During plant turnarounds or outages, you have limited time and resources to perform electrical maintenance, and it is important to prioritize the critical electrical equipment and equipment with the highest risk of impacting plant reliability. There are many predictive maintenance (PdM) technologies that can be applied prior to the outage to help assess the health of the electrical system. These technologies do not replace maintenance testing, but they can help you find some high-risk issues that must be addressed during the outage. Here are a few low-cost PdM activities that should be performed prior to any turnaround:
- Oil sample analysis. Perform oil sample analysis, including dissolved gas analysis, on all liquid-filled transformers and oil circuit breakers. A qualified person should pull the samples and send them to a qualified laboratory for analysis. When access to the sample ports is restricted or covered up, consideration should be given to the provision of a sample port extension capability so that oil samples can be taken easily and safely.
- Infrared Inspection. Perform infrared inspections, or thermographic surveys, on high- and low-voltage equipment where accessibility is not an issue. It should be noted this survey requires a direct line of sight to the area being surveyed to ensure acceptable results. This type of survey is very useful in identifying loose or bad connections, terminations and overloading conditions, and should be applied to electrical equipment (i.e., breakers, transformers, buses, surge arresters and cables terminations).
- Ultrasonic emission (UE) surveys. Perform UE surveys on high-voltage equipment only. It should be noted this survey requires a direct line of sight to the area being surveyed to ensure acceptable results. A UE survey is highly recommended for evaluating outdoor substation equipment with connections that are visible.
- SF6 gas analysis. For some higher- voltage devices, perform SF6 gas analysis for contamination, including moisture or air in-leakage. It should be noted many SF6 chambers are not provided with the capability for sampling. When sampling is not provided for, do not break the seal or distort sealed-for-life interrupters.
- Partial discharge (PD) testing (on-line). Perform a PD survey on high-voltage insulation systems. PD surveys are typically performed with a hand-held device with various sensors for different types of analysis (i.e., ultrasonic, capacitive-coupled or high-frequency current transformers). For critical buses, switchgear and cable terminations, consideration should be given to installing permanent sensors to accommodate PD surveys and trending. Additionally, capacitive couplers can also be installed in critical medium-voltage buses and motors to accommodate continuous on-line surveys and trending.
Use these technologies, as well as good old-fashioned physical inspections, to help determine priorities. Physical inspections should be performed on electrical equipment for the visual evidence associated with installation errors, equipment subassembly failures, poor equipment condition, overheating and corona. On outdoor, metal-enclosed switchgear, inspections should be performed to ensure proper structural integrity and weatherization. Performing InterNational Electrical Testing Association (NETA) testing on electrical gear will give you a much deeper dive into equipment reliability, but these technologies can help find major issues and can be accomplished with equipment running prior to the outage.
For more information, visit www.shermco.com or call (888) SHERMCO [743-7626].
