A Genset (or a power generator set) is a machineused to produce electrical energy from fuel. Depending uponthe type of application, the electrical energy produced by thegenset may be used as prime power (absence of utility) or backup power (utility is prime power). This application guide forthe relay protection of synchronous generators presents areview of the generally accepted forms of protection for thegenerator and its excitation system. It summarizes the use ofrelays and devices and serves as a guide for the selection ofequipment to obtain adequate protection. The guide isprimarily concerned with protection against faults andabnormal operating conditions for large hydraulic, steam, andcombustion-turbine generators. This guide is not a standardand does not purport to detail the protective requirements ofall generators in every situation. Standby and emergency usegenerators are specifically excluded. However, sufficientbackground information relating to protection requirements,applications, and setting philosophy is given to enable the userto evaluate the need, to select, and to apply suitable protectionfor most situations.