I have a situation where a 200 amp Cutler Hammer HJD breaker is tripping when the 75 HP Air Compressor is being started and it transitions from Wye to Delta. The Breaker trips instantly when Delta contact closes. I am aware of the Wye Delta transition inrush. But this is an application where the Wye Delta starting arrangement has been successfully used many times with no problems. And this is happening to (2) Identical installations of the Air compressor and breakers, same location. The question is "What site conditions create this unusual excessive inrush? Or is it the breaker that is extra sensitive?
Eng-Tips is the largest engineering community on the Internet
Intelligent Work Forums for Engineering Professionals
-
Congratulations waross on being selected by the Tek-Tips community for having the most helpful posts in the forums last week. Way to Go!
Tripping Circuit Breaker on Wye to Delta Transition 2
- Thread starter reelcoy
- Start date
-
1
- #3
This can be a real pain in the neck! I've just had an installation where two of the three 150kW motors started OK and the third identical motor kept tripping the breaker on changeover to delta (all open transition). In the end, swapped the breaker to another manufacturer and all is now OK!
Closed transition is the answer on big motors but it is expensive. I wouldn't have thought that 75HP would need closed transition.
Have a look at
Make sure that the connections allow the changeover to delta to be one that the motor "falls back 30°" rather than one that "pulls it forward 30°". This does help - sometimes.
Closed transition is the answer on big motors but it is expensive. I wouldn't have thought that 75HP would need closed transition.
Have a look at
Make sure that the connections allow the changeover to delta to be one that the motor "falls back 30°" rather than one that "pulls it forward 30°". This does help - sometimes.
-
1
- #4
Hello reelcoy
There are two major problems with the star delta starter.
Firstly, there is a very high torque and current transition that occurs when changing from star to delta, and second, if the motor does not develop enough torque in star to accelerate to full speed, it will change to full voltage (delta connection) at part speed and this will result in DOL start current (6 - 8 times the rated current of the motor).
This can also occur if the timer is set for too short a time.
Ideally, the motor will accelerate to full speed in star and then change to delta.
A closed transition star delta starter will reduce the magnitude of the reclose transient, but it will not overcome the high start current if the transition occurs at less than full speed.
Ensure that the transition only occurs when the motor has reached the highest speed that it can in star.
You will get major variations in performance between machines due to the wide variation in motor starting characteristics. Modern high efficiency motors tend to have inferior starting characteristics.
Best regards,
Mark Empson
There are two major problems with the star delta starter.
Firstly, there is a very high torque and current transition that occurs when changing from star to delta, and second, if the motor does not develop enough torque in star to accelerate to full speed, it will change to full voltage (delta connection) at part speed and this will result in DOL start current (6 - 8 times the rated current of the motor).
This can also occur if the timer is set for too short a time.
Ideally, the motor will accelerate to full speed in star and then change to delta.
A closed transition star delta starter will reduce the magnitude of the reclose transient, but it will not overcome the high start current if the transition occurs at less than full speed.
Ensure that the transition only occurs when the motor has reached the highest speed that it can in star.
You will get major variations in performance between machines due to the wide variation in motor starting characteristics. Modern high efficiency motors tend to have inferior starting characteristics.
Best regards,
Mark Empson
- Thread starter
- #6
This is a open transition Wye-Delta on brand new compressors, brand new breakers.The wye time is adjustable with a minimum of 10 sec and a max of 30. Adjusting the Wye time between the min and max did not make a difference. The units come up to full speed before transition and the loading of the compressor is on a time delay of 6 secs that initiates when the Delta contactor pulls in. One of the units started up and ran then was turned off. But then would not start after that. Then the other compressor start up was attemped and would not start, tripping the breaker on transition. Changing out the starter or changing to a closed transition is not an option with the Compressor manufacturer. They supplied the starter with the units and have had no problems with this arrangement elsewhere.
