Controlled Switching — Buyer´s Guide
B-1
Edition 2, 2006-09
Explanations
Explanations
Applications
Applications
The following applications apply to controlled switching:
Shunt capacitor banks:
Basic aim is to control closing to minimize the energizing transients (voltage
transients as well as inrush currents). To improve interrupting performance,
controlled opening can also be utilized.
Shunt reactors:
Basic aim is to control de-energizing to ensure reignition-free behavior. In
addition, controlled closing also serves as a useful method for minimizing
inrush currents.
No-load transformers:
The purpose of controlled no-load transformer switching is to minimize the
inrush currents (and voltage distortion) by taking residual flux into account.
Depending on the type of application and type of controller, controlled
opening can serve as support for controlled closing.
No-load overhead lines:
Controlled re-energizing or energizing of overhead lines ensures minimized
switching transients.
Load Characteristics
Shunt Capacitor
Banks
The shunt capacitor banks (or filter banks) may be grounded or
ungrounded.
Directly after de-energizing, the bank will be fully charged. Time relays
normally block energizing of the capacitor banks until they are discharged.
The shunt capacitor banks may be arranged either as a single bank or in a
back-to-back configuration.
Shunt Reactors
The magnetic as well as electric circuit may vary. The following types of
reactors may apply:
- Shell type
- Core type (single-phase units, five-limbed type or three-limbed type)
- Air core type
The electric circuit may be arranged in the following ways:
- Y-connected and solidly grounded
- Ungrounded (Y-connected or delta connected)
- Reactor grounded
Reactors are characterized by having a linear magnetizing characteristic
curve (by air gap).
Power Transformers
Iron core as well as electrical connection of the windings may vary.
Transformers are characterized by a non-linear magnetizing curve.
Uncompensated
Transmission Lines
Line is characterized by having no compensation equipment between
the line circuit breakers. With line CVT (Capacitor Voltage Transformer), a
healthy phase will be fully charged for some seconds after de-energizing.
Shunt Reactor
Compensated
Transmission Lines
Line is characterized by having shunt reactors connected to the line and
being switched together with the entire line.
The voltage of a healthy line will oscillate for some seconds (depending
on weather conditions and type of voltage transformers) with a frequency
determined by the degree of compensation.
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