Enemalta reported an “unprecedented” number of cable faults over the past week, leading to widespread power outages. People have been questioning why the high heat, to be expected in summer, has hit the energy provider’s distribution network. Jacob Borg asked Enemalta’s distribution engineer JOHN ZAMMIT for an explanation.

JB: Summers in Malta are always hot. What changed this year?

JZ: In past years, the heat has always increased gradually. This year, the temperature spiked suddenly, heating the ground rapidly and the cables buried underneath, which do not have a cooling medium. The cables’ weakest points are always at the joints. The elevated temperatures have accelerated the degradation of the insulation the cables are wrapped in, causing the cables to burn out. The degradation increases exponentially when the temperatures go up.

Enemalta technicians repairing a joint, the cables’ weakest link.

JB: What temperatures are these cables reaching?

JZ: We have not measured the temperatures. But there is very little heat loss between the surface and where the cables are buried. The sun’s heat is being absorbed by the asphalt, which is black.

JB: Why are faults occurring at night, when the temperatures are dropping?

JZ: Imagine a car radiator. The heat does not dissipate as soon as the engine is switched off. The stone and surrounding material retain the heat.

JB: Enemalta is saying the faults are not caused by an increase in demand. Can you explain?

JZ: We experienced a high load in the week prior to these problems. What happened was the sudden increase in temperature. In winter, demand was also high, but we were only experiencing one to two faults per month. The difference there is that the temperature was much cooler. What happened now was that the higher temperatures led to a large number of faults in a short time span.

JB: So cables are not being overloaded due to the spike in demand?

JZ: Cables cannot be overloaded, as they have an automatic cut-off to protect against that. In this case, the cables are not tripping, but burning up. The joints will always remain the weakest link. That’s where the cables are failing. They are like living things, which degrade over time. The problem is that the ground has heated up, and the cables aren’t being allowed to cool. There isn’t really anywhere for this heat to dissipate, as the surroundings are also hot. This accelerates the cable’s degradation and leads to the insulation failing.

Cables burn out when excessive heat degrades their insulation.

Upgrading work

Enemalta found itself in a similar situation two years ago, where power outages were also put down to the heat, coupled with the increased demand. Among others, over the past year-and-a-half, Enemalta has:

• Reinforced nine 11KV faults;

• Changed 120 kilometres of aerial lines;

• Upgraded 130 low-voltage reinforcement;

• Made upgrades to 41 transformers and replaced switchgear;

• Upgraded distribution centres in Marsascala, Tarxien and Mrieħel;

• Planned for distribution centre upgrades in Naxxar and Siġġiewi.