Tansformer power usage
Tansformer power usage
(OP)
I'm in maintenance at a graphic printing plant. Currently I am trying to find ways to lower the electrical bill. We have 14 480-volt transformers in the plant, they run constantly even when the machinery is not running. The units are idle two days every weekend and three full weeks a year. Is there any way to calculate the power consumption of these transformers when they are setting idle? I feel they should be shut down when not in use and brought back on one at a time to alleviate any electrical spikes at the meter.






RE: Tansformer power usage
I appreciate your idea. Yes, ou can measure the no-load power by connecting watt meter on the primary. This, if done for one transformer, may be you have a typical value that is applicable for all the transformers (they are all identical!).
Or else, you can ask the manufacturer for a copy of the factory test report which will include this information.
For switching off the transformers, you can draw up a scheme using the auxiliary contacts machinery power supply CBs or switches for automatic switching off. If your interest is to switch off only during weekends, manual action could be simpler.
Hope you have got atleast part answer.
Wish you all the best.
RE: Tansformer power usage
RE: Tansformer power usage
It is somewhat in vogue these days to trim energy use, and success can be dependent on diminishing numbers. Cutting loose some transformers may also reduce “standby” energy use, often present as transformer load but not mentioned in equipment literature. It’s difficult to say without some measurements.
A healthy portion of no-load losses are reactive [id est, of low power factor] so savings will to a large degree dependent on the utility rate structure, and plugging your measurements into varying facets of that rate. I would study the ranging capabilities of whatever portable load-logging instrument, to avoid “buried in the mud” inaccuracies.
Consider starting with one of the larger loads, and one of the smaller loads, and ramp from there. Depending on the served process, Monday mornings {after-weekend repowering} can be heartburn for maintenance personnel.
RE: Tansformer power usage
Mike
RE: Tansformer power usage
RE: Tansformer power usage
you have not mentioned the VA or KVA ratings of the transformers. Low ratings are usually no problem when switching on or off.
I assume that the 14 transformers operate 14 independant machines. It may be possible for the machine operators to get used to switching OFF an ON as required.
regards
RE: Tansformer power usage
I wouldn't expect much savings from shutting down idling transformers for two days out of the week. The small amount of current flow used in the transformer is mostly comprised of reactive power (kVAR), and the only kW used by the idling transformer is dissipated as a small amount of heat, which in turn is a cheap way to keep moisture out of the windings. The investment of time and materials used to de-energize and then sequentially re-energize these transformers would be greater than any savings, and the added stress to the transformers will definitely reduce their service life. The reduction in service life for multiple re-energization increases greatly with the size and primary voltages of the transformers. Check your electric bill for low Power Factor charges for a start to lower the energy cost. Keep in mind that ANY Power Factor charges are excessive, since they all can be eliminated with capacitors.
RE: Tansformer power usage
you should consider that there are two different values of transformer losses:
No load loss (losses in core)
Load losses (losses in the windings)
In an idle transformer only no load losses there will be only no load losses.
The calculation you suggested in your post dated Jan 5th does not take care of the different kind of losses. Usually no load losses are quite low compared to the transformers rating and I fully agree to DanDel.
RE: Tansformer power usage
RE: Tansformer power usage
RE: Tansformer power usage
Also, depending on who your power authority is and how they bill, there is usually a peak usage charge, which large motors can create large peak usages when they start. If you have any large HP motors not on drives, look at simple softstarts to eliminate inrush currents.
Also, often overlooked in power savings but critical, are zero-sequence harmonics. These are created when the three phases are not balanced, and they generate (or can generate) large neutral currents, which are wasted but you are charged for in some cases. Solution one is to balance loads on all phases on all branches as best as can be done. Solution 2 is some companies (PQI, Commonwealth Sprague and probably many more) have zero sequence harmonic filtering systems.