A properly sized and installed surge arrester will help prevent damage from surges and prolong the service life of other electrical equipment.
Quick answer
Network voltage | Recommended surge arrester voltage rating |
11kV | 9kV |
33kV | 27kV |
Introduction
Surge arresters are used in medium-voltage networks to protect power lines, distribution transformers and other equipment from damage inflicted by lightning or other medium-voltage transients.
Electricity is a great thing, but lightning strikes can be dangerous. Surge arresters protect your sensitive electrical equipment from surges that are caused by lightning or other medium-voltage transients.
What are surge arresters used for?
Electricity is a great thing, but lightning strikes can be dangerous. Surge arresters protect your sensitive electrical equipment from surges that are caused by lightning or other medium-voltage transients.
Surge arresters are used in medium-voltage networks to protect power lines, distribution transformers and other equipment from damage inflicted by lightning or other medium-voltage transients.
They are subject to strict international standards, with MOV technology having become the most widely applied technology for medium-voltage surge arresters. The key rating for a surge arrester is its voltage rating (Ur).
The surge arrester will absorb the surge energy and dissipate it as heat. The amount of heat depends on the amount of current flowing through a particular surge arrester, which is rated in kA at an operating temperature of 75°C (167°F).When selecting a surge arrester, you'll want to make sure that it's rated for the voltage of your circuit. A properly sized and installed surge arrester will help prevent damage from surges and prolong the service life of other electrical equipment.
It's important to select and install the correct surge arrester for your application.
When you choose a surge arrester for your application, it’s important to consider how much voltage you need to absorb and how long it needs to last. The rating on your surge arrester will tell you how much voltage it is designed for, as well as its maximum energy discharge capacity in kilojoules (kJ). The longer a surge arrester lasts during an electrical storm, the higher its rated kJ value should be.
A surge arrester must be selected carefully because it is designed for a specific application. The wrong type of surge arrester can cause damage to your system.
When buying surge arresters, it's important they meet international standards so they can be used safely wherever they go. They must also be tested and certified by an accredited testing facility before being sold worldwide.
Arrester rating vs MCOV
The most used rating for a surge arrester is its voltage rating (Ur). The rating is normally expressed in kilovolts (kV) and is determined by the arrester's design, construction and materials.
The rated voltage dates back to the days of silicon carbide arresters with gaps and is a number with which we're familiar. For this reason, it was adopted when the MOV arrester was introduced to the market. Although the rated voltage of the arrester isn't relevant for the actual operating voltage of the modern MOV arrester, it's still frequently used to designate an arrester.
The higher the rating, the more expensive they are to manufacture. It's important to note that this rating isn't the same as insulation voltage!
MCOV stands for the Maximum Continuous Operating Voltage.
The arrester's MCOV is determined by testing the arrester according to the standard IEEE C62.11 and is the most important voltage specification for arresters. It's a AC nominal voltage and always should be higher than the maximum line-to-ground voltage of the system in which the arrester is to be used.
How to size a surge arrester
For a proper calculation, you need to know the following parameters for your application:
System line to line voltage
Earthing type
With those in mind, apply it on IEEE suggestion table:
Generally, for solidly earthed systems, the best surge arrester for 11kV and 33kV will be the 9kV and 27kV rating
This information takes into account a cost-effectiveness analyses and risk return curves.
As you can see, there are many factors to consider when choosing a surge arrester. The best one for your application will depend on the application itself, which is why it helps to know the ratings and what they mean.
Will a mobile surge arrester perform better on this case?
Yes, although the varistor functioning will be the same, a mobile arrester will bring labor costs way down for arrester replacement, meaning it will worth on cost-efficiency very quickly. Check the mobile arrester technology here.
Conclusion
Generally, for solidly earthed systems, the best surge arrester for 33kV is the 27kV MCOV rating and for the 11kV networks it will be the 9kV MCOV rating. This product provides the highest level of protection for medium-voltage networks and can be used in many applications where other ratings may not be suitable. If you're looking for a product that will give your electrical equipment the best chance of surviving an unexpected electrical event, this is your smartest choice.
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