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Tests for the extension of prequalification of cable system (EQ)

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Bas Verhoeven Bas Verhoeven
Director Marketing & Sales KEMA Laboratories

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It was found that a prequalification (PQ) test will slow down development of the cable system and accessories. Since the test will take one year and any changes to the cable system would imply that the whole PQ-test has to be repeated on the new, improved cable system.
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Therefore a new test has been introduced in the latest edition of the IEC 60840 (2011) and IEC 62067 (2011), called the Extension of Prequalification (EQ).

When a prequalified cable system is changed by exchanging a cable and/or accessory with another one that is already prequalified in another cable system with the same or higher calculated nominal electrical stresses at the insulation screen of the subjected system, the current prequalification shall be extended.

Examples of the changes that allow an EQ are as follows:

For cables, a change from stranded to solid conductor or a change in insulated wires is used.

For joints, higher calculated electrical stress design or a change in the compound of the main insulation body or fixation of the cable ends on either side of the joint.

For terminations, higher calculated electrical stress of the stress cone or a change in filling medium.

The EQ-test may be performed in a laboratory and shall be performed on one or more samples of complete cable of the already prequalified cable system.

The cable system shall contain at least one accessory of each type that needs the extension of the prequalification.

The test sequence of the EQ that will have to be performed is almost the same as the test sequence of a complete type test. However, the test sequence for the EQ is extended with a heating cycle test without voltage, consisting of 60 cycles between the initial partial discharge measurement and the tan delta measurement.

In the case of an extension of prequalification of the cable, the measurement of resistivity of the semiconducting screens and all nonelectrical is part of the required test.

The EQ-tests can be performed in the KEMA Laboratories. After successfully performing the tests, a KEMA Certificate of Extension of Prequalification can be issued.

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