- Thread starter
- #7
We are putting a power logger on the system to see if there is anything going on that we can't see.
Walden indicated that he had the problem on one of the three 150KW units and changed to a different breaker manufacturer which fixed that unit. Was there any reason that one breaker design of the same ampacity will work better than another?
So that I can specify that breaker over the Cutler Hammer HJD200?
Thank you
Walden indicated that he had the problem on one of the three 150KW units and changed to a different breaker manufacturer which fixed that unit. Was there any reason that one breaker design of the same ampacity will work better than another?
So that I can specify that breaker over the Cutler Hammer HJD200?
Thank you
I had the same problem on one of my compressors. Main CB tripping at transition. The problem was as Marke said in his post, the motor was not turning fast enough in star at transition. This was a refrigeration motor so I will not go in depth of the cure. I am not real good with CB's but most have a thermo and a magnetic trip and suspect that it may be the magnetic trip that is tripping your CB. I know you have already checked motor current during star start. If yours is like mine then you should be pulling around twice FLA during star start, then after switch to delta mine is still pulling twice FLA for a couple of seconds until current rapidly starts falling off when the motor comes up to speed. What does the voltage and current balance look like in star start. What is your motor current with the compressor fully unloaded, in delta and up to full speed? I assume you have a balanced voltage on the line. Is the line side sized right for the motor? I'm just bouncing around some ideas. We have a couple of 200HP star/delta open transition screw air compressors and one 100HP and I could verify what the currents should look like during start instead of comparing them to my refrigeration systems if you like. If you have a working identical compressor then I would take measurement data from it and compare it to the malfunctioning ones. If you suspect the CB you could always swap it with the working one.
reelcoy, i think you have done your part as checking all neccesary parameters that apparently affects your compressor system like, running it unloaded, resetting time for transitions, using power logger, etc.
We have such CB (same OEM as yours)in the past that previuosly works fine but later it just trips out while starting the motor, though DOL configuration but we've found out as operation history unveils that this CB had tripped once against a motor phase to ground fault. However, upon restoring the machine frequent tripping of CB at starting occurs. With enough and thorough parameter inspections, i decided to replace the CB as suspected..then the latter operates smoothly and works fine.
I'd as some CB experts they said: once a CB particularly a MCCB's was tripped due to short circuits, its component will then vulnerable and sensitive to in rush currents. It is better then to replace a new CB rather than causing a nuisance tripping from the old one. I'm quite convince.
Any thoughts?
"Whenever you are asked if you can do a job, tell them, certainly I can! Then get busy and find out how to do it." Theodore Roosevelt.
We have such CB (same OEM as yours)in the past that previuosly works fine but later it just trips out while starting the motor, though DOL configuration but we've found out as operation history unveils that this CB had tripped once against a motor phase to ground fault. However, upon restoring the machine frequent tripping of CB at starting occurs. With enough and thorough parameter inspections, i decided to replace the CB as suspected..then the latter operates smoothly and works fine.
I'd as some CB experts they said: once a CB particularly a MCCB's was tripped due to short circuits, its component will then vulnerable and sensitive to in rush currents. It is better then to replace a new CB rather than causing a nuisance tripping from the old one. I'm quite convince.
Any thoughts?
"Whenever you are asked if you can do a job, tell them, certainly I can! Then get busy and find out how to do it." Theodore Roosevelt.
I also had the same problem with a 200 hp air compressor.
Did a lot of homework. The manufacture blew me off. They claim never to have had a star delta transition tripping problem as long as the appropriate CB is used, ie;one with a high enough RMS trip value, or no rms just thermal trip. I understand the problem to be during the open transition of star to delta (~50 ms.) The field collapses and generates a back EMF (most likely out of phase)into the power system. This will trip your CB when its RMS trip setting is right on the edge with the back EMF. I allways wanted... but never had the time to create an additional delay time of ~25 to 30 ms just by putting in a simply mechanical cube relay between the Delta controller output and the delta run power relay. The pull up time is 25 to 30 ms. My thinking is this extra time might allow the field the collapse further and not generate the large out of phase back EMF? Any thoughts on this?
