An HSC question (need help) (1 Viewer)

[iwannaacetheHSC]

A portable diesel engine generator is being used to supply electricity to the motor of an elevator in a mine shaft. The elevator motor draws a current of 15.0 amperes when used. It is noticed that the diesel engine driving in the generator initially slows significantly when the elevator is operated and its motor draws current from the generator. The reason for that is that........ (That is the question)

 

[someth1ng]

What year is this? It's such a mess question (in my opinion), also, how many marks is it worth?

 

[someth1ng]

A portable diesel engine generator is being used to supply electricity to the motor of an elevator in a mine shaft. The elevator motor draws a current of 15.0 amperes when used. It is noticed that the diesel engine driving in the generator initially slows significantly when the elevator is operated and its motor draws current from the generator. The reason for that is that........ (That is the question)

- When the motor is turned on, there is a sudden change in the emf in the coil causing a back emf to be produced which opposes the diesel engine driving in the generator causing it to slow down significantly (momentarily).
- The emf in the coil is then constant causing causing no net change of flux and hence, no back emf in the coil due to a supplied emf.
- Then when the motor is operating, to produces a constantly changing back emf with frequency proportional to the rate of rotational of the coil of the motor.
- The generator's speed then eases back into a more constant speed.

I think this is right assuming that I'm answering the question correctly.

 

[iwannaacetheHSC]

it was worth 1 mark,

not necessarilty an HSC question but an HSC specimen question

 

[Rathaen]

Shouldn't the initial slowing be due to a high current draw from the motor when it initially starts, due to the fact that the rotors are not moving? (and thus not generating any back-EMF)

So then as the motor begins to spin up, the coils rotate faster through the stator field, which generates an increasingly large back-EMF and balancing the current through the coil back to 15A.

 

[someth1ng]

Shouldn't the initial slowing be due to a high current draw from the motor when it initially starts, due to the fact that the rotors are not moving? (and thus not generating any back-EMF)

So then as the motor begins to spin up, the coils rotate faster through the stator field, which generates an increasingly large back-EMF and balancing the current through the coil back to 15A.

I'm pretty sure when the motor is running, there will be back emf due to a constantly change of flux resulting in the net current in the coil to be near 0.