Product description 3.3 Functional principle of the SIRIUS 3RW30 and 3RW40 soft 0RWRUWRUTXH 0 0 'LUHFW RQOLQH VWDUWLQJ 0 1RP 0 6RIWVWDUW YROWDJHUDPS 0 /RDG HJSXPS Q 1RP 0RWRUVSHHG Q Figure 3-4 Reduced torque characteristic of a three-phase induction motor during starting with a SIRIUS 3RW30 or 3RW40 soft starter Soft start /soft stop This means that, since the motor voltage is controlled by the electronic soft starter during the startup process, the consumed starting current and the starting torque generated in the motor are also controlled. The same principle is applied during the stop process.
This ensures that the torque generated in the motor is gradually reduced, so that the application can stop smoothly (the soft stop function is only supported by the 3RW40). The frequency remains constant during this process and corresponds to the mains frequency, in contrast to frequency controlled starting and stopping of a frequency converter. Bypass mode Once the motor has been started up correctly, the thyristors are subject to fully advanced control, meaning that the whole mains voltage is applied to the motor terminals. As the motor voltage does not have to be controlled during operation, the thyristors are bridged by integral bypass contacts that are rated for AC1 current.
This minimizes the waste heat generated during uninterrupted duty (which is caused by the thyristor's power loss), and minimizes heating up of the switching device's environment. The bypass contacts are protected by an integrated, electronic arc quenching system during operation. If they are opened in the event of a fault, e.g. if the control voltage is temporarily interrupted, mechanical vibrations occur, or the coil operating mechanism or the main contact spring has reached the end of its service life and is defective, the equipment is not damaged. The diagram below shows the method of operation of the SIRIUS 3RW30 and 3RW40 soft starters:
SIRIUS 3RW30 / 3RW40 Manual, 01/2010, 535 1995-02 DS01 19