Jims37
Electrical
- Jun 13, 2004
- 1
I need advice on providing power to a small factory in Haiti. The factory uses two machines that each have two motors labeled 380/220 volts/ 50 Hz, three-phase. (380 volts phase-to-phase with 220 volts phase-to-neutral). Feed is 4 wire because an electronic control box needs the 220 volts from one of the phases to neutral. One motor is 1.5 Hp. The other 0.5 Hp. These machines will be used to iodize salt. A precision chemical sprayer adds iodine as an auger passes the salt under the spray. The plant also requires 120 volts, 60 Hz for lab equipment and fluorescent lights. It also requires two 24,000 Btu/hr air-conditioning units. Air conditioning should be standard US residential units that are normally powered from 240 volts, 60 Hz single-phase. My thinking is that because the motors were designed for 50 Hz and will be run on 60 Hz, their voltage needs to be increased 20% to 456/263 volts (456 volts phase-to-phase with 263 volts phase-to-neutral). I realize their speed will be 20% faster than design, but this can be compensated for by adjustments to the control box that regulates the iodine dosage rate. I have considered the following:
1) Use a three-phase generator that supplies 208/120 volts Wye. Use a three-phase transformer to go from 208 volts three-phase to 456/263 volts Wye. Use single-phase transformer to go from 120 to 220 volts for the control box. This solution provides a full 120 volts for lab equipment and lights by breaking loads into three sets and obtaining 120 volts from each phase-to-neutral. This also would provide 208 volts for the air-conditioners, but 208 is low for typical 230 volt air-conditioners. My understanding from other parts of this forum is that typical air-conditioners are marked 208-230 volts and that this means nominal service voltage is 240 volts, with 220 to 230 volts typical at the compressor due to line losses. 208 is the very lowest voltage the air-conditioner is designed to run on. If I use 208 volts nominal from the generator, it could be 10 to 12% lower by the time it reaches the air-conditioners, due to line losses, generator regulation, etc. My concern with this solution is poor performance and service life from the air conditioners.
2) Use a three-phase generator with three 120 volt windings. Connect them zig-zag to provide 240 volts (120-0-120 volts), single phase to duplicate normal US household service. Use three, single-phase transformers connected to the three individual 120 volt windings of the generator. Even though these windings are already connected zig-zag, connections to each winding is accessible. Connect the 263 volt secondaries of these three transformers in a WYE to supply power to the 50 Hz, three-phase motors. Derive 220 volts for the chemical control box from a separate transformer. This solution requires de-rating the generator due to it being connected zig-zag for single phase, but this solution duplicates normal US 240 volts, center-tapped, single phase service and adequately powers the air-conditioners.
I apologize for such a long post. I would appreciate confirmation of whether I am on the right track or whether I have made a fundamental error.
1) Use a three-phase generator that supplies 208/120 volts Wye. Use a three-phase transformer to go from 208 volts three-phase to 456/263 volts Wye. Use single-phase transformer to go from 120 to 220 volts for the control box. This solution provides a full 120 volts for lab equipment and lights by breaking loads into three sets and obtaining 120 volts from each phase-to-neutral. This also would provide 208 volts for the air-conditioners, but 208 is low for typical 230 volt air-conditioners. My understanding from other parts of this forum is that typical air-conditioners are marked 208-230 volts and that this means nominal service voltage is 240 volts, with 220 to 230 volts typical at the compressor due to line losses. 208 is the very lowest voltage the air-conditioner is designed to run on. If I use 208 volts nominal from the generator, it could be 10 to 12% lower by the time it reaches the air-conditioners, due to line losses, generator regulation, etc. My concern with this solution is poor performance and service life from the air conditioners.
2) Use a three-phase generator with three 120 volt windings. Connect them zig-zag to provide 240 volts (120-0-120 volts), single phase to duplicate normal US household service. Use three, single-phase transformers connected to the three individual 120 volt windings of the generator. Even though these windings are already connected zig-zag, connections to each winding is accessible. Connect the 263 volt secondaries of these three transformers in a WYE to supply power to the 50 Hz, three-phase motors. Derive 220 volts for the chemical control box from a separate transformer. This solution requires de-rating the generator due to it being connected zig-zag for single phase, but this solution duplicates normal US 240 volts, center-tapped, single phase service and adequately powers the air-conditioners.
I apologize for such a long post. I would appreciate confirmation of whether I am on the right track or whether I have made a fundamental error.