Poor power quality can cost you big time
Franchisers and franchisees of such outlets as convenience stores, fast food operators and service stations are not necessarily used to intensive energy audits and energy saving measures, and as a result can pay significantly more for electricity than is strictly needed. JOHN CARRIER explores the opportunities for making big savings by concentrating on power quality, in particular energy savings through prevention of high supply voltages and its benefits for efficient solar energy generation.
You expect your morning shower to be uneventful, and the hot and cold mixing taps to control the water temperature to be on the same settings as on any other day. You’d notice a loss in water pressure immediately. High water pressure would cause more water flow and, if persistent, would add to the water consumption bill. There is great similarity with the electrical energy you purchase. The kilowatt-hours consumed over a month, or other given period, are equivalent to litres of water delivered – more water pressure delivers more litres. The higher the voltage (the equivalent of water pressure), the more kilowatt-hours and the more dollars spent on electrical energy.
Good power quality depends on constant voltage and other parameters (mentioned below). Constant voltage is the most important one, but equally important is that it’s at the right level. The other important power quality indicators are an absence of voltage spikes (these can blow up equipment) and an annoying ‘flicker’ (short, sharp variations in voltage) sometimes visible in lighting.
Organising a power quality survey can be quickly done at very moderate cost and start you on the energy cost saving journey.
RELATIONSHIP BETWEEN VOLTAGE AND ENERGY CONSUMPTION
Most connected equipment will consume more power, the higher the voltage. For example, a 10 percent rise in voltage increases power consumption by 1.1 by 1.1, or 21 percent. In mathematical terms, the power consumption is proportional to the square of the voltage. A 4.5-kilowatt air- conditioner rated at 230 volts will consume an extra 0.95 kilowatts, costing an additional 28 cents every hour if the voltage is 253 volts.
A 21 percent cost increase for a couple of minutes is one thing, but for extended periods it can be very costly.
Low voltage can also cause problems. A drop of six percent will reduce power by 0.94 by 0.94, or 12 percent. Low voltage can affect freezers, refrigerated display cases, lighting, fans and other motor-driven loads.
Given the importance of constant voltage at the correct value, power companies (the poles and wire people) are required to stick to tightly regulated boundaries on voltage highs and lows. In practice, electricity distributors don’t know whether, at your particular installation, they’re sticking to the standards!
This has come about because of a number of factors, a salient one being increased solar generation influencing voltage on the networks.
UNPREDICTABILITY IS THE BIG PROBLEM
Voltage at your installation will vary. Your neighbouring installations and varying conditions in the network see to that. It’s not a matter of reducing the voltage or increasing it by a certain amount – and leaving it set. Instead, constant adjustment to the correct value is required if both power consumption and correct functioning of electrical equipment are to be maintained. There is hardware available to do this, namely voltage regulators. But – and there always is a ‘but’ – there is no such thing as a free lunch, and voltage regulators generally consume energy.
A BORING BUT IMPORTANT DETAIL
Voltage regulators are not a common item in electrical installations as yet. In the past the necessity for these didn’t arise. For modern installations the voltage regulator should be able to supply a constant voltage lying between 230 and 220 volts for single-phase installations and 400 volts for three-phase installations. A 30-kilowatt or higher power customer is likely to have a three-phase installation. Voltage control with virtually no power loss can be achieved through computer-based, solid-state voltage regulators with feedback control. The feedback part measures the voltage at your switchboard and sends that measurement to the computer, which compares it with the supply voltage and computes the switching pattern for the solid-state switches to give you the required voltage.
Sophisticated and reliable! Solid-state switches are inherently very rugged – and there’s virtually no energy lost in the regulation process.
THE EXPECTED PAYBACK
A modest example may be a nominal 30-kilowatt consumer being supplied at mostly 240 volts. By using the voltage regulator to adjust to 220 volts (an equipment standard frequently encountered) the savings are worked out as follows…
The 30-kilowatt load is assumed to be the power drawn at 220 volts. Therefore, at 240 volts the power drawn is increased by the square of the voltage ratio of 240 divided by 220, equal to 1.09 by 1.09, or 18.8 percent. That’s a whopping increase amounting to an additional 5.6 kilowatts. With that sort of increase in electricity consumption, typical payback in savings through voltage control is usually under three years.
BUT WAIT – THERE’S MORE
Solar systems for commercial premises are getting more and more popular. Often you have sufficient roof area to generate your own power requirements when the sun is out. However, a little-known fact is that if voltage rises too much, your solar system is switched off. The typical top voltage where this happens is 264 volts. A fast food franchise operation could benefit significantly through the use of solar power, so maintaining voltage at a controlled level will allow the business to use all the solar power available.
In areas where there are a lot of solar installations, voltage rise is very likely to occur. In part, the voltage rise is due to the networks not having designed their systems with sufficiently heavy cable to accommodate the power supplied by the solar systems. As the solar system penetration grows, so do high voltage problems.
WHAT ELSE IS IMPORTANT?
Power factor is a very important feature of an installation because it can increase your electricity bill. Power factor is the ratio of minimum electrical current needed to power your motors, air-conditioners and lighting etc to that actually supplied. An installation with a power factor of 0.8 requires 25 percent more current than strictly needed. Increasingly consumers are being charged an additional monthly charge to cover the cost of the ‘apparent power’ that has to be supplied.
Apparent power is measured in kilovolt- amps (kVA), a similar unit to kilowatts (kW). Typical charges for smaller consumers in many jurisdictions is of the order of $20 per kVA per month and this can easily increase an annual electricity bill by 10 percent or more.
Power factor has become a sufficiently large problem that many grid companies also require solar systems to provide that extra current rather than having to supply it from the grid where it chews up more energy losses for the electricity distributor.
Power factor correction is another piece of hardware that can have very attractive payback times of two to three years in electricity savings. Basically, the power factor is corrected to within spitting distance of 1.00 and kept there irrespective of load variations.
Important to note is the requirement that the power factor is individually corrected on all three phases of three-phase installations – otherwise the worst phase will determine the size to the kVA monthly charge.
AND IN CONCLUSION
Apart from the political football that electricity is, there are technical issues that appear to reside in the ‘too hard’ basket of electricity networks. Power quality deterioration and, in particular, voltage, is one that consumers can end up paying for. Future-proofing your business by arranging a power quality survey and then implementing the findings makes great sense. ●
John Carrier, national sales manager, Power Parameters Pty Ltd.
This article also appears in the August/September issue of Facility Management magazine.
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