DOL STARTER MEANS DIRECT ON LINE STARTER WHICH IS USED 2
CONTROLS THE OVER LOADS BUT IN STAR-DELTA STARTER,FIRST WE
WILL CONNECT THE SUPPLY TO STAR.WHEN THE 80% RATED SPEED
OBTAINED,WE WILL CONNETED THE TERMINALS TO DELTA CONNECTION.
in DOL we are going to connect 3 phase supply directly but
it will capable for less current if more current flows
through it the starter will get damage. while starting the
motor it will take more current, for reducing this start up
current we r going to star-delta connection. in this first
will be in star conection after that it will turn to delta
When the motor is connected in Delta and started by DOL method, the voltage applied across a coil is the voltage between two phases i.e, 415V approx. Therefore the current inrush is high. In order to minimize the starting current, voltage across the coils should be brought low, which can be done if we connect the coils in star. During star connection the voltage across a coil is 240V (approx) which is 1/(sq root of 3)times that in delta which results in a simultaneous lowering of current also. This eases the stress on relays and conductors.When the motor attains 90% of its rated speed the coils are connected in Delta. therefore generating higher power.
the d.o.l is 0-5H.P MOTOR,AND STRE DELTA STRTER IS USE
ABOVE 5H.P MOTOR.
THE DOL IS CONNECTED TO DIRECT TO LINE.
THE STARE DELTA IS DO NOT CONNECTED TO LINE USE.
IN AUTOMATIC STARE DELTA STATER IS NO CHANGE OVER SWITCH
THEY CHANGE BY AFTER SOME TIME BY TIMER CKT.
IN STARE DELTA STRTER INITIALLY MOTOR STARTE IN STARE AFTER
SOME TIME THEY RUN IN DELTA.
in dol starter starting torque is high.which is on light load.it is connectrd direct to line and used below 5hp.
in star-delta starter starting torque is 60% and it reduced to 1/3and its then connected to delta.this starter is used above 5hp.
star delta ::This is a starting method that reduces the starting current
and starting torque. The components normally consist of three
contactors, an overload relay and a timer for setting the time in
the star-position (starting position). The motor must be delta
connected during a normal run, in order to be able to use this
dol :: this is also a starting method but some what dangerous for heavy motor who can carry heavy load. because this processes fed direct current to the motor.