Custom Search
|
|
|
||
 3.3.9 Bypassing Three-Phase Voltage Regulators. With the exception of the single-core,
3-phase induction regulator, the switching sequence of subparagraph 3.3.8 applies to each phase
of a 3-phase regulator. In such cases, three identical sets of switches would be used. Since the
single-core, 3-phase induction regulator has no neutral position within the regulation range where
the series winding voltage is zero, special facilities must be provided.
3.3.10 Regulator Protection.
3.3.10.1 Surge Protection. As previously stated, regulators are constructed very much like
autotransformers, having primary (shunt) and secondary (series) windings. Surge protection
requirements for regulators are consequently very similar to those for transformers.
3.3.10.2 Short-Circuit Protection. Because voltage regulators are connected in series in
the circuit, they may be subjected to exceptionally severe short-circuit currents. For this reason,
current-limiting devices are often installed in the circuit to limit possible fault currents to a value
that the regulator can withstand.
3.3.10.3 Thermal Protection. There is no inherent thermal protective device built into a
regulator. Consequently, the operator must be watchful for overloads that may damage the
regulator. Like transformers, regulators have some overload ability and may be overloaded under
certain conditions.
3.4 SWITCHES. A switch is a device for making, breaking, or changing the connections in an
electric circuit. Switches are normally divided into three classes relative to the operating
medium; air, oil, and vacuum switches.
3.4.1 General Purpose. Air switches are an essential element of electrical power transmission
and distribution systems. They provide positive, visible air-gap isolation for equipment, bus and
line sections and facilitate examination, maintenance, and repair. Oil and vacuum switches are
primarily used in underground distribution systems, especially where submersible switching
equipment is required. In addition, oil switches are often used on capacitor circuits.
3.4.2 Ratings. Switches are rated in terms of one or more of the following characteristics;
voltage, Basic-impulse Insulation Level (BIL), continuous current, short-time current, and
interrupting current.
3.4.2.1 Voltage Rating. The voltage rating is a value assigned for the purpose of
designating dielectric characteristics and should not be exceeded under normal operating
conditions.
3.4.2.2 Basic-impulse Insulation Level. This is the reference insulation level expressed as
3-22
|
 
|
|
|
||
