RST FRC-F Series, Manual

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9.581.140-6
Page:
117
13 Converter operation without travel contactors
13.1 General
Operation without travel contactors is
only permissible for RST frequency converter with the "Safe
Stop“ option (STO).
Application is permissible for asynchronous gear drives and permanently controlled gearless
synchronous drives.
The lifts must be designed according to lift directive 2014/33/EU
13.2 Scope of application
Use of the STO function (STO – Safe Torque Off) eliminates the need for using so-called travel
contactors for interruption of the flow of energy between the frequency converter and the drive unit in
accordance with the requirements as per EN 81-1 or EN81-20. With a high probability, it prevents the
occurrence of unwanted rotation of the drive in case of a fault.
Thanks to the fail-safe and two-channel design of the circuit, uncontrolled actuation of the switching
devices in the inverter of the frequency converter is prevented when the STO inputs are deactivated.
If asynchronous motors are used, a failure of switching components in the inverter of the frequency
converter will not result in torque. Thus, there is no uncontrolled movement of the lift car.
In combination with permanently excited synchronous drives, alignment of the drive up to half a
rotation is possible in case of a failure (short circuit of at least two switching devices). This must be
considered both in the mechanical and electrical design of the lift!
13.3 Safety instructions
Planning, design, installation and maintenance of safety-critical applications may only be performed by
qualified staff!
The STO function does not provide isolation from mains supply. Before any work on the electrical
components of the lift system, the plant must be isolated from power supply; the work must not be
started before the DC link capacitors of the frequency converter have discharged!
If the STO function is used, safety of the lift system can only be guaranteed if it is included in a higher-
order monitoring concept properly. The installation company supplying the lift system shall bear the
sole responsibility for the risk assessment required for this!