Circuitos Trifásicos Equilibrados e Ligação Estrela e Triângulo (#65)

Summary

This video explains key concepts in three-phase electrical systems, focusing on star (Y) and delta (Δ) connections. It details the relationships between line and phase voltages and currents, emphasizing the √3 factor in both voltage and current calculations. The video also highlights the phase shift of 30 degrees in both configurations and demonstrates how to calculate apparent, active, and reactive power in a three-phase system. The focus is on understanding these relationships for effective power calculations, avoiding the need to memorize complex tables and instead grasping the core principles.

Takeaways

• 😀 The star (wye) connection involves line voltage being √3 times the phase voltage and line current being equal to phase current.
• 😀 In a balanced star connection, the current in the neutral is zero. In an unbalanced system, neutral current exists to maintain balance.
• 😀 In a star connection, the line voltage and phase voltage are related by a factor of √3, and the phase voltage is always lower than the line voltage.
• 😀 In a star connection, there is a 30-degree phase shift between line voltage and phase voltage due to the nature of the connection.
• 😀 The delta connection has equal line and phase voltages, but the line current is √3 times the phase current.
• 😀 In the delta connection, the current entering the line is always higher than the current passing through the load, due to the way current splits at each node.
• 😀 For both star and delta connections, current and voltage relationships vary when switching between phase and line quantities, requiring careful analysis of magnitude and phase shift.
• 😀 The phase shift between line and phase quantities in both star and delta connections is not due to the load type but because of the connection configuration.
• 😀 In both star and delta systems, calculating power involves using formulas that include √3 and either line or phase voltages and currents, depending on the type of connection.
• 😀 To calculate apparent power in a three-phase system, the formula is √3 times line voltage times line current. For active and reactive power, the angle of phase current is used to adjust the values.

Q & A

What is the key difference between line voltage and phase voltage in a star (wye) connection?

In a star (wye) connection, the line voltage is √3 times the phase voltage. This means the voltage measured between any two line terminals is greater than the voltage measured between any phase terminal and the neutral.

How do line and phase currents differ in a star connection?

In a star connection, the line current is equal to the phase current, as the current entering the terminals of the source or load is the same as the current flowing through the individual phases.

What role does the neutral wire play in a star connection?

The neutral wire in a star connection is optional but can help balance the circuit, particularly in cases of unbalanced loads. If the circuit is unbalanced, the neutral wire carries the imbalance current, keeping the system in balance.

What causes the 30-degree phase difference between line and phase voltages in a star connection?

The 30-degree phase difference between the line and phase voltages in a star connection is due to the type of wiring configuration. It is not caused by the electrical characteristics of the load but by the geometry of the star connection itself.

In a balanced star connection, what happens to the neutral current?

In a balanced star connection, the neutral current is zero because the currents in the three phases are equal in magnitude and symmetrically distributed, leading to no need for current to flow through the neutral wire.

How does the delta connection differ from the star connection in terms of voltage?

In a delta connection, the phase voltage is equal to the line voltage, while in a star connection, the line voltage is √3 times the phase voltage.

What is the relationship between line current and phase current in a delta connection?

In a delta connection, the line current is √3 times the phase current because the line current is divided among the phases, but the phase current is the current flowing through the load.

Why is there a 30-degree delay between line and phase currents in a delta connection?

The 30-degree delay between line and phase currents in a delta connection occurs due to the geometry of the delta wiring configuration. This phase shift results from the way current is distributed across the three phases.

What is the formula for calculating apparent power in a three-phase circuit?

The formula for calculating apparent power in a three-phase circuit is √3 × Line Voltage × Line Current. This gives the total apparent power for the system in terms of the line voltage and current.

How do you calculate active and reactive power in a three-phase circuit?

To calculate active power in a three-phase circuit, you multiply the apparent power by the cosine of the phase angle. For reactive power, you multiply the apparent power by the sine of the phase angle.