Tripping Circuit Breaker on Wye to Delta Transition
Tripping Circuit Breaker on Wye to Delta Transition
(OP)
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?





RE: Tripping Circuit Breaker on Wye to Delta Transition
RE: Tripping Circuit Breaker on Wye to Delta Transition
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 http://w
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.
RE: Tripping Circuit Breaker on Wye to Delta Transition
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
http://www.lmphotonics.com
RE: Tripping Circuit Breaker on Wye to Delta Transition
RE: Tripping Circuit Breaker on Wye to Delta Transition
RE: Tripping Circuit Breaker on Wye to Delta Transition
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
RE: Tripping Circuit Breaker on Wye to Delta Transition
RE: Tripping Circuit Breaker on Wye to Delta Transition
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.
RE: Tripping Circuit Breaker on Wye to Delta Transition
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
RE: Tripping Circuit Breaker on Wye to Delta Transition
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.
RE: Tripping Circuit Breaker on Wye to Delta Transition
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.
RE: Tripping Circuit Breaker on Wye to Delta Transition
RE: Tripping Circuit Breaker on Wye to Delta Transition
RE: Tripping Circuit Breaker on Wye to Delta Transition
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.
RE: Tripping Circuit Breaker on Wye to Delta Transition
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.
RE: Tripping Circuit Breaker on Wye to Delta Transition
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Tripping Circuit Breaker on Wye to Delta Transition
RE: Tripping Circuit Breaker on Wye to Delta Transition
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Tripping Circuit Breaker on Wye to Delta Transition
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.
RE: Tripping Circuit Breaker on Wye to Delta Transition
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com