Generator /Motor Load

[sparky124]

I have a 60 hp 480V 3Ph motor and a 80 kw generator . Motor won't start while phase monitor is on line. If lead is disconnected to monitor motor starts however voltage drops briefly to 350 from 475. Is this typical of this type of load? Can I simply put a time delay on the phase monitor. Will this voltage drop damage the motor or generator?

[ March 25, 2005, 10:23 PM: Message edited by: sparky124 ]

 

[bob]

Re: Generator /Motor Load

I'm suprised the motor starts at all. You would normally call for a generator that is 2 or 3 times the rating of the motor to handle the starting amps. What is the motor used for?
Is the monitor checking volts, amps, frequency? Can't imagine why it would cause your problem.

Edit to change size to 2 or 3 times motor rating
per Onan Software.

[ March 26, 2005, 02:44 PM: Message edited by: bob ]

 

[kiloamp7]

Re: Generator /Motor Load

Gensets this size typically have a motor-starting rating & the current capability of the genset does not necessarily have to be 4 or 5 times the current rating of the motor, it just has to be designed for motor-starting duty.

Genset is probably rated 80KW at .8 power factor, which is 100KVA. Generally this should be sufficient to start a 60HP motor, unless for some reason the genset has an undersized engine spinning the generator.

Not sure what this "phase monitor" is doing, or how it is wired in. Does it have adjustments?

 

[mc5w]

Re: Generator /Motor Load

There are basically 3 different grades of 3-phase generators that Marathon makes. The best use a permanent magnet 300 Hertz auxiliary generator to power the voltage regulator and the brushless exciter for the power generator. These have the best voltage regulation and motor starting capability particularly with a Basler DVR2000 type voltage regulator.

The middle grade uses a voltage regulator that rectifies the 60 Hertz or 50 Hertz to power itself and the brushless exciter. This has lesser but still pretty good performance.

You do not want the bottommost level. These can only start a motor that is 1/10th maybe 1/6th the full load rating of the generator. If you have lots of small motors these do work.