DC resistance test, insulation resistance test, partial discharge test, aging test, insulation strength test, thermal stability test.
1.Inspection method
Routine test: A test of all finished cables in a manufacturing plant. The purpose is to check whether the product quality meets the requirements of the technical conditions in order to find the defects in the manufacturing process. It is a non-destructive experiment, such as the DC resistance of the conductor, insulation resistance time and Partial discharge test.
Type test: manufacturer do regular inspection on the comprehensive performance of products, in particular to a new product before setting a batch production, or structure, materials and process for a product with the change of test may affect the cable's performance. Through the type test: the product can be tested to meet the requirements of the operation, and can be compared with the old products. Such as insulation and sheath thermal aging performance, long-term stability test of power cables.
Acceptance test: After the cable installed, it is necessary to do the cable acceptance test in order to check the installation quality,and found in the construction of possible damage such as the installation of the withstand voltage test.
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| AC test and PD test |
2.Test items
The DC resistance of the conductor is measured by single arm DC resistance method and double arm direct current bridge method. The test procedure is more complicated than the former.
2.2 Insulation resistance test
Insulation resistance is an important index to reflect the insulation characteristics of wire and cable products, which is closely related to the electrical strength, dielectric loss, and the deterioration of insulation materials in the working state. At present, wire and cable insulation resistance measurement, in addition to using an ohmmeter (shaking table), used a galvanometer comparison high resistance meter method (voltage - current method).
2.3 Measurement of capacitance and loss factor
When the cable is connected with the AC voltage, the current flows through it. When the voltage amplitude and frequency are fixed, the capacitance current is proportional to the capacitance of the cable (Cx). For EHV cable, the current of the capacitor may reach the value of the rated current, which is an important factor to limit the capacity and transmission distance. Therefore, the capacitance of the cable is one of the main performance parameters of the cable.
Through measuring the capacitance and dissipation factor ,it can be found the insulation moisture , an insulating layer and a shielding layer off all kinds of insulation deterioration phenomenon, both in the cable or cable manufacturing operation are measured and capacitance of TAN 8. To high voltage cable, measuring Cx and TAN delta are under its working conditions, namely high voltage under the commonly used are high voltage capacitor bridge,now also began to use the current transformer ratio bridge.
2.4 Insulation strength test
The insulation strength of wire and cable is the ability that the insulation structure and insulation materials under electric field without breakdown. In order to check the quality of wire and cable and ensure the products operated safely, all types of wire and cable insulation generally have a dielectric strength test. Insulation strength test can be divided into withstand voltage test and breakdown test. High voltage experiment is a certain voltage which applied to the sample under certain conditions. After a period of time, we judge the product of whether it is breakdown.Time is generally higher than the rated voltage of the voltage test time, the voltage value and the pressure time. Through the withstand voltage test ,it can test reliability products on running voltage and find serious flaws in insulation, also found some shortcomings, such as the production process has serious external insulation damage. There are serious defects in the electric field distortion on the conductor insulation sharp; in the production of a penetrating defect or conductive impurity.
The breakdown test is to measure the breakdown field strength or breakdown voltage under certain test conditions. The breakdown test can be between ability and working voltage assessment cable withstand voltage safety margin. One of the important parameters in the design of cable when the breakdown field strength.
In the operation of general cable under AC voltage, but in HVDC transmission system and some special occasions are also under DC voltage, the high voltage cable may also suffer from atmospheric voltage (lightning) and over voltage attack.
Therefore, according to the experimental voltage waveform, can be divided into
1.AC (power frequency) voltage
2.DC voltage
3.Three insulation strength test of impulse voltage.
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| impulse voltage generator |
For oil filled cables, there is no local power generation; oil paper cable, even if there is partial discharge, is usually very weak, such as a few PC, so these cables in the factory test can not do partial discharge test. For extruded cables, not only the possibility of the local discharge, and the failure of partial discharge on plastic, rubber is more serious, with the increase of voltage level, work intensity increases, this problem becomes more and more serious, so the high pressure extrusion cable to do, in the measurement of partial discharge test in the factory test.
Many measurement methods of partial discharge, can exchange according to the instantaneous charge discharge, discharge pulse measurement (Electrometric method); can also be based on ultrasonic discharge generated by measuring the voltage (acoustic emission); can also according to the discharge light, measure the intensity of light (optical method). The cable is basically the use of electrical methods.
2.6 Aging test and stability test
The aging test is a test of whether the stability of the system can be maintained under the action of stress (mechanical, electrical and thermal).
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