What is the difference between the purifier motor and normal motor?

What kind of motor used for antenna drives? (Furuno Radars)

X-band Radar - DC Motor
S-Band Radar – Three Phase Induction Motor

Where is Dc motor used onboard?

Clear view screen
ME Governor.
AE governor
X band radar
DC Servo motor

Is it possible to improve insulation winding without stopping of Motor? If yes please explain the procedure.

In running condition, if we prevent excessive heat formation. Like, make sure that cooling fan is working fine. Space heaters are on during its stop time. Preventing the ingress of dust and moisture can help in improving insulation even in running condition

If we are minimising the vibration of equipment in running condition then also it is improving the insulation.

How will you set OCR of the motor, if the motor is carrying 10A current?

OCR is always set at FLC in case of the normal motor. But if the motor is carrying 105%of FLC then the motor should continue to run for minimum 2 hrs. And if current rises to 120% of FLC then OCR should activate within 2 hrs. That’s what D.T hall says.

Check the nameplate for the service factor.

For example, the service factor is 1.15 which means OCR settings is 15% + FLC

What does mean in the steering gear motor safeties there is 200% insulation?

The motor can withstand 200% of the load or motor winding can carry 200% of FLC

What is the minimum acceptable insulation resistance of a 440v motor?

You have to say that according to D T hall the minimum insulation resistance should be 1kilo ohm per volt... So for 440v, it should be 0.44 megaohm but for survey purpose, it should be 1mega ohm.

The minimum acceptable IR value for 440v system is 1mega ohm.

Why some motors on the ship is connected as star and some as Delta?

Star connected winding

Line voltage VL is equal to phase voltage Vph × √3.
Line current IL is equal to phase Iph current.
The induction motor starting torque is directly proportional to the Phase voltage. So starting torque is low in star connected winding.

Delta connected winding

Line voltage VL is equal to phase Vph voltage
Line current IL is equal to phase current Iph ×√3
So starting torque is high in delta connected winding.
Star connection for Low starting torque machines.
Delta connection for high starting torque machines.

What is the function of Servo motor in the main engine electronic governor control?

Servo motor control the fuel to engine decrease and increase defend on the command signal.

What is the function of unloader in air compressor?

To reduce the load on motor by keeping the drain valve open
This we do by keeping the drain v/v open. Then there will be no compression on the motor.
To avoid mechanical damage to the compressor.
It is fitted with a timer.
It will drain the accumulated moisture content. Which may have accumulated after the stopping of the compressor.

Application of synchronous motors on ship

Gyrocompass
Synchronous compensator in shaft generator
Electrical clocks

What happens to the motor if we completely shut off the discharge v/v of centrifugal p/p?

Pump pressure will reach to maximum. It causes the liquid will circulate in the pump and no displacement will be there. If continuously run pump will be overeat

If you closing suddenly,

The pipeline will be damaged due to water hammering.

Effects in positive displacement type pumps

Discharge pressure will continuously increase, and damage the pipe or pump.

If you closing suddenly,

The pipeline will blast without time delay.

Which motor is continuous running in purifier room?

Viscotherm motor

Viscotherm motor - Its induction motor usually

What happens when single phasing happens in star connected motor and delta connected motor?

In case the motor is running with 3 phase delta arrangement and single phasing occurred then the motor can run as open delta arrangement where FLC will be 100% at 50% load

After you stop the motor, with single phasing fault motor won’t run.

Star connected motor cannot be run while single phasing fault is active.

Why the air gap in the synchronous machine is large than the induction machine?

Induction motor work on mutual induction principle if the air gap will be more than leakage flux will be more mutual flux reduced EMF will reduce and power factor also reduces and noise increases

While in synchronous motor does not work on mutual induction principle we give separate supply to stator and rotor.

Thus the synchronous motor has a large air gap for low magnetising reactance to allow higher reactive and active power to be delivered whereas the induction motor has a small air gap for higher magnetising reactance to limit the reactive power drawn.

