Need help/advise

Status
Not open for further replies.
S

SeanKelly

Member
Had a call at a paper plant and need help. The plant has a 150 hp 480 volt bailer that compresses, cuts, and then bands of all types of paper. Whenever the blade throws to cut a good number of lights go down. The lighting is 277 volt fed from the same 600 amp breaker in the distribution gear. The general setup is 600 amp main feeding to 2 480 panels with parallel 350 copper. One of the panels has a 100A subfeed for a transformer that feeds 2 208 panels. The feed for the bailer itself is 3/0 copper on a 300 magnetic breaker. On the nameplate of the bailer itself it also states 292 FLA. I have limited experience with equipment of this size but I could use some help. Here are my questions and go easy on me.

- When I look up ampacity in the hp chart for 150hp 460v motors I get 180 amps. The nameplate also has a FLA of 292. What is the proper way to size the feed and disconnect to a piece of machinery like this?

- Could the undersize feeds to the bailer increase the load on the circuit and make the lights dim?

- Has any ever ran into problems where the load on a piece of equipment is only affecting certain phases of the service?

We are going back tomorrow with the right protective gear to do some testing and I will try and take some pics of the bailer feed/conduit work for entertainment purposes. Any input is greatly appreciated.
 
080505-0709 EST

SeanKelly:

buckofdurham has some good questions because this will tell you if something has changed.

I will add some points on troubleshooting.

I really do not understand your circuit relative to what beyond the main 600 A breaker is common to the lights and the motor. The impedance of this common path to both lights and the motor is one area of concern.

Does your motor remain on constantly and a clutch of some sort engage to do the cut, or is the motor directly connected to the cutter and the motor is started each time a cut is made? The later will involve motor inrush at startup as well as the load, the former will just be load current from the cutting operation.

For a given power output the input current increases as the voltage goes down and vice versa. This is probably reasonably valid over a +/-15% voltage change relative to nominal for a typical induction motor.

If the motor runs continuously, then mechanical inertia should supply some of the energy for cutting.

To troubleshoot I would monitor voltage at several points before and during the cut operation.
(1) Input to the 600 A breaker.
(2) Output of the 600 A breaker.
(3) The last point common to both motor and lights.
This should point you in the direction to investigate further.

You may also want to monitor motor current before and during the cut operation at the same time you do the voltage checks.

Are the lights fed from 3 phase, or are all the lights fed single phase from one pair of lines. Your implication is that not all lights dim when the cut operation occurs. This might imply a high resistance connection on one leg. Voltage measurements between all three legs and or neutral should identify this.

.
 
SeanKelly said:
- When I look up ampacity in the hp chart for 150hp 460v motors I get 180 amps. The nameplate also has a FLA of 292. What is the proper way to size the feed and disconnect to a piece of machinery like this?
Click to expand...
You have to size by the nameplate in this case. Is this a low speed or some other special type of motor that draws a lot more current than the standard motors that Table 430.250 is based on? Or are their other loads associtated with the equipment?
- Could the undersize feeds to the bailer increase the load on the circuit and make the lights dim?
Click to expand...
The undersize feeder should act to reduce the motor starting current, but will increase the time that the high starting current is required.
- Has any ever ran into problems where the load on a piece of equipment is only affecting certain phases of the service?
Click to expand...
As far as the lights, maybe some of them already have significant voltage drop on their branch circuits and the additional voltage drop from the motor operation drops them out.

That being said the most important question has already been asked...is this a new problem, or has the problem existed from the original installation of the equipment?
 
Went back today and got some readings on the bailer. The amperage spikes to 410 on A, 398 on B, and 412 on C when the blade on the bailer engages to make a cut. This process occurs roughly every 5 minutes. The lights just constantly ramp on and off. I think the whole service is designed wrong and now we are looking at ways to correct it. I think the reason this happened in the first place is the distribution gear has no remaining spaces and the 6 discos are already in place. I will keep you posted
 
Status
Not open for further replies.
Top