On-line diagnostiek van energiekabels (EET.5475)

The underground network for electricity distribution in the Netherlands mainly consists of cables for medium-voltage and low-voltage.
The low-voltage grid (with a network voltage of 220/380 V) is about 130.000 km in length. The part of the cable network for medium-voltage (applied at 10,000 V or 10 kV) has aa length of 100,000 km by approximation.

This project is directed to the maintenance of the medium-voltage network. The investment value of this network is estimated to be 4.537,80 euro. The maintenance and with that prevention of failures is an important issue for the network operators. And the need for prevention of failures has increased for the following reasons:

• users of electricity are more then ever depending on continuous supply
• Some users of electricity require a very reliable connection
• the electricitynetwork was build starting in the 1920-s en mainly in the 1960-s and 1970-s, consequently large parts of the network can be characterized as "old".
• the electricity market demands cost savings, thus postponement of investments: old networks should operate longer and under more stringent load conditions.

Since several years it is possible to diagnose cables. Weak spots can be localized with help of electrical signals that are generated at the weak spots. On the basis of this analysis and knowlegde of the cable system, the calbe system quality is judged and weak spots are located. If there are more weak spots in one cable that generate electrical signals, then it is still possible to treat these individually due to the signals can be separated with help of their velocity and time of arrival at the measuring location. This way of diagnosing the cable system also has important restrictions. The cable should be out of service operation for half a day. Moreover, during the diagnostic test the cable has to be energized with a separate mobile generator that is free of disturbances. Another disadvantage is the fact that specialized personnel is required for signal interpretation.

The present proposal describes the development of a new and unique diagnostic test system that does not have the above described disadvantages. The cable to be taken out of service operation or only for a short while and will be diagnosed on-line (thus, without an expensive separate high-voltage generator). Moreover, the cable system can be diagnosed for a long time if needed. The reslults can be seen with remote equipment ( via a modem); and at-site no specialized personnel is required anymore.

Some important technological and scientific steps have to be taken in order to realize this new diagnostic tool. these steps are the development of suitable sensors, signal processing, signal interpretation and time synchronization. The university in Eindhoven is experienced in EMC matters, the development of suitable sensors and the application of signal analysis. KEMA has at this moment (and probably as the only institute in the world) knowledge on time synchronization for long and complex cable networks (this knowledge is patented). Time synchronization is essential for on-line diagnostic measurements (and an important advantage for the present off-line diagnostic measurements). This is, because the electrical signals generated at the weak spots travel through the cable system at about 50% of the speed of light. These signals have to be measured at both cable ends with a high accuracy, including arrival times, making it possible to find the difference in arrival time at both cable ends. In this way it is possible to locate the weak spots.

The total duration of the project is intended to be 4 years, with two PhD students having a crucial role. The project will be run with guidance and facility support of the following experts c.q. potential users:

• Technical University of Eindhoven (specialized in EMC, diagnostics and the development of new measuring tools)
• Electricity companies, here as network owners (they have experience with off-line cable diagnostics as used at present and they are expert on cable networks) and
• KEMA (specialized in diagnostics, consultant, they heve developed the off-line cable diagnostics for the Dutch utilities and are patent holder for the time synchronization in cables, they are also experienced users of the off-line cable diagnostics.

At this research are involved three companies.

More information can be found on the website of the research group.

Er zijn vijf bedrijven bij dit project betrokken.