we have GT frame 7EA it has flow divider coupled by DC motor.
the question is why flow divider does have only DC motor not AC?

 

> we have GT frame 7EA it has flow divider coupled by DC motor.
> the question is why flow divider does have only DC motor not AC?

It first thought for a battery start on a dead grid? But 7EA's don't come with a diesel starter? AC or DC either will do the job. The 88FM is only pulsed for 5 seconds upon the opening of VS1.

Is there anything unique or unusual on these units? Black start requirement? or a heavy fuel/naphta/crude fuel piping purge upon a unit trip?

 

Because, in general, the motor is only used briefly during start-up on liquid fuel and not continuously while operating on liquid fuel.

Many liquid fuel flow dividers do not have these motors at all. They are usually only provided when the liquid fuel viscosity can be very low (such as when crude oil or bunker fuels are burned in addition to distillate (diesel) liquid fuels).

 

Dear CSA;

Until know I did not get the right answer?

my question was very cleared however I’ll repeat it again. why flow divider is connected by DC Motor why it is not connected by AC motor?

Take note
I know it is only conceder as a prime mover for it and then it will rotate continuously by fuel pressure. also if it is connected by AC motor, it will conceder same function which is only a prime mover.

 

The designers of the system apparently decided to use a DC motor instead of an AC motor.

That choice was made probably because some machines are what are termed "black-start" machines, and there is no AC available some times during starting (which is when the 88FM "helper" motor would be running), and so a DC motor would seem to be the best choice.

And, rather than have two similar systems, one with a DC motor and one with an AC motor for non-black start applications, they just standardized on the DC motor for all applications requiring the "helper" motor for the flow divider.

As Saudi_contract said--it could be an AC or a DC motor. The designers have decided to use a DC motor, and again, that's probably to minimize the number of designs and part numbers and for standardization.

Does that answer your question?

 

One reason may be that the unit was designed with black start capability. If so, since this motor is only briefly used during startup, at a time when the only AC power available would be from an inverter, DC was the only realistic option.