Datasheet

66
A4. DOL starter with lockable off:
This starter is exactly same as RAJA DOL starter with sheet steel
housing but the relay needs to be reset manually by pressing OFF
PB. Locking arrangement is provided for OFF push button; so
starter can’t be switched ON, inadvertently.
B. Star delta starting method:
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 1/3 rd 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
times of the rated current.
Advantages: low starting current
Disadvantages: Low / medium starting torque, longer starting
time, less simpler construction and wiring, requires more space
etc.
B1. Handle Operated Star Delta Starter (3LW42)
In this starter, the changeover from ‘star’ to ‘delta’ is done
manually through a control switch.
Construction:
It consists of a star-delta switch (3LAO), contactor (3TW02), an
overload relay (3UW50), “Reset” push button and a safety ‘ON’
push button.
Operation:
To start the motor, move the 3LAO switch handle from ‘O’ position
to ‘star’ (Y) position with the right hand and press the start’ - (I)
push button with your left hand. The motor starts and when it has
almost come to its rated speed (indicated when the motor hum
reaches a steady pitch), turn the handle to ‘delta’ position, still
ensure to keep the push button pressed. After switching to delta,
the push button and the switch handle can be released. To stop
the motor, bring the handle of the switch to ‘O’ position. If the
starter trips automatically due to any fault, the switch handle is
first to be brought to ‘O’ position and the bimetal relay has to be
reset.
B2. Semi automatic Star-Delta Starter (3TS02)
In this starter, the changeover from ‘star’ to ‘delta’ is done
manually by pressing ON push button.
I
y
= Current in Y-connection
I
D
= Current in Δ connection
Synchronous speed
Speed/rated speed
Current/rated op. current
Construction:
It consists of three contactors (3TW03), bimetal overload relay
(3UW50), and push buttons (ON-OFF, Reset) for control
command.
Operation:
To start the motor, ON’ push button is pressed and the same is
hold for 6 to 8 sec (starting time of the motor). After 6-8 sec, it is
left. After this, motor automatically changes over from star to
delta. The OFF push button has been provided to switch off the
entire circuit.