Today, I’ll give you a quick rundown on the difference between live front bushings and dead front bushings. Before we dive in, if you need to brush up on how transformers work, I recommend you check out our comprehensive guide to electrical transformers.
What is a transformer bushing?
A transformer bushing is an insulator that allows a conductor to pass safely through the tank wall of a transformer without making electrical contact with it.
What is a live front bushing?
It’s called live because the terminal is actually exposed. There is electricity flowing through it. Touching a live front bushing could result in electrocution. As a matter of fact, you don’t want to even get too near due to arc-flash concerns.
Parts of a transformer live front bushing
The bushing itself has several components. A spade is at the top of the bushing. This is the place where the actual termination is made with a mechanical lug or a crimp lug. Below the spade are the bushings made up of little ridges called waffles or sheds. These waffles help protect against something called creep. Creep is where a tiny arc travels across a surface area by “creeping” along with some small amount of water, dust, or oil. Waffles provide the necessary clearance to prevent creep by providing a larger amount of surface area. Finally, there is a stud where the bushing internally connects to the transformer core and coil.
What is a dead front bushing?
The majority of padmount transformers these days come with dead front bushings. These do the exact same thing as a live front bushing but it uses a fully insulated bushing. The obvious benefit is that you can open the cabinet and there is a very low risk of arc-flash. The fully rubber dead front bushing is terminated using a loadbreak elbow.
Both options have suitable applications.