A surge arrester is a device to protect electrical equipment from over-voltage
transients caused by external or internal events. Also called a surge
protection device or transient voltage surge suppressor, this class of device
is used to protect equipment in power transmission and distribution systems.
The energy criterion for various insulation material can be compared by
impulse ratio, the surge arrester should have a low impulse ratio, so that a
surge incident on the surge arrester may be bypassed, to the ground instead of
passing through the apparatus. To protect a unit of equipment from
transients occurring on an attached conductor, a surge arrester is connected
to the conductor just before it enters the equipment. The surge arrester is
also connected to ground and functions by routing energy from an over-voltage
transient to ground if one occurs, while isolating the conductor from ground at
normal operating voltages. This is usually achieved through use of a
varistor, which has substantially different resistances at different
voltages. Surge arresters are not generally
designed to protect against a direct lightning strike to a conductor, but
rather against electrical transients resulting from lightning strikes
occurring in the vicinity of the conductor. Lightning which strikes the
earth results in ground currents which can pass over buried conductors and
induce a transient that propagates outward towards the ends of the
conductor. The same kind of induction happens in overhead and above ground
conductors which experience the passing energy of an atmospheric EMP caused by
the lightning flash. Surge arresters only protect against induced transients
characteristic of a lightning discharge's rapid rise-time and will not
protect against electrification caused by a direct strike to the conductor.
Transients similar to lightning-induced, such as from a high voltage system's
fault switching, may also be safely diverted to ground; however, continuous
overcurrents are not protected against by these devices. The energy in a
handled transient is substantially less than that of a lightning discharge;
however it is still of sufficient quantity to cause equipment damage and
often requires protection. Without very thick insulation, which is
generally cost prohibitive, most conductors running more than a minimal
distance, say greater than about 50 feet, will experience lightning-induced
transients at some time during use. Because the transient is usually
initiated at some point between the two ends of the conductor, most applications
install a surge arrester just before the conductor lands in each piece of
equipment to be protected. Each conductor must be protected, as each
will have its own transient induced, and each SPD must provide a pathway to earth
to safely divert the transient away from the protected component. The one notable
exception where they are not installed at both ends is in high voltage
distribution systems. In general, the induced voltage is not sufficient to do
damage at the electric generation end of the lines; however, installation at the
service entrance to a building is key to protecting downstream products that are
not as robust. Types
Low-voltage surge arrester: Apply in Low-voltage distribution system,
exchange of electrical appliances protector, low-voltage distribution
transformer windings Distribution arrester: Apply in 3KV,
6KV, 10KV AC power distribution system to protect distribution transformers,
cables and power station equipment The station type of common valve
arrester: Used to protect the 3 ~ 220KV transformer station equipment and
communication system Magnetic blow valve station arrester:
Use to 35 ~ 500KV protect communication systems, transformers and other
equipment Protection of rotating machine using
magnetic blow valve arrester: Used to protect the AC generator and motor
insulation Line Magnetic blow valve arrester: Used
to protect 330KV and above communication system circuit equipment insulation
DC or blowing valve-type arrester: Use to protect the DC system’s insulation of
electrical equipment Neutral protection arrester: Apply in
motor or the transformer’s neutral protection
Fiber-tube arrester: Apply in the power station’s wires and the weaknesses
protection in the insulated Plug-in Signal Arrester: Used to
twisted-pair transmission line in order to protect communications and computer
systems High-frequency feeder arrester: Used to
protect the microwave, mobile base stations satellite receiver, etc.
Receptacle-type surge arrester: Use to Protect the terminal Electronic
equipment Signal Arrester: Apply in MODEM, DDN
line, fax, phone, process control signal circuit etc.
Network arrester: Apply in servers, workstations, interfaces etc.
Coaxial cable lightning arrester: Used on the coaxial cable to protect the
wireless transmission and receiving system
See also Lightning arrester
Surge protector Lightning rod
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