Ozone Smell Around Switchgear? Next Steps

Why do I smell Ozone around switchgear?

Anyone who has spent time in substations has probably noticed a metallic, chlorine-like smell every now and then. This smell is caused by ozone in the substation, but why is there ozone coming from switchgear, what is the significance, and what are the next steps? Ozone is one product of electrical discharge, the energy from a spark splits the O₂ molecules around it into O molecules, these molecules readily combine with nearby O₂ molecules to form ozone, O₃. Since ozone is created from sparks it is a good indication that there is surface partial discharge occurring on some equipment in the substation that can lead to catastrophic failure. Make it a practice when entering a switchgear room to smell for ozone and listen for the distinctive audible crackling sounds of partial discharge.

What is surface partial discharge?

Surface partial discharge, as the name suggests, occurs on the surface of insulation or between two pieces of equipment due to defects in the insulation, either from manufacturing or installation error. It can also be caused by dirt and dust buildup on equipment which can become conductive in high humidity. Surface partial discharge is the most common form of partial discharge. Even though PD is a very small discharge, over time it will break down the insulation and eventually cause failure. PD can occur on any equipment operating at or above 3.3 kV, some of the equipment where PD is most common are:

-Switchgear cubicles
-MV & HV cables and terminations
-Transformers
-Circuit breakers

Finding and eliminating partial discharge is one of the most important practices in maintaining equipment health. But once you are aware of partial discharge issues, what are the next steps?

Next steps after smelling ozone around switchgear

Another product of surface partial discharge is ultrasonic emissions. These emissions are typically above human audible range. However, using an instrument with an airborne ultrasonic microphone, like the UltraTEV Plus², these emissions can be detected and used to localize where the PD is occurring.

Ultrasonic detection is an online test, so the equipment does not need to be de-energized or removed from service. This allows many assets to be tested without causing a disruption to the operation of the equipment. Since ultrasonic emissions are a product of surface PD, after being detected, a visual inspection of the equipment can be carried out to find the discharge. PD breakdown of insulation causes electrical tracking and a white powder to build up on the insulation which can be easily spotted. An outage can then be scheduled to repair or clean the discharging equipment.

To learn more about Partial Discharge and the detection methods, check out our recorded webinar: Partial Discharge Testing Introduction below.