POWER FACTOR CORRECTION

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1 POWER FACTOR CORRECTION What is factor? Power factor is a way of describing how efficiently is consumed, either for a single piece of equipment or all electrical equipment within a site. It refers to in an alternating current (AC) electrical circuit. Power factor is an important issue for UK industry. It impacts on energy efficiency and electrical expenditure as well as the reliability and availability of the network infrastructure. 50 THE MARSHALL-TUFFLEX GUIDE TO ENERGY MANAGEMENT

2 POWER FACTOR CORRECTION HOW IS POWER FACTOR MEASURED? Power factor is measured between 0 and 1. A factor of 1 (known as unity) represents perfect efficiency, that is, a perfect match between drawn from the network and useful for the task. When a site s factor is less than 1, it needs to draw more current from the mains supply to deliver the required to operate electrical equipment. If a site s factor is less than 1, not only is additional being drawn, but poor factor is penalised by energy suppliers (known as reactive charges). Installing factor correction equipment will reduce energy usage and additional charges, often saving thousands of pounds per annum. If a 100kW motor operates at a factor of 0.75, the total or apparent (kva) required is actually 133kVA (100kW / 0.75). By improving the factor of the load to close to unity (0.99), the total drawn from the supply will be reduced to 101kVA (100kW / 0.99). This equates to a total reduction of 32kVA, or an overall energy saving of 24%. 51

3 USEFUL POWER V REACTIVE POWER Power drawn from the network consists of two parts useful and reactive. The combined useful and reactive determine the drawn from the network, that is, the total (also known as apparent ), measured in kva. kva apparent kvar reactive kw useful kw: useful required to complete a task kvar: reactive drawn in addition to useful kva: apparent total drawn from the network The thirst quenching portion of the beer represents kw. The foam head represents kvar. The total contents of the pint glass = kva. An analogy for explaining factor correction is the humble pint of beer. Power factor is the ratio of beer to the total contents of the pint glass. Total (kva) Useful (kw) Power factor = Useful = cos Total 100 kw The graph shows the relationship between useful and total. The horizontal grey line represents useful consumed by a 100kW machine, while the blue line shows drawn from the electrical supply, measured in kva. The angle shows the extent of the difference between useful and total. Causes of bad Any non-linear loads cause bad ; including arc welders, solenoids, induction heating equipment and induction motors. If a fully loaded 75 hp motor has a factor of 0.88; when it runs at half load the factor drops to All uncorrected reactive devices consume reactive ; it is just an aspect of how they work. There are several reasons why motors consume reactive : they may be oversized, operations may change, or they may be sized for the maximum load of a cyclical process. The best way of identifying inductive loads is through a factor survey. 52 THE MARSHALL-TUFFLEX GUIDE TO ENERGY MANAGEMENT

4 POWER FACTOR CORRECTION WHAT IS POWER FACTOR CORRECTION? Power factor correction denotes the introduction of capacitors to an inefficient system (basically the shock absorber of the system). The capacitors, whether static or automated, reduce current and improve the factor of a system, bringing it as close to unity as possible. Power factor correction technology increases electrical capacity by reducing the maximum kva drawn on an electrical system. This results in reduced electricity charges and prolonged life of electrical equipment. Effect of capacitors on factor Example 1 The angle is reduced; therefore the total drawn from the supply is less. However, there is still a lagging factor. Example 2 The addition of more capacitance brings the total down to almost a perfect factor. Example 3 Too much capacitance can lead to over-correction and, again, excess drawn from the network. This is called a leading factor. Example 1: Some capacitors fitted Total (kva) with no capacitors Useful (kw) Example 2: Near perfect factor correction Total (kva) with no capacitors Useful (kw) Example 3: Too much capacitance Total (kva) with no capacitors Total (kva) with capacitors fitted Total (kva) with capacitors fitted Useful (kw) Total (kva) with capacitors fitted 53

5 THE BENEFITS OF POWER FACTOR CORRECTION In the great majority of cases, poor factor is due to inductive loads, which can be compensated by adding capacitors into the circuit. Power factor correction capacitors enable the system to level reactive towards unity. Poor factor adds costs in three main ways: Additional reactive charge from utility company Unnecessary current drawn from the network Reduction in electrical equipment life expectancy What savings can be made? If factor is less than unity (1), then factor correction will always save money. Poor factor is penalised by energy suppliers, these charges are called reactive charges. There are also high maintenance costs related to not having factor correction in place. Power factor correction saves money and pays for itself many times over. The payback period will differ for each site. However, potential savings can be calculated with a factor survey. Typical ROI is less than 12 months. Power factor correction has many benefits: Reduced consumption Lower electricity bills Improved quality Power stabilisation Less heat Less current Extra kva from existing supply Reduced transformer and distribution equipment losses Voltage drop reductions in long cables Increased supply capacity Increased life expectancy of electrical equipment 54 THE MARSHALL-TUFFLEX GUIDE TO ENERGY MANAGEMENT

6 POWER FACTOR CORRECTION MARSHALL-TUFFLEX POWER FACTOR CORRECTION SOLUTIONS All of our Power Factor Correction solutions are bespoke and tailored to a specific site s requirements. Our units are manufactured in the UK, using quality components and steel enclosures to prevent corrosion and exposure to harsh environments. They can be installed on large plant/ equipment as well as at the incoming mains. We can supply dimensions and outline drawings, allowing enclosures to be built in advance of the unit delivery in order to minimise project time. Once installed, our Power Factor Correction units start saving money immediately. Other than the recommended annual inspection, they require no maintenance. Project management assistance Installation support Reduced consumption Improved quality Increased supply capacity Increased life expectancy of electrical equipment Lifecycle of factor correction equipment If looked after in-line with manufacturer s recommendations and operated within the correct supply and demand parameters, Power Factor Correction units should have a life expectancy well in excess of 10 years. It is important to understand that a unit s effectiveness can deteriorate over time; therefore it is worth checking equipment on an annual basis. 55