This standard is applicable to measuring the ideal shielding coefficient of cable metal sheath and armor layer. The test frequency is 50Hz. The test accuracy is ±10%. GB 5441.9-1985 Communication cable test method Ideal shielding coefficient test under power frequency conditions GB5441.9-1985 Standard download decompression password: www.bzxz.net

1 Scope of application
National Standard of the People's Republic of China
Test methods for communication cable
Iest methods for communication cableTest for ideal screening factor measuredat power frequency
The standard is applicable to the ideal screening factor of the metal sheath and armor layer of the most widely used cable. The test frequency is 50H.
Test accuracy = 10%.
2 Test equipment
The wiring schematic diagram of the test system is shown in Figure 1
The test instrument should meet the following requirements:
2.1 AC stabilizer: voltage is 220V, capacity ~ 5kVA, and stability is not less than 11%. UDC 621.315.2
621.39:621
GB 5441. 9—65
2.2 Voltage regulator: voltage is 250V: capacity 2~4kVA. 2.3 Current booster: Maximum output voltage is not less than 4, capacity is not less than 3kVA, output waveform (including voltage booster, current booster) requires that the deviation of all current values ​​from the same phase sine fundamental wave does not exceed 10% of the sine fundamental peak. 2.4 Current measurement device: The current sensor is 500/5A, 0.5 level; the standard non-inductive resistor is 0.12, 0.1 level; the minimum millivolt range of the product is 1mV.
2.5 resistor! Device: Measuring membrane resistance K, -1002; the variable range of the variable anode box is (0-10) × (0.01 + 0.1 + 1 + 10 - 100 - 1000) $2 c
National Bureau of Standards 1985-09-29 Issued
1986-06-01 Implementation
GB5441.9-85
-0= 000-00*
GB 54419--85
2.6 AC digital voltmeter: Display six digits, not less than one hundred thousand digits: the minimum range is not greater than 0.2. It can also be composed of a current digital meter that meets the above requirements. 27 Current: The main guard is made of yellow or copper, and the surface quality should ensure good contact. 2.8 High current loop: It is a rectangular frame, one side is the sample metal sleeve, and the other side can be composed of a round copper tube with an outer diameter of r and a thickness of not less than 3mm (solid copper is also allowed). The distance w in Figure 11 is 400mm. The inductance of the measuring loop formed by the current frame and the sample is within 2+0.1μH. For the measuring device even for ordinary current, the three sides of the frame can be formed by two parallel copper bars, and the distance between the two copper bars is approximately equal to their original length. The outer radius r of the hollow copper tube can be selected according to L=2μH and the outer diameter D of the sample metal sleeve, and the following calculation is used: 16.34-lnD-
lnr =
Where: D--outer diameter of the sample metal sleeve, mm; r--outer radius of the frame round copper tube, mm
L--inductance of the test loop, H.
2.9 Voltage measurement line: Insulated wire with a conductor diameter less than 0.5mm, as shown in Figure 1, is placed parallel to the surface of the high current frame. For a high current frame consisting of two parallel copper bars, it can be placed between the copper bars. 3 Sample preparation
3.1 Sampling: Take a sample of about 1400mm long from the tested cable. 3.2 According to the requirement of , =1000±5mm, remove the jacket or outer layer outside the armor layer at both ends of the sample. According to the length and width of the current loop, remove the armor layer and its lining at both ends of the sample to expose the metal sheath. 3.3 According to GB3048.4-83 "Test Method for DC Resistance of Conductive Core of Wire and Cable", measure the DC resistance of the metal sheath on the length of the sample 1.
