Datasheet

65
Useful technical information
Method of starting
A. DOL starting method:
The most economical and popular method of starting squirrel
cage induction motors, is direct-on-line, 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.
Advantages: High starting torque, shorter starting time, simple
construction and wiring, space saving etc.
Disadvantages: High starting current
Types:
Agricultural Starters
A1. RAJA DOL starter
Construction
Contactor:
The DOL starter up to 10 HP is fitted with 3TW02 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
contact rating of this contactor is 20 A. This high contactor rating
has made RAJA starter the most suitable starter for applications
where current for given HP is higher than that of the conventional
motors’ e.g.. Submersible pumps etc.
Bimetal Overload Relay:
The RAJA direct-on-line starter is fitted with 3UW50 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.
This relay is automatic reset type and can not be reset by hand.
Push buttons
Push buttons are used for switching ‘ON’ and ‘OFF’ the starter.
Operation:
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 ‘no-voltage’ 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.
A2. RAJA DOL stater in open execution:
This starter is exactly same as DOL starter with sheet steel housing
except the enclosure and push buttons. The contactor and
birelays are wired and mounted on the plate. It is expected that
the user provides for the housing for this starter and also for the
ON-OFF arrangement by way of push buttons or any other means.
A3. RAJA DOL starter with hand reset:
This starter is exactly same as RAJA DOL starter with sheet steel
housing but in this case the relay needs to be reset manually. The
OFF button on the housing is also used as reset button for
resetting the relay after overload.