If your focus is energy savings, is it a good idea to invest in solutions to improve PQ? Can PQ solutions help to save energy?
The relationship between Energy management and power quality management is getting more complex, especially in modern electrical networks with high concentration and dependency on power electronics. The non-linear nature of cause-effects in improving the energy efficiency and power quality further adds to this complexity. An in-depth understanding of linkages, overlaps and influencing forces between energy efficiency and power quality is key to improving both.
Power Quality events in the electrical network influence the efficiency of energy utilisation for various processes, equipment and devices. Events such as Low Voltage Profile, Dips, harmonic current or current unbalance observed in the electrical network will adversely affect the energy efficiency in the short and long run. Distorted currents also affect the voltage quality which in turn reduce the energy efficiency in several indirect ways. Other events such as low Power Factor, transient currents, harmonic distortions etc. affect the energy efficiency.
This article focuses on understanding the relation between a variety of PQ events and its impact on energy efficiency at various levels in the electrical network. We also delve on the possibility and scope of PQ improvement as an instrument to achieve significant energy savings.
NON-LINEAR LOADS – IMPACT ON QUALITY AND EFFICIENCY
The root cause for poor PQ is the presence of non-linear loads in the electrical network. A nonlinear load in a power system tends to introduce a switching action and as a result current interruptions. This particular behaviour of the current consists of multiples of the fundamental frequency of the system termed as harmonics.
Several articles on APQI platform discuss the role of harmonics in deteriorating power quality.
More loads in our power system are now non-linear
Typical examples of nonlinear loads that generate harmonic currents include computer CPUs and Monitors, Office Printers, Industrial PLCs, VSDs, Refrigeration/Water Coolers, Smart TVs, LED Lights etc.
Harmonic Spectra of a Refrigerator
Harmonic Spectra comparing 3 Brands of CFL Lights
Source Residential Loads Modelling by Norton Equivalent Model of Household Loads – Scientific Figure on Research Gate. Available from: https://www.researchgate.net/figure/Harmonic-Spectra-of-3-different-types-of-CFLs_fig2_251997527 [accessed 29 Mar, 2019]
Harmonic Distortion observed in industrial VFDs
Assessment of the energy efficiency estimation methods on induction motors considering real-time monitoring – Scientific Figure on Research Gate. Available from: https://www.researchgate.net/figure/Harmonic-voltage-distortion-of-the-variable-frequency-drive-The-figure-shows-that-the_fig6_329901150 [accessed 29 Mar, 2019]
But what’s more interesting is how some of the key technologies that are being promoted for delivering better energy efficiency affect the Power Quality.
|Technology||Applications||Energy Efficiency View||Power Quality View|
|LED Lights||Industrial and Commercial Buildings, Street Lights||25%-80% less energy than traditional fluorescent or HPMV / HPSV incandescent||Low PF, induces high THD (v) and Inrush Currents|
|VFDs||Elevators, Motors, Process Automation, HVAC Equipment etc.||Reduce energy consumption by as much as 60%||With the inductances, the typical THD (Total Harmonic Distortion in current) is around 30%. Without the inductance, it can be 70% to 120%.|
|SMPS in PCs and Other devices||PCs, LED Screens, Control Systems, BMS in commercial buildings etc.||Higher power conversion efficiency from AC to DC with Current and Voltage Characteristics||Large third-harmonic currents (up to 87% of the fundamental) are present in all kinds of computers|
|Power Storage Batteries||Electric Vehicles charging stations, UPS||Pure EVs use about four times less energy than a new internal combustion engine car||EV Chargers are EV) chargers are highly nonlinear power system that have poor PF and high harmonics|
|Inverters to convert DC to AC||Solar PV Panels||Environment friendly energy with much lower operational costs||Harmonic and radio frequency noise because of the high-speed switching, can get worst in case of improper earthing.|
|Wind Power Plant||NA||Large-scale Environment friendly energy with much lower operational costs||Flickers, potential risks of large current surges in the grid|
Many different studies, point to the fact that the applications of energy saving technologies mentioned above are growing at a breakneck speed. This means the non-linear loads in the electrical network will continue to grow for a long range of years ahead.
