Impact of Last-Mile Power Factor

My article published in the May 2022 Newsletter of the Global Smart Energy Federation.

In the January/February, March and April 2022 GSEF Newsletters, I wrote about the changing facets of power systems reliability/resiliency, grid inertia and reactive power issues in a world of high renewable energy penetration. This month, I examine the changes in last-mile power factor (residential and small commercial) due to electronically controlled appliances. This article explains the nuances.

As explained in my last article, the concept of reactive power in AC systems is confusing to many people. The notion that the same active power (KW) will draw differing currents based on power factor (pf) is perplexing. For example, for the same KW load, the current drawn will be 11% higher at 0.9 pf than at 1.0 pf, about 18% higher at 0.85 pf and a whopping 25% higher at 0.8 pf. This is very hard on equipment, cables/wiring/plugs and can cause overheating. But the retail consumer is hardly aware of these issues.

The last-mile connection (residential/small commercial) and its load characteristic is undergoing a transformational change. About 40 years ago such loads were largely resistive with electric heaters, stoves, washer/dryers, hot water tanks, air-conditioners and incandescent light bulbs. The fractional-hp motors used in such appliances were split-phase capacitor-start type. In effect, loads then were close to unity power factor (likely 0.95 pf). This healthy power factor, allowed the utilities to not focus on reactive power draws.

All this has changed now. Today, most homes and small businesses have the same appliances but they are electronically controlled. New add-ons include LED lights, electronic ballasts, microwave ovens, inverter-based air-conditioners, heat-pumps, personal computers, printers, TV set-top boxes, and home networking/data storage. Recent developments include EV car chargers, rooftop PV and battery systems. Many of these now are architected for residential and small business applications.

The plethora of such electronic devices in many cases is degrading the last-mile power factor. I have seen poor 0.87 pf in wealthy single-family urban residences in developed countries (worst being 0.77 pf). I have witnessed 3-phase 415V incomer cables overheat/fail due to low pf in small business industrial parks in the Middle East. I have seen branded electronic ballasts/drivers rated at 0.59 pf and new commercial buildings exhibiting poor power factor. The list goes on. In each case the owner (or the contractor) was buying certified products manufactured by reputed companies. No rules were broken.

Since most appliances are rated for 10% overload, any power factor below 0.9 pf at full rated load is a safety hazard. Putting it another way, the derating factors that need to be applied (to maintain safety margins) is 11% for 0.9 pf; 18% for 0.85 pf and 25% for 0.8 pf operations. This means that a standard residential or small business service connection will need to be upgraded to higher amperage connection, for the same full load if the power factor drops below 0.9 pf. At a community level, the utility distribution transformer (DT) would need capacity (KVA) upgrades to allow for such poor power factor operations in its last-mile.

With each utility owning 20,000 to 50,000 such small transformers (or more), poor power factor would mean applying a huge derating factor to its existing stock or replacing its stock with higher capacity units. For example, a fleet of 20,000 transformers at 400 KVA each can individually cater to about 375 KW maximum load at 1.0 pf (total 7,500 MW). But at 0.85 pf operation, it would mean derating each transformer to 310 KW for the same 400 KVA (a reduction of 18% or 1,300 MW) or alternatively replacing it with new 500 KVA DTs (and upgraded cable sizes) for the same 375 KW load (capacity addition of 2,000 MVA). At a national level, large countries like USA, India, China, Saudi Arabia, Brazil, South Africa which all have substantial residential loads, this last-mile power factor impact could mean an extra 20,000-50,000 MVA capacity addition in generation, transmission and distribution systems. No matter how one looks at this, poor power factor is very punitive for all stakeholders.

So, the question is, do electronic controllers degrade power factor and is there a fix? The answer is yes, if designed cheaply and it does not have to be this way. I have seen industrial electronic driver designs for LED/CFL/Induction lights, that offer 0.9 pf or better (albeit at a higher cost). By its nature, electronic controls rectify /invert /modulate AC waveforms inside these appliances. Such control provides energy conservation, output flexibility and sometimes even lower size. But if such controls are not designed well, they create a “backend” problem with poor power factor utilization for the consumer. If the consumer has many such products in their premises, then this situation (on an aggregated basis) is significant at the point of entry connection.

Large industrial and commercial customers improve their power factor to avoid paying higher demand charges, so this issue is only with residential and small business consumers who are metered for energy only. A second issue is that retail consumers buy certified appliances, lights and home gadgets, so how can one blame them for poor choice? If equipment standards and utility code obligations are well specified, certified and monitored, this problem can be resolved.

As a first step, standards bodies and certification agencies should pay attention to this and a minimum power factor of 0.9 pf must be ensured in all such product certifications. It should be mandatory for the appliance labels to denote the overall power factor for each appliance at the plug-level. For example, if all major “white-goods” appliance and LED manufacturers are mandated to produce products that meet 0.9 pf, the matter is easily settled. Better still, a five-star rating can be attributed for those appliances than show better than 0.9 pf.

As a second step, utilities must start paying attention and monitor retail power factor at the consumer and community levels. In my view, this problem already exists today and needs to be resolved. There are several aspects and a few are heighted below:

1.????Most Grid Codes have a minimum pf of 0.9. If not, get regulatory approval to enact one.

2.????Initiate an audit to see how far and deep is this problem.

3.????Start a campaign and make consumers aware of poor power factor.

4.????If smart meters are deployed, pf measurement is easy. Send alerts for pf<0.9 on such bills. If not, install a few smart meters at critical DT locations as proxy.

As a third step, it is time we held all customers accountable. Poor power factor affects everybody not just the individual customer. Fortunately, retail tools are available to manage this today which were not possible even 10 years ago. There should a reward for good power factor (say 0.9- 0.95 pf) and penalties for those below 0.9 pf. If left unchecked, the utilities will not be able to manage this all on their own.

Raising awareness across millions of small consumers and making them understand the impact of poor power factor, will be a very long-drawn effort. The consumer’s technical comprehension is very limited and even a small fix could be seen as a significant expense for them. But not initiating this could become a public relations nightmare later (for the utility) when this problem spreads everywhere.

As a cautionary note, aiming for a perfect unity power factor (or close to unity) is also not good. A few leading utilities that implemented this in developed countries in the past are “paying” for it now (more in a future article).?