All articles img

Bushings Testing and Maintenance: Why Preventative Care is More Important Now Than Ever Before

September 22, 2023

As key components of HV substations, bushings allow conductors to transfer energy from one insulated medium to another. To understand transformer bushings and their importance, we need to first understand the function of a transformer.

Transformers are used to step up or down an electrical voltage supply. Aiding the transformer to safely distribute a high, low, or medium voltage supply is the bushing. A bushing is an electrical insulator, allowing safe passage of electrical current while preventing unwanted incidents.

Bushings are internally insulated by using a variety of methods including:

• Oil-impregnated paper

• Resin bonded paper

• Resin-impregnated paper

• Or SF6 gas

Being such an integral piece of equipment on HV power transformers, bushings failures can cause catastrophic loss of power and revenue due to long replacement lead times. Which is why the regular testing and maintenance of bushings is so important by today’s standards. In addition to the potential of significant loss of revenue, there are also high safety risks to surrounding equipment and personnel should a bushing not perform correctly. To avoid any safety hazards or significant loss of power distribution and revenue, it is critical to maintenance your existing equipment to extend its life.

Routine maintenance tests fall under two categories: Field and Laboratory. Each have their own pros and cons, which are ultimately determined on a case-by-case basis.

Field Testing

Field testing provides the monetary benefit such as little to no outage time, especially when using an online monitoring system. While field tests can prove effective, they also pose constraints due to the limited amount of testing that can be conducted in the field to determine bushing health and longevity. In addition, field testing is currently limited to low voltage equipment.

Laboratory Testing

Lab testing opens the door for a wide range of testing to determine overall bushing and transformer health. Since the lab equipment is far more sophisticated when compared field testing, solutions for maintenance and repairs are easily determined. The downside, of course, is the cost. When factoring in outage time, plus the cost of shipping the bushing to the lab, laboratory testing tends to be more costly. However, the cost for testing and maintenance upfront equates to pennies on the dollar should a bushing need to be replaced, especially when exponentially long lead times for delivery are factored in.

Bushing Testing Methods

Measuring power factor and capacitance are the two most common field bushing tests. Both of which can accurately diagnose issues for up to 10kV. In addition to these field tests, bushing testing methods consist of:

• Online monitoring

• Thermography

HV lab, or OEM test floor methods also consist of testing for capacitance but includes dissipation factors. Laboratory testing includes not only an oil analysis but incorporates a simulated operating environment for thorough diagnosis.

As a proponent of grid modernization, Voltyx is an integrated solutions provider focused on guiding our partners through the intricacy of modernizing the electrical infrastructure. Through vision, strategy, service, and support, Voltyx and its’ family of operating companies offer robust services for the energy industry including maintenance, acceptance testing, installation, and commissioning. For more details on these services and how Voltyx can assist with your energy site, visit or email us at

About Voltyx

As the holding company of five operating companies – EPS, NASS, EPST, TLS, and NOMOS, Voltyx is an integrated power solutions provider focused on guiding our partners through vision, strategy, service, and support. The Voltyx family has served the electrical grid for more than 40 years and is united at the core by providing exceptional testing, engineering, maintenance, grid equipment, and cyber security services. Our reputation for safety, innovation, and service is built on a foundation of well-leveraged resources and competencies, driving reliability back to our partners.

For more information about Voltyx and our family of operating companies, visit