To truly achieve and sustain the energy efficiency goals in the long-term calls for investments to address and solve the adverse side effects of energy efficient technologies on the PQ of the electrical network.
BALANCE BETWEEN EFFICIENCY AND QUALITY TO MOVE AHEAD
Riding solely on Energy Efficiency narrative is a risky proposition. The impact of poor PQ poses serious threats to reliability and availability of the electrical network. To ride ahead, businesses will need to achieve the balance between investments in energy efficiency and PQ improvement. This calls for an all-round approach that achieves the energy efficiency goals in tune with the reliability and availability of the electrical network.
Given below is a list of key global and equipment based solutions that complement the energy efficiency goals by improving the PQ.
AC line reactor or DC link reactor (DC choke)
VFD, being a non-linear load, is a source of harmonics on the power line. Harmonic current from the VFDs leads to heating of the transformer and cables to the VFD. This in turn, reduces the capacity of the cable and transformer. The DC Choke is used to mitigate the impact of harmonics from VFDs across various applications.
Passive filters are widely used to solve the power quality problems, especially current harmonics in R-L Loads. In addition to that, the passive filters provide Reactive power compensation, and help to improve the Power Factor.
Improving PF required to reduce the phase difference between voltage and current. Inductive load require some amount of reactive power for them to function. This reactive power is provided by the capacitor or bank of capacitors installed parallel to the load.
Zero Sequence Filters / Neutral or Triplen Harmonics Filter
ZSF help to reduce rms value of line current. This is achieved by reducing zero sequence harmonic current generated by single phase non-linear loads in three phase systems. The ZSF can reduce this large neutral current (up to 90%).
Active Front End (AFE)
AFE is a controllable rectifier that provides bidirectional power exchange between AC and DC power. This helps to regenerate reusable power to the mains and thus helps to reduce the cost of power through wastage or non-maintenance of PF.
Active Harmonic Filters
Modern active harmonic filters come with multiple functions including harmonic filtering with damping, isolation and termination, reactive-power control for PF correction and voltage regulation, built-in load balancing, voltage-flicker control etc.
Phase shifting Transformers
Given the inductive nature of the power system, it is important to ensure the flow of power between load and source with a phase lag between the terminals. Phase shifting transformers help to achieve the goal.
Note: The energy efficiency benefits from solutions listed above depend on their careful application engineering, design, functioning scope, placements, nature of electrical network and several other variables.
While the solutions listed above along with other similar technologies to improve PQ help to enhance energy efficiency, the magnitude of energy savings varies significantly for each of the solutions. Prioritizing and planning for investments in improving PQ to drive greater energy savings therefore calls for deeper investigations. The realistic assessment of potential energy savings from a new technology that’s being introduced, must also include the potential risks to PQ to achieve the balance in efficiency and quality.
It is also observed that the solutions that primarily improve PQ are being increasingly promoted as the one’s that will help to achieve significant energy savings. Are the lines for energy efficiency and quality finally blurring? Or is it just a marketing gimmick?
PQ SOLUTIONS AND ENERGY SAVINGS – A REALISTIC VIEW
An interesting shift is underway in the Power Quality solutions industry in the last few years. In most instances, until a couple of years ago, the PQ solutions were pitched like an insurance. The promise was predominantly to save the electrical network from all sorts of power disturbances such as interruptions, sags, harmonics, transients etc. But with easy availability of budgets for energy efficiency programs and the intangible nature of poor PQ, solution providers are finding it to be more advantageous to highlight the energy cost saving aspects, directly visible in monthly utility bill, in their products. With that, today there is an intense competition among suppliers to state the benefits in terms of energy saving potential from the PQ improvement solutions. This has also led to mis-selling, overstatement of benefits by the suppliers and a general dissent among the customers to trust the benefits from solutions to improve PQ.
