This is the point where I am going to ask you to take my hand and to trust me. Okay, you don’t have to take my hand, but you do have to trust me. We are going to start using some terms before totally going into the theory behind them. I promise that we will get more in-depth into these concepts in future lessons. When dealing with DC circuits the only thing that opposes current is the resistance in the circuit. As we will learn in later units, AC adds a component that opposes current as well. This is called reactance and it runs 90 degrees to the circuit resistance. This means it is not possible to add them together arithmetically; it has to be done using the Pythagoras’ theorem. When you add these two together, you get a total opposition to current flow called impedance. The triangle that is created when adding the resistance to the reactance is known as an impedance triangle. In an impedance triangle, the resistance (r) is always on the bottom of the triangle, the reactance (x) always goes on the side and the hypotenuse is always the impedance (z). When dealing with a purely resistive circuit, the power being dissipated is in the form of heat or light and is measured in watts and is known as true or active power. It is a product of I2R. In an AC circuit with inductance, watts are still present. There is also a reactive power present as current passes across the reactance. This power is called reactive power and is also called wattless or quadrature power. Its unit is the Vars. Much like the impedance triangle, we can not just add the two powers together to get overall power. They must be added using the Pythagoras’ theorem. Their sum is equal to the apparent power (VA). When calculating for reactive power, we are still able to use the power formulas. We just have to use them with reactance instead of resistance. When building an impedance or power triangle, the resistive component always goes on the bottom of the triangle and the reactive component always goes on the side.
When a circuit containing both resistance, R, and inductance, L, is connected to an AC circuit, the voltage and current will be out of phase with each other by some amount between 0° and 90°.
is true power. VARs represents the product of the volts and amperes that are 90 Degrees out of phase with each other, such as the voltage dropped across the inductor and the current flowing through the inductor.
VARs is often referred to as
quadrature power, or wattless power.
Volt-amperes (VA) is the apparent power of the circuit.the value found by multiplying the applied voltage by the total current of an AC circuit. Ap-parent power is measured in volt-amperes (VA) and should not be confused with true power, measured in watts.
defined as a measure of the part of the circuit that impedes, or hinders, the flow of current.
VARs is an abbreviation for
volt-amperes-reactive and is the amount of reac-tive power (VARs) in the circuit. VARs should not be confused with watts, which is true power. VARs represents the product of the volts and amperes that are 90 Degrees out of phase with each other,
VARs is often referred to as
quadrature power, or wattless power.
why is this called apparent power (VA)
because it is the value that would be found if a voltmeter and ammeter were used to measure the circuit voltage and current and then these measured values were multiplied together
is a ratio of the true power to the apparent power. It can be calculated by dividing any resistive value by its like total value.
The angular displacement by which the voltage and current are out of phase with each other is called angle theta |
Of the different power values in an rl circuit, which one is known as wattless power?
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