I have seen it done on very small machines, but then you could argue that it is not necessary as the current is always so low.
Mark Empson
Advanced Motor Control Ltd
When you say that the pump is unloaded, are you sure that mechanically the load reflected to the pump is actually reduced?
What type of pump is this and how are you controlling the load?
If it is a turbine pump, or a moving cavity pump, or some multi stage pumps, closing down the discharge side...
Open transition switching is always going to result in transients to flux the iron.
If switching is too son after the disconnect, the rotor will still be generating and depending on the phase relationship between the "generated voltage" and the line voltage, and the magnitude of the generated...
Waross
Yes I agree.Have gone to 40% plus on many occasions.
It depends on the generator set up and configurations.
If a three phase averaging AVR is used, plus external excitation (permanent magnet generator for excitation) you can commonly go to full voltage starting with some sag, but no...
I have seen a high earth current in a number of installations of bore hole pumps with a steel riser.
If the cables down the well to the motor are not perfectly fed down the bore with the motor, you can end up with a partial turn of one phase around the riser and it acts like a short circuited...
Hello Guilhermebr
This could be Middlebrook instability.
Do you have a harmonic filter in series with the input to the VFD?
Do you have a Hi Z impedance on the input to the VFD?
I usually find Middlebrook in a rural installation with a single VFD on a dedicated transformer and many KM of...
Well said Jeff.
In addition to Jeffs comments, there are major differences in start characteristics due to the variation in High Slip characteristics of different induction motors.
Typically, you will need to develop around 40% torque initially to start the pump, and usually you would look at 3...
Hi Lionel
That is a good summary from a suppliers perspective and I believe would be pretty well the defacto attitude towards harmonics across the board.
Here, in New Zealand, we do have rural areas where the accumulation of the harmonic currents on the local network can result in harmonic...
A three phase rectifier that is balanced will draw ODD harmonics minus the triplens, so expect to see 5th, 7th, 11th, 13th .... with the amplitude reducing as the harmonic number increases. (multiples of 3 balance out.)
Harmonic mitigation may be required by regulation. - it is needed in some...
Hi
A bit more information would be a great help in providing the best advice.
If the manufacturer recommends that you do an ID Run, then there could be a valid reason for this.
1. There are many variations on two themes when it comes to the waveform generation within the drive. Essentially...
The drive runs a routine called ID Run, or Auto-Tune whereby it feeds different waveforms/frequencies to the motor in order to determine what the motor characteristics are.
Often, there are two choices, a static ID Run where the motor does not turn, and a rotating ID Run where the motor tunes...
Part of the bus charging mechanism of the VFD??
Rotate the phases around and see if the trip moves to a different phase.
Mark Empson
Advanced Motor Control Ltd
FacEngrPE
There are some who believe that any motor with a VFD installed, will save energy.
I have a saying that I have used for forty odd years, You can only save some of the energy that is being wasted.
A motor that is running at say 93% efficiency, is not wasting much energy, so the energy...
Hello Muthu
Yes, VFDs can be used on turbine and positive displacement pumps, but you must use them correctly and for the right reason.
If you consider a standard centrifugal pump, then varying the speed of the impellor is essentially the same as varying the diameter of the impellor and there...
Hello Loghman_ra
To engineer the best solution, you need to have all the facts.
"evacuating the floods" - this statement suggests that this is a high flow low head application and commonly served by the use of a turbine pump rather than the more usual centrifugal pump.
A turbine pump has very...
I would normally use a 4-20mA control valve on the discharge side of the pump, start with the valve closed to about 10 - 15% open and with submersible pumps, the minimum start current in this state, is commonly around 250%. When the pump is up to full speed, open the valve slowly in a manner to...
Hi Bill
I would be looking at SVG to get good tracking.
The issue is that with a good modern motor, you are looking at a reactive current around 6 times the motor rated current at zero speed, around 3 times at 50% speed and about 0.2 times at just below rated speed and if you want a good...
Totally agree about the starting reactive current, but the power factor changes with the slip of the motor and if you are able to correctly compensate a rapidly moving target, you can significantly reduce the intial start current. You need a very high speed compensation loop though, as a pump...
Both the VFD and the soft starter can be used up to 11KV.
If you are using a soft starter, it pays to look at the high slip performance of the motor, especially the Locked Rotor Current and the Locked Rotor Torque.
As you reduce the start current, you reduce the start torque by the current...
Any centrifugal load, will increase the motor load as the speed is increased, and generally, the fan or pump is very reliant on discharge pressure to limit the motor load. This is a function of the pump or fan operational curves and this is fundamental to operation of such a mechanical device...