Studies are now underway to assess if PQ solutions can be leveraged to deliver realistic energy savings benefits, if any. Findings from a few studies that observe little or no benefits to improvement in energy efficiency from PQ solutions are provided below for reference:
- A study by EATON in USA observed that the real savings from kW Loss Reduction by installation of PF Correction Capacitors were just 1-4% as compared to the promised 11-30% savings
- A study by R&D Engineers of EMCO in India observed that the use of harmonic filters in a Textile mill that used VFDs could were up to 1% of rated load capacity
- A study of household appliances by professors from the Electrical Engineering Department, Eindhoven University of Technology states that only a small reduction in energy losses is observed by reducing the voltage when the load is more reacting as a constant impedance (most of the lighting)
Clearly, there is a weak link in terms of validating the stated benefits to energy savings from the PQ improvement solutions by the suppliers. Aggressive claims tested mostly under standard conditions, twisted terminology used to advance the sales logic, presenting select facts to drive sales are creating confusion among the customers. The relatively lower levels of awareness, extensive lobbying by suppliers and lack of standards has further added to the confusion.
The view of energy savings offered by EPRI is of help in this regard. According to EPRI, energy savings should be looked at from the scope of saving energy that is being wasted. So, the potential for savings in energy (which was basically never put to work) is only theoretical. The view can help to assess and qualify the right solutions in PQ improvement that are in tune with aiding the energy savings.
Traditionally, Energy Efficiency has always had the advantage of greater awareness and priority in terms of investments. The hard cash savings and traceability through the measure of electrical power consumption, coupled with a large number of technology and solutions is driving the energy efficiency wave.
Power Quality, on the contrary, has found relatively less attention in comparison, probably owing to its complex and not-so-straightforward nature. But, that is changing slowly. The modern Electrical networks are much more dynamic and thus prone to a greater risk of reliability and availability as compared to the past. However, observing the recent trend where solutions to improve PQ are being pitched aggressively to deliver on improving energy efficiency call for a more cautious approach.
The relation between efficiency and several power quality events is evident. Poor PQ leads to energy losses. However, arriving at the exact amount of the energy losses remains to be a challenge for the consumers. While it is practically not possible to remove 100% deviation among the PQ parameters, the use of mitigation devices will help to improve the energy efficiency. A thorough cost-benefit analysis of the use of mitigation tools and devices should be performed primarily for PQ improvement. The linkages to energy efficiency should be carefully considered for realistic benefits they can deliver.
The low hanging fruits for better energy efficiency through PQ continue to be PF improvement and reduction of harmonics. The former will result in immediate returns in terms of savings of penalties from utilities, while the latter will help to drive energy savings in the long-run through better performing equipment with longer life.
But above all, given the adverse PQ implications of several widely adopted energy saving technologies means that planning with a focus on the energy savings alone is not advisable. After all as end user we must define “What we want!”
- Harmonic Analysis of VFDs Poonam Kaur Ritula Thakur (Asstt. Prof., Dept. Of Electrical Engg. NITTTR Chandigarh) – http://www.ijmer.com/papers/Vol4_Issue5/Version-4/IJMER-45045557.pdf
- Elevator Drives, Power Quality and Energy Savings by Jonathan Bullick and Brad Wilkinson – https://www.elevatorbooks.com/Content/Site125/FilesSamples/179618pdf_00000088493.pdf
- Increasing Energy Efficiency by improving Power Quality – JOSEPH F.G. COBBEN, VLADIMIR ĆUK, WIL L. KLING Electrical Engineering Department, Electrical Energy Systems Eindhoven University of Technology
- Power Quality Solutions and Energy Savings – What is Real? – EATON Power
- A case study of Power quality improvement and energy saving in textile industry using solid state harmonic filter – M.K.Pradhan, Kamlesh Keharia, Rajesh Darapu, B. Mariappan R & D Department, EMCO Limited, Thane, India