calculate voltage
calculate voltage
(OP)
We are using an outdated DA program to record test data. our system calculates start current from the rms measured by a few yokagawa's. the start current is calculated
Irms/Vrms X Vrated= Istart
to really mess things up upon motor start we are seeing a 36% Vdrop
A 500Kw motor being powered By a cummins 2Mw gen through a 1-4 trans. any assiatnce would be great.
Irms/Vrms X Vrated= Istart
to really mess things up upon motor start we are seeing a 36% Vdrop
A 500Kw motor being powered By a cummins 2Mw gen through a 1-4 trans. any assiatnce would be great.






RE: calculate voltage
RE: calculate voltage
RE: calculate voltage
RE: calculate voltage
RE: calculate voltage
What does the generator say on its data plate???
What is the current drawn by the motor???
Need at least 2 things to calculate voltage.
Like the power and the current.
Is the trans a step up or down?
RE: calculate voltage
If the motor starting current is known, the rated terminal voltage is unknown and output HPs are unknown, the motor has to be properly analyzed for all its parameters, not only for the start current.
RE: calculate voltage
But we are experiencing a 36% voltage drop at start. And as i understand at motor start if there is a Vd of 36% then the I will be proporitionally decreased.
RE: calculate voltage
RE: calculate voltage
Calculating the starting current accurately is not a simple task. There are many factors to consider including the generator winding impedances, transformer impedance, genset voltage regulator and speed control performance, motor winding data and mechanical load.
Assuming full voltage starting of a "typical" 500kW motor and 2MW genset, my Caterpillar motor starting program says you should expect roughly 34% instantaneous voltage dip. The transient reactance of the Cat unit is 36%. So 34% instantaneous voltage drop would indicate roughly 100% of rated current, or 3100A (rated current at nameplate kVA).
RE: calculate voltage
RE: calculate voltage
RE: calculate voltage
I'm confused about the load bank. Explain in more detail what you are doing with it. "Astart/Ameasured = Vstart/Vmeasured" doesn't make sense if "Ameasured and "Vmeasured" are measured while running. During starting the current is much higher than normal while the voltage is lower than normal.
I think you would be wise to invest in the services of a qualified engineer if the results of this analysis are important.
RE: calculate voltage
or at least that was tge idea from our Test engineers.
I was tols that that is a start only equation and if our system was reading correctly we should be able to run that cal and have it come out right. Now our voltage is Rms not start voltage. Our system which I have no idea why does not measure start V or I, it calculates the I from the Rms Values. That did not seem right to me either. to get the voltage drop at start they are taking Irms/Vrms X 2300V (Rated V) = Vd although probably over simplified is that correct at the motor.
RE: calculate voltage
I still confused about how you're measuring voltage dip. When you refer to "RMS" quantities, do you mean these are values for the unloaded condition? RMS means "root mean square". Running and starting values are normally expressed as RMS.
Very simply,
Vdip = Istart * Z'd
where Istart is the starting current of the load and Z'd is the direct axis transient impedance of the generator and all quantities are complex. Z'd should be available from the generator nameplate. It may be shown as X'd and R.
RE: calculate voltage
the start current is for the customer, we manufacture and test large cryogenic pumps.
///Please, who is the motor-pump integrator?\\\
and the customer wants every piece of data available.
///It appears that you, as a pump manufacturer, would be responsible for pump data only. The motor-pump set integrator would be responsible for the motor electrical data and its starting requirements via the generator power supply. The generators usually have some leeway in the voltage dip control when it comes to the starting motor load. There are also industry standards covering this, e.g. IEEE Std 141-1993 Section 3.11.6 Effect of Motor Starting on Generators.\\\