Elevator feeder conductors vibrates upon start up of the elevator motor. You can actually see the conductor jump around in the disconnect switch. Has anybody ever runa cross a situation like this and what are possible causes/remedies? Would voltage drop be an issue here?
feeder conductors vibrate
- Thread starter bwyllie
- Start date
- Status
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: feeder conductors vibrate
I have also seen it. I even heard and felt vibrations at the breaker that fed the elevator. The engineering firm performing a review attributed the cause to higher than normal currents that resulted from an inadequate service transformer. We thought (I was a member of that firm at the time) that the service was significantly undersized, that the internal voltage drop during motor start caused too low a voltage to be available at the motor terminals, which of course would cause the starting current to be abnormally high. The utility company disagreed with the results of our review. Last I heard, the problem persists.
For that particular building, there were two elevators. Tenants would complain that their lights dimmed once or twice a week, and sometimes their computers would shut down (i.e., on loss of power ? due to low voltage). I recall having put forth the suggestion that the problems occurred when you had both elevator motors starting at the same time. Sure, it is a random event. And even if you have two people experimenting by closing the doors at the same time and pushing the button for the next floor, there is a good chance that the starting transient for one elevator motor will have finished before the other begins. But the time interval of motor starting is not of zero seconds duration. There is some amount of time at which a motor's starting current is at or near its peak value. Once in a while, on a random basis, the starting transients of two such motors will overlap. It would be at those times, infrequent though they may be, that the light flickering and power losses would be most noticeable. If the power system is not designed to handle such a transient, the impact of such a large starting current (two motors at the same moment) could be quite severe.
I have also seen it. I even heard and felt vibrations at the breaker that fed the elevator. The engineering firm performing a review attributed the cause to higher than normal currents that resulted from an inadequate service transformer. We thought (I was a member of that firm at the time) that the service was significantly undersized, that the internal voltage drop during motor start caused too low a voltage to be available at the motor terminals, which of course would cause the starting current to be abnormally high. The utility company disagreed with the results of our review. Last I heard, the problem persists.
For that particular building, there were two elevators. Tenants would complain that their lights dimmed once or twice a week, and sometimes their computers would shut down (i.e., on loss of power ? due to low voltage). I recall having put forth the suggestion that the problems occurred when you had both elevator motors starting at the same time. Sure, it is a random event. And even if you have two people experimenting by closing the doors at the same time and pushing the button for the next floor, there is a good chance that the starting transient for one elevator motor will have finished before the other begins. But the time interval of motor starting is not of zero seconds duration. There is some amount of time at which a motor's starting current is at or near its peak value. Once in a while, on a random basis, the starting transients of two such motors will overlap. It would be at those times, infrequent though they may be, that the light flickering and power losses would be most noticeable. If the power system is not designed to handle such a transient, the impact of such a large starting current (two motors at the same moment) could be quite severe.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: feeder conductors vibrate
That was one of the several recommendations that my (former) engineering company had given to the owner. Another recommendation was to have the utility upsize their transformer. Another was to interlock the two elevator control systems, to prevent simultaneous starting transients.
beanland
Senior Member
- Location
- Vancouver, WA
Moving Wire
Moving Wire
Conductors move when the magnetic field of one repels or attracts the magnetic field of the other AND they are not secured. It is well known that overhead utility wires bounce around during high current events. So, the starting inrush may cause the conductors to move. Step 1) secure the conductors before they break or come loose. Step 2) use soft start or other current reducing techniquest to lower current. Increasing the size of the utility transformer may make the problem worse and may raise available fault currents above equipment ratings.
Moving Wire
Conductors move when the magnetic field of one repels or attracts the magnetic field of the other AND they are not secured. It is well known that overhead utility wires bounce around during high current events. So, the starting inrush may cause the conductors to move. Step 1) secure the conductors before they break or come loose. Step 2) use soft start or other current reducing techniquest to lower current. Increasing the size of the utility transformer may make the problem worse and may raise available fault currents above equipment ratings.
Charlie:
I had a very similar problem at the first building I designed. Tenants said about once a week the lights would go off for a fraction of a second. We looked at all the loads (it was a medical office building) and decided something similar was happening. We thought maybe the Xray was firing at the same time as some other large draw equipment. The owner had us call in a "expert" who did line monitoring for a couple of weeks. He issued some report, and he got the POCO to tighten some overhead lines.
A couple of weeks later, I overheard the HVAC engineer talking about some problems they were having with the air handlers. Apparently, the entire system would go into a "failure" mode and completely shut down. The HVAC tech would come in and hit the reset button, and everything would start at once. When the HVAC tech solved his problem, he also solved our problem.
Steve
I had a very similar problem at the first building I designed. Tenants said about once a week the lights would go off for a fraction of a second. We looked at all the loads (it was a medical office building) and decided something similar was happening. We thought maybe the Xray was firing at the same time as some other large draw equipment. The owner had us call in a "expert" who did line monitoring for a couple of weeks. He issued some report, and he got the POCO to tighten some overhead lines.
A couple of weeks later, I overheard the HVAC engineer talking about some problems they were having with the air handlers. Apparently, the entire system would go into a "failure" mode and completely shut down. The HVAC tech would come in and hit the reset button, and everything would start at once. When the HVAC tech solved his problem, he also solved our problem.
Steve
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