How are cable lines 6-10 sq. High voltage cable test

It is influenced by various environmental factors: soil shift and its weight, temperature fluctuations and other influences, on which the insulation characteristics in one way or another depend. Over time, the insulation deteriorates. For this reason, it is important to test the 10 kV cable increased voltage. Thanks to this procedure, it will be possible to determine its condition and replace it in a timely manner. As a result, trouble-free operation of the cable line, the absence of accidents and other unpleasant situations, the solution of which requires large expenditures. But what voltage is tested for a 10 kV cable?

Cable 10 kV with XLPE insulation: how and how is it checked?

Checking a cable with XLPE insulation for a voltage of 6/10 kV is carried out with an alternating voltage with a frequency of 0.1 Hz for 30 minutes (after repair - 20 minutes). 30 kV - cable test voltage 10 kV, 18 kV - cable 6 kV. Special VLF equipment is used, created by foreign manufacturers (High Voltage Diagnostic, Switzerland; High Voltage, USA; Seba, Germany, etc.).

The test procedure for a 10 kV cable is as follows:

1. All elements of the cable line, tunnels and channels in which it is located are inspected. If the end couplings have flaws, then the check continues only after they have been eliminated. The cable shields are grounded.
2. The test voltage is applied to the cable (the timer controls the time), and it slowly rises to the required value (the voltage value is specified using the VLF equipment kilovoltmeter).
3. The magnitude of the voltage and its change in polarity is demonstrated by a kilovoltmeter. One polarity value often differs from another by five to ten percent.
4. At the end of the set time with a special handle, the voltage slowly decreases to zero.

The test of a 10 kV cable can be carried out with an alternating rated voltage for 24 hours, applied between the metal screen and the core. You need to act like this:

All elements of the line should be inspected, and if the end couplings have flaws, they must be eliminated.
. When checking the cable insulation, voltage is applied to each core, and the screen is grounded.
. Carefully raise the voltage to the limit value and keep it unchanged throughout the entire time. The time must be calculated from the moment the limit value is set.

Checking the cable sheath when laying it in the ground is carried out once every 5 years (if the cable does not have electrical breakdowns during operation). When carrying out earthworks or observing soil precipitation, landslides, erosion, an extraordinary test is performed. Upon completion of the work, an additional check is also carried out. In this case, direct current and a kenotron installation of the KII-70 type are used to test the cable. The voltage from this device is applied in turn to each core, grounded by a metal sheath.

For a 6 kV cable, the leakage current should not be more than 200 μA, for 10 kV - up to 500 μA.

6/10 kV cable with impregnated paper insulation: how and how is it checked?

Checking this type of cable is implemented by increased voltage of the rectified current. 60 kV - the value of the test voltage for a cable of 10 kV, 36 kV - for a cable of 6 kV. In both cases, the check lasts 10 minutes. A special device such as AID-70M is used. You need to act in the same sequence as with the previous cable.

Testing of high-voltage cable 10 kV with increased voltage is carried out in accordance with GOST. The value of the applied voltage is indicated in GOST or in the specifications for certain cables.

The following standards for testing a 10 kV cable are established:

In the case of re-laying and recent laying, before switching on and before the trench is backfilled;
. operated - during a long shutdown, after repair activities (not according to plan or according to schedule).

The check is carried out at the following intervals:

Once every 5 years - spare cable lines.
. Once every 3 years - the main cable lines.
. Once every 12 months - spare and main lines that feed critical users.

Now you know how to test a 10 kV cable, so this process will not cause you any difficulties. The main thing is to adhere to current regulations and observe safety precautions.

All testing and WMD work can be carried out by personnel admitted to these works and having the appropriate mark in the safety certificate. When carrying out these works, you can only use test and measuring facilities that have been tested and annually certified in the FIS. electrical networks. The use by personnel of electrical networks of installations belonging to other organizations (CPU, subscribers) is prohibited.

CL 6-10-35 kV are tested:
newly laid and after re-laying - before backfilling the trench and before turning it on;
in operation - scheduled according to the schedule, unscheduled - after repair or a long shutdown (in excavation, etc.). CL up to 1 kV are tested:
newly laid and after laying - before switching on;
unscheduled - after repair. CL 6-10-35 kV are tested:
1 time per year - for PKL and RKL supplying especially responsible consumers;
1 time in 3 years - all other PCL;
1 time in 5 years - all other RKL;
internal cable jumpers in RP and TP are tested only newly laid and after repair.

The norms allow not to test cable lines up to 60 m long, which are outputs from the switchgear, transformer substation to overhead lines.
A one-time test of several series-connected RKLs with power transformers disconnected is allowed; beams of parallel CL; double or paired CL.
The magnitude and duration of the test voltage applied to the conductors of the cable lines is given in Table. one.

2. Periodicity. Norms, schemes for testing cable lines.

2.1. Cable lines with a voltage of 6, 10.20, 35 kV are tested:

• newly laid and after laying, before backfilling and before switching on,
• in operation: according to the schedule (scheduled tests), after repair, long shutdown, etc. (unscheduled tests).

2.2. Cable lines with voltage up to 1 kV are tested:

• newly laid - before switching on,
• after repair, steaming, flooding, etc. (unscheduled tests).

2.3. Cable lines 6, 10, 20 and 35 kV with paper insulation, including cable inserts and dropouts on overhead lines, are tested:

• a) 1 time per year - for PKL and RKL, supplying especially responsible consumers and life support facilities of the city;
• b) 1 time in 3 years - for the rest of the PCL;
• c) 1 time in 5 years all other RKL;
• d) it is allowed not to test:
  • CL which are conclusions from RP and TP to overhead lines,
  • CL to be decommissioned in the next 5 years,

2.4. Cable lines 10, 20 and 35 kV with XLPE insulation, including cable inserts, are tested:

• after CL repairs,

2.5. Tests of protective plastic sheaths of 10-20 kV cables with XLPE insulation are carried out:

• before putting the cable into operation,
• after repairs of the main insulation of cable lines,
• in cases of excavations in the protected zone of KL and the possible violation of the integrity of the shells associated with this,
• periodically - 2.5 years after commissioning, then 1 time in 5 years.

2.6. Testing of PCL using testing laboratories or portable test facilities is carried out from the RP. If it is impossible to conduct them from the RP (no access, etc.), the tests can be carried out from the side of the power center. In this case, the application must indicate the reasons for the need to carry out these works from the power center.

2.7. Simultaneous testing of several series-connected distribution cable lines is allowed with disconnection of power transformers, parallel cable lines, double or twin cable lines.

2.8. Cable throws and inserts are tested without disconnecting from the overhead line, and at the same time, the arresters installed on the overhead line must be disconnected.

2.9. The value and duration of the test voltage applied to the cable conductors is indicated in Table No. 1.

Table No. 1

2.10. For testing cable lines with direct rectified voltage, test facilities mounted on vehicles (see clause 7.1, scheme 1) and small-sized portable facilities (see clauses 7.2., 7.4.-7.10.) are used.

2.11. Cable lines with XLPE insulation are tested with ultra-low frequency alternating voltage, which is generated by special installations (see clause 7.11 - 7. 14.), These installations can be performed as stationary, mounted on a car (clause 7.11), and as mobile, transported by any road transport suitable for this (clause 712 -7.14).

2.12. To test the sheath of cable lines with XLPE insulation, test facilities - generators are used direct current with a maximum output voltage of up to 5 kV (clause 7.15.) It is allowed to use high-voltage test facilities designed for testing cable lines with paper-oil insulation, provided that the following conditions are met:

• Output voltage control should be carried out on a digital display or a kilovoltmeter scale, where 5 kV is at least a quarter of the scale.
• Leakage current control should be carried out using a microammeter, manually turning off the test setup when the current exceeds 300 µA.

2.13. When testing insulation, voltage is applied in turn to each core (phase) of the cable line, while the other two, together with the sheath, are grounded.

