1. What
is the slip of an induction motor at the time of start?
A. 100%.
2. What
is the protection against single phasing?
A. Negative
sequence protection.
3. What
are the protections normally provided for HT motor?
i.
Over current (Inst.)
ii.
Thermal O/C
iii.
Stalling
iv.
Earth fault.
v.
Negative sequence.
vi.
Temperature
4. What
is the difference between VCB and motor starter combination?
A. VCB
can make and break in fault conditions, contactor cannot. Hence fuses are used.
5. What
are the possible causes of excessive vibration on a running motor?
i.
Faulty bearing.
ii.
Unbalance on rotor.
iii.
Misalignment.
iv.
Faulty foundation.
v.
Rotor bars open.
6. What
are the units of measurement for vibration and spike energy?
A. Vibration
Velocity – mm/sec, spike energy – gse.
7. How
do you measure sleeve bearing clearance?
A. Plastic
gauge or lead gauge wire to placed between the shaft and bearing and bolt
tightened to normal and measure flattened thickness of the gauge.
8. Explain
different Insulation classes and the corresponding temperature rise allowed.
Y – 90
A – 105
E – 120
B – 130
F – 155
H – 180
C – 180
Above 180 to 220°C
9. What
is the max speed obtained by 3 phase induction motor with normal state supply?
N= 120F/P=120X50/2= 3000RPM
10. What
is the advantage of star delta starter over DOL starter?
A. Limiting
starting current.
11. Why
single phase motor is not self starting.?
A. No
revolving field.
12.
What are
the insulation resistance values for different voltages of Motors?
Motor
|
Minimum (IR)
|
Maximum (IR)
|
|
a)
|
250V
|
1.25 M Ohms
|
Infinity
|
b)
|
440V
|
1.5 Ohms
|
Infinity
|
c)
|
3.3KV
|
4.5 M Ohms
|
Infinity
|
d)
|
6.6KV
|
7.6 M Ohms
|
Infinity
|
e)
|
11KV
|
12 M Ohms
|
Infinity
|
13.
What are the causes for Motor is overloaded?
(a) Overload;
(b) Short circuit for motor winding; (c) Single Phasing; (d) Loose connection
of power cable; (e) Bearing problem.
14.
How to find the motor speed and write equation?
By
“Tacho Motor”
Equation = 120F/P
N=
Speed; F =Frequency; P=Number of Pole
15.
What is 1 Phasing preventer?
In
single phasing if one fuse blown out the Motor will run in the same condition,
Motor will take start.
Single
phasing preventer is a relay which is used to prevent the equipment from single
phasing. If any fuse blown the Motor will take higher |Current. In that case
the humming sound will come.
16.
What are the types of Bearing?
a) Ball
Bearing
b) Roller
Bearing
c) Bush
Bearing
d) Taper
Roller Bearing
e) Sleeve
Bearing
f) Thrust
Bearing
17.
What is Thrust Bearing? Where generally it is
used?
Where
Sleeve Bearing used.
a) Thrust
Bearing is used for vertical plane mounted motors in drive End side.
b) Sleeve
Bearing is used for HT Motors in DE and NDE side.
18.
YPM of Motor
a) Obtain
the work permit
b) Switch
off the breaker and lock it
c) Put
caution notice in breaker and push button station
d) Switch
‘ON’ the Earth switch
e) Disconnect
Fan cover and clean physically
f) Open
the Terminal cover
g) Check
the Tightness of Terminals
h) Check
the Earth connections
i)
Insulation resistance and winding resistance to
be checked
j)
Switch “OFF” the Earth Switch
k) Switch
“ON” the breaker and start the Motor
l)
Check the load current
m) Close
the Permit
19.
The Motor is not stopping what will be the
problem?
a) The
“OFF” Button “NC” not open
b) The
Contact get jammed
20.
What is slip ring induction motor? How to take
connection from Rotor?
To
get high starting Torque, we include external resistance to the Rotor winding.
After motor attain full speed Rotor winding one short circuited.
By
using Slipping, Carbon brushes connections are taken from Rotor winding.
21.
Which are the protection used for Motors?
a) Overload
relay
b) Earth
leakage relay
c) Single
Phasing preventer
d) Stalling
Relay
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