15 Sep 2023
By Don A. Genutis
After performing electrical testing for over 70 utility-scale renewable energy projects in 17 states, tallying over 5GW of renewable energy (enough to power over 1M homes!), experts in the field have discovered which maintenance practices provide the highest ROI for utility-scale solar investments. Per dollar spent, the following five electrical tests and techniques represent the most effective practices for preventing outages and increasing production. These practices cover the majority of common equipment failure modes in the most efficient manner possible. All these techniques can be performed safely without requiring an outage at solar sites.
1 Online partial discharge survey
Partial discharge is a partial failure of medium or high voltage insulation. Over time, this can progress to complete failure, resulting in unplanned outages and equipment damage. Conducting an online partial discharge survey is highly recommended as the highest ROI technique, but often overlooked by many maintenance providers who lack the necessary knowledge to employ this sophisticated technology. Statistics indicate that up to 90 percent of all medium voltage equipment failures occur due to partial discharge activity.
The good news is that partial failures produce signals that can be safely detected through a partial discharge test, while the electrical system remains in service. By safely connecting passive specialized split-core current sensors around the grounded MV cable concentric shields, experts can record electromagnetic signals to detect and analyze dangerous partial discharge events in the MV terminations, cables, and transformer windings, as well as in the MV breaker or MV switchgear assembly in applicable equipment design.
2 Dissolved Gas Analysis (DGA)
Many equipment designs incorporate fluid-filled transformers that are typically filled with FR3, a natural and environmentally-friendly fluid. Since transformer fluid is used to provide insulation and cooling for the transformer windings, the condition of the fluid is critical to transformer health. By taking a small fluid sample and performing laboratory analysis of the gases contained in the sample, abnormal transformer conditions such as arcing, partial discharge, and overheating can be detected. This information can then be used to plan remediation before complete failure occurs.
Examples of surface PD damage in MV Switchgear
3 Infrared thermography
Infrared cameras have been proven effective in detecting loose connections, which often contribute to a high percentage of conductor-related failures. Loose connections or overdutied components in inverters can lead to fires. In addition to detecting inverter connection issues, infrared technology can identify overheated connections in substation equipment. Not only are they safer for all involved (because they take the place of an on-site electrician), more recently, infrared inspections have become an efficient way to detect module problems such as open strings, damaged modules, and soiling. Using UAV drones to conduct module infrared inspections has been particularly effective in ensuring accurate condition assessment. Drones are also much faster—a maintenance electrician would need to drive all of the panels and scan them with a handheld instrument, adding time and expense.
4 Visual inspections
The value of simplicity should not be overlooked when it comes to maintaining electrical integrity. Visual inspections performed by qualified technicians play a crucial role in identifying various types of defects, ranging from abnormal transformer gauge indications to rodent ingress damage. Unfortunately, the importance of visual inspections is often taken for granted. To ensure the effectiveness of these inspections, it is essential to conduct them regularly, depending on specific equipment types. Additionally, checklists should be used to record and trend inspection results to provide a comprehensive overview of the equipment's condition. This practice helps in identifying any potential issues early on and allows time for prompt corrective actions.
5 Radio Frequency Interference (RFI) surveys
Radio frequency interference (RFI) surveys provide a unique approach to detecting defects in substations. Similar to the principles of partial discharge surveys, RFI surveys focus on identifying radiated signals caused by insulation defects. Outdoor substation defects create radiated signals that are emitted into the air, much like a small radio transmitter. Specialized antenna-based analyzers are used to detect and analyze RFI signals associated with defects in various equipment, including outdoor cable terminations, insulators, instrument transformers, capacitors, circuit breakers, surge arresters, and power transformers. To ensure comprehensive defect detection, it is recommended to complement RFI surveys with ultrasonic camera techniques for surface defect pinpointing, and infrared techniques for detecting thermal problems. By integrating these technologies, a thorough and complete assessment of substation defects can be achieved.
The five techniques described above provide excellent coverage for the most common types of equipment failure modes. They do so safely and efficiently, are cost-effective, and do not require an outage. Implementing these practices will help avoid unplanned outages, prevent equipment damage, and maximize production at your utility-scale solar power plant. In the end, the return on investment of implementing a comprehensive program incorporating all of these methods usually exceeds 20X ROI.
Don A. Genutis is a General Manager at HALCO, a RESA Power company. With over 35 years of experience in the power industry, Don is a true leader in electrical testing and a driving force in advancing no-outage testing techniques. He has authored 50 technical articles for NETA World, and has been featured in EC&M and Uptime magazines. In 2019, he published his book, "Partial Discharge & Other No-Outage Testing Methods," which summarizes his extensive work and findings. In 2023 HALCO Testing Services joined RESA Power.
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