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This paper was written by a Working Group of the IEEE Power System Relay Committee to provide guidance to the industry to better coordinate generator protection with generator control. The paper discusses specific calculation methods that can be used to insure generator protection and excitation system control are fully coordinated. It also specifically addresses the coordination of relays with generator full load capability and machine steady state stability limits. Because of recent blackouts, NERC (North American Electric Reliability Council) is developing standards [1-3] for the coordination of generator protection and control. This paper provides practical guidance on providing this coordination.

The fault behavior of an inverter interfaced distributed generator (IIDG) is determined by its control, which is significantly different from a conventional generator. This paper examines in detail the key features of IIDG's fault behavior with respect to interference with distribution protection. As an example, the fault behavior of a commercially available photovoltaic converter is shown through a hardware-in-the-loop (HIL) simulation using real-time digital simulator (RTDS). A case study is then performed using the HIL setup to investigate the impact of IIDG on the recloser-fuse coordination in the fuse saving mode. The results illustrate that due to fault current limiting behavior of inverters, IIDG marginally impact primary and back-up protection in a distribution system. But with high penetration level, IIDGs may disturb the recloser-fuse coordination.

Windfarm electrical systems present some unique challenges for protection. The grid tie and wind turbine generators provide multiple sources of fault currents to be considered. Collector feeders become isolated ungrounded systems during faults due to separation from the centralized collector bus reference ground. Ground faults on feeders will result in unfaulted phase voltages rising to line levels. In addition, severe transient overvoltages can be produced, which can degrade insulation, resulting in eventual equipment failure.This paper reviews the overall requirements for comprehensive windfarm protection. It also focuses on the particular problem of feeder ground faults. A novel, yet simple solution is presented that makes use of peer-to-peer (GOOSE) messaging via the IEC 61850 protocol. The characteristics of the GOOSE message are discussed with respect to speed and reliability and communications architecture is presented. The performance of the resulting protection scheme is quantified. Wind-Turbine Protection ConsiderationsThe type of wind turbine unit will have some bearing on the protection requirements. There are several WTG configurations in commercial operation today. This discussion focuses on the doubly fed induction generator (DFIG). Figure 1 shows a single line diagram of a typical WTG and the location of the IED.In this configuration a variable-pitch wind turbine is connected through a gearbox to a wound rotor induction machine. Back-to-back voltage-sourced converters are used to connect the rotor circuit to the machine terminals in order to provide variable speed control. The WTG step-up transformer has three windings. The high voltage winding is delta connected. Both LV windings have grounded-wye connections. One LV winding is connected to the stator circuit, the other to the rotor circuit. The high voltage winding of the transformer may be connected to the grid through a circuit breaker or through fuses. Figure 1 WTG Single Line 1-4244-0995-0/07/$25.00