DNV GL’s LVRT testing solution

The wind energy segment has witnessed several key developments over the past few years with increased capacity additions, allocations through competitive bidding and a reassessment of the country’s wind energy potential. However, evacuation of the growing wind energy capacity is becoming a challenge due to the lack of proper grid infrastructure, which leads to voltage fluctuations and reactive power. A cost-effective and efficient solution to help wind turbines cope with the dip in voltage and recover from it during grid integration is low voltage ride through (LVRT).

At the Windergy 2017 forum held in April, DNV GL launched a full suite of LVRT testing solutions in India. The Norway-based company has many years of experience in the segment and has conducted 20,000 LVRT tests on 50 different wind turbines.

In order to enable smoother grid integration, the Central Electricity Regulatory Commission (CERC) recently released grid code guidelines, wherein it has mandated these tests to be conducted on all grid-connected wind turbines. With increased wind energy capacity expected to be added to the grid every year, the challenges of voltage dip and recovery of the wind turbine assume greater importance. Mathias Steck, executive vice-president and regional manager, APAC, Energy and Renewables Advisory, says that lack of LVRT testing could be detrimental to the entire power system in the region and hence making it mandatory is a good move by Indian regulators. This was the case in western China where wind farms could not take the low voltage dip and had to be shut down, which created a huge gap in the grid. Following this, China made LVRT mandatory for wind turbines.

DNV GL’s test time is typically around three months, which could increase or decrease depending on the wind turbine and ambient conditions. The container is located between the grid and the turbine through which medium to low voltage conditions are simulated to test the turbines reaction and its low voltage ride-through capability. The turbine operators then receive a test report and data record, which consist of dip master information, relevant data, remaining voltage and affected phases, among other details.

There are currently 25 test facilities operating across the globe, most of them owned and maintained by DNV GL. According to Steck, even though the Indian market is relatively new, the company is planning to set up one facility in the country, given the wind energy potential and the upcoming capacity. The company has brought in its team from China to cater to its current orders in India, which is also training the Indian team to handle the equipment, as it needs extreme care to deal with the high voltages.

New turbines that have not yet been installed will undergo LVRT testing once in their lifetime before commissioning. Further, if new variants of this turbine are introduced, depending on what has changed, the turbine might have to undergo the test again. However, the testing of existing turbines is not as easy as it requires the testing of very old generators that may not sufficiently respond to voltage changes. The LVRT test contributes to a one-time marginal increase in the capital cost of the wind turbine, about 2.5-3 per cent. Of the additional cost, the largest component is the rental charge of the testing container. The test could run simultaneously with generation from the turbine and only one turbine would have to be tested to assess the LVRT capability of the entire wind farm, thereby keeping the opportunity costs negligible. DNV GL is currently marketing its services in India as a package deal for new turbine models, which includes load measurement, noise measurement, power quality and LVRT. However, for its existing turbines, there will be a stand-alone testing service.

DNV GL is currently working with one client in India and trying to create awareness about the LVRT concept. While there is a huge demand for LVRT in the country following the CERC mandate, the seasonality of winds poses a major challenge for LVRT testing. Testing is usually restricted during the period between May and September, which, according to Steck, will increase the backlog of orders for testing in India. Besides, there is little awareness regarding LVRT in the country, despite the CERC’s mandate. In addition, there are logistical challenges associated with the transportation of sensitive equipment to remotely located wind farms, which could damage the equipment.