Views: 0 Author: Site Editor Publish Time: 2026-10-16 Origin: Site
Surge arresters are an important part of insulation coordination in medium-voltage power distribution networks. They help protect transformers, switchgear, circuit breakers and other electrical equipment against transient overvoltages caused by lightning and switching operations.
However, selecting the correct surge arrester is not simply a matter of matching the arrester's rated voltage to the nominal voltage of the distribution system.
An 11kV network does not automatically require an 11kV-rated arrester. The same applies to 22kV and 33kV networks. The appropriate configuration depends on the system's highest operating voltage, neutral grounding arrangement, temporary overvoltage conditions and the insulation characteristics of the equipment being protected.
For utility companies, EPC contractors and electrical equipment distributors, understanding these parameters is essential before requesting a quotation or approving a product specification.
This guide explains how to evaluate metal-oxide surge arresters for 11kV, 22kV and 33kV distribution applications, and what technical information buyers should confirm with a manufacturer.
The nominal system voltage is usually the first information provided in a surge arrester inquiry.
A buyer may ask for an 11kV surge arrester for transformer protection, a 22kV arrester for an overhead distribution feeder or a 33kV arrester for a substation project.
These descriptions identify the application, but they do not provide enough information to determine the final arrester rating.
Most medium-voltage metal-oxide surge arresters are connected between the phase conductor and earth. The voltage continuously applied across the arrester therefore depends on the phase-to-earth voltage, which is influenced by the network configuration and neutral grounding method.
The highest system voltage must also be considered. Electrical networks may operate above their nominal voltage within permitted limits, and the arrester must remain suitable throughout the specified operating range.
Consequently, two projects using the same nominal voltage can require different surge arrester ratings.
The correct selection begins with the electrical characteristics of the network, not merely the voltage printed in a product title.
Neutral grounding is one of the most important factors in medium-voltage surge arrester selection.
In an effectively grounded system, phase-to-earth voltage is generally controlled by the grounding arrangement. Under normal balanced conditions, the phase-to-earth voltage is approximately the phase-to-phase voltage divided by the square root of three.
An isolated-neutral or resonant-grounded network behaves differently during a single-line-to-ground fault. The voltage of an unfaulted phase relative to earth may rise significantly, and that condition may persist until the fault is cleared.
This difference affects the electrical stress imposed on the surge arrester.
For example, two 22kV distribution projects may have similar normal operating voltages but different neutral grounding arrangements. Selecting identical arresters without evaluating their earth-fault behavior could lead to an unsuitable continuous operating voltage or temporary overvoltage rating.
This is why manufacturers should ask for the grounding method and earth-fault clearing conditions before confirming the arrester model.
For projects where the grounding arrangement is unclear, a single-line diagram or utility technical specification is often the most useful starting point.
Two parameters appear frequently in metal-oxide surge arrester datasheets:
Rated Voltage (Ur) and Continuous Operating Voltage (Uc), also known as MCOV.
Although both are expressed in kilovolts, they describe different operating requirements.
The continuous operating voltage, Uc, is the maximum power-frequency voltage that may be applied continuously across the arrester terminals under the manufacturer's specified conditions.
The rated voltage, Ur, is a characteristic assigned to the arrester and associated with its ability to withstand specified temporary power-frequency voltage stresses. It must be considered together with the manufacturer's temporary overvoltage capability.
Temporary Overvoltage, or TOV, is particularly important because a power-system fault or abnormal operating condition may expose the arrester to elevated voltage for a limited period.
A suitable arrester must remain thermally and electrically stable under the expected continuous and temporary voltage stresses.
However, choosing an excessively high arrester rating is not automatically safer. For a given arrester design, increasing the voltage rating may also increase its protective residual voltage, reducing the protective margin available to the connected equipment.
The objective is therefore to balance two requirements:
The arrester must withstand the voltage stresses of the network while providing an appropriate protective level for the equipment.
This principle is central to the selection recommendations in IEC 60099-5.
Although the fundamental selection process is similar, each project should be reviewed individually.
In 11kV distribution networks, surge arresters are commonly considered for distribution transformers, overhead lines, switching equipment and other exposed electrical installations.
The first step is to confirm the highest system voltage and neutral grounding arrangement. The selected arrester's Uc and TOV capability must then be checked against the actual operating conditions.
The insulation withstand level of the transformer or other protected equipment is also important. An arrester that can withstand the network voltage may still provide insufficient protection if its residual voltage is too high for the required insulation coordination.
Therefore, buyers should provide the transformer or equipment data rather than requesting an arrester based only on the term “11kV.”
For a 22kV network, the same principles apply, but the higher operating voltage and project-specific grounding conditions may lead to a different arrester configuration.
A key consideration is the expected phase-to-earth voltage during both normal operation and earth-fault conditions.
Utilities may also specify particular discharge-current ratings, residual-voltage limits, insulation requirements or external insulation configurations.
Where the arrester will be installed on an exposed overhead feeder, the installation arrangement and environmental conditions should be reviewed together with the electrical parameters.
The suitable product is determined by the complete technical requirement, not by a universal arrester rating for all 22kV networks.
In 33kV distribution and substation applications, insulation coordination becomes especially important because the arrester must protect equipment with defined dielectric withstand characteristics.
A buyer should confirm the highest system voltage, grounding arrangement, temporary overvoltage conditions and the required protection level.
For installations involving transformers, switchgear or cable terminations, arrester location and connection length can also influence the effective protective performance at the equipment terminals.
A product described as a “33kV surge arrester” should therefore be treated as a starting point for technical discussion—not a final, universally applicable specification.
A metal-oxide surge arrester limits transient overvoltage by conducting surge current when its voltage-current characteristic reaches the relevant operating region.