1. The deviation of the value of the DC resistance measurement of the length 1 and the value of the value converted to 1m when the measurement value of 1km length is converted to 1m should be greater than 11%. 3.4 Select the conductor connected to the induced voltage measurement line from the cable core, and the conductor should be as close to the center of the cable as possible. The insulation layer of the selected conductor should be removed at both ends. On the outside of the current loop (as shown in Figure 1), a thin copper coil is tied tightly on the metal sleeve to make an electric injection loop, and the measuring line is electrically connected to the selected cable core conductor. The center distance of the voltage loop and the current loop is 20 meters. 3.5 At the two ends of the sample where the current loop is installed, the armor layer and the metal sleeve should be properly connected. 4 Test steps
4.1 Pre-test inspection:
4.1.1 Check the connection and dimensions of each part of the test system according to the provisions of 1. 4.1.2 Check each connection part. The contact must be good, especially the connection part of the current test loop, such as the connection between the current loop and the sample, the connection between the sample's armor layer and the metal sleeve, etc. 4.1.3 Check the voltage adjustment knob of the test instrument. It should be directly at the starting "zero" position. 4.2 Connect the 50Hz power supply to the test system and turn on the power of all test instruments. Heat for 15 minutes, and then perform the following live inspection.
4.2.1 Use an oscilloscope to observe the output waveform of the current booster. It should be ensured that it is a normal waveform without obvious distortion. 4.2.2 Before the test, slightly increase the output voltage of the voltage regulator to make a small amount of current flow through the metal sleeve of the sample. Observe whether the reading of the AC digital meter is stable. If the reading is positive, check all parts of the system, especially the current loop. Check whether the contact of all parts is good. After the fault is eliminated, the formal test can be carried out. 4.3 First put the single-pole single-throw switch 9 in the off position, then switch it to the off position, and read and record the voltage of the sample and the induced voltage on the core line respectively.
5 Test results and calculations
5.1 The test results are calculated according to the following formula:
GB5441.9--85
Wu Zhong: us—
-the ideal shielding coefficient when the interference voltage on the metal sheath of the cable sample is ; V——the induced voltage on the core, mV;
V.-the longitudinal interference voltage on the metal sheath of the cable sample, mV. (2)
5.2 When a large current (several hundred amperes) flows through the metal sheath, the heat of the cable increases the protective layer. At this time, the ideal shielding coefficient calculated by formula (2) should be corrected as follows: Yn2
R-(RR)yes
Formula: 2-corrected theoretical shielding coefficient when a large current of 12 flows through: R-the DC resistance of the metal when a small current flows through (Rp)-the DC resistance of the metal sheath when a current flows through (R. bZxz.net
0s-the ideal shielding coefficient calculated according to formula (2) when a large current flows through (1,); V-the induced voltage of the core of the line when a small current flows through (mV); V2-the induced voltage of the core of the line when a large current flows through (1), mV. 6 Precautions
6.1 Current entry and measurement of the current frame The voltage lead-out wire should be as short as possible: the medium current incoming wire and the voltage measuring lead-out wire should be as close as possible or twisted together, and the wire carrying large current should be as far away as possible from the wire carrying small current. 6.2 When the digital voltmeter reading is inaccurate, the shielding coefficient can be measured with the resistor divider 8 to compare with the test result of the digital voltmeter. At this time, the switch 9 should be placed in the position first, and then switched to the position, and the standard variable resistor box should be adjusted to make the V of the digital voltmeter equal to the reading, and read the reading of the standard variable resistor box R. At this time, the digital voltmeter should be inaccurate. The ideal shielding factor is: Yos
Where: R-standard variable resistance box reading,; R. ——100% fixed measurement film resistance, 2. R
(4)
6.3 When testing armored steel tape cables, in order to prevent the influence of residual magnetism, the sample should be demagnetized in advance for each measurement, that is, the current on the cable metal sheath should be gradually increased until the maximum test current is reached, and then the current should be uniformly reduced to zero within a few seconds. During the test, the current should be adjusted to increase in one direction from small to large. 6.4 The current of the metal sheath should be increased in one direction from small to large. The resistance is very small (especially the aluminum sheath). In order to obtain a large sheath voltage, a large current (hundreds of amperes) must be passed. Therefore, the test must be done quickly to avoid the increase of the heating resistance of the metal sheath and the test error. 6.5 When there is a difference in the test results, the armor layer and the metal sheath welding sample shall be used as the standard. Addendum
085141.9-85
This standard was proposed by the Ministry of Machinery Industry of the People's Republic of China. This standard was issued by the Shanghai Electric Research Institute of the Ministry of Machinery Industry. This standard is calculated from the Shanghai Cable Research Institute of the Ministry of Machinery Industry.
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