Scramode
Did a lot of homework. The manufacture blew me off. They claim never to have had a star delta transition tripping problem as long as the appropriate CB is used, ie;one with a high enough RMS trip value, or no rms just thermal trip. I understand the problem to be during the open transition of star to delta (~50 ms.) The field collapses and generates a back EMF (most likely out of phase)into the power system. This will trip your CB when its RMS trip setting is right on the edge with the back EMF. I allways wanted... but never had the time to create an additional delay time of ~25 to 30 ms just by putting in a simply mechanical cube relay between the Delta controller output and the delta run power relay. The pull up time is 25 to 30 ms. My thinking is this extra time might allow the field the collapse further and not generate the large out of phase back EMF? Any thoughts on this?
Scramode
LionelHutz
Electrical
It's basically because the motor magnetic fields and terminal voltages go out of phase while transitioning. You get a large current surge to re-establish the in-phase magnetic field.
Doing an open transition requires a breaker that allows a large instantaneous current without tripping.
FYI, I know one a chiller manufacturer that will not use open transition because the torque transients are damaging to the equipment.
Scramode - try going somewhere around 10 to 50 times your quoted times for a delay depending on the motor size. Some large motors can still have a significant terminal voltage even after being de-energized for few seconds.
Doing an open transition requires a breaker that allows a large instantaneous current without tripping.
FYI, I know one a chiller manufacturer that will not use open transition because the torque transients are damaging to the equipment.
Scramode - try going somewhere around 10 to 50 times your quoted times for a delay depending on the motor size. Some large motors can still have a significant terminal voltage even after being de-energized for few seconds.
I would check the following:
1. If this is new installtion, that is this particular starter was being commissioned for the first time, check for rolled phases for delta connection. That is motor tries to run in reverse direction in delta.
2.Does the breaker have adjustable instantaneous/ magnetic setting? If so set it to high. Many are left at low setting.
3. Check that the time delay for star run is apppropirate, does the motor come up to acceptable speed before the transition? Say 80% of the rated speed.
4. Was breaker tested by a testing company?
If all failing replace the breaker with a good tested breaker.
1. If this is new installtion, that is this particular starter was being commissioned for the first time, check for rolled phases for delta connection. That is motor tries to run in reverse direction in delta.
2.Does the breaker have adjustable instantaneous/ magnetic setting? If so set it to high. Many are left at low setting.
3. Check that the time delay for star run is apppropirate, does the motor come up to acceptable speed before the transition? Say 80% of the rated speed.
4. Was breaker tested by a testing company?
If all failing replace the breaker with a good tested breaker.
- Thread starter
- #15
Hello,
Sorry for the feedback delay and thank you for the interest. We did a Power log on the system. With no real answers coming from it. Since reading the information and using the fluke 1735 is new to me. The information created more questions than answers. When reviewing the spreadsheet information. One oddity for me was during Wye start up the 3 phases indicated near balanced current draw then when it trasitioned to Delta contactor and subsequent tripping of the breaker the spreadsheet shows only one phase rising above and beyond the current level of wye starting one phase at zero and the other phase in the middle.
At this point the Compressor Manufacturer will not send the issue to their engineering unless the unit is wired according to their print which calls for (3) 125 Amp time delay fuses. The customer does not want to run fuses in the process plant. Additionaly during the power logging and attempted starts of each unit. One of the units started. The technician did not log that attempted start. And the only difference he noted at the time that this unit started and ran was that other pieces of process equipment were not running. So I am waiting to hear the results of the attempted start up with all other equipment shut down. As the first test. Then since the customer does not want fuses installed they are going to try another brand MCCB.
