Configuration
6.9 Switching of capacitive loads
SIRIUS - SIRIUS 3RT Contactors/Contactor assemblies
106 Manual, 09/2017, A5E03656507120A/RS-AE/006
Switching of capacitive loads
Applications
The 3-pole capacitor contactors can be used to switch capacitive loads.
Besides switching power capacitors in reactive-current compensation systems, they are also
used to switch on converters.
Capacitor contactors are suitable for capacitors with and without reactor protection.
Switching of capacitive loads
The inrush current of a capacitor increases with the short-circuit power of the line.
The capacitor's inrush current is at its highest when it is connected directly to the transformer
or in parallel with existing capacitors. This is similar to capacitor banks for reactive power
compensation, for example, when a capacitor is connected in parallel to existing capacitors.
The charging current is taken not only from the line. Current is additionally drawn from the
parallel-connected capacitors.
To meet this requirement, 3RT26 capacitor contactors have precharging resistors to reduce
the inrush current. They are designed to convey the inrush current in such applications, and
are weld-resistant for peak inrush currents in accordance with the technical data.
In the case of 3RT26 capacitor contactors, the precharging resistors form a component part
of the contactor.
The precharging resistors are activated via leading auxiliary contacts before the main
contacts close. During switching, after attenuation of the peak current, they are decoupled
again.
Attenuation of the inrush current peaks also reduces interfering harmonics in the supply.
The precharging resistors are separately protected reliably against detrimental mechanical
influences by the robust precharging resistor enclosure.
Thanks to the innovated, technical principle of precharging resistor decoupling, the 3RT26
capacitor contactors have an enhanced useful life in comparison with their predecessor.
can be found in the chapter ...
About operation with frequency converters Configuration information for use downstream of
frequency converters (Page 164)
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