- What is Maximum Power Transfer Theorem?
As discussed in the section on Th´evenin’s theorem, any DC network of sources and resistances can be replaced by a single voltage source in series with a resistance connected across the load:
The maximum power transfer theorem states that the power delivered to the load is maximum when the load resistance, RL is equal to the internal (source) resistance, Rs of the DC power supply.
In other words, it can be said that the load resistance must match the Th´evenin’s resistance for maximum power transfer to take place i.e.,
(Rs = RTH )= RL
When this occurs, the voltage across the load resistance will be Vs/2 and the power delivered to the load is given by
which clearly demonstrates maximum power delivered when Rs = RL. Under this condition, the maximum power will be:
- Define Super node?
A supernode exists when an ideal voltage source appears between any two nodes of an electric circuit. The usual way to solve this is to write KCL equations for both nodes and simply add them together into one equation ignoring the voltage source in question. However, this would mean one less equation than the number of variables (node voltages) present in the circuit. A constraint equation can be easily specified given by the magnitude of the ideal voltage source present between the nodes and the respective node voltages. The following example will help clarify this scenario.
- What does the term Supermesh means?
A supermesh exists when an ideal current source appears between two meshes of an electric circuit. In such a situation, like supernode, mesh equations are written for the meshes involved and added giving a single equation. Again, there would be one less equation than the number of variables (mesh currents) and hence a constraint equation is needed. This would be based on the magnitude of the ideal current source present between the two meshes and their mesh currents.
- What do you mean by Phasors?
Addition of two out-of-phase sinusoidal signals is rather complicated in the time domain. An example could be the sum of voltages across a series connection of a resistor and an inductor.
Phasors simplify this analysis by considering only the amplitude and phase components of the sine wave. Moreover, they can be solved using complex algebra or treated vectorially using a vector diagram.
- What does the term Power Factor shows?
The term cos φ is called the power factor and is an important parameter in determining the amount of actual power dissipated in the load. In practice, power factor is used to specify the characteristics of a load.
For a purely resistive load φ =0 Degree, hence Unity Power Factor
For a capacitive type load I leads V , hence Leading power factor
For an inductive type load I lags V , hence Lagging power factor
Clearly, for a fixed amount of demanded power, P , at a constant load voltage, V , a higher power factor draws less amount of current and hence low I2R losses in the transmission lines. A purely reactive load where φ → 900 and cos φ → 0 will draw an excessively large amount of current and a power factor correction is required.
- Differentiate between Real and Apparent Power?
It is important to highlight that in AC circuits, the product of voltage and current yields the apparent power which is measured in volt-amperes or VA
KW which is also written ad Kilo-Watt is the real power that is actually converted to the useful work.
KVAR is also termed as Kilo-Volt Reactive this power is used for magnetic field excitation and flows back and forth between source and load.