To reduce the total test time, when testing short (up to 1 km) CL with XLPE insulation, made of single-core cables, it is possible, if the capacity of the installation allows, to combine all three cores and test them simultaneously. If a breakdown occurs during the test, repeat the phase-by-phase test of each core to identify the damaged one.

2.14. During the test period of each phase of the CL with paper insulation, periodically and at the last minute of the test, the leakage current is counted according to the reading of the microammeter.

If during the test the leakage current increases or current surges appear, the duration of the test should be doubled. In the future, if the cable line cannot be brought to breakdown at a given test voltage, then it is tested with increased voltage according to the standards for new cables - 6-fold voltage for 10 minutes each phase. If the cable line passed this test without breakdowns, then it can be included in the work by decision of the chief engineer of the district.

When testing cable lines with XLPE insulation, leakage current control may not be carried out, however, during the test, it is necessary to control the test voltage using a kilovoltmeter. The maximum deviations of the kilovoltmeter needle during a periodic change of polarity in both directions relative to zero (see clauses 7.9.1. - 7.9.5), indicating the set value of the test voltage, during the test should not decrease by more than 15%.

If such a decrease is recorded, the test time should be increased to 1 hour. If during this time the cable line passed this test without breakdowns, it can be put into operation.

2.15. A cable line with a voltage of 6, 10, 20 and 35 kV is considered serviceable if it has withstood the test voltage for the time specified in clause 2.9. of this instruction (taking into account the additions according to clause 2.14.). For a cable line made of 3 single-core cables with XLPE insulation, the results of testing the protective sheath are additionally taken into account, which must withstand the test with direct rectified voltage in accordance with the norms of clause 5 of Table No. 1.

2.16. After a repair test, a cable line with a voltage of up to 1 kV is considered to have passed the test if the insulation resistance measured by a 2.5 kV megohmmeter is not lower than 0.5 mΩ. At lower resistance values, when testing with a 2.5 kV megohmmeter does not lead to a breakdown of the cable insulation, the cable should be tested using a burning installation. If during the test it is not possible to achieve a decrease in insulation resistance, the CL, by decision of the chief engineer of the district, can be included in the work.

2.17. Testing and switching on the cable line 6 - 35 kV after repair should be carried out within the time limits specified in paragraph 6 of the "Regulations on the organization and conduct of emergency recovery work at the Moscow Electric Grid Company OJSC".

2.18. When testing the sheath of single-core cables with XLPE insulation, the test voltage is applied between the CL screens and the ground. To do this, the screens of each of the cores of the cable line, in order to avoid mutual electrical contact between themselves and the ground loop, are disconnected from the ground loop on both sides of the line and separated in different directions. For cable line screens of 6-10 kV, if they are combined at construction lengths (cable screens of 20 kV and above are not combined), it is enough to ensure at both ends of the cable line only the absence of contact with the ground loop. The working ground of the test facility is connected to the ground loop in the switchgear cell or, when working from a pit, to the ground created from metal stakes in accordance with the provisions of clause 6.3.6. this manual.

2.19. Leakage currents and unbalance factor when testing paper insulated cable lines are recorded for additional insulation evaluation, especially for terminations. The limit values ​​of the leakage current and the asymmetry factor depending on the test voltage are given in table No. 2.

Table number 2

2.20. In those cases when, during testing, the leakage current or the asymmetry coefficient exceeds the limit values, it is necessary to inspect the terminations and insulators at both ends of the cable lines, eliminate visible defects (dust, moisture, etc.), after which, if no visible defects are found, perform re-test. If, during the repeated test, increased values ​​of leakage currents and asymmetry coefficient are preserved, but there are no shocks of leakage current and its further growth does not occur, the cable line can be included in the work by decision of the chief engineer of the area.

2.21. The protective sheaths of each phase of the CL with cross-linked polyethylene insulation must withstand the test with a constant rectified voltage of negative polarity of 5 kV for 5 minutes. The leakage current must not exceed 200 µA.

