Generator Excitation & Power Factor - Electric motors & generators engineering - Eng-Tips
I'm trying to visualize the relationship between the exciter field in a lags the voltage (lagging power factor) then the source current must be the. Voltage versus VAr/power-factor regulation on synchronous generators heating on the generator or excessive overcurrent operation of the excitation system. excessive overcurrent operation of the excitation system. Maintaining a constant reactive systems, voltage regulators, var/power factor controllers. I. INTRODUCTION . inverse relationship of field power between the two modes of regulation.
When a conductor is moved in the vicinity of that magnetic field or when the magnetic field is moved in the vicinity of the conductor, voltage is generated into that conductor. When a closed loop is formed by connecting a load to the conductor being moved through the magnetic field, current flows through the load. Dc current field current is sent through the generator rotor windings and that produces magnetic field refer to item 1 above.
When the generator is synchronized to the grid, current flows from the generator stator windings into the grid refer to item 3 above.
Due to inductive and capacity loads, when the voltage and current starts from the zero point in the alternating current cycle, one reaches its maximum value before the other and that makes one lags behind the other by a certain angle in the cycle and if you find the cosine of that angle between the current and voltage, it gives you power factor p.
The higher the field current, the stronger the generator rotor magnetic field strength the higher the generator terminal voltage, and therefore the higher the reactive power generated to supply these inductive loads and hence the bigger the angle of lag between the current and voltage.
If you find the cosine of a bigger angle, you will get a lower value which gives you your p. The lower the field current, the weaker the generator rotor magnetic field strength the lower the generator voltage, and therefore the lower the reactive power generated to supply these inductive loads and hence the smaller the angle of lag between the current and voltage.
Now, most generators I have seen has a p. However operating such generators at this p. This heats up the generator stator windings and reduces the lifespan of the generator so please be cautious. You can draw two power right angled triangles with the same base; one with a longer height bigger VAr and the other with a shorter height smaller VAr and find the cosine of both angles, that would help you to understand better.
Power factor - Wikipedia
DPFC is useful when standard power factor correction would cause over or under correction. Importance of power factor in distribution systems[ edit ] 75 Mvar capacitor bank in a kV substation Power factors below 1. This increases generation and transmission costs. For example, if the load power factor were as low as 0. Line current in the circuit would also be 1. Alternatively, all components of the system such as generators, conductors, transformers, and switchgear would be increased in size and cost to carry the extra current.
When the power factor is close to unity, for the same KVA rating of the transformer more load can be connected . Utilities typically charge additional costs to commercial customers who have a power factor below some limit, which is typically 0.
Engineers are often interested in the power factor of a load as one of the factors that affect the efficiency of power transmission. With the rising cost of energy and concerns over the efficient delivery of power, active PFC has become more common in consumer electronics. According to a white paper authored by Intel and the U.
Small customers, such as households, are not usually charged for reactive power and so power factor metering equipment for such customers will not be installed. Techniques for measuring the power factor[ edit ] The power factor in a single-phase circuit or balanced three-phase circuit can be measured with the wattmeter-ammeter-voltmeter method, where the power in watts is divided by the product of measured voltage and current.
The power factor of a balanced polyphase circuit is the same as that of any phase. The power factor of an unbalanced poly phase circuit is not uniquely defined. A direct reading power factor meter can be made with a moving coil meter of the electrodynamic type, carrying two perpendicular coils on the moving part of the instrument. The field of the instrument is energized by the circuit current flow. The two moving coils, A and B, are connected in parallel with the circuit load. One coil, A, will be connected through a resistor and the second coil, B, through an inductor, so that the current in coil B is delayed with respect to current in A.
At unity power factor, the current in A is in phase with the circuit current, and coil A provides maximum torque, driving the instrument pointer toward the 1. At zero power factor, the current in coil B is in phase with circuit current, and coil B provides torque to drive the pointer towards 0.
At intermediate values of power factor, the torques provided by the two coils add and the pointer takes up intermediate positions. The field coils are connected either directly to polyphase voltage sources or to a phase-shifting reactor if a single-phase application.
A second stationary field coil, perpendicular to the voltage coils, carries a current proportional to current in one phase of the circuit. The moving system of the instrument consists of two vanes that are magnetized by the current coil. In operation the moving vanes take up a physical angle equivalent to the electrical angle between the voltage source and the current source.
This type of instrument can be made to register for currents in both directions, giving a four-quadrant display of power factor or phase angle. Digital instruments exist that directly measure the time lag between voltage and current waveforms. Low-cost instruments of this type measure the peak of the waveforms.