Ac Theory Level 3 Lesson 1 (2024)

FAQs

What is the basic AC theory? ›

If a machine is constructed to rotate a magnetic field around a set of stationary wire coils with the turning of a shaft, AC voltage will be produced across the wire coils as that shaft is rotated, in accordance with Faraday's Law of electromagnetic induction.

The power factor is the cosine of the angle of the impedance. Since a pure capacitive circuit has no real component of the impedance, then the power factor is 0.

Looking at the graph, the current wave seems to have a “head start” on the voltage wave; the current “leads” the voltage, and the voltage “lags” behind the current. Voltage lags current by 90° in a pure capacitive circuit.

Therefore, it is true that 100% of the apparent power is used or consumed in a purely resistive circuit. This is not the case in circuits that have reactive elements, such as inductors and capacitors, where the current and voltage are out of phase with each other.

Thus, when connecting an electric circuit to an AC source, the AC voltage that passes through the circuit carries a sinusoidal shape that can be given by the mathematical formula: v = V ∗ c o s ( ω ∗ t ) where v (lowercase) is the instantaneous voltage at time t and V (uppercase) is the voltage amplitude or the maximum ...

Alternating Current (AC) is a type of electrical current, in which the direction of the flow of electrons switches back and forth at regular intervals or cycles. Current flowing in power lines and normal household electricity that comes from a wall outlet is alternating current.

PF = kW / kVA

A steel stamping operation runs at 100 kW (Working Power) and the Apparent Power meter records 125 kVA. To find the PF, divide 100 kW by 125 kVA to yield a PF of 80%. This means that only 80% of the incoming current does useful work and 20% is wasted through heating up the conductors.

Therefore, the power factor of pure inductor and pure capacitor circuit is zero.

Power factors are usually stated as leading or lagging to show the sign of the phase angle. Capacitive loads are leading (current leads voltage), and inductive loads are lagging (current lags voltage).

A capacitor charges up when the AC reaches its peak in an AC circuit and releases the charge when the AC decreases. This behavior allows the capacitor to act like temporary storage that causes the current to lead voltage by 90 degrees. Electrical engineers use capacitors to improve the power factor in an AC circuit.

What is the formula for capacitance in AC circuit? ›

The property of a capacitor to store a charge on its plates is called its capacitance, (C). Thus a capacitors charging current can be defined as: i = CdV/dt. Once the capacitor is “fully-charged” the capacitor blocks the flow of any more electrons onto its plates as they have become saturated.

The usual waveform of alternating current in most electric power circuits is a sine wave, whose positive half-period corresponds with positive direction of the current and vice versa (the full period is called a cycle).

If the load of the circuit is purely resistive, then there is no lag between the voltage and the current in the circuit. This means that both the current and voltage reverse their polarity at the same time. Then at any given instant of time, the product of voltage and current i.e. the power is either positive or zero.

Purely Resistive Circuit

Hence, these are often called non-inductive circuits. Properties. No presence of inductance and capacitance. The backward movement of both the alternating current and the voltage can be observed.

The reactive power formula is Q = V × I × sin(φ), where Q is the reactive power, V is the voltage, I is the current, and φ is the phase angle between the voltage and the current. The power factor is crucial in the reactive power formula, as it affects the amount of reactive power required to sustain the circuit.

A standard air conditioner or cooling system works by using a specialized chemical called refrigerant, and has three main mechanical components: a compressor, a condenser coil and an evaporator coil. These components work together to quickly convert the refrigerant from gas to liquid and back again.

AC power circuit principle

An alternating current is generated through an ac generator if a magnet or a magnetic field is rotated along with a stationary set of wires or coils. We can also say that if any coil is rotated around a stationary magnetic field, then an alternative current sets up using an ac generator.

AC circuits are powered by an alternating source such as alternating currents or voltages which are sinusoidal and change periodically in direction and magnitude. In other words, voltage or current oscillates in a sine wave pattern and varies with time. The current repeats its value after each time interval T=2π/⍵.

Alternating current, or ac, theory is concerned with the mathematical analysis of the steady-state behaviour of electrical circuits in which the currents and voltages vary periodically with time.