{"id":3618,"date":"2026-10-15T14:17:41","date_gmt":"2026-10-15T06:17:41","guid":{"rendered":"http:\/\/www.bafeivalveco.com\/blog\/?p=3618"},"modified":"2026-10-15T14:17:41","modified_gmt":"2026-10-15T06:17:41","slug":"what-are-the-dielectric-strength-requirements-for-medium-voltage-switchgear-insulation-48ce-57c9f4","status":"publish","type":"post","link":"http:\/\/www.bafeivalveco.com\/blog\/2026\/10\/15\/what-are-the-dielectric-strength-requirements-for-medium-voltage-switchgear-insulation-48ce-57c9f4\/","title":{"rendered":"What are the dielectric strength requirements for medium voltage switchgear insulation?"},"content":{"rendered":"

When I first started working in the medium voltage switchgear industry 12 years ago, I didn\u2019t realize how much dielectric strength sits at the heart of every reliable installation. I remember a customer reaching out to me in 2014, panicking because their new switchgear had failed a routine insulation test on-site. They\u2019d sourced units from a cheap overseas supplier, and the dielectric strength was far below what their local utility required. That experience stuck with me, and it\u2019s why every time we design or supply medium voltage (MV) switchgear now, we don\u2019t just check boxes on a spec sheet\u2014we prioritize dielectric strength as the non-negotiable foundation of our work. Medium Voltage Switchgear<\/a><\/p>\n

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First, let\u2019s define what dielectric strength actually means here, because it\u2019s easy to mix it up with general insulation performance. For MV switchgear, dielectric strength is the maximum voltage an insulating material can withstand before it breaks down, allowing electrical current to leak or arc across what\u2019s supposed to be an insulating gap. It\u2019s measured in kilovolts per millimeter (kV\/mm), but in real-world switchgear terms, we care far more about how that translates to safe performance across the entire range of operating conditions: from temperature swings in a steel mill in Ohio to humidity levels in a coastal power plant in Singapore, even during lightning strikes or sudden load surges.<\/p>\n

Medium voltage switchgear sits between low voltage (under 1kV) and high voltage (above 52kV), so our baseline range is typically between 1kV and 52kV, with most common installations falling between 15kV and 35kV. The dielectric strength requirements for these systems aren\u2019t arbitrary\u2014they\u2019re set by two core sets of standards: international IEC standards and regional ones like ANSI in North America, since those are the frameworks our customers around the world rely on. Let\u2019s break down the key requirements by voltage class, because that\u2019s where most of our customers start when specifying gear. For a 15kV switchgear unit, the standard required power frequency dry withstand voltage is 42kV, while wet withstand is 38kV. For a 35kV unit, that jumps to 95kV dry and 85kV wet. These numbers aren\u2019t pulled from thin air; they account for the maximum temporary overvoltage a system might see during a fault, plus a safety margin that\u2019s critical for preventing catastrophic failures.<\/p>\n

But here\u2019s what many new customers don\u2019t realize: dielectric strength requirements don\u2019t end at the factory test. The insulation inside switchgear isn\u2019t just a solid material\u2014we use a combination of materials: epoxy resin for busbars, silicone rubber for insulators, even air or sulfur hexafluoride (SF6) gas for enclosed units. Each of these materials has its own dielectric strength, but they also interact with each other and the environment inside the switchgear enclosure. That\u2019s why one of the most important tests we run in our facility is the partial discharge (PD) test, which checks for tiny, invisible leaks in insulation that don\u2019t show up during standard voltage tests. A unit might pass the 42kV dry withstand test, but if there\u2019s a tiny void in the epoxy busbar insulation, that void will cause PD over time, eroding the insulation until it fails. For us, we cap PD levels at less than 10 picocoulombs for all our MV switchgear, well below the 50 picocoulomb limit set by standards, because we want our customers to go years without having to troubleshoot insulation issues.<\/p>\n

Another critical factor is the ambient conditions the switchgear will operate in, which changes the required dielectric strength. For example, customers installing switchgear in desert climates with temperatures that swing from -10\u00b0F to 120\u00b0F can\u2019t use the same insulation as someone installing in a tropical rainforest with 95% humidity year-round. At high temperatures, insulating materials like epoxy can lose up to 20% of their dielectric strength, so we adjust our design to use higher-grade epoxy with a thermal rating of 155\u00b0C, which maintains its dielectric properties even when operating at 100\u00b0C internal temperatures. For coastal installations where salt spray is a problem, we use silicone rubber insulators with hydrophobic coatings, which repel water and prevent the formation of a conductive layer on the surface that would lower the effective dielectric strength. We had a customer in Dubai a few years ago who told us their old switchgear failed every summer because of high humidity\u2014when we upgraded their insulation materials and adjusted the dielectric test voltage to account for their local conditions, they haven\u2019t had an issue in six years.<\/p>\n

