Video transcription

Good day to all and welcome to this online course.
In this video, we will conduct an overview of the principles of breaking electrical circuits.
Produced by Zensol Automation in collaboration with Hydro-Québec.

At the end of this video, the participant will be able to understand the principle of the ICOS synchronous
command

the ICOS synchronous command.
What is the principle of the ICOS synchronous command?
Example of a breaker opening on an inductance to ground.
Example of a breaker closing on an inductance.

What is the principle of the ICOS synchronous command?
ICOS is a French acronym, meaning Synchronous Order Command Interface.
It is a controlled switching device that sends an open or close command to the circuit breaker to
synchronize its operation to the zero crossing of the current amplitude.
ICOS is used only during controlled operations Which means during intentional operations, It does not
intervene during protection operations Such as breaking a short circuit.
ICOS is also used on other devices such as shunt coils, capacitor banks and some transformers at 315
and 735 thousand volts.
On opening, ICOS avoids resetting the breaker.
On closing, ICOS limits high inrush currents.
It is an interesting alternative to eliminating certain pre-insertion contacts.

Example of a breaker opening on an inductance to ground.
The controlled opening of a shunt inductance avoids re-lighting the breaker. A re-lighting occurs when
the dielectric properties between the contacts of the breaker, on an attempt to break on zero current is
too weak compared to the voltage present. To avoid this situation, the opening of the contacts is set to
obtain an arc time (time between the start of the mechanical opening of the contacts and the zero
crossing of the current) on the order of 5 to 6 milliseconds depending on the breaker specifications.
In some applications for an inductance to ground, the reference to detect the zero crossing is the
current on Phase A on the negative slope of the signal. The target angles for each phase, relative to the

reference signal, is 180 on Phase A, 300 on Phase B and 240 degrees on Phase C. Thus, using the opening
times, the arcing times and the target angles, the relay calculates the needed delay before sending the
opening commands on each breaker phase.

Example of a breaker closing on an inductance.
Several strategies may be programmed to achieve a controlled close according to the disruptions we
wish to avoid.
– Maximum voltage to avoid current asymmetry.
– Zero voltage to reduce electrical stress in the inductance.
– Intermediate voltage value to avoid extreme cases of dielectric and mechanical constraints.
One strategy is to close each phase in order to establish the beginning of electrical conduction
(beginning of the electrical arc) at the point where its voltage is equal to half its peak value. Since there
is no current flowing in the inductance before the breaker closes. The reference signal is the voltage on
Phase A (zero voltage on the negative slope of the signal). Thus, from the closing times, the pre-arc
times and the target angles, the relay calculates the necessary delay before sending the close commands
for each of the breaker’s phases.

Question
In which case is the ICOS command used?
A), Intentional operations,
B), Transient short circuit,
C), Permanent short circuit,

The correct answer is A), Intentional operations. See slide 4 for more details.

References
Zensol, Circuit breaker library
Zensol, Circuit breaker timing
Schneider Electric, Cahier technique chronométrage 125.