Safely managing electrical power assets at wind farms

By Kerry Heid, President & CEO
Shermco Industries

This article is part of Windpower Engineering & Development’s February 2017 issue. A complete digital version of the issue is here.

A few years ago, the InterNational Electrical Testing Association (NETA — an organization that offers standards and accreditation of third-party electrical testing) conducted a study that showed 23% of protective devices in electrical distribution systems, such as circuit breakers, do not follow their proper operating characteristics. In fact, the study also found that over 10% of installed circuit breakers failed to function at all.

While the likelihood of a faulty protective device in an electrical system depends on several factors, such as usage, design, manufacturing type, and the operating environment, NETA’s results serve as an important safety reminder to the utility and wind industries. Typically, components that are engineered to protect electrical equipment (and worksite personnel) upstream are exercised regularly on, but can sit idle for weeks or months at a time. They remain “mechanically frozen” until one day these devices are expected to kick-in and work on demand.

A proper understanding of how a circuit breaker works and is tested (including how those results are analyzed) is critical for a well-maintained site — even if repairs or overhauls are performed by an outside contractor. Ultimately, the facility owner or manager is responsible to ensure all breakers and electrical systems are routinely tested for reliability and, most importantly, safety.

One downside of component failure in non-life threatening mechanical equipment is downtime and lost revenue. Component failure of an electrical system, however, can have devastating results. Engineers and technicians working in electrical environments today often take extra precautions against flash hazards by suiting up in full flame-resistant gear with flash-resistant face shields — even when opening an inverter enclosure or a transformer that’s in seemingly ideal working order.

An “arc-in-a-box” – the incident energy for an arc in an enclosure also called flashover – means that opening the door sends all that energy directly outside towards the worker.

Safety must remain paramount at electrical sites. That is the message from organization such as NETA and the CSA Group, which provide guidelines and best practices on how to work more safely around electricity. These guidelines have been of particular relevance in Canada, which only recently published a national guideline for electrical equipment maintenance. CSA’s Z463 – Maintenance of Electrical Systems is an advisory document intended to close the gap in Canada between safe electrical equipment design and installation (covered by the Canadian Electrical Code) and O&M equipment procedures.

CSA Z463 is currently a voluntary guideline but it is based on principles of predictability, due diligence, expected failure modes, and pre-emptive scheduled maintenance to avoid system downtime and, most importantly, risk of serious personnel injury. In combination, NETA and CSA standards cover switchgear, transformers, power cables, switches, circuit breakers, relaying protection, and rotating machinery. CSA Z463 is currently going through a revision process, which will convert it to a standard that’s released in 2018.

Unfortunately, most hazardous electrical events happen when someone is operating the equipment posing significant risk of personnel injury and loss of equipment. That is why it is imperative to follow good standards and ensure electrical equipment and devices are in good working order from the start. Here are some tips.

Acceptance testing & commissioning
Field-acceptance testing should adhere to NETA standards and occur before electrical systems are energized for the first time. This process involves certified engineers and technicians going to a site with appropriate field-testing equipment to:

  • Fully test and re-test equipment such as cables, transformers, and generators. This includes stressing the insulation of cables and looking for defects in terminations.
  • Inspect equipment for manufacturers’ faults or defects from transportation or installation issues.
  • Check engineering design functions of components and make sure instructional drawings match the installation work.
  • Test contractor’s installation methods and craftsmanship.
  • Verify equipment works together as a system.

It is important to log this process because it provides a critical baseline of data prior to powering the system. This baseline data should be used for the lifespan of the electrical power-distribution equipment.

Routine maintenance
Once equipment is verified and off to a good start, it is essential to set up a routine maintenance program. Equipment maintenance is critical to the reliability of electrical distribution systems, system uptime, and to avoid a catastrophic failure or dangerous arc or ground faults.

There are two types of maintenance for electric distribution systems: online and offline.

Along with electrical contractor licensing, it is important that site workers receive specific training regarding electrical power plant maintenance and testing, and that employers hire staff with the appropriate qualifications. Here qualified workers are performing a medium-voltage test as part of the site’s regular electrical system maintenance program.

Offline testing involves powering off all energized systems to safely access equipment (so it is safe to touch by hand) for testing. Technicians will need to partially disassemble electrical systems to hook up the appropriate test equipment.

It is important to test all cables and insulation systems, and simulate faults to check for ground and arc faults, and potential short circuits. NETA is an ideal source to follow for electrical equipment maintenance because it provides specific and step-by-step guidance on equipment testing and what to look for with each different component.

Online testing means there is a lot that technicians can check without shutting electrical equipment down. For instance, it is possible to use infrared scans and corona cameras. Infrared cameras locate heat sources and can be used to check electrical connections and spot temperatures that exceed expected operating temperature. A corona camera (corona is the ionization of the nitrogen in the air, caused by an electrical field) can measure arcing across an insulator and help spot insulation degradation issues.

It is also advisable to test oil samples from transformers, another basic online maintenance practice. A routine online and offline maintenance plan is essential to avoid electrical downtime and prevent more serious problems.

Worker qualifications
Worker competency has become a major issue in the electrical industry. Just as it is essential to ensure electrical equipment is in top working order, it is just as important to ensure those installing, testing, maintaining, and working near electrical systems are fully qualified to do so.

Just because someone is an electrician does not mean they are certified to work on a balance of plant at a wind farm. He or she may know how to safely work around live wire but if their career was focused on residential or commercial construction, those electrical systems are very different than at a power plant.

Electricians, engineers, and technicians all have different skillsets and qualifications depending on the sector worked in. Specified training and experience are keys to properly installed and maintained utility and wind-power plants. Training is also imperative to worker, and full crew and site safety.

Beyond electrical contractor training and licensing, it is important that workers receive specific training regarding electrical power plant maintenance and testing — and that employers hire staff with the appropriate qualifications. NETA currently offers four levels of certification for electrical test technicians for electric distribution power systems. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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