When you size a surge arrester for an 11kV to 33kV overhead feeder, three mistakes show up again and again. Specifying by system voltage alone and ignoring MCOV. Ordering a 5kA unit for a high lightning corridor that needs 10kA. Using an LV arrester on the MV side, or the other way around. Any one of those can leave a transformer unprotected even though the purchase order looks complete.
This page is a field-style selection note for overhead distribution. If you need product options while reading, browse L&R Electric’s surge arrester series.
What the Arrester Actually Does on the Pole
On an overhead line, lightning and switching surges arrive much faster than any breaker can react. The arrester stays almost insulating at normal voltage. When the surge hits, the metal oxide blocks clamp the overvoltage and dump energy to earth, then recover. That is why lead length and earthing quality matter as much as the catalog rating. A long earth lead can erase a good residual voltage figure on paper.
Most distribution units today are gapless metal oxide arresters, often called MOA. For a short principle refresher, see how a lightning arrester works.
Start With Voltage and Duty, Not Housing Color
For an 11kV line, engineers commonly look at rated voltages around 9kV to 12kV and check that MCOV sits above the highest continuous phase-to-earth voltage on that network. For 22kV and 33kV feeders, move up the same way. Do not stop at “33kV arrester” on the drawing. Ask for rated voltage, MCOV, residual voltage at the selected discharge current, and the IEC 60099-4 duty class.
Discharge current is the next filter. Many light distribution packages use 5kA. In lightning-prone corridors, coastal feeders, and exposed ridge lines, 10kA distribution class is the safer default. Station class belongs in the substation, not on every pole transformer.
Pollution decides creepage. Inland dry areas can live with standard sheds. On a 33kV coastal or industrial feeder, ask for extended creepage and a housing that sheds salt or dust. Polymer sheds handle that job better than porcelain in most outdoor distribution work today.
Polymeric Has Taken Over Most Outdoor Lines
Ten years ago, porcelain still won many utility tenders by habit. That habit is fading. For new overhead distribution, polymer is now the practical first choice: lower weight on the crossarm, less shatter risk during transport, better contamination behavior, and easier handling for line crews.
Keep porcelain when the site asks for it. Some older substations, heavy mechanical supports, or buyer specifications still call for porcelain housings. Outside those cases, ordering porcelain “because that is what we always used” usually adds weight and logistics cost without improving protection.
| Check point | Polymeric | Porcelain |
|---|---|---|
| Best fit today | New overhead feeders, coastal lines, transformer poles | Legacy substation specs, heavy support structures |
| Crew handling | Light, lower drop damage risk | Heavy, higher break risk if dropped |
| Pollution / salt | Strong outdoor performance with proper creepage | Needs cleaning more often in dirty areas |
| Typical rating examples | HY5W / HY10W distribution classes | Y10C style station or heavy outdoor units |
Compare product details here: polymeric surge arrester and porcelain surge arrester. For substation type notes, see types of lightning arrester used in substations.
Put the Arrester Where the Surge Hits First
Protect the transformer first. Mount the arrester as close as you can to the MV bushings and keep the earth path short and solid. Every extra meter of lead raises the voltage that reaches the winding during a steep front surge.
After transformers, the next useful points are cable risers, overhead-to-underground transitions, open line ends, and poles that feed critical laterals. In high isokeraunic areas, some utilities also add line arresters on exposed spans. Do not scatter arresters randomly. Place them where energy enters equipment or where reflected surges concentrate.
Distribution Class, Station Class, and LV Are Not Interchangeable
For pole transformers and MV feeders, stay with distribution class unless the protection study says otherwise. Station class units carry higher energy capability and belong near substation equipment. An LV surge arrester protects the low voltage side and secondary circuits. It does not replace the MV arrester on the pole.
If your RFQ mixes “33kV line arrester” and “LV SPD” in one vague line item, split them. Different standards, different mounting, different failure modes.
What to Put on the Purchase Spec
Send the supplier more than a voltage label. A usable inquiry should include:
- System voltage and earthing method
- Required rated voltage and MCOV
- 5kA or 10kA discharge class, plus residual voltage target if you have one
- IEC 60099-4 reference and any local utility annex
- Polymer or porcelain housing, plus pollution level or minimum creepage
- Mounting style, disconnector need, and earth terminal details
- Altitude if above about 1000 m, because insulation and rating margins change
Many line packages also pull in insulators, fuse cutouts, and disconnect switches in the same order. Keep the arrester datasheet tied to the same voltage class as those parts.
Field Questions We Get Most
Is “surge arrester” different from “lightning arrester”?
On distribution projects, buyers use both names for the same metal oxide unit. What matters is the rating sheet, not the title on the quotation.
Should I still buy porcelain for a new 11kV feeder?
Only if the utility specification forces it. For a new outdoor feeder, polymer is the default we recommend.
How close should the arrester sit to the transformer?
As close as the bushing layout allows. Short HV lead, short earth lead, solid clamp to the tank earth or pole earth system. Long flying leads are the quiet killer of otherwise correct selections.
Can one catalog model cover 11kV and 33kV?
No. Each unit is built for a voltage class. If the network has mixed feeders, split the BOM by voltage and duty.
Next Step
If you already know the feeder voltage, lightning level, and mounting style, send those three points with quantity. L&R Electric can match polymeric, porcelain, or LV units from the surge arrester range and return a rating proposal instead of a generic catalog dump.
