Electrical power factor correction

This chapter introduces the basic items of design and specification for the principal systems and components of an electrical industrial installation. Electrical supply systems are discussed with regard to interface with the supply authorities and the characteristics. Salient features of switchgear, transformers, protection systems, power factor correction, motor control equipment and standby supplies are identified and discussed together with reference to the relevant codes of practice and standards. The equipment and systems described are appropriate to industrial plant installations operating at typically 11 kV with supply capacities of around 20MVA. 

Recently there has been growing interest in power factor correction circuitry. Power factor, which is defined as the ratio of the apparent required power to the actual true power, ultimately affects the circuit s efficiency, thus varying the cost of electricity. It seems that almost all AC-powered equipment now require some form of active power factor correction in order to operate efficiently. Active power factor correction utilizes electronics to force the input current to look like a... 

Arc furnaces are operated in conjunction with large capacitor banks and harmonic filters to improve the power factor and also to filter the harmonic frequency currents so they do not unduly affect other power users sharing the same power fines. It is not uncommon to see arc furnaces supplied from dedicated utility power fines to minimize their impact on other power users. The presence of large capacitance in an electrical system can result in voltage rise due to the leading reactive power demands of the capacitors, unless they are adequately canceled by the lagging reactive power required by the loads. This is why capacitor banks, whether for power factor correction or harmonic current filtration, are switched on when the furnace is brought on line and switched off when the arc furnace is off line. 

In an electrical system, if the power factor is 0.80, 80% of the apparent power is converted into useful work. Apparent power is what the transformer that serves a home or business has to carry in order for that home or business to function. Active power is the portion of the apparent power that performs useful work and supplies losses in the electrical equipment that are associated with doing the work. Higher power factor leads to more optimum use of electrical current in a facility. Can a power factor reach 100% In theory it can, but in practice it cannot without some form of power factor correction device. The reason why it can approach 100% power factor but not quite reach it is because all electrical circuits have inductance and capacitance, which introduce reactive power requirements. The reactive power is that... 

When large power factor correction capacitors are present in an electrical system, the flow of capacitive current through the power system impedance can actually... 

Polystyrene capacitors have exceptionally low tan S values (< 10 q, making them well suited for frequency-selective circuits in telecommunications equipment. Polymer capacitors are widely used for power-factor correction in fluorescent lighting units, and in start/run circuitry for medium-type electric motors used in washing machines, tumble-dryers and copying machines for example. They are also used in filter circuits to suppress radio frequencies transmitted along main leads. Such interference noise may originate from mechanical switches, furnace controllers and switch mode power supplies it not only spoils radio and television reception but can also cause serious faults in data-processing and computer equipment. 

The electrical supply equipment is the second biggest equipment package after the mechanical equipment. The package includes the transformer/rectifier (T/R) sets and bus bars for providing DC power to the cells, the associated power factor correction equipment and harmonics filtration equipment, and the service transformers and circuitry. This equipment will typically comprise about 15 - 25 % of the cellhouse cost. The cost is heavily influenced by whether or not an electrical substation is included, and by the redundancy requirements for the T/R sets. A plant can choose to have no spare T/R capacity, partial redundancy, or full redundancy. Such cost savings must be weighed against the cost of lost production when a T/R set fails. 

A complete discussion of the benefits of modern electrical systems over their predecessors is out of the scope of this paper. However, several major benefits of modern AC drive systems will be briefly outlined. A modern AC drive system is capable of being operated at unity power factor, or even leading power factor to provide power factor correction to the remainder of the hoist plant. The performance is far superior to previous DC drive systems whose power factor is dependent on speed, ranging from 0.1 to 0.8 during a typical duty cycle. The improved power factor will result in significant savings in electricity cost, and in power factor correction equipment that may otherwise be required. 

Power Factor Correction. Chlor-alkali cell rooms, along with their high electrical power demands, tend to have low power factors. If uncorrected, these increase the... 

With DC electric motors, power factor correction is sometimes used to improve the power factor of the drive [30]. This is done by incorporating capacitive components into the circuit. Capacitors produce leading reactive power whereas the phase-controlled rectifiers produce lagging reactive power. Thus, by adding appropriately sized capacitors, the power factor of the drive can be improved. 

To recover the cost of supplying large amounts of reactive power, some utilities impose a financial penalty on customers with large electric loads. Even so, the economic incentive to improve power factor is minimal. When penalties are assessed, they may not be high enough to justify the cost of power factor correction. 

The non-polarized type is often found in electrical installation work for power-factor correction. A paper-dielectric capacitor is non-polarized and can be connected either way round. 

Unique operating characteristics of fuel cell power plants are as follows. Beneficial operating characteristics of fuel cells saves cost and other benefits include load following, power factor correction, quick response to generating unit outages, control of distribution line voltage and quality control can control real and reactive power independently control of power factor, line voltage and frequency can minimize transmission losses, reduce requirement for reserve capacity and auxiliary electric equipment fuel cells have an excellent part load heat rate and can respond to transmission loads. 

