GB/T 31489.1-2015DC extruded cable systems for power transmission at a rated voltage up to and including 500kV—Part 1: Test methods and requirements (English PDF)

3.1 Line commutated converters (LCC)

The voltage polarity of the cable system changes when the power flow is reversed. It is used for high-voltage direct current transmission system.

3.2 Voltage source converters (VSC)

The voltage polarity of the cable system does not change when the power flow is reversed. It is used for high-voltage direct current transmission system.

3.3 Transmission cable

HVDC cables in unipolar or bipolar HVDC transmission systems.

3.4 Return cable

LV/MV DC cables for return flow in unipolar HVDC transmission systems. It can be used for full-line connection between converter stations. It can also be used for partial connection between converter stations and electrode stations.

4.1 Test voltage

See Table 1 for the test voltage.

4.2 Cable design thermal parameters

Tc,max - the maximum operating temperature of the cable conductor, which is declared by the manufacturer.

4.3 Test conditions

4.3.1 Heating method

a) VSC, positive impact of same polarity operation b) LCC or VSC, negative impact of reverse polarity operation

c) VSC, negative impact of same polarity operation d) LCC or VSC, positive impact of reverse polarity operation

e) LCC or VSC, positive impact of lightning f) LCC or VSC, negative impact of lightning Use direct current or alternating current to heat the conductor, with help of external insulation or cooling means. Verify the actual temperature difference delta T in the insulation and the conductor temperature Tc in the test.

4.3.3 High load (HL)

High load includes a continuous heating phase. During the first 8h of the heating phase, the conductor temperature shall not be lower than Tc,max and the temperature difference within the insulation shall not be lower than delta Tmax, which shall be maintained until the end of the high load test.

4.3.4 Zero load (ZL)

Heating is not carried out.

4.3.5 Ambient temperature

Unless otherwise specified in the test, the test shall be carried out at ambient temperature (20 ± 15)°C.

4.3.6 Polarity reversal test (PR)

The polarity reversal test starts with positive polarity voltage first. The voltage polarity is reversed 3 times every 24h load cycle (equal distribution). One of the reversals shall coincide with the stop time of the load current in the 24h load cycle. It is recommended that the time for polarity reversal shall not exceed 2min.

4.3.7 Superimposed impulse voltage test (S/IMP)

Before the first impulse voltage is applied to the test object, the test object shall be heated until the temperature of the conductor is not lower than Tc,max and the internal temperature difference of the insulation is not lower than delta Tmax for at least 10 h. And the test object has been subjected to U0 (corresponding polarity) for at least 10 h.

Maintain DC voltage. Superimpose the impulse voltage on the test object for 10

6.1 Scope of type test approval

Type tests are also valid for other cable systems within the scope of this Standard if the following conditions are met.

6.2 Test object

All components (cables and accessories) of the cable system shall be type tested. Each component can be tested in different test loops. These test loops shall contain all relevant components of the cable system.

6.3 Non-electrical type test

6.3.1 Cable structure inspection

Conductor inspection, insulation and non-metallic sheath thickness, metal sheath thickness and outer diameter measurement of cables shall be carried out according to the provisions of 9.1.4, 9.1.7, 9.1.8 and 9.1.9 respectively, which shall comply with the provisions of relevant product standards.

6.3.3 Mechanical and physical properties of cable's non-metallic sheath

The mechanical and physical properties of the cable's non-metallic sheath shall meet the requirements in Table 3.

6.3.6 Scraping test of non-metallic outer sheath

For land cable specimens after bending test in 6.4.3.1, the non-metallic outer sheath shall be subjected to scraping test according to JB/T 10696.6-2007 and GB/T 2952.1-2008, which shall meet the corresponding requirements.

6.3.7 Corrosion extension test (only applicable to aluminum sleeve)

For land cable specimens after bending test in 6.4.3.1, the aluminum sleeve shall be subjected to corrosion expansion test according to JB/T 10696.5-2007 and GB/T 2952.1-2008, which shall meet the requirements.

