Cable Type Test -IEC 60840 International Standard
Why Cable Type Test is Required:
Cable type test is essential for both cable manufacturer and cable usurer; manufacturer being satisfied type testing that followed all necessary standards and quality plan and will ensure customer satisfaction; usurer also being convinced that the product they are purchasing is manufactured as per required standard. Ultimately cable type test makes manufacturer and customer confident and satisfied that the cable will work satisfactorily after switch on to energize the line for a long life time without trouble.
Please note that, in this post cable type test means type test only for cable; don’t confused with type test for cable systems, cables and cable accessories; also for references this post is written on the basis international standard IEC 60840 “power cables with extruded insulation and their accessories for rated voltages above 30 kV (Um=36kV) up to 150 kV (Um=170 kV)- test methods and requirements” and part of this contains copyright rules and ownership goes to as per original source documents. If you interested for more details, please visit main site.
Summary of cable type test as per IEC standard:
Cable type test is typically carry out by specified laboratory. To understand the cable type test first of all need to know to complete the type test actually which tests should be carry out. The following summary list will help to understand the scope of cable type test requirements before carry out the test.
- Range of type approval;
- . Electrical type tests;
- Test voltage values;
- Bending test;
- Partial discharge test at ambient temperature;
- Tan §measurement;
- Heating cycle voltage test;
- Lightning impulse voltage test followed by power frequency voltage test;
- Resistivity of semi-conducting screens;
- Non-electrical type tests on cable components and on completed cable.
Range of type approval:
Rated voltage range, cross-sectional area range, constructional procedure, variation of calculated electrical stress at conductor screen and insulation screen range condition should be met.
Electrical type tests:
To pass the electrical type tests on a completed cable first of all need to choose a piece of cable at least 10 meter length. Some series of test as per IEC standard requirements need to performed on that piece of cable, such as- bending test; tan lamda measurement test; heating cycle voltage test; lightning impulse voltage test; partial discharge test at ambient temperature; examination of the cable on completion of the these tests.
Test voltage values:
As per IEC standard 60840 test voltage values are shown in the table, but important considering point is that ensure the insulation thickness is correct as per IEC standard 60811-1-1 of the piece of cable which used for test. If insulation thickness is not same as requirement, no problem, just need to adjust the test voltage value as per insulation thickness.
|Table- Test Voltage Values|
As per IEC standard the bending test procedure is as below-
The cable sample shall be bent around a test cylinder (for example, the hub of a drum) at ambient temperature for at least one complete turn and unwound, without axial rotation. The sample shall then be rotated through 180° and the process repeated.
This cycle of operations shall be carried out three times in total.
The diameter of the test cylinder shall not be greater than:
-for cables with plain aluminum sheaths:
-36 (d + D) + 5 % for single-core cables;
-25 (d + D) + 5 % for three-core cables;
-for cables with lead, lead-alloy, corrugated metallic sheaths or with longitudinally applied metal foils (overlapped or welded) bonded to the over sheath:
-25 (d + D) + 5 % for single-core cables;
-20 (d + D) + 5 % for three-core cables;
-for other cables:
- 20 (d + D) + 5 % for single-core cables;
-15 (d + D) + 5 % for three-core cables.
d is the nominal diameter of the conductor, in millimeters;
D is the nominal overall diameter of the cable, in millimeters.
NOTE: A negative tolerance is not specified, but testing at diameters below the specified values should only be done by agreement with the manufacturer.
Partial discharge test at ambient temperature:
The partial discharge test performed as per requirements of IEC standard 60885-3, in the table test voltage values the test voltage range is mentioned in column 5 as ‘partial discharge test’; the test voltage shall be raised gradually to and held at 1.75 U0 for 10 second and then slowly reduced to 1.5 U0.
Tan lamda measurement:
The procedure of tan lamda measurement is mentioned in IEC 60840 is quoted in below- “The sample shall be heated by a suitable method and the temperature of the conductor determined either by measuring its resistance or by thermocouples on the surface of the screen/sheath, or by thermocouples on the conductor of another sample of the same cable heated by the same means. The sample shall be heated until the conductor reaches a temperature which shall be 5°C to 10 °C above the maximum conductor temperature in normal operation. The tan shall then be measured at a power frequency voltage of U0 at the temperature specified above”.
Heating cycle voltage test:
Heating cycle test voltage is mentioned in table- test voltages values are 2 times. Cable assembly as bending test/ U-bend, cable heated 5 to 10 degree above the conductor maximum temperature. Cable heated for 8 hours and stay for 2 hours then natural cooling for 16 hours. This process carried out 20 times.
Lightning impulse voltage test:
The impulse voltage shall be applied according to the procedure given in IEC 60230 on cable assembly heated 5 to 10 degree above the conductor maximum temperature. This test followed by a power frequency voltage test at 2.5 times of test voltage U0 for 15 minutes as shown column 4 in test voltage values table.
Physical check and examination is carried out during test, if there any degradation visible in cable.
Resistivity of semi-conducting screens:
This measurement of resistivity of semi-conducting test is carried out on separate piece of cable.
Non-electrical type tests:
The non-electrical type test may perform by checking and testing as follow:
- Mechanical properties of insulation;
- Mechanical properties of over sheaths;
- Compatibility of materials;
- Mass test on PVC over sheaths;
- Pressure test at high temperature on over sheaths;
- PVC over sheaths low temperature test;
- Heat shock test for PVC over sheaths;
- Ozone resistance test for EPR and HEPR insulations;
- Hot set test for EPR, HEPR and XLPE insulations;
- Density of HDPE insulation;
- Carbon black content of black PE over sheaths;
- Shrinkage test for PE, HDPE and XLPE insulations;
- Shrinkage test for PE over sheaths;
- Hardness of HEPR insulation;
- Elastic modulus of HEPR insulation;
- Fire conditions test;
- Water penetration test, etc.
After completed the type test of sample for a series of cable (considering the cross sectional area of cable, voltage rating of cable, construction procedure of cable etc.) it is considered that the other cables within the same series are valid and certified that no need separate test for individual lot.