Modern Protective Relay Enables Generator Operating at Wide Range of Frequencies and Different Phase Rotation

This paper presents application and performance of microprocessor-based protective relay when applied to a bi-directional generator. The two-shaft gas turbine drives the generator to deliver energy to local load or to the grid. This generator is unconventional in design and operation with the capability of delivering power at a wide range of frequency as low as 10Hz and different phase rotation. Traditional generator protection when applied to such generator application faces several challenges, such as: Performance limitation of instrument transformers at low-frequency operation Frequency impact on the phasor estimation Reduction in the output capability of the generator with respect to frequency - impacting power-based protection functions Change in the generator output voltage with respect to frequency to maintain the V/Hz ratio Improper operation of unbalance protection due to change in phase rotation Varying load flow level and direction results in the improper operation of protection functions like out-of-step, loss of excitation, reactive power, power factor, distance protection, etc. Ability to switch phase rotation for pumped storage applications.