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Tests

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Tests after installation


Test of cable insulation by increased voltage.


a) test by voltage of industrial frequency.

Insulation of cables after installation must endure the test by voltage of industrial frequency using one of the following methods:

1) The nominal linear voltage of the network is U = (6; 10; 15; 20; 30; 35), applied between the cable conductor and copper screen. Test duration is 5 min.

2) Nominal phase voltage of the network U0 = (3,6; 6; 8,7; 12; 18; 20,2; 64) within 24 hours.

Method of test is selected upon agreement with the manufacturer


b) Tests according to ћЁ 60502-2, 2005

According to the requirements of the international standa(IEC and others) the test with voltage 6U0 is
not recommended, as such test is destructive and can lead to the decrease of the term of employment of cable lines and, first of all, cable muffs.

International standard ћЁ 60502-2, 2005 recommends to hold the test with straightened voltage, the duration of application of the full test voltage 15 min.

Rated voltage U, kV

6

10

15

20

30

35

Test voltage, kV

14,4

24

34,8

48

72

80,8


When the test is held the leakage current must decrease and stabilize. If the leakage current is not decreased, as well as in case of its increase or instability the test should be held until the defects are found, but not more than for 15 min.
During the test the voltage is applied in turn to each cable, other phases and all screens must be earthed.

After tests it is necessary to earth the conductor for the time not less than 1 hour.


c) test by alternating voltage with frequency 0,1 Hz.

The test is held by alternating voltage with frequency 0,1 Hz, applied to each phase within 15 minutes.

Rated voltage U, kV

6

10

15

20

30

35

Test voltage, kV

18

30

45

60

90

105


Definition of integrity conductors and phasing of cable lines.

The test is done during exploitation after the finish of montage of cable and joints or disconnecting of cable cores.


Definition of resistance in cable conductors.

The test is done for lines with voltage 20, 30 and 35 kV. Reof the conductors to the direct current at the tempe20 ∞C, given at 1 km of cable length, must correspond to the meanings:


Conductor
material

Resistance, Ohms/km, no more at nominal conductor cross-sectional area, mm2

35

50

70

95

120

150

185

240

300

400

500

630

800

Cooper

0,524

0,387

0,268

0,193

0,153

0,124

0,0991

0,0754

0,0601

0,0470

0,0366

0,0283

0,0221


During exploitation after restorative and major repairs it is allowed to increase the norm of electric resistance for 3%.

If the length of the conductor is different from 1 km and the conductor temperature is different from 20 ∞C, the folloformula of calculation is applied:



where:

R20 Ц electric resistance of 1 km of the conductor at 20 ∞C, Ohm


T Ц conductor temperature when its resistance is checked, ∞C


Rt Ц measured electric resistance of the conductor with length L km at the temperature t ∞C


a Ц temperature coefficient of resistance, 1/∞C, equal to 0,00393 for copper conductors (and 0,00403 for aluminium conductors)

L - length of the tested conductor, km.

Measurement of working electric capacity of cables.

The test is done for lines with voltage 20, 30 and 35 kV. The measured capacity, given at specific value (1 m of length), must not be different from the results of the plant tests for more than 5%.

Measurement of current spreading in single-core cables.

Irregularity of current spreading in conductors and screens of cables must not exceed 10%.

Test of earthing device.

The test is done according to recommendations of the deviceТs manual and the rules of technical exploitation of electric devices.

At the lines the resistance of earthing at termination muffs is measured as well as metal constructions of cable wells.

Test of the plastic cable jacket by increased straightevoltage (for cables installed underground).

Straightened voltage 10 kV is applied between copper scrof the cable, detached from the earth and connected to cable conductor, and ground during 1 min.

After the test it is necessary to earth the conductor and the screen for the time not less than 1 hour.


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