Sangernm
New member
- Location
- Arlington,VA
Hi all-
I recently just had a design meeting with a general contractor about a high-rise residential building my firm is deisigning. One of the recommendations the contractor made to me was to try and eliminate the ATS that we had designated for switching over all elevator loads, transfer the elevator loads to another ATS, and resize the other ATS to handle the elevator loads in addition to its existing loads. The contractor's reasoning for this was that previously they had encountered situations where upon loss of normal power and in emergency mode the elevator motors were acting as generators on the way down during recall and injecting power back into the feeders and as a result caused either the ATS, ground fault relay, or OCPD upstream of the ATS to trip (i can't remember which one). The contractor said that a way to prevent this was to balance the ATS out with more emergency loads that would be drawing power from the feeders so as to cancel out the power that was be injected into them by the elevator motors and so the sensing device upstream would not see an imbalance in power flow.
I would like to know if anyone has had any experience with this situation before and how they dealt with it. I am aware that motors are capable acting like generators upon loss of power, and that computer software such as Dapper can be used to perform selective coordination studies, but I would like to know if there are any types of general guidelines to follow to predict this type of behavior, or general baseline numbers to use in either ATS size or OCPD trip settings before diving into a coordination study.
Regards
I recently just had a design meeting with a general contractor about a high-rise residential building my firm is deisigning. One of the recommendations the contractor made to me was to try and eliminate the ATS that we had designated for switching over all elevator loads, transfer the elevator loads to another ATS, and resize the other ATS to handle the elevator loads in addition to its existing loads. The contractor's reasoning for this was that previously they had encountered situations where upon loss of normal power and in emergency mode the elevator motors were acting as generators on the way down during recall and injecting power back into the feeders and as a result caused either the ATS, ground fault relay, or OCPD upstream of the ATS to trip (i can't remember which one). The contractor said that a way to prevent this was to balance the ATS out with more emergency loads that would be drawing power from the feeders so as to cancel out the power that was be injected into them by the elevator motors and so the sensing device upstream would not see an imbalance in power flow.
I would like to know if anyone has had any experience with this situation before and how they dealt with it. I am aware that motors are capable acting like generators upon loss of power, and that computer software such as Dapper can be used to perform selective coordination studies, but I would like to know if there are any types of general guidelines to follow to predict this type of behavior, or general baseline numbers to use in either ATS size or OCPD trip settings before diving into a coordination study.
Regards