Services Power Networks
As a complement to our manufacturing, we offer a range of services to network companies and contractors. This applies to both assembly and pre-commissioning tests of newly installed cables, cable fault location and analysis of older cables, where insulation and cable shield are assessed as a basis for future actions. In order to perform these services, experienced operators with appropriate equipment are required, which we can provide at Nexans.
Sheath testing is an important test performed before commissioning. The test controls the insulation ability of the outer sheath against ground and ensures that the cable is not damaged during transport or installation and all joints are dense. In case of a sheath fault, it will be located and repaired in conjunction with the testing and troubleshooting.
VLF test (Very Low Frequency)
The VLF test is an isolation test for PEX-insulated cable, using very low frequency AC voltage. The method is not destructive to good isolation but destructive at bad. This means that weakened insulation should break down during the test under controlled manner and not in service with power failure as a consequence. The test replaces isolation testing with DC voltage. It does not give a measurement result, it will only show that the cable is OK or not.
Tangens Delta Measurement (Tan δ)
The Tangens Delta measurement is used to control the presence of water trees (treeing) in PEX-insulated cable. Treeing is weakenings in the insulation that sooner or later leads to cable fault. With a Tangent Delta measurement, you can assess the status of the insulation and identify affected cables, which can be used as a basis for future actions.
Earth connection test
The test involves control of cable shield and longitudinal earth conductor together with other external ground connections. The test is also called Ymer measurement or return current measurement. In the case of new installations, it is primarily a method that ensures the condition of the longitudinal earth conductor. On older cables, moisture beneath the outer sheath can cause corrosion or even interruptions on the cable screen, which affects the cable's ability to handle earth fault currents.
Nexans can also measure, assess and give action proposals to cables that don´t pass the test above.
After all tests, protocols are sent to the network owner or the subcontractor.
Cable fault location
With a portable and powerful cable fault location system (surge generator and TDR), Nexans is well prepared for locating most types of cable faults in ground. Our sheath fault location equipment can be very effective to find other types of cable faults as well.
Mounting of cable accessories
Nexans offers assembly of joints and termination of medium and high voltage cables. Both after installation or for delivery on specially adapted drums.
Condition check of older cables in the 12-24 kV networks.
Cables to focus on:
• Cables from the 70s (outer conductive layer of graphite and conductive bands).
• Cable sections that don´t pass the earth connection test.
• Cables with PVC sheath (AXKJ).
• Plowed cables where sheath testing has not been performed.
Measurements that are performed:
- Corroded screen.
Detect the occurrence of punctual corrosion, (metallic connection is missing).
- The Delta Delta measurement.
Detect the occurrence of treeing.
Measurements usually provides three action proposals:
1.Cable OK = No action.
2.The cable partially aged = further investigations or new tests in 3 to 8 years.
3.Cable has bad values = plan for exchange.