Our Service

We can help you

Test before commissioning

Sheath test is an accepted pre-commissioning test where the insulation capacity of the outer sheath against earth is checked and ensures that the cable is not damaged during installation or transport. Even more serious damage, which affects the cable insulation system, is usually detected during the test. It also shows if joints and other accessories have become sealant.

If any sheath faults is detected, the damage is located and repaired immediately, provided that excavation assistance is available.

 

Ground connection control involves checking a section's ability to handle fault currents. Both in the cable shield or via earth conductor and other external earth connections. The test must always be performed before commissioning of a new cable or after interventions in an existing  cable section.

In the case of a new installation, it is mainly a measurement for checking the condition of the longitudinal earth conductor, but if older cables are included in the section, it is also a method that checks the status of the cable shield.

The test is also called Ymer, screen or return current measurement.

 

VLF test (Very Low Frequency) is an insulation test with low frequency AC voltage for medium and high voltage systems. The method is non-destructive with good insulation. On the other hand, weakened insulation or faults that occur during the installation of joints / terminations can be broken down during the test period. The section may then fail during the test, under controlled manner, and not during operation with unplanned power outages and the risk of affecting other equipment as a result. The test is performed with a higher voltage than the operating voltage, up to 3 times higher. It completely replaces "meggering" with DC voltage.

The sample can be extended with PD measurement where partial discharges (glimmers), mainly due to inadequate installation of accessories, are detected.

 

Condition control of older cables

The Tan Delta measurement is used to check the presence of water trees (treeing) in PEX-insulated cables. Treeing is weakening’s in the insulation that sooner or later leads to PD and then a breakdown. With a Tan Delta measurement, you can assess the status of the insulation and identify weaknesses even before they affect the network. The measurement is performed on non-energized cables where VLF voltage is used up to double operating voltage.

 

Moisture under the outer sheath is common on older cables, which can cause weakening or even interruption in the cable shield due to corrosion. This affects the cable's ability to handle earth fault currents or the ability to perform an effective insulation test. The problem is often detected during the ground connection control that is performed after changes in the cable network, but there are other times where deteriorating screen connection can be suspected.

With a screen resistance measurement, the conductivity at different voltage levels can be measured and the condition assessed.

 

Cables to focus on:

•  Cables that have failed without external influences or other "natural" causes.
•  Cables with outer conductive layers of graphite and conductive tape. Common in the 70s.
•  Cable sections that fall outside the approved values ​​during earth connection control.
•  Cables with PVC sheath.
•  Cables where sheath testing has not been performed.
•  Existing cable sections that are planned to be joined to new ones.

 

The measurements result in three levels of action proposals:

Measurement results without remarks - no action.

Minor signs of aging. Further investigation alt. new controls in x number of years.

• Strong weakening. Sometimes even the test has been interrupted in advance as a precautionary measure. Action required. Either urgently or in the long term of all or parts of the section.

Documentation of tests performed is provided to the customer.

 

Cable troubleshooting

With a surge generator, TDR and other troubleshooting equipment, Nexans is well prepared for most types of cable faults in the ground. Both in the high and medium voltage networks but also on the low voltage side where we often look for cable faults on e.g. street light cables.

 

Assembly of cable accessories

Installation of cable terminations to be delivered on drums adapted to the customer's wishes. For example, with an extra long inner end to reach up to a cable pole and is used as a bypass cable for service work in the overhead line network or shorter lengths within switchgear yard up to 84 kV.

• We also offer installation of joints and terminations up to 84 kV on site