This standard specifies the test equipment, sample preparation, test steps, test results, calculation and precautions for the dielectric loss tangent test. This standard is applicable to the measurement of the dielectric loss tangent (tgδ) value of cables under power frequency AC voltage, but not for winding wire products. GB/T 3048.11-1994 Test methods for electrical properties of wires and cables Dielectric loss tangent test GB/T3048.11-1994 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Test methods for electrical properties of electric cables
Dielectric loss faclor testwwW.bzxz.Net
GB/T 3048.11-94
Replaces GB 3048.11-83
Test methods for determining electrical properties of electric cables and wlresDielectric dissipation faclor measurement1 Subject content and scope of application
This standard specifies the test equipment, sample preparation, test steps, test results, calculation and precautions for dielectric loss tangent test. This standard is applicable to the measurement of dielectric loss tangent (tg) value of cables under power frequency AC voltage, but not for winding wire products. The general requirements, definitions and periodic calibration requirements for electrical properties test of electric cables and wlres are specified in GB/T3048.1. 2 Reference standards
GB/T3048.1 General principles for electrical properties test methods of electric cables and wlres3 Test equipment
The test equipment shall meet the following requirements.
3.1 Test power supply
3.1.1 In addition to using general voltage regulators and step-up transformers to generate the required high-voltage test power supply, a coupled resonant circuit can also be used. The test power supply should meet the test voltage and capacitance current requirements required for the corresponding sample test. 3.1.2 The test power supply should be an AC voltage with a frequency of 40 to 6011. The voltage waveform should be close to a sine wave, the two half-waves are basically the same, and the ratio of the peak value to the effective value is ±5%.
3.1.3 The maximum error of the effective value of the test power supply voltage should not exceed ±3%. It can be measured by a voltage transformer, an electrostatic voltmeter or a capacitive voltage divider connected in parallel with the high-voltage output of the test power supply. 3.2 Measuring instrument
The measurement of the dielectric loss tangent (tg) can be done by a standard capacitor-Sillin bridge or a standard capacitor-current comparator bridge.
3.2.1 Standard capacitors
The rated working voltage of standard capacitors shall be greater than the maximum test voltage required by the corresponding samples and meet the following conditions: Capacitance accuracy ±0.05%:
b. tg5×10 5.
3.2.2 Measuring instruments
Silin bridge (shall be shielded as a whole and equipped with shielding potential regulator) or current comparator bridge shall meet the following conditions: a. tga measurement range 1×10 *～1. 0;
b. tg measurement accuracy +0.05%±1×10-1. 4 Sample preparation
4.1 The selection of samples shall be in accordance with the product standards and shall be randomly selected. 4.2 The length of the sample shall be in accordance with the product standards, but shall not be less than 1m (excluding cable terminals). Approved by the State Administration of Technical Supervision on May 19, 1994, and implemented on January 1, 1995
GB/T3048.11-94
4.3 The length of the terminal part of the sample and the method of making the terminal should ensure that no flashover discharge or internal breakdown occurs along its surface under the specified maximum test voltage.
4.4 In order to improve the accuracy of the measurement, it is allowed to cut a protective ring at the end of the tested sample and ground the ground end of the non-tested part. 4.5 The requirements for the oil pressure or air pressure of the oil-filled or gas-filled cable sample shall be in accordance with the product standards. 4.6 The test electrode of the sample shall have a certain insulation resistance value to the ground. 5 Test steps
5.1 Unless otherwise specified in the product standard, the wiring should be in the following manner. 5.1.1 The core conductor of the single-core cable is connected to the high-voltage end, and the metal sheath or shield or additional electrode is connected to the measuring electrode. 5.1.2 For split-phase lead-sheathed cables, connect each core conductor to the high-voltage terminal in turn, and connect the other cores to each other and connect to the metal sheath, shield, and measuring electrode.
5.1.3 For multi-core cables, connect each core conductor to the high-voltage terminal in turn, and connect the other cores to each other and connect to the measuring electrode together with the additional electrode; or connect each core conductor to the high-voltage electrode and connect the other core conductors to each other and connect to the measuring electrode together with the metal sheath, shield or armor. 5.2 Unless otherwise specified in the product standard, all strands shall be measured at the ambient temperature of the test site, and the temperature difference between the sample and the ambient temperature shall not exceed ±3.
5.3 Before the test, a thermometer (with an accuracy of ±0.5°C) shall be used to measure the ambient temperature, and the distance between the thermometer and the sample shall not exceed 1 m. 5.4 During the measurement, the voltage shall start from a lower value (which shall not exceed 10% of the test voltage value specified in the product standard). Slowly and steadily increase to the specified voltage value (the voltage deviation shall not exceed ±3% of the required value), and then perform bridge balancing (the galvanometer sensitivity shall start from the lowest value). After the measurement, the voltage should be reduced to 40% of the specified test voltage, and then the power supply should be cut off. The galvanometer should be adjusted to the lowest value.
6 Test results and calculations
6.1 According to the circuit of the measuring bridge used in the test, calculate the 1g8 value of the sample. 6.2 The test report should include the model, specifications and accuracy of the measuring bridge used, the effective value of the voltage applied during the measurement, and the environmental conditions (including air temperature and relative humidity) of the corresponding tg? value, etc. 7 Precautions
7.1 The relative humidity of the test environment should not exceed 85%. 7.2 Before measurement, the sample should first undergo a power frequency AC withstand voltage test (the maximum effective value of the test voltage required for measuring tg is applied to the sample, and it is continuously maintained for 5tlin, and the sample should not have any abnormal phenomenon). 7.3 The connection line between the standard voltage and the sample and the measuring instrument should use a screen knock cable of the same specification and length that meets the requirements of the measuring instrument.
Additional instructions:
This standard was proposed by the Ministry of Machinery and Electronics Industry of the People's Republic of China. This standard is under the jurisdiction of Shanghai Cable Research Institute of the Ministry of Machinery and Electronics Industry. This standard was drafted by Shanghai Cable Research Institute of the Ministry of Machinery and Electronics Industry and others. The main drafter of this standard is Yang Wencai.
This standard was first issued in 1965, revised for the first time in November 1983, and revised for the second time in May 1994.
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