An operations department manager complained about an increase in her overhead allocation for electricity. She correctly pointed out that there have been no configuration changes since the last allocation assessment three years ago, and production output is the same. She asks you how the department can be using more electricity when nothing different is being done.
Your research reveals that her department’s usage has increased 12%. For other departments, usage has changed between -2% to +5%. Power monitor logs good power factor. How can you answer her question?
The list of potential causes is long, but fortunately the list of likely causes is not. Here are three:
- Harmonics. Do you have baseline data on harmonics? If so, you can identify "what’s changed." If not, then evaluate the harmonic content and correct as needed.
- Motors. Check the filters and clean or replace as needed. Correct for excess vibration, and also check the lubrication history and current condition. Use a thermal camera to find hot spots.
- Cables. Cable insulation deteriorates over time. As it does, small amounts of current leak to ground.
This last cause is reason for major concern. You want to see a gradually sloping line in your cable data trends. A sharp bend means cable insulation has badly deteriorated and it’s time to repair or replace that cable. In this case, however, you may already be well past the bend. This level of power consumption increase hints could mean severe and widespread cable deterioration. You may be at risk for multiple faults to ground any day now.
A shutdown for testing and repair is far less expensive than an unintentional shutdown, especially if the cause is a catastrophic cable fault. If you don’t have history on your critical cables, then the smartest move may be a mass replacement.