Then there\u2019s the issue of transient overvoltages\u2014think lightning strikes or switching surges that happen in milliseconds. These overvoltages can be two to three times the normal operating voltage, so the dielectric strength of the insulation has to handle that spike without breaking down. That\u2019s why our switchgear is designed with impulse withstand voltage requirements too. For a 15kV unit, the impulse withstand is 95kV, and for 35kV it\u2019s 200kV. This test simulates a lightning strike hitting the power line, and we\u2019ve had customers tell us these impulse tests made all the difference when a nearby storm took out a competing unit but theirs kept running. I still get a message every year from a food processing plant in Iowa that told us their switchgear kept their production line running during a derecho in 2020, when thousands of other units failed due to insulation breakdown from surge voltages.<\/p>\n

A common mistake we see new customers make is cutting corners on dielectric testing to save money. A few years ago, a mining company approached us after switching to a cheaper brand of 15kV switchgear that kept failing during their night shifts, when load surges were highest. They\u2019d only paid for the power frequency withstand test at the factory, not the impulse or partial discharge tests. When we tested the units they had on-site, their dielectric strength was 30% below what was required for impulse voltage, and the PD levels were over 200 picocoulombs. We worked with their engineering team to replace the insulation in those units and supplied our own gear that met all the required test thresholds, and they\u2019ve been a loyal customer ever since. That experience taught me that dielectric strength isn\u2019t just a technical spec\u2014it\u2019s a safety and reliability issue that can make or break a customer\u2019s business.<\/p>\n

So what does all this mean for our customers when they\u2019re specifying medium voltage switchgear? It\u2019s not just about picking the right voltage class\u2014it\u2019s about making sure the dielectric strength is tailored to their specific operating environment, that all required tests are performed, and that there\u2019s a margin for unexpected conditions. Here at our company, we don\u2019t just sell you switchgear and walk away. We work with each customer to assess their site conditions, their load requirements, and any local regulations before we even design the unit. For example, a substation in a remote area with limited maintenance access needs higher dielectric strength and more robust insulation than a unit in a facility with a full-time electrical team. We also provide full test reports with every unit, including dielectric strength test results, PD levels, and impulse test data, so our customers can show compliance to their utilities and insurance providers.<\/p>\n

I know that for many people in the industrial or power sector, dielectric strength sounds like a technical buzzword that\u2019s hard to wrap your head around. But the bottom line is this: if your MV switchgear doesn\u2019t meet the required dielectric strength for your application, you\u2019re putting your team at risk of arc flashes, your equipment at risk of downtime, and your business at risk of costly repairs or lost production. In the 12 years I\u2019ve been in this industry, I\u2019ve seen more avoidable issues come from insufficient insulation and low dielectric strength than from any other technical failure. And with more facilities adopting renewable energy sources like solar and wind, which add variable load to the grid, the demand for reliable, high-dielectric switchgear is only going to grow.<\/p>\n

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If you\u2019re in the market for medium voltage switchgear, or if you\u2019re experiencing issues with current insulation performance, we\u2019d be happy to walk through your specific needs with you. Our team has decades of experience working across industries, from manufacturing and mining to power utilities and renewable energy projects, and we can help you specify the right dielectric strength requirements for your site. Don\u2019t settle for units that just meet the minimum base specs\u2014insist on testing that accounts for your environment, your load, and your long-term reliability needs. Reach out to our team to discuss your project, and we\u2019ll provide a customized solution tailored to your requirements.<\/p>\n

Step Up Transformer<\/a> References
\nIEC 62271-100, High-voltage switchgear and controlgear – Part 100: AC switchgear and controlgear for rated voltages above 1 kV and up to and including 52 kV
\nANSI C37.06, American National Standard for AC High-Voltage Circuit Breakers Rated on a Symmetrical Current Basis
\nNEMA SG-6, Standard for Switchgear, Medium Voltage, 1 kV through 38 kV, AC<\/p>\n

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Huachi Electric Co., Ltd.<\/a>
We’re well-known as one of the leading medium voltage switchgear manufacturers in China, featured by quality products and good service. Please rest assured to buy customized medium voltage switchgear made in China here from our factory. Contact us for more details.
Address: Plastic Park, Tongyu Street, Luqiao District, Taizhou City, Zhejiang Province
E-mail: HCDQ2026@163.com
WebSite: https:\/\/www.huachi-electric.com\/<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

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