Generators and AC induction Motors (Capacitor Sizing?)
Generators and AC induction Motors (Capacitor Sizing?)
(OP)
I own a Northstar 15KW generator. I am running an HTC 500 (7.5Hp)planetary grinder(240VAC)on a VFD. It runs fine when no other loads are connected. I can have 110VAC angle grinders (2) with Shop vacs running together. As the angle grinders are turned on and off, it sets a fault on the VFD. The amp in rush is a bit much. Is it possible to add capacitor(s) to cushion this current inrush?





RE: Generators and AC induction Motors (Capacitor Sizing?)
Does the fault cause the VFD to shut down?
How do you measure the current inrush?
Bill
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"Why not the best?"
Jimmy Carter
RE: Generators and AC induction Motors (Capacitor Sizing?)
RE: Generators and AC induction Motors (Capacitor Sizing?)
Please be very careful - the DC link caps will operate at about 340V DC or so and can deliver more than enough current to kill you ten times over. As for how much capacitance you need to add, it's difficult to say. Look on Ebay for something around 2200uF and at least 400V rating and and try it. It will be a big capacitor - beer can / pint glass sized.
RE: Generators and AC induction Motors (Capacitor Sizing?)
RE: Generators and AC induction Motors (Capacitor Sizing?)
Adding caps to the DC link essentially increases the energy stored in the drive to the point where it can ride through the momentary dip without dropping below the trip threshold.
RE: Generators and AC induction Motors (Capacitor Sizing?)
Your controls may need tweeking.
Your no load frequency should be 61.8 Hz.
You may want to check the stability setting.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Generators and AC induction Motors (Capacitor Sizing?)
Keith Cress
kcress - http://www.flaminsystems.com
RE: Generators and AC induction Motors (Capacitor Sizing?)
A 15 KVA machine probably has a conventional AVR. A lot of smaller economy model machines don't have an AVR. On some smaller machines the excitation is supplied by capacitors. Adding capacitors to these machines will drive the voltage up.
If you have an AVR then you may have too much stability dialled in. This will cause slow voltage response to load changes.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Generators and AC induction Motors (Capacitor Sizing?)
RE: Generators and AC induction Motors (Capacitor Sizing?)
Big electrolytic cap: ~£100.
New larger generator: ~£10,000?
RE: Generators and AC induction Motors (Capacitor Sizing?)
RE: Generators and AC induction Motors (Capacitor Sizing?)
RE: Generators and AC induction Motors (Capacitor Sizing?)
You just might want to check the stability and the no load Hz before spending money.
If your frequency is a little low, the UFRO feature of the AVR may drop the voltage in response to sudden loads.
A 15 KVA set should not have issues with an angle grinder if it is set properly.
Bill
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"Why not the best?"
Jimmy Carter
RE: Generators and AC induction Motors (Capacitor Sizing?)
RE: Generators and AC induction Motors (Capacitor Sizing?)
Check your voltage.
Check your frequency. If you can find an old, old electric clock with a synchronous motor drive it can be used to check the frequency.
The specs show a speed of 3600 RPM. The industry standard world wide would be 3600 RPM plus 3%, or 3708 RPM. The voltage is speed dependant. At 3708 RPM the voltage should be about 124 volts. At full load the speed should drop to 3600 RPM and the voltage drop to 120 Volts.
With capacitor voltage control you won't have a stability adjustment or UFRO.
Speed is probably the issue, If the voltage is low when the speed is correct, let us know.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Generators and AC induction Motors (Capacitor Sizing?)
RE: Generators and AC induction Motors (Capacitor Sizing?)
Keep in mind none of us are suggesting you open up the drive to add capacitance. On a 7.5HP drive there should be DC link screw terminals at its field wiring terminal blocks.
Please keep Scotty's warnings firmly in mind..
Keith Cress
kcress - http://www.flaminsystems.com