Protection Testing of a Real-Time Generator Relay and a Physical Relay with a Real-Time Synchronous Machine Model

Protection of an organisation's generator is a wise investment, and many fault scenarios need to be considered before the relay engineer is satisfied with his/her protection application and the generator is adequately protected against electrical faults. Simulation of these fault scenarios was not readily available with conventional d-q based machine models. Therefore a previously introduced real-time electromagnetic transient synchronous machine model, useful for testing stator-ground fault protection schemes, is used for closed-loop tests involving a physical relay and a real-time relay model. This machine model requires the knowledge of actual distribution of the windings in addition to the d-q parameters of the generator under study. Conventional d-q based synchronous machine models also lack the ability to test differential protection schemes because faults can not be placed within the windings. This presentation discusses a synchronous machine model that can use d-q data and also simulate faults within the windings without knowledge of the winding distribution to test generator differential protection schemes. Setting a '100% Stator Ground Protection Scheme' based on 3rd harmonic in a proper manner requires taking voltage measurements at various loading conditions and is the recommended method for providing a secure setting. Because the ground protection is not securely set until these measurements are taken and these measurements require the generator to be loaded from 0 to 100% load, the protection engineer must use a less secure method for stator ground protection during these load measurement tests. Testing Phase Differential Protection with conventional d-q models is not possible because the phase currents are not available from within the generator; they are normally only available at the generator terminals. Generally the new phase-domain real-time machine model requires physical machine data for the windings. However conventional d-q data can be used to generate the inductances of faulted windings (based on the assumption that the original windings were sinusoidally distributed). When d-q data is used, the model will not provide the proper 3rd harmonic characteristic but it will provide access to the phase currents from within the generator and the terminals, thus it is possible to fully test the phase differential protection during the simulation. When testing protection relays it is necessary to inject voltage and current at nominal secondary and transient levels. However because of high fault levels, it may not be feasible to subject a physical relay to numerous faults while the relay engineer is setting up the simulation, relay settings and fault scenarios. Having a real-time relay model is the next best thing to having a physical relay in a closed loop test environment. The protection engineer can fine-tune his/her simulation parameters and relay settings without risk of possible damage to the physical relay or the voltage and current amplifiers.