Theses and Dissertations Collection

Evaluation of relay misoperations provides an opportunity to improve the design of

backup protection schemes. Existing generator station backup protection schemes use

distance protection (21) or voltage controlled/restrained overcurrent protection (51V)

elements for clearing phase faults that are not cleared by either line protection or

generator protection. Many schemes also use transformer ground overcurrent protection

(51NG) for backup protection for ground faults on the system. Since generator

protection can respond to faults with fault resistance accurately only when there is

no remote infeed from the other terminals, designing a secure backup protection for

a generating station during remote infeed conditions is a challenge. Apart from the

remote infeed, fast response of automatic excitation controllers also affects the current

seen by the generator protection relay. Considering these effects, different vendors

have different approaches for setting the 21 element. In order to analyze these recommendations,

this thesis studies the performance of backup protection schemes

applied at a thermal power station connected through a breaker and half scheme

using Real Time Digital Simulator (RTDS) simulations. This thesis proposes a new

approach to enhance the performance and coverage of backup protection schemes by

using the IEC 61850 standard by using measurements from multiple VT locations

in the same relay to enhance protection security.. In addition to that, this thesis

also address the challenges associated with the existing generator breaker failure

protection schemes based on breaker auxiliary contacts and undercurrent elements

and proposes a solution using a synchronism check element which uses sampled

values. These two techniques can be used in existing generating station protection

schemes to improve the reliability and security of these schemes.