Some of today’s hot topics in the industry are about save cost with more efficient products. Reducing electric energy cost by switching from SCR to SMPS rectifiers is presented by some as a significant cost savings due to improved Power factor.
Power Factor should not be confused with efficiency. Power factor is defined as the ratio of real power absorbed by the load to the apparent power flowing in the circuit. Power factor only describes a ratio and efficiency tells you how much energy is lost as heat not used in your process.
Common inaccurate statements we have heard include:
- 40% cost of energy savings is achievable when switching technologies.
- Power factor penalties due to SCR rectifiers can add significant cost to your electric bill.
- Just measuring the line current can be an accurate indication of power you are buying.
Measuring line current only gives an indication of Reactive power & Real power vector sum together. You do not necessarily pay for the reactive power. Your individual situation as to the real dollar cost for this will vary by location. But in general, up to 50% KW consumed during peak times are provided no charge KVAR on your bill prior to a penalty being assessed. This explains why the utility requests only a 0.90 PF and not 1. This reactive energy actually helps to stabilize the grid. In conclusion, not all KVAR is bad. In fact, some is needed.
How much money can I actually save?
The KVAR penalty only appears on your bill if the SCR rectifiers are running below their designed specification.
EXAMPLE: The rectifier rated for 30V but operating at 22V would result in a penalty an average of $0.009/kVarh; So if an SCR unit has a PF of 0.7, which results in 40 % higher total power intake versus a SMPS with a PF of 0.9 or better the penalty would not exceed 2-3% of the kWh you are paying for on your bill. Note KVar can come from other sources in the factory as well such as drives or motors and can compensate against the rectifier demand. As a result, the penalty can be much lower or fall well within the “no additional charge” window from the utility.
ROI
Using similarly priced 16V 4000A SCR vs SMPS. 70 kWh as usage, the U.S. average cost of Industrial electricity at $0.18/kWh = 70 x .18 x 8hr per day x 365 days = $36,792 x 3% (if penalty actually applies) = $1104/year. This is nothing to disregard however the cost of replacement system can be significant. For a properly rated SMPS with similar up front, capital expenditure it would pay back is 15 years based on PF (if penalties apply).
What other options are there?
Check your electric bill to see if you are actually being penalized and charged more for poor power factor.
- Rectifier construction and efficient design for your process can be as effective in saving $.
- Consider Material used in the design such as Aluminum vs. Copper (Copper is better.) Rectifiers built with Copper are likely to be more efficient overall.
- Consider PF correction for the entire facility. Factories today may already have PF correction due to many sources of KVAR in the shop. An upgrade in Plant wide PF correction may be better option.
- Do a power study for each rectifier individually and be sure the rectifier is not malfunctioning. Claims of 25% efficiency for an SCR based rectifier can only be possible if the unit needs repair.
If you would like to save money and make your process more efficient, contact American Plating Power. At American Plating Power we proudly offer both SCR and SMPS technology and want to help you decide which one is right for your application.
Please contact our knowledgeable sales staff to help you make informed decisions on your rectifier upgrades.
