Electrical Acceptance Testing for Wind Energy Sites

Good design and good construction means reduced maintenance costs


The wind industry in North America is booming. Yes, it always seems like it’s on a roller coaster, but 2015 looks to be the best year ever. The USA already has over 62GW on-line, but a further 14GW are under construction with completion expected by the end of 2105. An additional 5 GW are in the final stages of development. AWEA’s best estimate is 80 GW by Jan 2016.

Any way you look at it, that’s a lot of energy — requiring a lot of construction in a fairly short period of time. The race is now on to complete projects and get them commissioned and making power as soon as feasible.

That’s all fine and good, but it is also critical that the sites are energized safely and with the best chance for reliable performance for the years to come.

At the end of the construction phase, all of the good work of the various contractors comes to a conclusion and it’s time to assure it was all done according to specification. That’s where site acceptance testing comes in. But which electrical components should be tested? What testing criteria should be used? Most importantly, who should perform the testing? Let’s see…

The high-voltage components of a wind project normally include everything outside of the turbine itself. In some designs, the step-up transformer is located inside the turbine, so that should be considered as well; but as those designs are always dry-type units, the testing has a different scope.

For our purposes, let’s look at a traditional design where the step-up is an external oil-insulated pad-mount transformer at each turbine, feeding a collection system at high voltage through a series of collection points, and finally brought together at a utility-grade substation for transmission onto the grid.

Here, the critical elements are the multiple transformers, the collection cables and the related splices, terminations, as well as the ground scheme. Of course, the substation is a project in itself, and includes all of the typical utility equipment: GSU transformer, protective relays, switchgear, and grid reliability communications devices.

All of that is pretty obvious; what is really being tested falls into three distinct areas:
• Did the engineering firm design the system properly so it will be safe and reliable?
• Did the OEM of the equipment supply what was intended? Is it in proper working condition?
• Did the electrical contractor correctly assemble and install all of the components?

It is also critical that all one-line drawings be confirmed and/or updated to accurately reflect what was actually built. This is critical for future maintenance inspections and testing. One often-overlooked — but important — element of the acceptance process is the confirmation of any coordination studies, arc flash hazard analysis, and other safety-related component testing.

According to both the NFPA 70B Recommended Practice for Electrical Equipment Maintenance and the CSA Z463 Guideline on Maintenance of Electrical Systems, it is critical to safety compliance that the equipment work properly when energized. This can only be confirmed by initial testing as well as periodic testing. Establishing a solid baseline for trending analysis is also useful for Preventative (PM) and Predictive Maintenance (PdM) planning. So, reliable performance, reduced maintenance costs, and a safer work environment are all drivers for competent and thorough acceptance testing.

Of course, the manufacturer’s specifications and recommendations should always be followed, but the overall system performance is evaluated based on visual and mechanical inspections, electrical testing, and comparison with expected testing values. To that end, industry consensus standards have been developed to assure proper consideration is given to this testing.

Since 1972, the International Electrical Testing Association (NETA) has published Standards for Acceptance Testing for Electrical Power Equipment and Systems (ATS), and, since 1975, the companion MTS Maintenance Testing Standards. In 2013, the ATS was approved as an American National Standard (ANSI). These documents provide both the test methodologies and expected results for testing most types of electrical equipment and serve as the basis for a good acceptance test plan.

Additionally, NERC/FERC guidelines provide critical information for substation settings and reliability expectations. Experienced engineering support and well-trained technicians should be very familiar with these standard procedures, and should be able to apply them to the unique requirements of a wind generation facility.

The value of testing by a true third party is that the scope of work and the expected results are defined and managed by the hiring owner of the wind site. This assures a true, unbiased review of the engineering and construction before commissioning and take over. Many problems can be identified and rectified while the site is still offline, reducing incidental losses and allowing the responsible contractor address the issue safely and efficiently.

The technicians who perform the testing should be well-trained and experienced. Again, ANSI/NETA Standard for the Certification of Electrical Testing Technicians (ETT) is well established as a benchmark for qualifications.

Each testing crew should be led by a Level III or higher certified technician, and all crew members should be capable of completing the testing with a complete knowledge of the hazards involved as well as the ability to make decisions regarding the serviceability of the equipment and system.

A company that is designated as a NETA Accredited Company will meet all of these criteria. It is the site owner’s responsibility to provide all of the engineering documentation such as short circuit analysis, coordination studies and protective device settings as well as drawings and equipment manuals.

Qualified testing companies can review the scope and jointly develop a plan for testing. They should notify the owner before any testing and report the results of any deficiencies as soon as practical so corrections can be made. A detailed final report including baseline results should also be provided in a timely manner.

Good electrical system design should always include consideration of the maintenance that must be performed over the life of the system. Acceptance testing can be useful in confirming the effectiveness of this aspect, as well as establishing the baselines required for performance trending.

Wind generation sites do have a specific set of performance issues that should be addressed. Often, due to cost restrictions possibly based on short the financial goals, there is little consideration given to the future cost of maintenance.

Good examples include the current issues many sites face with oil-insulated transformers that were built and installed according to specification but are not proving reliable in the field. Knowing this is an issue, the testing company should provide trending oil analysis during the acceptance process.

There have also been many issues with faulty high-voltage cable terminations and splices within the collection system. These cables should be tested carefully using sensitive equipment to assure that no imminent faults exist, not just the typical high potential testing.

What about the turbines? Since turbine commissioning typically falls to the OEM, they hold the risk for any premature failures. Certainly, however, a full set of test results and warranty actions should be made available for each turbine before the responsibility is assumed by the owner at the end of warranty. All of these test results, especially those that can trended, should be utilized in conjunction with a condition based monitoring plan to form the basis for good maintenance planning.

Acceptance testing, therefore, should be more than just a final step of the construction phase of a project. It should be utilized to assure that the owner is getting what he is expecting: a well-designed, properly constructed, and safe power generation facility.