There is no CORONA like a CORONA

Corona Effect (Corona Discharge)

The Corona Effect has been giving headaches to the photovoltaic industry long before the current pandemic, and rest assured, it has nothing to do with Covid-19. Nor Corona Beer!

So, what exactly is this Corona Effect? The definition is:

It is an electrical discharge caused by the ionization of a fluid such as air surrounding a conductor that is electrically charged.

Risk Factors

Based on our observation of the cable behavior over the past decades, we have defined the most significant risk factors which lead into the corona effect:

#1 Central Inverters

To be more precise - central inverters without DC harmonics filters are the primary cause. During our observations, we have never encountered this problem with string inverters, nor central inverters which were equipped with DC harmonics filters.

#2 Location of the PV Plant

We noticed this problem to be heavily accelerated by high humidity/heavy rain areas. I can′t speak on behalf of other companies, but we have observed the corona effect in France, Italy, southern parts of Japan, India, Indonesia, Thailand, Sri Lanka or Greece

#3 Cable robustness

We should rather say - wall thickness. The corona effect can be eliminated by using the UL/EN based cables, which require thicker insulation layers than the EN, resp. IEC based cables. Based on the collected data, we have never observed the damage of corona effect with cables, which have an insulation of 2.3mm or more. Anything below 2.3mm and/or mechanically damaged cable insulation tend to be affected with corona effect more likely. There is a sub-group in this risk factor - cables with inhomogenities in the insulation material of the cable.

#4 Low quality of cable management/poor cable handling

Many of you already realized that a vast number of incidents/failures are linked with lousy quality of materials and/or workmanship. It is not different with the corona effect incidents - sharp metal edges, poor quality of fixation elements and other areas which might cause a mechanical damage of the cable surface are also contributing to the corona effect seriously.

How to be on the safe side?

If possible, ask your central inverter supplier to integrate the harmonics filters into the system

If you intend to use central inverters in the described humid/rainy areas of the planet, make sure you use a good quality (sufficient thickness) cables. If you want to be on the safe side, use cables which have both EN50618 and UL4703 certifications. You will pay more, but you can rest assured that the cable will resist.

Pay attention to the workmanship. Use symmetric cable ducts as a part of grounded metallic structure. Wherever is the risk of sharp edges, use a short piece of PE/PVC pipe to protect the cable. Do not use rubbish clips or fixation elements. Saving money of what cost you 0.001% of the cost of investment is really not a good idea!

REMARK - if you see damages as what I demonstrated above, please, do not blame the cable manufacturer. There is a very high probability that the root-cause lays somewhere else. Instead - ask your cable supplier for the help & assistance with solving the problem. I am sure that the supplier will be happy to assist.