Working with a paper mill here in Savannah and their power factor correction is a complete mess. They've got 1200 KVAR of capacitors but Georgia Power is still hitting them with penalties on Schedule TOU-8. Plant operates three shifts with wildly different loads - 2.8 MW during day shift, 1.1 MW nights, almost nothing on weekends. Current setup has fixed capacitors that overcorrect during low load periods. Anyone dealt with automatic switching systems that actually work?
Capacitor bank sizing nightmare at paper mill
Eleanor, I've installed probably fifteen automatic PF correction systems in Louisiana mills and manufacturing. The key is getting the switching logic right for your load profile. With that much variation you need at least 4-6 steps of capacitance. ABB and Schneider both make good controllers but you need someone who understands the timing delays to prevent hunting. What's your current PF range throughout the day?
Juan, thanks for jumping in. PF ranges from 0.68 lagging during heavy production to 0.94 leading when they're running minimal equipment with full capacitance. Georgia Power penalizes anything outside 0.85-0.95 range so we're getting hit both ways. The plant has old paper machine drives that create tons of harmonics too. Worried about resonance issues with additional capacitors.
Harmonics are definitely a concern with paper mills. Had a similar situation in Wisconsin with a corrugated plant. Ended up specifying detuned reactor capacitor banks to avoid the 5th and 7th harmonic resonance points. Cost about 20% more than standard caps but eliminated the risk of blown fuses and nuisance tripping. Your electrical contractor should run a harmonic study before sizing anything.
Karen's right about the detuned reactors. For your application I'd recommend 6% reactors minimum, maybe 7% if the harmonic distortion is really bad. Also consider the ambient temperature in your electrical room - paper mills run hot and capacitors hate heat. Size for at least 110% of rated KVAR and spec 105°C rated units. The extra cost pays for itself in reliability.
Getting quotes now for automatic system with detuned banks. One vendor wants $47K for ABB Capacitor VAR Plus system with 8 steps totaling 1800 KVAR. Another is proposing custom-built solution for $31K but I'm skeptical about support. The ABB seems expensive but their tech support has been solid on other projects. What's the group's experience with warranty issues on these systems?
ABB support is excellent but their prices are getting ridiculous. I've had good luck with Eaton's PowerVar systems - about 25% less cost and comparable performance. The key is making sure whoever installs it understands the commissioning process. I've seen too many systems that work fine initially but develop problems because the switching logic wasn't tuned properly for the specific load.
Pete raises a good point about commissioning. Budget for at least 40 hours of startup and tuning time. The technician needs to observe operation through multiple production cycles to set the time delays correctly. Too fast and the system hunts, too slow and you get penalized during load transitions. Also make sure they program seasonal compensation - capacitor KVAR output varies significantly with temperature.
Excellent advice everyone. Went with the ABB system after negotiating price down to $41K including commissioning. Installation scheduled for October shutdown. Juan, would you mind if I contacted you offline about the programming parameters? I want to make sure we get the switching logic optimized from day one. These penalties are killing the client's budget.
Absolutely Eleanor, happy to help. Send me your load profile data and I'll review the settings before startup. The ABB controller has about 30 adjustable parameters so getting them right initially saves a lot of headaches later. Good choice on waiting for the scheduled shutdown - trying to install capacitor systems while the plant is running is asking for trouble.
Eleanor, one more tip - make sure they install individual fusing on each capacitor step. I know it adds cost but I've seen single blown capacitor take out an entire bank when they used group fusing. Paper mills are tough environments and you want maximum system availability. Also spec outdoor rated enclosures even if installed inside - the humidity and paper dust will kill standard electrical equipment.