Big success for CT testing in India

Electrical Tester – 18 January 2019

Author: Ajay Goyal, Managing Director, Megger India

Current transformer test sets have long been in high demand in India, but users had only a handful of brands to choose from. However, Megger recently entered this challenging market and, in 2016, the company achieved a notable success by securing a single order from Power Grid Corporation of India Limited (PGCIL) for no fewer than 106 of its latest MRCT test sets.

During 2014, PGCIL planned to double the number of its 765 kV and 400 kV substations to over 200, with each substation having a minimum of 15 CTs. To ensure correct operation, it was essential for the key parameters of each CT to be verified against the manufacturer’s data as part of the commissioning process. To carry out this verification, PGCIL considered using primary injection testing, but this involves time-consuming set up procedures and the use of large, heavy test sets. The company decided therefore to adopt secondary injection testing.

A market survey of the available CT test sets showed that the Megger MRCT offered a number of key features that met PGCIL’s technical specifications. Before it was ready to place an order for the instruments, however, PGCIL needed to be sure that the instruments fully matched strict technical and commercial qualification criteria, and that they could be shown to operate satisfactorily on one of the company’s 765 kV sites.

When the Megger team examined the qualification criteria in detail, it found that, as things stood, it was unable to meet some of these. For example, the bidding documents stipulated that the instrument must have a performance certificate from a 400 kV substation in India. But after Megger had provided demonstrations at a number of PGCIL sites and engaged in in-depth discussions with the company’s engineers, PGCIL relaxed some of its bidding requirements. Megger’s Dallas factory then arranged for the remaining qualification documents to be supplied.

The next requirement was for Megger to demonstrate successful operation of the MRCT in a high noise 765 kV PGCIL substation but this was far from easy to arrange. To locate a site where the demonstration could be carried out, technical and product experts from Megger India travelled extensively to various regions of PGCIL and also visited private customers such as Sterlite Grid. However, they encountered numerous problems, including the difficulty of taking the plant out of service so that the tests could be performed, sites in hard-to-reach locations, and the need for multiple validation sessions to confirm that  the instrument was delivering accurate and repeatable results.

More technical discussions were then held, as a result of which Megger upgraded the MRCT to incorporate 4 kV knee-point voltage testing, a DC option, nameplate guessing and a turret CT testing feature. Adding these features was a major challenge, but the Megger team in Dallas managed to complete the work in just two weeks.

Megger India then tested and validated the new features on around 35 CTs (765 kV and 400 kV) in preparation for a final demonstration to PGCIL. For turret CT testing in particular, Megger made eight site visits and tested close to 40 turret CTs in 765 kV substations. This exercise revealed not only that the features had been correctly implemented, but also that they delivered better results than instruments from other manufacturers.

Finally, Megger carried out a formal demonstration of the MRCT for PGCIL, which confirmed that it fully met the PCGIL technical requirements and also showed that the multi-tap testing capability of the MRCT delivered big savings in test time compared with standard instruments. The exceptional performance of the MRCT, the willingness of Megger to enhance the standard design so that it complied with the tender specification and the company’s ability to demonstrate that all of PGCIL’s key requirements had been met, combined with very competitive pricing, allowed Megger to secure the order for 106 test sets.