Problems in starting synchronous motor in a pump station
Problems in starting synchronous motor in a pump station
(OP)
Hi folks,
A 5.5 MW, 6.9 kV synchronous motor did not start when it is energized. Then we moved the rotor position and the motor starts. We have observed that the motor only runs if the rotor is in a particular position.
I wonder if anybody has faced a problem like that.
A 5.5 MW, 6.9 kV synchronous motor did not start when it is energized. Then we moved the rotor position and the motor starts. We have observed that the motor only runs if the rotor is in a particular position.
I wonder if anybody has faced a problem like that.
Best Regards,
Herivelto S. Bronzeado
Brasília, Brazil
http://www.linkedin.com/profile/view?id=46319837&a...





RE: Problems in starting synchronous motor in a pump station
RE: Problems in starting synchronous motor in a pump station
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Problems in starting synchronous motor in a pump station
OT:
I had a case of sympathetic inrush in a number of pump stations a few months ago. Caused even harmonics which made a filter resonate (was not supposed to see any even harmonics) and "pumped up" the DC link in idling VFDs. Your articles were very helpful.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Problems in starting synchronous motor in a pump station
The motor does not rotate during starting.
waross,
The amortisseur (damping) winding is not open.
Skogsgurra,
The rotor winding is short circuited by a resistor during motor starting.
(Obs.: Could you, please, send the reports (if any) on your case of sympathetic inrush? I am happy in hearing that my papers wee helpful to you. Thank you!)
Best Regards,
Herivelto S. Bronzeado
Brasília, Brazil
http://www.linkedin.com/profile/view?id=46319837&a...
RE: Problems in starting synchronous motor in a pump station
We are suspecting that it may be a magnetic locking between the stator teeth and the rotor teeth, knowing as a "cogging" phenomenon or magnetic locking of induction motor (mind that the synchronous motor atarts as a induction motor).
I wonder if you all could comments on that suspecting. Thank you.
Best Regards,
Herivelto S. Bronzeado
Brasília, Brazil
http://www.linkedin.com/profile/view?id=46319837&a...
RE: Problems in starting synchronous motor in a pump station
Is this motor with brushless excitation or with DC sliprings?
Muthu
www.edison.co.in
RE: Problems in starting synchronous motor in a pump station
How are you starting?
DOL? VFD? Soft Start? Other method?
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Problems in starting synchronous motor in a pump station
Have you had some activity on the motor or the problem occurred during normal operation .Large current and moment are at the start so you should be brave and turn the rotor if motor will not start.Did you controlled inrush current and are they symmetrical .
RE: Problems in starting synchronous motor in a pump station
Is the field fed by sliprings? Are there bad spots on the slip rings?
Is the air space clean? I had a motor that had magnetic dust accumulate in the air gap. It would spin free but would lock up when trying to start.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Problems in starting synchronous motor in a pump station
What is the field data and what size of resistor are you using?
Assuming the motor is otherwise healthy, cogging would be a design issue.
RE: Problems in starting synchronous motor in a pump station
RE: Problems in starting synchronous motor in a pump station
The motor is with DC sliprings.
waross,
We try to start directly and also with Soft Start.
The field is fed by DC sliprings. There is no damage to the amortisseur winding nor bad spots on the slip rings. The air space clean.
During the starting when the motor did not move, we just move the rotor to another position and it runs normally. ????????
LionelHutz,)4 Mar 16 14:01
The motor is brand new. The rotor has both squirel cage and field windings. We try to start directly and via Soft Start. Just now, I don not know the size of the resistor. We also change it trying to solve the problem.
Parchie,
"Quote (LionelHutz)
Assuming the motor is otherwise healthy, cogging would be a design issue.
I agree. IIRC, this problem was already solved decades ago by using skewed slots in the rotor!"
We also think that it is a design problem. Last week the manufacturer taked the motor to factory.
I will report the work result when to motor return to the pump station.
Thank you all for the "brain storm" in this subject.
Best Regards,
Herivelto S. Bronzeado
Brasília, Brazil
http://www.linkedin.com/profile/view?id=46319837&a...
RE: Problems in starting synchronous motor in a pump station
RE: Problems in starting synchronous motor in a pump station
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Problems in starting synchronous motor in a pump station
Good luck !
RE: Problems in starting synchronous motor in a pump station
Too high an oil pressure may force the dry shaft against the top of the journal. A half of a turn would carry enough oil to the top of the journal to substantially reduce the stiction.
Years ago I was involved with multiple starts on strings of five DC generators with a combined output of 5750 HP.
The sets did not have turning gear and did not have oil pumps. They had to be manually turned enough revolutions for the oil rings to carry oil up to the shaft.
Dry Babbitt bearings are a drag, Really a drag. grin.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Problems in starting synchronous motor in a pump station
We have observed that the motor only runs if the rotor is in a particular position..."
The OP's reply to warcross was, "...The amortisseur (damping) winding is not open."
What tests were conducted to confirm the amortisseur winding is NOT open?
The statement declaring that when the rotor position is moved and then the motor starts... is a signature
indicator of an open bar circuit.
John
RE: Problems in starting synchronous motor in a pump station
Years ago, we did a rotor rewind of a salient pole 750 RPM motor which had a three phase rotor winding in the pole faces for starting and separate DC fed field coils for running.
Right now, we are rewinding a 25 year old synchronous induction motor where the rotor, after starting as an induction motor, is fed DC near the synch speed by shorting two phases. The phase that carries the full DC current has wider slots and a wider slipring.
Both are very interesting constructions of ye old, which present day bean counters wouldn't allow, let alone understand.
Muthu
www.edison.co.in
RE: Problems in starting synchronous motor in a pump station
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Problems in starting synchronous motor in a pump station
Since synch motors have a larger air gap than the normal wound rotor motor, it is not an easy conversion. The air-gap in a synchronous induction motor is taken care of at the design stage.
Also, since the DC current in one phase is twice that of other two phases, a straight conversion will result in rotor overheating in that phase unless the copper size is increased for that phase.
Here are some pics of the 3.3 KV, 2000 HP, 12 pole synch induction motor rotor we are currently rewinding at our shop showing the different slot sizes and slipring sizes.
Muthu
www.edison.co.in
RE: Problems in starting synchronous motor in a pump station
Muthu
www.edison.co.in
RE: Problems in starting synchronous motor in a pump station
RE: Problems in starting synchronous motor in a pump station
The pics seem OK in my browser. It often has issues with oversized pics.
Yours
Bill
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Problems in starting synchronous motor in a pump station
RE: Problems in starting synchronous motor in a pump station
Muthu
www.edison.co.in