6.3.8 Water penetration test

6.4 Electrical type test of cable system

6.4.1 Inspection of cable insulation thickness for electrical type test

Before the electrical test, the insulation thickness of the cable section used for the test shall be inspected according to the method specified in GB/T 2951.11-2008, so as to check whether the insulation thickness exceeds the value declared by the manufacturer.

6.4.2 Summary of electrical type test

See Figure 5 for the electrical type test procedure of the cable system. In addition to 6.4.7, 6.4.8, 6.4.9 and 6.4.10, the rest tests shall be carried out on the same test object.

6.4.3 Mechanical pretreatment before electrical type test

7.1 Scope of accreditation

Normally, the prequalification test shall be carried out after the development test is completed. It can also be agreed upon by both parties. The prequalification test only needs to be carried out once, unless the material, manufacturing process, structure or design parameters of the cable system are substantially changed.

7.2 Overview of prequalification test

A cable system with a rated voltage of 80 kV and above shall be subjected to a prequalification test.

7.3 Test arrangement

Cables and accessories shall be installed according to the installation manual provided by the manufacturer, including a certain amount and level of auxiliary materials, such as lubricating oil.

7.4 Long-term voltage test

The minimum test duration for the prequalification test is 360 days. The conductor temperature and insulation temperature difference of the cable system shall be controlled at the design level. Design levels of accessories and adjacent cables can be different.

7.5 Superimposed impulse voltage test

The superimposed impulse voltage test after the long-term voltage test varies with different projects. The recommended impulse voltage is UP2, O = 1.2U0, UP1 = 2.1U0 (if applicable).

7.6 Inspection

Inspect anatomical cables and disassembled accessories with normal or corrected vision.

There shall be no signs of deterioration (such as electrical deterioration, leakage, corrosion or detrimental shrinkage) affecting the proper operation of the cable system.

7.7 Acceptance criteria, retest and test interruption

The criterion for the prequalification test is that the test object does not break down after all the tests. The test system shall be inspected according to 7.6.

8.1 Transmission cable

Each delivered length of cable shall withstand negative polarity DC voltage UT between conductor and shield.

8.2 Cable accessories

8.2.1 Prefabricated joints and terminations

Prefabricated joints are usually used for connection between DC land cables. The terminal is used for the connection of DC land cables and DC submarine cables. The main insulation of prefabricated accessories shall be subjected to the DC voltage test specified in 8.1.

8.2.2 Factory joints for submarine cables

Factory joints are often used for large lengths of submarine cables. There are at least the following 4 ways to check the quality of factory joint insulation.

8.2.3 Repair joints of submarine cables

For prefabricated submarine cable repair joints, conduct routine tests according to 8.2.1.

For molded submarine cable repair joints, routine tests cannot be carried out. Sample tests shall be carried out in accordance with 9.4, so as to control the quality level of repair joints.

8.3 Return cable

Each length of return cable sent shall be subjected to an AC voltage test between the conductor and the sheath. The test voltage and time shall be agreed upon by the supplier and the buyer.

9.1 Transmission cable

9.1.1 Test item

The sample test items for transmission cables are as follows. […]

9.1.2 Test frequency

Sample tests of items a) ~ g) in 9.1.1 shall be carried out on a sample drawn from the production batch of cables of the same type and specification. But it shall not exceed 10% of the total number of cables in any contract. Round up to whole number.

9.1.3 Retest

If a specimen taken from any cable fails to pass any of the tests specified in 9.1.1, a specimen shall be taken from each of the other two cables in the same batch to test the failed test items. If the two additional test specimens have passed the test, the other cables in the batch shall be considered to meet the requirements. If one of the additional test specimens still fails the test, the batch of cables shall be considered as non-compliant.

9.1.4 Conductor inspection

The conductor structure shall meet the requirements of GB/T 3956-2008.

9.3 Repair joint and terminal

For prefabricated repair joints and terminals that are routinely tested in accordance with 8.2.1, the sample test is no longer applicable. The molded submarine cable repair joints shall be subjected to sample test according to the provisions in 9.4.

9.4 Field molded joint

Field molded joints cannot be routinely tested. The sample test frequency of molded joints shall be 1 for every more than 50 joints of the same cable contract. The recommended test items are as follows. […]