Circuitos Trifásicos - Exercícios - parte: 1/2 (#66)

Summary

This video focuses on calculating electrical parameters in a three-phase circuit, specifically with star (wye) and delta configurations. It covers how to determine line and phase voltages and currents, explaining the relationship between them. The video also emphasizes the importance of RMS values and illustrates how to calculate active and reactive power for capacitive loads using complex impedance. Through a detailed example, the video demonstrates how to apply these formulas, providing viewers with a clear understanding of the step-by-step process of solving these types of electrical problems.

Takeaways

• 😀 The analysis involves a three-phase electrical system with star connection (Y-Y).
• 😀 Phase voltage is calculated using the reference angle of 10 degrees and the impedance of the load.
• 😀 The line current can be found by multiplying the phase current by √3 and applying a 30-degree phase shift.
• 😀 The phase current is determined by using the phase voltage and the load's impedance, calculated in the complex form.
• 😀 The complex impedance of the load is given as 20 - j15, which suggests a capacitive load.
• 😀 Calculating the phase current involves using the formula: phase current = phase voltage / impedance.
• 😀 The line current is found by multiplying the phase current by √3, with a phase shift of 30 degrees.
• 😀 The power calculation involves three times the product of phase voltage and the conjugate of phase current.
• 😀 The total active power (P) and reactive power (Q) are computed using the complex values of the voltage and current.
• 😀 All calculations are in RMS values, and no peak values are used in this analysis, which is important for accurate results.
• 😀 The final power results include 10.444 kW of active power and 7.84 kVAR of reactive capacitive power, with a phase angle of -37 degrees.

Q & A

What is the main focus of the lesson in the transcript?

The main focus of the lesson is on analyzing three-phase AC circuits, specifically in star-star or triangle-triangle configurations. It covers how to calculate phase and line currents, as well as how to determine active and reactive power.

How is the phase current calculated in the given three-phase circuit?

The phase current is calculated by dividing the phase voltage by the impedance of the load. This is based on the concept of using the monofasical equivalent for an unbalanced or balanced load.

What is the relationship between phase and line current in a three-phase system?

The line current is related to the phase current by the formula: line current = phase current × √3, with the line current lagging the phase current by 30 degrees.

Why is the use of RMS values emphasized in the calculations?

RMS values are emphasized because they represent the effective value of AC voltages and currents, making calculations consistent and accurate. Peak values are not typically used in these types of AC power analyses.

What is the significance of the phase angle in calculating the current?

The phase angle indicates the phase difference between the voltage and current. It is crucial for determining the real and reactive power components of the system. A negative phase angle, as in this case, indicates a capacitive load.

How is the total power in the three-phase system calculated?

The total power is calculated using the formula: total power = 3 × phase voltage × phase current × cos(θ), where θ is the phase angle. This provides the active power and, through a similar process, the reactive power is also calculated.

What does the negative phase angle indicate about the load in this system?

A negative phase angle indicates that the load is capacitive. This is confirmed by the given impedance values and the resulting phase angle, showing that the current lags the voltage.

Why is it important to convert peak values to RMS values?

Converting peak values to RMS values ensures consistency in calculations, as RMS values are the standard for working with AC circuits. This allows for accurate power, current, and voltage calculations in the system.

How are the active and reactive powers in the system determined?

The active power is determined by multiplying the RMS phase voltage, RMS phase current, and the cosine of the phase angle. The reactive power is found similarly, using the sine of the phase angle to calculate the reactive component of power.

What are the final results for the active and reactive power in the system?

The final results are approximately 10,444 watts of active power and 7,840 volt-amperes reactive power, with a phase angle of -37 degrees, which corresponds to a capacitive load.