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Pharos University

Pharos University. EE 369 : Electrical Power For Mechanical Engineers “ Mechanical Engineering Dept.” EE 385: Electrical Power & Machines “ Electrical Engineering Dept.” Prepared By: Dr. Sahar Abd El Moneim Moussa. Review On Ac Circuits. Review on AC Circuit. Basic Principles:

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Pharos University

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  1. Pharos University EE 369: Electrical Power For Mechanical Engineers “ Mechanical Engineering Dept.” EE 385: Electrical Power & Machines “ Electrical Engineering Dept.” Prepared By: Dr. SaharAbd El MoneimMoussa Dr. SaharAbd El MoneimMoussa

  2. Review On Ac Circuits Dr. Sahar Abd El Moneim Moussa

  3. Review on AC Circuit • Basic Principles: • Sinusoidal voltage source: it is a source that produces voltage that varies with time as sine wave • Waveform: Where: T: periodic time: the time of one complete cycle. f: number of cycles per second = 1/T Hz ω: angular frequency of the sine wave = 2πf rad/sec T Dr. Sahar Abd El Moneim Moussa

  4. Equation: V(instantaneous)= Vm sin ωt Where: Vm : The maximum voltage value & it is knows as the amplitude Vrms : Root mean square of the voltage = • Symbol: ~ V(t)= Vm sin ωt Dr. Sahar Abd El Moneim Moussa

  5. V(t)= Vm sin ωt • Resistive Circuit • Circuit diagram: • Equation: V= Vm sin ωt , I= Imsin ωt • Waveform: “in terms of the time domain” • Phasor diagram: ∴The Resistive current is in phase with the voltage Im Vm Dr. Sahar Abd El Moneim Moussa

  6. Xc = 1/ωc Ω • Capacitive Circuit • Circuit diagram: • Equation: V= Vm sin ωt , I= Imsin (ωt+90) • Waveform: • Phasor Diagram: Where: θ is the angle between the voltage and the current (cosθ is called the power factor ) ∴The Capacitive current leads the voltage by 90o Im θ Vm Dr. Sahar Abd El Moneim Moussa

  7. XL = ωL Ω • Inductive Circuit • Circuit diagram: • Equation: V= Vm sin ωt , I= Imsin (ωt-90) • Waveform: • Phasor Diagram: Where:θ is the angle between the voltage and the current ( cosθ is called the power factor ) ∴The Inductive current lags its voltage by 90o Vm θ Im Dr. SaharAbd El MoneimMoussa

  8. Impedance Circuit • Circuit diagram: • Equation: V= Vm sin ωt , I= Imsin (ωt-) • Waveform: • Phasor Diagram: Where: θ Vm Im Dr. SaharAbd El MoneimMoussa

  9. Why Power Systems Use Alternating Current (AC) • The output of power stations comes from a rotary turbine, which by it's nature is AC and therefore requires no power electronics to convert to DC. • Transformers constitute major part in power systems , as transformers can only operate for AC system, this system has been adopted to all power systems. • When a fault on the network occurs, a large fault current occurs. In an AC system this becomes much easier to interrupt, as the sine wave current will naturally tend to zero at some point making the current easier to interrupt. Dr. Sahar Abd El Moneim Moussa

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