Power Factor Investigation - Assignment Example

? Synchronous Motor for Power Factor Correction Insert s Insert of 14th March Outline I. Introduction II. Definition of power factor III. Relationship between current, voltage, and power factor IV. Rules governing the operations of a synchronous motor V. Power factor correction VI. Power factor correction using motors VII. How synchronous motors help in power factor correction VIII. Advantages of synchronous motors over capacitors Synchronous Motor for Power Factor Correction Power factor correction is vital for industries and other power consumers with large inductive loads. It is also beneficial to power utility providers. The reason is that unfavorable power factor presents a risk to equipment because it can cause too much current to damage equipment, and in some areas, it attracts additional charges from the power suppliers who need to develop greater capacity for generation simply because of poor power factor in the system (Meier, 2006). This makes it necessary to use suitable means to correct the power factor. This paper examines the use of the synchronous motor for power factor correction. There are several ways of defining power factor depending on the context of study. However, all the definitions come from the understanding that electrical power manifests in three ways. These are real power denoted as P (also known as true power or active power), reactive power denoted as Q, and apparent power denoted as |S| (Singh, 2008). Apparent power is the magnitude of complex power denote as “S” which is the vector sum of real power and reactive power (Singh, 2008). Each of the three manifestations of power has a different measure. The unit of measurement of real power is in watts (W) that of apparent power is Voltage-Amperes (VA), while that of apparent power is in Reactive-Volt-Amperes (VAR) (Meier, 2006). The ratio obtained by comparing real power to apparent power is the power factor. Before introducing motors to this discussion, it is important to consider the relationship between power factor on one hand, and electrical voltage and current on the other hand. Power factor normally comes in when discussing alternating current (AC). AC takes on a sinusoidal waveform. When the voltage and the current are in step, real power is equal to apparent power. Therefore, the power factor is unity. However, there are cases when the voltage leads or lags the current. The cause for this is when the circuit has an inductive load such as a motor. The motor stores power in its coils, reducing the actual power (real power) available to drive it. The total power supplied to the motor in this case represents the apparent power, obtained by multiplying the voltage and the current (VA). If there is a difference between the supplied power (apparent power) and the power in use (real power), then the power factor reduces to a value less than unity. Depending on its severity, it may require correction (Singh, 2008). The theoretical framework governing the operation of motors includes Fleming’s right hand rule and faradays laws of electromagnetism. When the thumb, the index, and the middle finger are at right angles, Fleming’s right hand rule describes the direction of the thrust by the thumb; the index finger shows direction of the electromagnetic field, while the middle finger shows the direction of the current. Faradays laws on the other hand state as follows, there is an EMF induced in a coil whenever the flux through the coil changes with time. The magnitude of induced EMF is directly proportional to the rate of change of flux and thirdly, the direction of the EMF is such as to oppose the change in flux. Electricity distribution companies provide power as apparent power but it bills customers based on the real power they consume. Therefore, a low power factor makes power more expensive to the consumer with increasing severity as power factor drops. This is why it is important to invest in equipment for power factor correction. Motors tend to be the largest loads in electric power systems. Motors are inductive loads that cause power factor to drop as a resulting of the motor drawing more current from the source. This excessive load is dangerous for windings of the motor. There is need to reduce this excessive current to a safer power factor. The internationally accepted minimum power factor is 0.8. Reactive power produces the magnetic fields in the machine that enable it to generate torque. On the other hand, active power is the power consumed because of the resistance of the motor. If the active part of the impedance of the motor is not large enough, the coils draw a higher current. If it is high, the motor supplies lesser current to the source. The higher the reactive power, the intense will be the field. Reactive power is responsible for setting up the magnetic field. There are two commonly used solutions to correct power factor. The use of capacitors creates a power pool that discharges when the current is lagging to reduce the factor by which the current lags. Capacitors take in the extra power supplied as apparent power and discharge it. The result is that the power factor rises towards unity. The limitation of capacitors is that they can only correct lagging current and not the other way round. Another method used to correct power factor is by using synchronous motors. Synchronous machines normally generate AC power for supply to the grid, or for small-scale uses such as AC diesel generators. They also run loads such as fans and compressors. However, they come in handy as a means of correcting power factor because they make it possible to produce either a lagging or leading current based on the degree of excitation in the coils. This is why they find application as compensators in large power systems for reactive power. When there is no mechanical load on the motor, the purpose of synchronous motor is to maintain power factor because its acts as a variable capacitor when the field is over excited. When the field is under excited, it acts as an inductor so the power factor can either be increased or decreased with the help of excitation (Meier, 2006). The name for a synchronous motor used for power factor correction is synchronous condenser. The synchronous motor acts either as a capacitor or as an inductor when used as a compensator. It does this by the effect it produces based on the action of the reactive power. This effect comes about because of the excitation in its coils, which may be either high or low. The type of excitation defines the magnitude and the sign of reactive power. When the synchronous motor is over excited, it acts a capacitor and the sign of reactive power becomes negative. It stores charge in its coils based in the excess current due to high reactive power. When the motor is under excited, the reactive power is positive since it will act as an inductor. In this case, it generates electricity, which compensates for the degree of disparity between the real and the apparent power in the system. The synchronous motors uses reactive power to help manage power factor based on the degree of excitation in the coils. The excitation alters the magnitude of reactive power making it possible for the motor to regulate power factor as the need arises. The main advantages of synchronous motors as opposed to capacitors is that they are easier to install and maintain compared to capacitors. In addition, their capacity to work with either lesser than appropriate reactive power or excessive quantities of reactive power makes them more versatile than capacitors. Their major disadvantage is that they have greater maintenance requirements because they have moving parts. Reference List Meier, A., 2006. Electrical Power Systems: A Conceptual Introduction. New York, NY: John Wiley and Sons. Singh, S.N., 2008. Electrical Power Generation Transmission and Distribution. 2nd ed. New Delhi: PHI learning. Read More