Ed Sirett wrote in message ...
daestrom wrote:
"Rob" wrote in message
om...

Hi,

I have a 3000 rpm 11.8 KVA Fisher Panda generator that has both 1 and
3 phase outputs. I am looking to use the 3 phase output to power a 3
phase motor of around 10kW to drive a bow thruster in a barge at
approx 1500rpm. A colleagu has a Northern Lights 10KVA genset and
successfully powers a 9kW 3 phase motor in a similar set up. Would
appreciate any pointers - such as need for a capcitor bank to meet the
surge on starting.


I have no direct experience of this. However the power requirements of
the bow thruster won't approach anything like the rated 10KW until the
speed of the propellor is fairly close to the 1500 rpm.
IIRC the power required is proportional to the cube of the prop speed.

^ This bit is the key.^

The power factor of the motor will be poor on starting but improve as
the prop comes up to speed and a pf of 0.8 is plausible giving 11.8 kVA
* 0.8 = 8.9 kW.

Does your colleague have capacitors? What sort of over current
protection?
The fact that he/she has it working means it's possible in principle and
there is nothing that makes you setup different.


But there is another factor, that motor start current is many times
rated run current. So the only thing that'll keep it going thru the
start period is heavy gen speed drop reducing motor current. Thre's
only one way to find out if your gen will do this reliably without
stalling.

There is a way round it tho, and that's to electrically reduce the
motor power during start. Several methods possible:

1 electronic start control unit
2 massive series resistor and switch
3 switching down the output V on the gen, if it has this option
4 starting the motor coils in series then switching to parallel

2 is the one you can use with any setup, the rest depend on equipment
or money.

It should be possible, and some gens will manage it with no start-up
provisions, but you certainly cant count on that without trying it.


Regards, NT