A Negative-Phase-Sequence-Overcurrent Relay for Generator Protection [includes discussion]

Negative Sequence-Based Schemes for Power System Protection - Review and Challenges

“…ANSI standards allow negative sequence current 2 of 5-10% in generators with short time limits defined as ( 2 ) 2 t [7]. Unbalanced currents causes the negative sequence component of current in the stator of the generator to rise [8]. These unbalanced conditions result in heating of the rotor that leads to mechanical stress on the rotating components due to induced double frequency currents caused by these negative sequence currents [7].…”

“…Reference [7] showed a detailed structure of the negative sequence overcurrent relay. The negative sequence current components have serious effects on the supersynchronous resonance of turbine blades, so that [8] suggested using Static VAr Compensator (SVC) to reduce or block the negative sequence current at generator terminals. This method could be considered the most suitable via blocking the negative sequence current; as long as the compensation circuit is guaranteed to operate only during unbalanced events and with very well designed harmonic filters.…”

“…However, [39] discussed using the compensation algorithm with neural networks by providing a CT inverse function. Reference [8] argued that the neutral CT with its lower ratio (to calculate zero and negative sequence current) provides greater sensitivity than higher ratio phase CTs.…”