Power Supplies and Controls. Induction heating furnace loads rarely can be connected directiy to the user s electric power distribution system. If the load is to operate at the supply frequency, a transformer is used to provide the proper load voltage as weU as isolation from the supply system. Adjustment of the load voltage can be achieved by means of a tapped transformer or by use of a solid-state switch. The low power factor of an induction load can be corrected by installing a capacitor bank in the primary or secondary circuit. 

The power factor cos 6 is always a positive fraction between 0 and 1 (as long as 161 < 90°). The smaller the power factor, the greater the current that must be supplied to the circuit for a given active (useful) power output requirement. The increase in current associated with low power factors causes greater line losses or requires an increase in the capacity of the transmission equipment (wire size, transformers, etc.). As a result, for industrial applications there is often a power factor charge in the rate structure for supplying electricity. The usual situation is for loads to be inductive, and the industrial consumer may add capacitance to their circuits to correct the lagging power factor. 

Power factor in an alternating current circuit is defined as the ratio of actual circuit power in watts (W) to the apparent power in voltage amperes (VA). The need for correction arises from fact that the majority of A.C. electrical loads take from the supply a lagging quadruple current (voltage amperes reactive, var) and thus operates at a lagging power factor due to the reactive (rather than capacitive) nature of their construction. 

Several different definitions and expressions can be applied to the term power factor, most of which are probably correct. Apparent power (S) in an electrical system can be defined as being equal to voltage times current ... 

Select standard size motor. A motor that is loaded to 85 percent by a 79.1-hp impeller will require a minimum size of (79.1 hp)/0.85 = 93.1 hp, which means a 100-hp (75-kW) motor. This motor and impeller assembly is correctly sized for conditions with the design gas flow. However, because of the gassed power factor, that is, P/P0 = 0.38, should the gas supply be lost for any reason, the impeller power would increase to 78/0.38 = 205 hp and seriously overload the motor. To avoid this problem, some method (typically electrical control) prevents motor operation without the gas supply. When the gas supply is off, the control either stops the agitator motor or, in the case of a two-speed motor, goes to a lower speed. 

A coil, or any similar device, is said to generate self-induction or, in brief, it creates a circuit with inductance. Electric motors, for example, are wired through numerous coils with high inductance. Thus, electric motors, if not corrected, can have very low power factors. 

Whatever the precise mechanisms of conduction, the macroscopic conductivity observed in any conducting polymer will depend strongly on the morphology of the sample and on whether it is oriented and, if so, to what degree, because these factors will influence both intra- and inter-chain mobility. For these reasons the conductivities of samples prepared under very similar conditions may differ considerably. The above account has merely attempted to indicate some of the types of process that may be involved in conduction in these relatively new materials, for which it is certain that no single mechanism can explain all the experimental results. Even when a particular theoretical description fits the conductivity, it cannot be accepted as the correct mechanism unless it can also accoimt for the observations of magnetic susceptibility, thermo-electric power, photoconductivity and other properties. 

Fi correction factor to ATim, fraction h enthalpy HP horse power 7 electrical current k ratio of specific heat = Cp/Cy m, M mass flow AP pressure drop P pressure PE power factor Q heat content r compression ratio = P2IP1 T-[, ti supply temperature of hot (cold) stream T2, ti target temperature of hot (cold) stream ATi hot end temperature approach AT2 cold end temperature approach ATim logarithmic mean temperature differenee (LMTD)... 

Power factor meters are available for measurement of a given load. It is usually less expensive in the long run, however, to hire a local electrical contractor to conduct a PF survey and recommend correction methods. Possible sources of PF problems include transmitters, blowers, air conditioners, heating equipment, and fluorescent and high-intensity discharge lighting-fixture ballasts. 

Acard, C. 1981. Power factor measurement and correction. Plant Electrical Systems. Intertec, Overland Park, KS, March. 

The cost of electric power was estimated as the sum of four terms. The first is the cost to provide the steam flow (in pph) noted in Table 4.11. That value was converted to a requirement for energy as 945 BTU/lb steam, and the conversion factor of 3415 BTU/kilowatt (kW). The second term was the power cost to continually operate the air amplifier, taken to be a 6 HP motor. The third term was the power cost to operate a 3 HP water pump for condensed water and solvent vapor fed to the decanter. The fourth term is a general allocation of 52 kW for miscellaneous and unspecified needs. This value was taken from the reference of Appendix A2, Footnote 12, page 34. Both the third and fourth terms were corrected for the actual capacity of activated carbon using the six-tenth power rule used to estimate capital investment. The sum has the units of kW hours. 

Select standard size motor. A motor that require a minimum size of (79.1 hp)/0.85 = 93 motor and impeller assembly is correctly sized because of the gassed power factor, that is, P/Pq the impeller power would increase to 78/0.38 = this problem, some method (typically electrical supply. When the gas supply is off, the control two-speed motor, goes to a lower speed. 

---