2.22. Features of testing the insulation of 6-10 kV cable lines with end terminations (SC) made of heat-shrinkable materials:

• If an end seal made of a heat-shrinkable material is installed on the CPU on the tested CL, then tests are allowed to be carried out from the RP only with a completely de-energized cell on the PC.
• The rise of the test voltage and the counting of leakage currents should be carried out when the test voltage is reached in stages. At the first stage, controlling the values ​​of the test voltage using a kilovoltmeter, gradually increasing it to a value of 5 kV, after which a pause of 10-15 seconds should be maintained during which the leakage current should be measured, first on a scale of 10 mA, and then on a scale of 1 mA. If the current on the scale of 10 mA is higher than 1 mA and there is no tendency to decrease, the test should be stopped. Repeated tests will need to be carried out by the PC.
• If the leakage current on the 10 mA scale is less than 1 mA, switch the device to the 1 mA scale and measure the leakage current, which, with a good cable, should not exceed 500 μA. After that, the voltage rise can be continued in steps of 5 kV until the test voltage is reached. The leakage current is monitored every 5 kV, similarly to the above.
• If during the test there was a breakdown of the cable, it is necessary to disconnect the test installation from the mains, preventing the voltage from rising again, both on the damaged phase and on the remaining untested phases.
• When testing CL with an alternating voltage of 0.1 Hz, in the absence of the possibility of controlling leakage currents, tests should be stopped immediately upon breakdown or the first signs of an increase in load. That is, when the specified test voltage level is not set for more than 5 periods at the initial stage of the test, or when during the test a decrease in the level by more than 10% is recorded for more than 3 periods of the specified test voltage oscillation frequency.

2.23. Paper-insulated cable lines with XLPE-insulated cable inserts less than 15 meters long can be tested with direct rectified voltage in accordance with the norms of Table 1. If there is an insert with XLPE-insulated cable more than 15 meters, the test is carried out with ultra-low frequency alternating voltage. In this case, the cable sheath with XLPE insulation is not tested.

All testing and WMD work can be carried out by personnel admitted to these works and having the appropriate mark in the safety certificate. When carrying out these works, it is possible to use only test and measuring installations that have been tested and annually certified in the SII of electrical networks. Use by personnel of electric networks of installations belonging to other organizations (CPU, subscribers) - prohibited.

CL 6-10-35 kV are tested:

• newly laid and after re-laying - before backfilling the trench and before turning it on;
• in operation - scheduled according to the schedule, unscheduled - after repair or a long shutdown (in excavation, etc.).

CL up to 1 kV are tested:

• newly laid and after laying - before switching on;
• unscheduled - after repair.

CL 6-10-35 kV are tested:

• 1 time per year - for PKL and RKL supplying especially responsible consumers;
• 1 time in 3 years - all other PCL;
• 1 time in 5 years - all other RKL;
• internal cable jumpers in RP and TP are tested only newly laid and after repair.

The norms allow not to test cable lines up to 60 m long, which are outputs from the switchgear, transformer substation to overhead lines.

A one-time test of several series-connected RKLs with power transformers disconnected is allowed; beams of parallel CL; double or paired CL.

The magnitude and duration of the test voltage applied to the conductors of the cable lines is given in Table. one.

Table 1

And today we will talk about testing cables with paper-impregnated, plastic and rubber insulation with increased rectified voltage.

Insulation control power cable voltage above 1000 (V) is produced by the applied voltage method, which allows you to detect defects that can reduce the electrical strength of its insulation during further operation of the cable.

Preparation for testing the cable with increased voltage

Let me remind you right away that an employee over 18 years of age who has undergone special training and knowledge testing (reflected in the table of special work of his certificate) is allowed to conduct high-voltage tests (high-voltage tests). It looks like this.

By the way, for you I have specially created online — you can test your knowledge.

Before testing the power cable with increased rectified current voltage, it is necessary to inspect it and wipe the funnels from dust and dirt. If during the inspection insulation defects are visible or the outer surface of the cable is heavily contaminated, then it is forbidden to start testing.

You should also pay attention to the ambient temperature.

