Lightning protection for rotating machines

FIGURE 1 lists the valve-type machine-arrester and capacitor ratings recommended for each voltage class of machine together with their method of application. It is important that the arresters at the machine be valve type. They always should be applied with capacitors that are located either reasonably close to the arresters or between the arresters and machine. This combination prevents the occurrence of steep-front surges resulting from a sudden voltage drop when the arrester discharges.