We are independent & ad-supported. We may earn a commission for purchases made through our links.
Advertiser Disclosure
Our website is an independent, advertising-supported platform. We provide our content free of charge to our readers, and to keep it that way, we rely on revenue generated through advertisements and affiliate partnerships. This means that when you click on certain links on our site and make a purchase, we may earn a commission. Learn more.
How We Make Money
We sustain our operations through affiliate commissions and advertising. If you click on an affiliate link and make a purchase, we may receive a commission from the merchant at no additional cost to you. We also display advertisements on our website, which help generate revenue to support our work and keep our content free for readers. Our editorial team operates independently of our advertising and affiliate partnerships to ensure that our content remains unbiased and focused on providing you with the best information and recommendations based on thorough research and honest evaluations. To remain transparent, we’ve provided a list of our current affiliate partners here.

What is Dielectric Strength?

By Paul Scott
Updated May 17, 2024
Our promise to you
About Mechanics is dedicated to creating trustworthy, high-quality content that always prioritizes transparency, integrity, and inclusivity above all else. Our ensure that our content creation and review process includes rigorous fact-checking, evidence-based, and continual updates to ensure accuracy and reliability.

Our Promise to you

Founded in 2002, our company has been a trusted resource for readers seeking informative and engaging content. Our dedication to quality remains unwavering—and will never change. We follow a strict editorial policy, ensuring that our content is authored by highly qualified professionals and edited by subject matter experts. This guarantees that everything we publish is objective, accurate, and trustworthy.

Over the years, we've refined our approach to cover a wide range of topics, providing readers with reliable and practical advice to enhance their knowledge and skills. That's why millions of readers turn to us each year. Join us in celebrating the joy of learning, guided by standards you can trust.

Editorial Standards

At About Mechanics, we are committed to creating content that you can trust. Our editorial process is designed to ensure that every piece of content we publish is accurate, reliable, and informative.

Our team of experienced writers and editors follows a strict set of guidelines to ensure the highest quality content. We conduct thorough research, fact-check all information, and rely on credible sources to back up our claims. Our content is reviewed by subject-matter experts to ensure accuracy and clarity.

We believe in transparency and maintain editorial independence from our advertisers. Our team does not receive direct compensation from advertisers, allowing us to create unbiased content that prioritizes your interests.

Dielectric strength is an engineering term that refers to the maximum voltage an insulating material can withstand before breaking down or failing. This is a definitive characteristic of insulation materials and is used to grade new types or test the integrity of existing installations. Dielectric strength tests typically consist of exposing insulators to short duration, high voltage values while scanning for leakage or insulation breakdown. The voltages used to test the dielectric strength of insulators usually range from 5,000 to 400,000 volts (5–400 kV). Oils used as insulators in transformers and switchgear are checked by tapping a small sample and testing it in a specialized test rig.

Insulation breakdowns are a major cause of electrical failures and accidents which cause millions of dollars of damage and many, often fatal, injuries every year. Establishing the integrity or dielectric strength of insulating elements is an important part of any electrical installation's maintenance regimen. It is also a critical part of the development of new insulating materials. The dielectric strength of any insulator is the maximum voltage it can withstand without failing. This is established by exposing the insulating material to very high voltages in an environment where leakages or breakdowns of the insulation are accurately measured.

Also known as hipot testing, dielectric strength testing is carried out by a wide selection instruments with differing capacities. These range in size and output values from small bench top units capable of generating test voltages of 5 kV to large installation testers which can have outputs of 400 kV or more. Insulation testers may feature alternating current (AC) or direct current (DC) outputs with current values ranging from approximately 10 mA to 400 OVA. Specialized testers are also available which can test the breakdown values of fluid samples taken from transformer and switchgear oil baths.

The testing of insulating oil is particularly important because the dielectric strength of these fluids are subject to many environmental variables such as moisture and carbon contamination. Moisture in insulating oil is a major problem caused by the condensation of airborne moisture inside the transformer casing. Only small amounts of moisture are necessary in a large transformer's oil bath to cause a catastrophic failure. For this reason, regular tests should be carried out to establish the dielectric strength of switchgear and transformer oil. Solid insulators such as the PTFE sheaths on high tension cables can also degrade with time; exposure to ultraviolet radiation, chemicals, and lubricants or excessive heat and should be tested regularly to ensure their integrity.

About Mechanics is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Discussion Comments
By SkyWhisperer — On Aug 09, 2011

@everetra - Unfortunately, you have described a reality that tends to be more common than it should be.

I remember seeing a picture of a substation fire. It was an extreme amount of electricity, and you could see several successive photos where large electric arcs were forming above the substation, (kind of like a Tesla’s coil) before the fire engulfed it.

I don’t know what the voltage range was for the dielectric testing of insulating equipment in the utility industry, but I would venture to guess that someone didn’t properly test that substation equipment.

By everetra — On Aug 09, 2011

It appears from the article that in order to really test the dielectric levels of insulators, the voltages have to be pretty high.

I imagine then that you could have a situation with a poorly insulating material, but which didn't break down because there was never a large enough spike in voltage to create a problem.

This would create a ticking time bomb, in my opinion. These materials would be inherently defective, in that sense, but the defects would not show up unless they hit a really huge spike in voltage.

By allenJo — On Aug 08, 2011

Dielectric strength is a concept I remember back in the good old days when I was an electronics hobbyist.

I used to build circuits and the components would have various resistance levels. Capacitors, in particulars, were defined by their electrical charge and their dielectric strength. The plates that separated the capacitors provided resistance and the net effect was that it would increase the capacitance of the component.

About Mechanics, in your inbox

Our latest articles, guides, and more, delivered daily.

About Mechanics, in your inbox

Our latest articles, guides, and more, delivered daily.