Siemens - Starters
Starter can be used if the high inrush current of the motor does not cause excessive voltage drop in the supply circuit. It can be used to start small agriculture water pumps, compressors, fans and conveyor belts.etc.
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DOL: As we know, A direct on line starter can be used if the high inrush current of the motor does not cause excessive voltage drop in the supply circuit. It can be used to start small agriculture water pumps, compressors, fans and conveyor belts.etc.
The DOL starter up to 10 HP is fitted with 3TS3 Contactor. This contactor is specially designed by Siemens considering the requirements of industry as well as agriculture. Considering the specific need of the agricultural pump set applications, Siemens has designed a special wide band coil (200-400V). This coil operates reliably even when there is wide voltage fluctuation.
The Starters will now come with 3TS Contactors which will in turn make the starter more reliable with enhanced electrical and mechanical life.
The most economical and popular method of starting squirrel cage induction motors, is direct-online, where the starter is connected directly across the supply. However, the starting current at the moment of switching Direct-on-line can be as high as 6-8 times the rated current.
High starting torque, shorter starting time, simple construction and wiring, space saving etc.
High starting current
The RAJA direct-on-line starter is fitted with 3UW5 relay. These relays are computer calibrated and therefore, offer accurate protection. The main benefit of this bimetal relay is the built-in single phasing protection in addition to the overload protection. Relay has Automatic reset function after cooling time of 4 sec approx, completely reduce Manual dependency
Push buttons are used for switching ‘ON’ and ‘OFF’ the starter. Twin push button comes with ‘Locked Off’ feature which helps in avoiding nuisance switching ON of pump.
In DOL starting, the ‘ON’ push button is pressed, which energizes the contactor coil, thus switching on the circuit. When the OFF’ push button is pressed, the contactor is de-energized, switching off the circuit. The bimetal relay under normal functioning of motor plays no active part in the starter. But under overload, single phasing or locked rotor conditions of Motor, the bimetal relay cuts-off the supply to the contactor coil, tripping the circuit. The contactor itself provides the necessary ‘novoltage’ protection in so far as it will drop out in the case of a supply failure, and for restarting on resumption of supply, the ‘ON’ push button will have to be pressed again.
- 3TW72 range of DOL starters are having option of 200-400 V Coil voltage which takes care of wide fluctuations in supply.
- Accurate protection under single phasing & overload.
- With ISI marking, it ensures more safety for the end user.
- With 3TS contactors fitted into it, ensures more electrical and mechanical life of the Starter.
- With Locked off feature, ensures that undesirable switching on of the Starter is prohibited.
- No Auto start only Auto reset of Bimetal relay and it needs Manual Acknowledgement to again ON the Starter.
- 0.25kW to 7.5kW
- 0.33HP to 10HP
(For Single Phase connection)
In star delta starting, initially the motor windings are connected in star. This reduces the starting current by 1/3 rd of the full load current also the voltage by (1/√3) of the rated value. As the torque is proportional to the square of the voltage, the starting torque also get reduced to 1/3rd of it’s full load value. Once the motor attains approximately 80% of the rated speed, the windings get connected in the delta formation.
Thus by star delta starting, the starting current is reduced to 2 to 2.5 times the rated current unlike DOL starting, where it is 7 to 8.
low starting current
Low / medium starting torque, longer starting time, less simpler construction and wiring, requires more space etc.
It consists of a star-delta timer (3RP), contactor (3TS3), and overload relay (3UW51),
In this starter, the changeover from ‘star’ to ‘delta’ is done automatically after a preset time by using a timer.
- 7.5kW to 18.5kW
- 10HP to 25HP
Table A: Automatic Star – Delta Starter Type Ref: 3TE7291-0A
Other Tables:
