1000 hp reciprocating compressor synchronous motor alignment 2

[dithomas]

The foundation of a 50 year old 1000 HP reciprocating compressor was recently rebuild. The synchronous motor is of the type where the rotor is attached to the compressor shaft. It is now time to get the stator back in place and aligned.

How does one account for the magnetic center of the stator with the position of the rotor fixed by the compressor.

Thank you in advance for your assistance.

 

[waross]

It's been a long time but let's take a guess, Synchronous machines generally include an armortisiue??? squirrel cage damper winding. This is used to start synchronous motors. Conventional wisdom was that prolonged operation on the damper winding would result in overheating of the damper winding.
I think that the starting current was about the same as a same sized induction motor. (approx. 6 times FLC)
The relatively higher resistance of the squirrel cage damper winding compared to an induction motor may have reduced the starting current a little but not much.
Does anyone have any hard numbers on this??

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[electricpete]

If starting current is similar to induction motors then the high unbalanced mag pull is probably similar to induction motors during start. I'd be curious to know if this machine has D.O.L. start.

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(2B)+(2B)' ?

 

[dithomas]

To answer a few questions:
The 2300V motor starts across the line, the field application is of the SCR type with auto synchronizing, and manual field current control. The motor starts and synchronizes in a couple of seconds. The field is applies when the AC components induced in the field reduces in frequency to a point that indicates close to 0% slip.

The field current will drop about 15% from ambient to operating temp for to rotor winding resistance increasing. With field current at the rated value the motor will operate at a 0.80% leading PF looking like a capacitor on the system. Magic!!!!

There are starting (damping) bars in each rotor pole connect to a ring on each side of the rotor. The starting torque is developed in these bars. Photo (not to clear) attached. There must be a cool off time for these bars between starts.

I watched one of these motors start with bad connection on the rotor bars to the ring and it looked like a 4th of July Pin Wheel.

Dan