High voltage insulators are some of the most important components in the power industry. The performance of these components depends highly on environmental factors, which can affect the insulation capabilities and consequently lead to flashovers.
Since flashovers are highly undesirable on any power system operation, it is important to know how exactly environmental factors affect electrical insulators and even more important, what can be done to counteract these effects to ensure minimum power interruptions. Let’s find out.
Gas Breakdown Theory: Temperature and Pressure
Scientists John Towsend, Heinz Raether and Friedrich Paschen studied the ionization process of a gas (such as air) and the factors that contributed to creating an avalanche effect of electrons between two points with a voltage potential difference. This research known as the gas-breakdown theory allows us to understand how flashover voltage is affected by environmental factors.
For instance, temperature is an energy source in the form of heat that accelerates the vibration of particles and that generates an electrostatic force, which induces electrons’ conduction and therefore induces gas breakdown. In other words, increasing temperature will cause that the flashover voltage will be lower.
Pressure on the other hand, affects the distance between particles in a gas. A higher pressure implies less distance between particles, which means that the flashover voltage needs to be higher in order for the particles to reach the kinetic energy required for the breakdown.
Now, how does this translate to high voltage insulators?
Contamination and Humidity vs Flashovers
According to what we discussed before, high voltage insulators in locations with high temperature conditions will likely have lower flashover voltages and therefore longer creepage distances in order to provide effective flashover insulation protection. Moreover, locations with lower atmospheric pressure will also act against in the prevention of electric arc formations. Considering these two factors, you will notice that transmission lines, substations and other electrical equipment located in coastal, industrial or desert regions are probably the most affected by environmental factors and weather related power outages.
However, there is another important environmental factor in coastal regions and that is contamination. When a high voltage insulator surface is under wet conditions (high humidity) and it is contaminated with high levels of salt, cement, dirt or any other contaminant, this will lead to pollution induced flashovers. This occurs because a combination of water and contaminants creates a conduction path that leads to an excessive leakage current, which degrades the insulator and eventually initiates the insulator flashover.
RTV Coating: A Long Term Solution To Prevent Flashovers in High Voltage Insulators
To mitigate the effects of environmental factors, preventive maintenance procedures are performed. This implies in most cases the use of silicone greases applied on the insulator’s surface or constant live line washing. However, these methods have proven to be ineffective in many cases for long-term scenarios, meaning high operation and maintenance (O&M) costs are needed to prevent power interruption in transmission lines.
In this matter, using an RTV coating for insulators is probably one of the best solutions to this issue on the long-term, representing only a fraction of the O&M costs that would be required with traditional methods. The RTV coating can be easily applied on the insulator by spraying two or three coats to obtain the minimum thickness and taking just about 1 hour of curing time.
A Midsun RTV coating provides an insulation protection against flashovers thanks to its hydrophobic properties that prevent the creation of a conduction path for contaminants and that significantly suppress the magnitude of leakage currents, corona effect and even reduce the surface temperature of the insulator. All of these benefits translate into significantly increasing the flashover voltage of the insulator and therefore provide a much better reliability of the power system, substantially reducing O&M costs and avoiding failures or line tripping.