Answer / ionp

When DOL Starter is employed the motor is loaded with full
load voltage in starting, which causes high starting
current in the circuit.
Torque is proportional to square of Voltage so employing
DOL starter we achieve High Starting Torque. Which in turn
help Motor to attain its rated speed quickly.
Available Pull out Torque help load to accelerate quickly.
The starting current which can be 5 to 7 times of full load
current can be born by motor & Associated cables etc. for
few seconds during starting & does not causes any unwanted
heating & heat losses.
Hence we prefer DOL starters where high Starting Torque is
required.
On the contrary With Star-Delta starter Starting Voltage is
1/3rd of rated Voltage & Starting current is almost 3
times. This low voltage will cause insufficient torque in
starting & time taken to attain full load speed is more, in
turn more heating & losses. Also when Motor switches to
delta mode the current kick is almost 5 times the FLC, Thus
system is subjected to 2 current kicks.

Answer / naresh

The name itself indicates direct online starters and these
starters will employed for low rating motors, because in
low rating motors the loaded torque is also low and
capacity of starting current will not be such high enough
to make severity, but the protection of motor at voltage
levels is important. DOL starter not only ensures on & off
but the magnetic opearting coil functions in proportion to
the rated voltage. at low voltage the magentic coil trips
down and at high voltages the coil gets damaged. here the
coil used is very sensitive to the voltage and hence it is
voltage protection device and the bi-metallic strip inside
starter makes it current protection device.where as mcb is
only current protection device.

Answer / m s venkateswara rao

Normally Starters are used to reduce the starting current. But selection of the starter is based on the type of application whether starting torque is required high, medium, normal.Normally any motor during starting will take 4 to 5 times of full load current.Up to 10 Hp usually will use DOL because of motor full load current is 13 Amps and during starting will take 65 Amps as a result supply system dos not get affect. Above 10 HP usually motor full load currents are high and during starting will draw high starting current which will affect out supply system ie voltage drop, for which all associated equipment connected with the system will be affected.Usually above 10 HP motors with a application of medium torque will use star/ delta starter to reduce starting current. If the application is required high starting torque will use dol starter irrespective of the rating of the motor.

Answer / ali

i have seen many dol motors r just running on mcb without
creating any porblem for last 4-5 years dol startor are
soft stator which is manually operated suppose in an
industry to cut metals having hacksaw machine(dol motor)
which is merely operating on mcb suppose machine in ON
suddenly there is a breakdown in electrical supply & will
resume after 2 hour & operator will assume 2 hour is
sufficient time to clean the machine & these is a good time
lets take full advatage of it & he started to cleaning the
machine & forget to OFF the mcb he is cleaning & removing
burs from blade teeth suddenly suply resume 1 hour before
than the mentioned time what will happen??????????

we have taken HV test of 2.5 k and Megger test on 11 kv HT cable.here it shows no fault but when we are charging the same cable with 11 kv supply why the VCB 11 kv gets tripped can anybody define the possible cause of fault ?

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