This standard specifies the test equipment, sample preparation, test steps, test results, calculation and precautions for measuring insulation resistance using the galvanometer comparison method. This standard is applicable to measuring the insulation resistance of wires and cables. The measurement range is 10 to the 5th power to 10 to the 11th power Ω, and the measurement voltage is 100~500V. GB/T 3048.5-1994 Test methods for electrical properties of wires and cables Insulation resistance test Galvanometer comparison method GB/T3048.5-1994 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Test methods for determining electrical properties of electric cables and wires
Insulation resistance test galvanometer comparison method
GB/T3048.5—94
Test methods for determining electrical properties of electric cables and wires G 3n48.5--83Determining insulation resistanceComparison-galvanometer method1 Subject content and scope of application
This standard specifies the test equipment, sample preparation, test steps, test results, calculation and precautions for measuring insulation resistance using the galvanometer comparison method.
This standard is applicable to measuring the insulation resistance of wires and cables, with a measurement range of 105~10120V and a measurement voltage of 100~~500V. Unless otherwise specified in the wire and cable product standards, the measurement should be carried out indoors or in water with an ambient temperature of 20±5℃ and an air relative humidity of no more than 80%.
The test temperature of insulation resistance at working temperature should be specified in the relevant product standards. The temperature error should not be greater than +2°C. The temperature error during the arbitration test should be ±1°C. The general requirements, definitions and periodic calibration requirements for the electrical performance test of wires and cables are specified in GB/T3048.1. .2 Reference standards
GB/T3048.1 General principles for electrical performance test of wires and cables 3 Test equipment
The wiring schematic diagram of the measurement system is shown in Figure 1. The main components should meet the following requirements: 3.1 The current constant of the galvanometer is not greater than 10-\2/mm. 3.2. The shunt coefficient of the shunt should be able to vary within the range of 1/10000~1/1. And the adjustment level should be no less than 5 levels, and the critical voltage should be equal to or slightly greater than the external critical resistance of the galvanometer, but not more than 20%. 3.3 The standard resistance value is not less than 1050, and the relative error is not more than ±5%. 3.4 The output voltage of the DC power supply is stable, and the output voltage change does not exceed ±1%. 3.5 The bases of shielded galvanometers, shunts, standard resistors, measuring wires and line elements should all be connected to the shield. The insulation resistance between the shielded element and the shield should be at least 200 times greater than the standard resistor. When a battery is used as the lighting power supply for the galvanometer, the power supply must be placed in the shielding system. If an AC power supply is used, one end of the low-voltage side of the step-down transformer must be connected to the shield. Approved by the State Administration of Technical Supervision on May 19, 1994, and implemented on January 1, 1995
4 Sample preparationWww.bzxZ.net
GB/T 3048.5 94
Figure 1 Schematic diagram of the wiring of the base measurement system for the DC comparison method E-DC power supply, Rn standard resistor, R-sample insulation resistance, shunt, i--galvanometer: V-DC voltmeter SH-metal pole shield (dashed line); S, DC voltage switch S sample short-circuit switch S: reversing switch 4.1 Unless otherwise specified in the product label, the effective length of the sample should not be less than 10m, and the covers outside the insulation at both ends of the sample should be carefully stripped off, taking care not to damage the insulation surface.
4.2 The sample should be placed in the test environment for a long enough time to allow the sample temperature to balance with the test temperature and remain stable. 4.3 When immersed in water, the length of the two ends of the sample exposed to the water surface should be no less than 250mm, and the length of the insulation part exposed should be no less than 150mm. When tested in air, the length of the insulation part of the end of the sample exposed to the sheath should be no less than 100mm. The exposed insulation surface should be kept dry and clean. 5 Test steps are generally as follows: 5.1.1 For metal sheathed cable, shielded cable or armored relay samples, for single-core, the insulation resistance between the conductor and the metal sheath or shielding layer or armoring layer should be measured; for multi-core, the insulation resistance between each conductor and the other cores connected to the metal sheath or shielding layer or armoring layer should be measured separately. For non-metallic sheathed cable, non-shielded cable or unarmored cable samples, they should be immersed in water. If the insulation resistance between the single-core conductor and water is measured, the insulation resistance between the multi-core conductor and the other cores connected to water should be measured separately. The sample can also be tightly wound around the metal test rod. For single-core cables, the insulation resistance between the conductor pair and the test rod is measured. For multi-core cables, the insulation resistance of the remaining cores of each conductor pair connected to the test rod is measured. The outer diameter of the test rod shall be in accordance with the product standards.
5.1.2 Measurement and recording error,
The measured resistance value is 1×10102 and below, not more than ±10%; the measured resistance value is 1×10\2 and above, not more than ±20% 5.2 Connect the sample to the measurement system. The measurement error of the effective length of the sample should not exceed 10 5%. 5.3 Measure the standard resistance Rn. Close the switch S2 and then close S1, and adjust the shunt coefficient of the shunt P appropriately so that the galvanometer G has a clear deflection reading. Record the deflection reading α and the shunt ratio. 5.4 Measure the insulation resistance R of the sample:
5.4.1 Disconnect the switch S2, and adjust the shunt coefficient of the shunt P step by step so that the galvanometer G has a clear deflection reading. Record the deflection reading α, shunt ratio and charging time 1.
5.4.2 The charging time should be sufficient to achieve basic stability during measurement. Unless otherwise specified in the product standard, the charging time is I tnin.
5.4.3 Record the temperature during the test.
5.5 When repeating the test, before applying voltage, the switch S should be closed first to short-circuit the sample for discharge. The discharge time should not be less than 4 times the charging time of the sample.
6 Test results and calculations
6.1 The insulation resistance of the sample is calculated according to the following formula:
Wu Zhong.R-
Insulation resistance of the sample, M0;
Standard resistance, M0;
GB/T 3048. 5--94
The deflection reading of the galvanometer when measuring the standard resistance, the shunt coefficient of the shunt when measuring the standard resistance; the deflection reading of the galvanometer when measuring the sample; the shunt coefficient of the shunt when measuring the sample. 6.2 The insulation resistance per kilometer length is calculated according to the following formula: Rr = R
Where: R.-
Insulation resistance per kilometer length, M2·km1
Effective measurement length of the sample, km.
6.3The insulation resistance per kilometer at 20℃ is calculated as follows: R = KR.
Where: R-
The insulation resistance per kilometer at 20℃, MQ·km·Insulation resistance temperature correction coefficient, specified in special documents. 6.4The number of significant digits in the calculation result should be consistent with the product standard. 7 Notes
(1)
7.1When necessary, it is allowed to add protective rings on the insulating surface of both ends of the sample. The protective ring should be close to the insulating surface and connected to the shielding of the measurement system.
7.2If the measurement results are significantly different due to the residual charge on the sample, it must be fully discharged first. For such samples, whether it is the first measurement or repeated measurement, it must be fully discharged. 7.3For the complete set of instruments used to measure insulation resistance, attention should be paid to the shielding connection method inside and outside the instrument, otherwise the measurement error will increase.
Additional instructions:
This standard is 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 drafters of this standard are Zhu Zhongzhu and Jin Biaoyi. 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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