Controlled Switching — Buyer´s Guide
B-5
Edition 2, 2006-09
Explanations
Explanations
Definitions
Reference
For all Switchsync™ controllers, the reference is a busbar voltage
transformer signal. Any phase-to-ground or phase-to-phase voltage can be
used.
A reference point is a reference voltage zero with positive derivative.
Reference voltage frequency is continuously monitored and adaptation is
automatically done for frequency variations.
For special applications where the phase shift between voltage and
current may not be constant, like when interrupting a loaded arc furnace
transformer, it is possible to use a current / voltage converter and switch
with reference to a current zero rather than a voltage zero.
This will ensure a fixed contact separation target with respect to the wave
shape of the current.
Targets
The targets for controlled switching may either be fixed or be determined by
the interrupting conditions
Controllers E3, E23 and F236 are used to switch the controlled circuit
breaker at fixed switching instants (fixed making or contact touch instants
and/or fixed arcing times at interruption).
For controllers L83 and T83 the switching instants will vary. The
targets will vary depending on the previous interrupting conditions and
target for the next making operation is determined by load side voltage
measurements.
Phase Shifts
All targets are expressed with respect to a reference time instant, that for
all controllers is a busbar voltage zero or, in special applications, a current
zero.
For controlled closing, the target(s) are defined as a certain phase shift(s)
with respect to the reference.
For controlled opening, the ultimate targets are certain contact separation
instants with respect to the phase shift of the load currents. Since the
reference is a busbar voltage and the targets are to be expressed with
respect to this it is assumed that there is a true phase shift of 90 electrical
degrees (lagging or leading depending on inductive load or capacitive load)
between the currents and phase-to-ground voltages.
Input Command
Remote switching command given to the controller
Waiting Time
The time between the final reference point and initiation of the output
command is called waiting time.
The waiting time (internally created by the controller) fills, together with
circuit breaker operating time, the gap between the last detected reference
point and the final target.
Output Command
Delayed command from the controller to the circuit breaker. The command
is processed in such a way that the activation of the closing and/or opening
coil occurs at instants that will result in the intended optimum making
instants and/or contact separation instants, assuming that make times and
opening times are predictable.
