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published: 09.11.2015

Malta Sicily 120 km 220 kV AC interconnector monitored by Omnisens.

At 120 km Enemalta’s Malta-Sicily interconnector is the longest AC cable of its type in the world. The 220 kV cable, supplied by Nexans Norway, comprises a 95 km subsea section reached via a tunnel from the new Maghtab, Malta, terminal station. In Sicily, Italy, a 20 km buried section joins the cable to Terna’s network at the Ragusa substation.

To provide condition monitoring all along its length the cable is fitted with an Omnisens temperature sensing system. Based on fiber optic distributed sensing (DTS) the system monitors the temperature of the cable via two interrogators, one housed in Sicily and one in Malta. To optimize the cable performance a Nexans Dynamic Rating System, (DRS) completes the package.

The distance capabilities of Omnisens Brillouin-based DTS means that most interconnectors and long export cables, which were previously only monitored at the shore ends, can now be monitored along their entire length, detecting temperature anomalies all long the cable. Read the Case Study.

Why is this important for Enemalta interconnector? The cable environment changes dramatically along its route and each of these sections can be ‘mapped’ into a specific zone in the monitoring system. On its journey from Malta to Italy, the cable passes through a tunnel and an HDD section before reaching the 95 km subsea part. On the Italian side, another HDD section is followed by a direct buried 20 km cable. To conserve a particular ecosystem subsea, over a short section the cable is not buried, but rests on the seabed, clad in cast iron shells for protection. 

Each of these environments (tunnel, HDD, subsea, direct buried), as well as changes in the cable structure, itself result in different thermal resistivity so the operating temperature under load will be different. Even when buried, water currents and changes in the seabed can affect the cable’s temperature. The monitoring system can be set to alarm for different temperature events in different zones and the evolution of temperature hot and cold spots can be seen. The Dynamic Rating System compares the temperature with the load, thus providing an insight into how much more load the cable can carry and for how long.

By linking into the Italian grid, the interconnector with a capacity of 200 MW and capable of bidirectional flow, provides not only the security of electricity supply for Malta, it importantly enables the islands to take advantage of lower European electricity prices.


More about power cable monitoring here:

Read the Case Study here:



 

interconnector, malta, sicily, Enemalta, subsea, buried cable, Terna, HV, AC long cable