Why we cannot use star delta starter instead of autotransformer starter?

Star delta has low starting torque compared to auto transformer, also star-delta is open transition while the auto is closed-loop which does not affect the surges in motor

Starting current also more in star delta as compared to auto transformer.

Star Delta starting torque 33%

But some motor needs starting torque 50%

Why soft starter firing angle 3°-177°?

Because @ 177 degrees it will supply minimum voltage at 3 degree it will supply the maximum voltage

The thyristor will not fire before 0.7 volts

So initial 3 degrees is gone

Similarly, it will not get any gate pulse from 177-180 degrees

So the last 3 degrees is gone

Where is damper winding placed in the synchronous motor?

On rotor, it is lapped

It is an additional winding shorted with centrifugal switch

Why we are using star-delta starter instead of we can run with DOL starter with star connection?

In star connection line voltage is low. So if we run it on the lower voltage we need more current for the same power output.

So with more current, more losses, more heat will generation.

Some surveyor expecting the voltage to torque relation. In delta phase voltage is equal to line voltage so more voltage more torque so we are using delta connection for high power motor for high torque, whereas in star connection torque is less.

What is the IP rating for engine room motor?

It's minimum 44 and for the deck, it's minimum 56

Why resistor and inductor are connected with the armature in synchroscope?

An inductor is connected to shift the current 90 degrees as compared to the resistor

But what is the purpose of it? It is taking supply from 2 phases of bus bar which already has a phase difference, then why this extra phase shift is required?

To turn a single-phase induction motor we need to shift the phases to get starting torque

Otherwise, in single-phase induction motor, there are two similar fields rotating in the opposite direction.

So to produce phase lead we use a capacitor in a fan. And we are use inductor in synchroscope to produce phase lag.

If motor immersed in Seawater what will happen?

The electric motor IR value will go down to very low levels.

Low insulation resistance will cause an Earth Fault alarm to be triggered.

How to control the crane motor speed on the ship?

We are using the pole change method for controlling the speed.

In cargo cranes nowadays VFD is used

Mostly wound rotor motor is used in cranes as it provides high starting torque and speed control through external resistance

Can we increase a motor speed above rated speed using VFD?

Yes we can increase the speed above rated speed by increasing the frequency, frequency is directly proportional to the speed, and by increasing the firing rate of IGBT we can increase frequency.

If a motor is continually operated at above-rated speed could damage the motor.

What will happen in star - Delta starter, if it does not change over to delta mode?

It stands to reason that for an increase in load, for the lower voltage being supplied in star mode (254V instead of 440V) current will have to increase and therefore more heat produced whilst running and finally burn out. Remember, burn out will not take place immediately, but over a period of time.

What is the type of turning gear motor?

A reversible double squirrel cage induction motor

To increase the starting torque of squirrel cage induction motor, there are two windings (inner cage and outer cage conductor bars) in the Rotor.

In soft starter out of six thyristors, three are gone then what will happen?? And what we can do onboard?

We can bypass the soft starter (diodes), thus motor get full voltage

If 3 out of 6 diodes is gone, in the soft starter, the average value of output voltage of starter, which is available at motor terminals is reduced. As 2 diodes per phase are used (one for positive and other for negative half-cycle work) is used. Motor speed reduced and it can also stop it if there is the insufficient voltage at motor terminals.

How to reverse a single-phase induction motor?

The direction of rotation of single-phase induction motor can be reversed by changing the polarity of either starting (auxiliary) winding or running (main) winding. We will preferably change the polarity of starting winding in which capacitor connected to get better starting torque.

What is the difference between the purifier motor and normal motor?

Purifier motor take high current in starting

Purifier motor since it draws high starting current has class F insulation. Secondly, it does not trip due to overload being bypassed for a certain duration of time, usually, until bowl picks up speed (anywhere between 10-15mins duration)