How electricity affects ADSS cables? The tracking effect and corona discharge

When we talk about self-supporting aerial installations, one of the most common applications for long-distance transmission is the laying of fiber optic cables in high-voltage towers.

Current high-voltage structures post a very attractive type of installation because they reduce the investment in infrastructure needed to create new fiber optic links, these being, already built-in. But the lines in high-voltage towers usually present great challenges, commonly seen in equipment that handles high electrical voltages: the tracking effect and corona discharge.

What is the tracking effect?

Also known in the industry as dry banding or electrical arborescence, the tracking effect refers to the dielectric destruction of insulating material, an irreversible process derived from partial electrical discharges which advance within or on the surface of a dielectric material when it is subjected to prolonged high-voltage electrical stress.

Corona discharge

Another risk that aerial self-supported cables run when they are installed in high-voltage towers is the corona effect, also known as corona discharge, defined as the ionization of a gas that surrounds a charged conductor. For a fiber optic cable installation, the gas is the air itself, which surrounds a transmission line. 

The corona effect is present in all devices and installations that work with or conduct electricity. In our daily lives, this is usually not perceptible and does not affect us significantly due to the voltages and electrical potentials that we normally use. However, in high-voltage towers, the voltages that run on their lines are very high (from 66 kV to 115 kV), causing the corona effect produced by these conductors to be considerably wide.

When exposed to outdoor conditions, cables are influenced by two important factors: the relative humidity of the air and the pollution index of the environment. With more humidity, more water condenses on the surface of the cable; and the greater the pollution of the environment, the more particles (dust, heavy metals, minerals) will be trapped in the water droplets formed. 

These drops with impurities become conductive, when the corona effect of the high-voltage line reaches two drops that are close enough to each other, an electric arc is created, generating heat between them and degrading the jacket material of the cable.

Cable protection and anti-tracking materials

It’s strongly recommended to use anti-tracking materials when laying ADSS fiber optic cables next to equipment and facilities that handle electrical potentials of 12 kV up to 25 kV. These can better resist the effects of electrical discharges, mitigating the effects of ionization, heating, and degradation of cables. 

Anti-tracking materials are divided into two large classifications, class A materials and class B materials:

Class A materials

Class A materials are those that meet resistance criteria based on the applied voltage and pollution index tested under the IEEE P1222 2011 standard, this is considered to be the “standard” on the market.

Class B materials

Class B materials are those that are not under the standard, this doesn’t mean that these materials do not serve to protect against the tracking effect, but rather, they are governed by parameters or special conditions defined by the manufacturer, either for special applications or more stringent requirements, this class could be defined as “custom”.

Tips for ADSS cable installations in high-voltage towers

Preparation is key. It’s necessary to take into account the pollution index and the installation voltage when a self-supporting fiber optic cable is laid on a long-distance, high-voltage tower. As long as we are within the parameters established by the IEEE P1222-2011 standard, we can use a class A material, which is more accessible in the market; for more severe environmental conditions or higher voltages, it is necessary to use class B materials. 

Contact your cable manufacturer to ascertain the type of material that can be used to better protect the integrity of the cable in your installation,  meeting the conditions to which the cable will be exposed.

How can we help you?

Our WAVEOPTICS® engineers and sales experts are looking forward to helping you enable your installation, contact us today and check our wide variety of ADSS fiber optic cables available with anti-tracking or standard jacket materials here.

 

References via

• Dodd, S. J. et al. (2003). Influence of morphology on electrical treeing in polyethylene blends. IEEE Proceedings Science Measurement and Technology. Issue 2 (150), pp. 58-64.
• Checa, L. M. (1988). Lineas de transporte de energia (3.a ed.). Marcombo.