Hello.
I am trying to find a product and I'm hoping it exists somewhere, although I've not had luck finding anything yet. We have a 50KW UPS which is an EM power source for an elevator. The only loads on the UPS are elevator related. The motor is regenerative with no way to disconnect the regenerative function while on emergency (some elevators do have this ability). So, to comply with 620.91 we need to add a load to absorb the regenerative power. In addition, we need to protect the UPS as it's internal circuitry is not designed to handle regenerative power on the output. We are installing an ATS so that in normal mode, the UPS output is isolated from the elevator. There is sufficient load in the building to always absorb the energy from the motor. When on EM, the ATS transfers and we have a N.O. Definite Purpose Contactor which then closes and brings a bank of resistors into the circuit (to absorb the regen power). We're using the EM transfer contact on the ATS to control this relay. It seemed like a good design to me but then I wondered about one possible situation. There is no signal from the UPS to the elevator to let it know that the EM source is running low. It's very unlikely but still possible that the elevator could be moving at the exact moment that the UPS runs out of power. If this happens, then the contactor will open and the resistors will no longer be in the circuit and there will be nothing to protect the UPS or act as breaking resistors for the motor. I can easily solve this by changing the contactor to Normally Closed and connecting it to the normal power relay on the ATS. Then the resistors would be in the circuit under EM power or if neither EM nor utility power were present. I thought this would be an easy thing to do, but I just cannot find a contactor with greater than 30A contacts. We need a 3-pole, NC, with 50A (or larger) contacts. I've checked several mfg's and we can add (2) aux poles at NC but no more. Lighting contactors have interchangeable poles (NO or NC), but the ones I can find only allow the contacts to be NO/NC up to 30A (above this they are fixed at NO). Theoretically we could use 2 contactors with auxiliary poles, but this seems like a product that could, and should exist. I don't think there is any technical reason why an NC contactor could not be built at higher ampacities.
Does anyone know of a product or think of anything I'm missing? Thanks.
I am trying to find a product and I'm hoping it exists somewhere, although I've not had luck finding anything yet. We have a 50KW UPS which is an EM power source for an elevator. The only loads on the UPS are elevator related. The motor is regenerative with no way to disconnect the regenerative function while on emergency (some elevators do have this ability). So, to comply with 620.91 we need to add a load to absorb the regenerative power. In addition, we need to protect the UPS as it's internal circuitry is not designed to handle regenerative power on the output. We are installing an ATS so that in normal mode, the UPS output is isolated from the elevator. There is sufficient load in the building to always absorb the energy from the motor. When on EM, the ATS transfers and we have a N.O. Definite Purpose Contactor which then closes and brings a bank of resistors into the circuit (to absorb the regen power). We're using the EM transfer contact on the ATS to control this relay. It seemed like a good design to me but then I wondered about one possible situation. There is no signal from the UPS to the elevator to let it know that the EM source is running low. It's very unlikely but still possible that the elevator could be moving at the exact moment that the UPS runs out of power. If this happens, then the contactor will open and the resistors will no longer be in the circuit and there will be nothing to protect the UPS or act as breaking resistors for the motor. I can easily solve this by changing the contactor to Normally Closed and connecting it to the normal power relay on the ATS. Then the resistors would be in the circuit under EM power or if neither EM nor utility power were present. I thought this would be an easy thing to do, but I just cannot find a contactor with greater than 30A contacts. We need a 3-pole, NC, with 50A (or larger) contacts. I've checked several mfg's and we can add (2) aux poles at NC but no more. Lighting contactors have interchangeable poles (NO or NC), but the ones I can find only allow the contacts to be NO/NC up to 30A (above this they are fixed at NO). Theoretically we could use 2 contactors with auxiliary poles, but this seems like a product that could, and should exist. I don't think there is any technical reason why an NC contactor could not be built at higher ampacities.
Does anyone know of a product or think of anything I'm missing? Thanks.