During this process, a voltage remains across the arrester terminals. This is known as the residual voltage.
Residual voltage is an important parameter because the purpose of the arrester is not merely to conduct a lightning surge. It must limit the voltage stress imposed on the protected equipment.
For example, when protecting a distribution transformer, the arrester's protective level should be evaluated against the relevant insulation withstand level of the transformer, with appropriate consideration of the required protection margin.
Installation also matters.
Long connecting leads can introduce additional voltage during a rapidly changing surge current, which may increase the voltage experienced at the equipment terminals. This is why arrester placement, conductor routing and grounding connections form part of the overall protection design.
For EPC and substation projects, the protective performance should be considered at the equipment being protected, not only at the arrester terminals.
Another common procurement question concerns nominal discharge current.
Metal-oxide surge arresters may be offered with different nominal discharge-current classifications, including 5kA and 10kA configurations.
However, a 10kA nominal discharge-current rating does not, by itself, prove that an arrester is the best choice for every project.
Nominal discharge current is associated with a specified impulse-current test characteristic. It is not the same as the arrester's total energy-handling capability or its maximum ability to withstand every possible surge event.
Selection may also involve charge-transfer capability, energy performance, residual voltage, short-circuit performance and the requirements defined by the applicable standard.
For distribution networks, a technically appropriate arrester should meet the expected electrical stresses and protection requirements without unnecessary overspecification.
The buyer should therefore compare the complete datasheet rather than selecting a product solely because it carries a larger kA number.
Electrical ratings are only part of the selection process.
Surge arresters installed on overhead lines and outdoor substations may be exposed to dust, moisture, industrial pollution, coastal salt contamination and temperature variation.
These environmental conditions influence the required external insulation performance and housing configuration.
Polymer-housed metal-oxide surge arresters are commonly used in outdoor distribution applications. Their final suitability depends on the specified material design, insulation characteristics, creepage distance, mechanical requirements and test documentation.
An installation near the coast may require a different external insulation configuration from one in a relatively clean inland location, even if the electrical system voltage is identical.
Altitude should also be disclosed when the project is located above the normal service conditions covered by the relevant equipment specification.
Rather than selecting a product only by its external shape, buyers should provide environmental information so that the manufacturer can evaluate the appropriate configuration.
Technical documentation is particularly important for utility tenders, EPC contracts and international distribution projects.
IEC 60099-4 addresses gapless metal-oxide surge arresters used on AC power systems above 1kV, while IEC 60099-5 provides selection and application recommendations.
When reviewing products, buyers should distinguish between a manufacturer's general statement of conformity and the actual test documentation available for a specific model.
A type-test report should be checked against the offered product's model, rated voltage, electrical characteristics and applicable test standard.
The existence of a report for one model does not automatically mean that every arrester in the manufacturer's catalogue is covered by the same test results.
A more useful purchasing process is to request the technical datasheet, dimensional drawing and applicable test documentation together.
This allows engineers to evaluate the proposed product against the project specification before approving the equipment.
DGG Power supplies medium- and high-voltage transmission and distribution equipment, including polymer-housed metal-oxide surge arresters for power distribution applications.
Our surge arrester range includes configurations for different network voltages, insulation requirements and installation arrangements, including products intended for 11kV, 22kV and 33kV distribution applications.
DGG Power also offers multiple product structures and can discuss project-based configurations according to the customer's electrical and mechanical specifications.
For projects requiring supporting technical documents, product datasheets, drawings and available model-specific test documentation can be reviewed during the selection process.
The final arrester model should be confirmed according to the actual system conditions rather than simply matching a product name to the network voltage.
For utilities, EPC contractors, distributors and project buyers, our objective is to support a practical selection process from technical inquiry through product configuration and quotation.
Does an 11kV network require an 11kV-rated surge arrester?
Not necessarily. The appropriate arrester rating depends on the highest system voltage, neutral grounding arrangement, Uc requirement, temporary overvoltage conditions and insulation coordination.
Is the rated voltage (Ur) the same as MCOV (Uc)?
No. Ur and Uc describe different voltage characteristics. Uc relates to continuous operating voltage, while Ur is associated with specified arrester voltage-duty requirements. Both must be evaluated alongside TOV capability.
Can the same surge arrester be used for every 22kV network?
Not automatically. Different grounding arrangements, earth-fault conditions, insulation levels and utility specifications may require different configurations.
Should I always choose a 10kA arrester instead of a 5kA model?
No. Nominal discharge current is only one selection parameter. Residual voltage, charge and energy capability, system conditions and the project specification must also be considered.
What documents should I request from a surge arrester manufacturer?
Request a technical datasheet, dimensional drawing, applicable test documentation and information covering the proposed model's voltage ratings, protection level and environmental suitability.
Can DGG Power support surge arrester selection for utility and EPC projects?
DGG Power can review the supplied electrical parameters and project specifications to help identify suitable surge arrester configurations and provide corresponding product and technical-document information.
Selecting a metal-oxide surge arrester for an 11kV, 22kV or 33kV distribution system requires more than identifying the nominal network voltage.
The most important decisions involve the relationship between system grounding, continuous operating voltage, temporary overvoltage capability and the protection level required by the connected equipment.
Nominal discharge current, external insulation, installation arrangement and technical documentation must then be evaluated as part of the same selection process.
For power utilities, EPC contractors and electrical equipment distributors, confirming these parameters before ordering can help reduce specification errors and improve coordination between engineering and procurement teams.
Looking for metal-oxide surge arresters for an 11kV, 22kV or 33kV project?
Send DGG Power your network voltage, grounding method, required Uc or Ur, nominal discharge current, installation environment, technical specification and purchase quantity.
