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Compressor Starting

Compressor Starting

Compressor Starting

(OP)
We are trying to start a reciprocating compressor by Autotransformer. We can only achieve 5% flicker limit by using 40% tap. The load torque curve we received is as below,
Speed   Torque
0%      12.5%
10%      6%
20%      10.4%
30%      17.5%
39%      26.9%
49%      38%
59%      50%
69%      63%
79%      76%
88.5%    88%
98%      100%     

With this load torque, we will never start the compressor even with aross the line.

I am assuming something wrong is wrong with this curve. We may have to request a different curve, such as minimum flow start curve, no load startup curve. Any suggestions?

Any inputs would be apprecisted.



 

RE: Compressor Starting

(OP)
I made a mistake on those conversion. I should devide those torque values by motor full load torque valuse.

How long does it take to start a compressor by 40% Tap seeting?

RE: Compressor Starting

No idea. I'm guessing it won't start. That isn't something that can be answered easily. I would need a lot more info and have to find even more ambition to actually calculate that.
 

RE: Compressor Starting

On the 40% voltage tap, you have only 16%  of normal motor torque.


 

"The more the universe seems comprehensible, the more it also seems pointless." -- Steven Weinberg

RE: Compressor Starting

Fix the unloader on the compressor. I have never seen a large reciprocating compressor started without an unloader. If you try to start loaded the motor will probably stall.

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

RE: Compressor Starting

Waross nailed it. Verify unloader time setting. Too short, your motor will stall.

RE: Compressor Starting

(OP)
The calculated compressor acceleration time is 25s since the weak system and high inertia.

Voltage dip on supply bus is 40% and the total innertia is 6375+4196=10571 (lb.ft2).

It seems to me it is too long such a compressor DOL.  

RE: Compressor Starting

What size of compressor motor do you have? What is the supply voltage? Are you on a transformer or a distribution primary circuit?

Quote:


Voltage dip on supply bus is 40% and the total innertia is 6375+4196=10571 (lb.ft2).
You may have to resort to alternate methods to start this compressor.
One approach may be to use a smaller pony motor on a VFD to spin the main motor and compressor up, unloaded and go DOL when it is up to speed. You may want to consider comparing the phase angle of the residual voltage at the motor terminals to the line voltage and go DOL when the residual is in phase with the line to minimize current surges when the main contactor puts the main motor DOL.
BUT: If the supply is as soft as I understand, youmay have problems with with voltage dips during normal running. (For instance when the unloader cycles.)

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

RE: Compressor Starting

(OP)
2200Hp motor and supply voltage is 4160V, which is step down from 3MVA-Pri 25KV.

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