produces or transient currents, to ground without injury to line insulators, transformers, or other connected equipment. Use of lightning arresters is essential in all areas of power line construction. These include distribution, secondary, intermediate, and station distribution. The four different specifications of arresters, mentioned above, have different sparkover voltages, current discharge capabilities, and maximum surge discharge capabilities.
Figure 4-34. - Distribution cutouts (fused).
Secondary arresters are used on service and other low-voltage alternating-current circuits. Distribution arresters are used on primary distribution systems to protect insulators, distribution transformers, and other equipment. Intermediate type of lightning arresters are often used on substation exit cables and other locations on the distribution system, needing a high level of lightning and surge protection. Substation types of arresters are used in substations and generating stations to provide a high level of surge protection for the major pieces of equipment. Surge voltages can be generated by operating switches in the electric transmission system as well as by lightning.
Various types of lightning arresters are in use today. The valve, pellet, and air gap (fig. 4-35) are the most common and likely-to-be-seen types in the field.
A switch is used to disconnect or close circuits that may be energized. High-voltage switches are operated remotely using a variety of mechanisms or manually. Depending on their purpose in the system and their physical makeup, switches are divided into three general classes: air, oil, and vacuum switches. These three classes can be further subdivided (depending on their function) into what is referred to as disconnects, circuit breakers, or reclosers.
As their name implies, air switches are switches whose contacts are opened and use air to insulate their contacts when current flow is interrupted.
Figure 4-35. - Types of lightning arresters.Continue Reading