Commissioning process and acceptance test of a sub-harmonic protection relay

Numerous technical papers have been published discussing the topic of SubSynchronous Resonance (SSR) and more recently about new protection devices capable of detecting and protecting against the detrimental effects of SSR. The advent of such protection devices has created the new challenge of testing and commissioning such devices. Commissioning subharmonic protection devices require following a process that differs from the traditional testing and commissioning process of microprocessor devices. This paper presents the experiences of the authors during the commissioning of Subharmonic Protection Relays and describes the process that was followed prior to the site visit and then during the actual commissioning of the relay. The paper will review the following topics: •The characteristics of a Sub-Harmonic Protection Relay •The engineering process for the determination of settings •The determination of test cases to make sure all the features of the relay are properly tested •The use of a real time digital simulator for the preparation of COMTRADE files to be used during the relay testing •The process followed at site to commission the relay by using advanced relay test equipment capable of playing back COMTRADE files. During the commissioning process of sub-harmonic protection relays the authors discovered that there is very little understanding on SSR and SSCI phenomena, on the engineering behind the selection of settings for sub-harmonic protection IEDs and on the process of testing and commissioning such IEDs, hence the need to educate the Protection & Control community. The paper describes the use of software capable of simulating and modeling power systems, similar to PSCAD™/EMTDC™ or RTDS tm for the creation of test cases in COMTRADE format that will be used to test de relay. Prior to the creation of test cases, the process requires the review of power system simulation cases that were used to determine the relay settings in order to create COMTRADE test cases that will confirm that the relay responds as expected. The process requires testing for: •Sub-harmonic frequency ranges - making sure the relay does not misoperate for frequencies outside the desire frequency range •Sub-harmonic magnitudes - making sure the relay does not misoperate for sub-harmonics with magnitudes below the set thresholds •Protection features at the fundamental frequency