Sorry for the feedback delay and thank you for the interest. We did a Power log on the system. With no real answers coming from it. Since reading the information and using the fluke 1735 is new to me. The information created more questions than answers. When reviewing the spreadsheet information. One oddity for me was during Wye start up the 3 phases indicated near balanced current draw then when it trasitioned to Delta contactor and subsequent tripping of the breaker the spreadsheet shows only one phase rising above and beyond the current level of wye starting one phase at zero and the other phase in the middle.
At this point the Compressor Manufacturer will not send the issue to their engineering unless the unit is wired according to their print which calls for (3) 125 Amp time delay fuses. The customer does not want to run fuses in the process plant. Additionaly during the power logging and attempted starts of each unit. One of the units started. The technician did not log that attempted start. And the only difference he noted at the time that this unit started and ran was that other pieces of process equipment were not running. So I am waiting to hear the results of the attempted start up with all other equipment shut down. As the first test. Then since the customer does not want fuses installed they are going to try another brand MCCB.
- Thread starter
- #16
Update,
I figured out that I was seeing minimum,average and Max when trying to interpet the readings. Which means that the transition from Wye to Delta run had higher current than the starting current. The customer has decided to install fuses as the compressor manufacturer has suggested. And the start up is scheduled for tuesday the 17th. I will let you know what happens.
I figured out that I was seeing minimum,average and Max when trying to interpet the readings. Which means that the transition from Wye to Delta run had higher current than the starting current. The customer has decided to install fuses as the compressor manufacturer has suggested. And the start up is scheduled for tuesday the 17th. I will let you know what happens.
If they are going to put fuses on a compressor(yuck!) Make dang sure they add a $100 phase loss detector between them and the motor. Interlock the contactor with the phase loss detector. Very cheap insurance for a very expensive motor that can be damaged by a $10 fuse.
Keith Cress
Flamin Systems, Inc.-
Keith Cress
Flamin Systems, Inc.-
If the motor is wired right then at transition to delta there should not be an appreciable increase of current that you can see with your clamp on ammeter as long as the motor is turning fast enough. My problem with the refrigeration compressor was the motor load when the compressor slide valve was at 0%. The liquid ammonia injection cooling solenoid had wire draw on the valve that was allowing liquid ammonia into the compressor when turned off. When the compressor was turned on this presented an additional load for the motor and it was turning app. 30% slower at transition and that tripped its main CB. I took the motor rear bearing cap off and put a contact tachometer on the shaft. I could not really tell that the motor was turning slower by listening. Another thing to try is to uncouple the motor from the compressor and see if the CB trips.
If much liquid at all got into the compressor why hasn't it slugged? Why are the connecting rods not bent? Or are they?
Keith Cress
Flamin Systems, Inc.-
Keith Cress
Flamin Systems, Inc.-
itsmoked, I had in an earlier post but not in my last post included that it was a screw compressor. I only included my experience because these two machines are similar in many ways even though mine are almost a scale factor of 10 larger in size. With my liquid ammonia cooling injection solenoid, it was not a lot of ammonia that was in the screw but enough to bog it down. Too much ammonia could have caused catastrophic failure of the compressor as it is designed to pump a gas and not a liquid.
At the time I also thought that it was the circuit breaker and sent it out for testing. It came back with a good report but the magnetic trip was a little off on the down side but in their oppinion was not causing my problem. I was under a lot of pressure to replace the circuit breaker but resisted becaue of the price and then investigated the refrigeration side by visiting that type of forum and gleaning a lot of good information not unlike I receive here.
At the time I also thought that it was the circuit breaker and sent it out for testing. It came back with a good report but the magnetic trip was a little off on the down side but in their oppinion was not causing my problem. I was under a lot of pressure to replace the circuit breaker but resisted becaue of the price and then investigated the refrigeration side by visiting that type of forum and gleaning a lot of good information not unlike I receive here.
- Status
Similar threads
- Locked
- Question
- Locked
- Question
- Locked
- Question
- Locked
- Question