benefits of power companies: Timely and accurate test results help power companies to reasonably arrange cable maintenance and replacement plans, avoid power outages and increased maintenance costs caused by cable failures, and improve the economic and social benefits of power companies.