The ambient temperature should only be positive, because at negative air temperatures and if there are water particles inside the cable, they will be in a frozen state (ice is a dielectric), and such a defect will not appear during a high-voltage test.

Immediately before testing the cable with increased voltage, it is necessary to measure the resistance of its insulation. You can read more about this in the article. .

As I said above, the test of power cable lines is carried out with an increased voltage of the rectified current.

The increased rectified voltage is applied to each core of the power cable in turn. During the test, other cable cores and metal sheaths (armor, screens) must be grounded. In this case, we immediately check the strength of the insulation between the core and the ground, as well as with respect to other phases.

If the power cable is made without a metal sheath (armor, screen), then we apply an increased voltage of the rectified current between the core and other cores, which we first connect to each other and to the ground.

It is allowed to test with increased voltage all the cores of the power cable at once, but in this case it is necessary to measure the leakage currents in each phase.

We completely disconnect the power cable from or the busbar, and separate the cores at a distance of more than 15 (cm) from each other.

We figured out the test circuit for the rectified voltage of power cables. Now we need to decide on the size and duration of the tests. To do this, open the desktop books: PTEEP and PUE.

You can also use the electronic version of these books. I suggest you download right now and completely free of charge the electronic version.

I made the task a little easier for you and compiled a general table taking into account the requirements of the PUE (Chapter 1.8, clause 1.8.40) and PTEEP (Appendix 3.1., Table 10).

The duration of testing cable lines with voltage up to 10 (kV) with paper and plastic insulation after installation is 10 minutes, and during operation - 5 minutes.

The duration of testing cable lines with voltage up to 10 (kV) with rubber insulation is 5 minutes.

Now let's consider the normalized values ​​of leakage currents and asymmetry coefficients when testing cable lines with increased rectified current voltage.

Here there is a slight disagreement between the PUE and PTEEP (values ​​from PTEEP are indicated in brackets).

If the power cable is insulated with cross-linked polyethylene, for example, PvVng-LS(B)-10, then it is not recommended to test it with a constant (rectified) voltage, besides, its test voltage is significantly different. I talked about this in more detail in a separate article about.

Power cable testers

Well, we have smoothly moved on to what is used to test cables with an increased voltage of the rectified current. In ours, we use either the AII-70 test apparatus, or AID-70, or IVK-5. The last two devices are used most often on the road.

We will talk in more detail about these devices in the following articles, and if you do not want to miss the release of new articles on the site, then subscribe to receive notifications by mail.

Method of testing the cable with increased voltage

Suppose we need to conduct operational tests of a 10 (kV) power cable of the AASHv brand (3x95).

With the help of the AII-70 or IVK-5 apparatus, at a speed of 1-2 (kV) per second, we raise the test voltage to a value of 60 (kV). From this moment, the countdown begins. During all 5 minutes, we closely monitor the magnitude of the leakage current. After the time has elapsed, we record the resulting leakage current and compare it with the values ​​in the table above. Next, we calculate the asymmetry coefficient of leakage currents by phases - it should be no more than 2, but sometimes it can be more (see table).

The unbalance factor is determined by dividing the maximum leakage current by the minimum leakage current.

After high-voltage testing of the cable, it must be re-produced.

The cable is considered to have passed the test if:

• no breakdown, flashover, or surface discharges occurred during the test
• during the test there was no increase in leakage current
• the value of the cable insulation resistance has not decreased

It happens in practice that the leakage currents exceed the values ​​indicated in the tables. In this case, the cable is put into operation, but the period of its next test is reduced.

If during the test the leakage current began to increase, but the breakdown does not occur, then the test must be carried out not for 5 minutes, but more. If after this the breakdown does not occur, then the cable is put into operation, but the period of its next test is reduced.

Results and test report of the cable with increased voltage

After testing the cable with an increased voltage of the rectified current, it is necessary to draw up a protocol. Below I will give you a protocol form (example) used by our electrotechnical laboratory (click on the picture to enlarge).

P.S. This concludes the article on testing the cable with increased voltage. If you have questions about the material, then ask them in the comments.