© Siemens AG 2009 Wye( * )-delta function ( ∗Δ ) starting ue. This prevents a simultaneous tripping of the motor starter protector and overload relay. In order to keep the current peaks in the line supply as low as possible, contactor assembly are frequently used as wye-delta starters to start induction motors. However, to make worth- while use of * Δ starting, a low load torque is required during starting. Only then can the motor approximately reach its rated speed in the * stage before switching to Δ operation. Soft starting with soft starters What is the basic principle of a soft starter? Soft starters limit the starting current and starting torque.
This reliably prevents mechanical stress and mains voltage dips. The motor voltage is reduced using phase control and is in- creased from an adjustable starting voltage up to the mains voltage within a specific ramp time. Soft starting and stopping reduces the stress on connected equipment, thus ensuring prolonged smooth and trouble-free production. An overload relay should be used for motor overload protec- tion. Normally, this is located directly in the motor feeder cable U1, V1, W1, as shown in the circuit diagram. Using this ar- rangement, the overload protection is effective in both the * and Δ circuit. The overload relay should be set for 58 % of the rated motor current.
L1 L2 L3 Q1 U L1-L3 U L1 L2 L3 > L1-L3 G1 Principle of the operating angle of the mains voltage for solid-state elements in soft starters = Operating angle M 3 ~ 5 1 3 1 3 5 1 3 5 ■ 3RW30 soft starters for the soft starting of three-phase K1 N 2 4 K2 6 2 4 6 K3 2 4 6 asynchronous motors for simple applications - performance range: Up to 55 kW at 400 V (75 hp at F1 NSB0_01770 460 V) W1 V1 U1 W2 V2 U2 M 3~ ■ 3RW40 soft starters with integrated functions: solid-state motor overload and intrinsic device protection and adjust- able current limiting - Performance range:
up to 250 kW at 400 V (300 hp at Circuit diagram main circuit for circuit 460 V) A * Δ timing relay is required for switching from the * to the Δ circuit. These timing relays are specifically designed for these types of applications and ensure safe, reliable switcho- ver. The respective timing relays are listed in the Catalog LV 1 "Low-Voltage Controls and Distribution". The specified combi- nations are designed for a starting time of 10 seconds in * op- eration. In order to prevent damage to the * contactor in the event of a motor blockage, operation should switch to Δ mode within a maximum of 10 seconds. ■ The 3RW44 solid-state soft starters offer the following:
- Soft starting and stopping - Solid-state motor overload and intrinsic device protection - Adjustable current limiting - Numerous functions for higher-level requirements - Performance range: up to 710 kW at 400 V in the inline circuit and up to 1200 kW at 400 V (1700 hp at 460 V) in the inside-delta circuit Further information on SIRIUS soft starters is available on the Internet at: http://www.siemens.com/softstarter In the tables, circuit breakers are used for starter combinations (without overload releases). However, 3RV10 motor starter protectors with the same rated current can also be used for motor protection instead.
In this case, the rated motor current of the motor starter protector must be set to the maximum val- Introduction 8 Motor voltage Direct Wye- Soft startingdelta starter 100% 58% Ramp time Time Motor current Direct starting Wye- delta Soft starter Rotat. N speed nN Motor torque MDirect starting MWye- delta MSofM t N Rotat. starter speed nN NSB0_01999 > >