Pengukuran Daya (Ekki Kurniawan)

Summary

This video lecture provides an in-depth guide on measuring electrical power in both DC and AC circuits. It covers basic principles of power measurement using voltmeters and ammeters for DC, and explores effective power calculations for AC, including concepts like voltage, current, and the power factor. The lecture also explains the use of wattmeters, current transformers, and methods for measuring three-phase power. Various practical techniques are demonstrated, alongside common measurement tools. The session concludes with practical examples and calculations to solidify understanding of power measurement techniques in electrical systems.

Takeaways

• 😀 The video explains how to measure electrical power (both DC and AC) and provides the methods for calculating it.
• 😀 To measure DC power, a voltmeter and an ammeter are used. The power is calculated by multiplying voltage (V) and current (A).
• 😀 For AC power, the effective value (RMS) of voltage and current is used to calculate power, similar to how DC power is calculated, but using an additional factor of 'cosine theta'.
• 😀 The power in an AC circuit depends on the type of load: resistive, inductive, or capacitive. The phase relationship between voltage and current varies accordingly.
• 😀 In a resistive load, voltage and current are in phase, while in an inductive load, current lags voltage, and in a capacitive load, current leads voltage.
• 😀 The power factor is the ratio of real power (P) to apparent power (S), and it is calculated as cos(θ).
• 😀 The video discusses how to measure the total power using a wattmeter and how modern instruments can also measure energy consumption (kWh) and other parameters.
• 😀 When measuring three-phase power, instruments like wattmeters or voltmeters are used. Transformers may be employed to scale down high currents and voltages for accurate measurements.
• 😀 Different methods for measuring three-phase power include using three individual wattmeters or by measuring voltages and currents for each phase separately.
• 😀 For complex three-phase systems, methods such as the Aron method or Brondle theory can be used for simplified power calculations using fewer instruments (e.g., 2 ammeters and 2 voltmeters).

Q & A

What is the basic method for measuring power in a DC circuit?

In a DC circuit, the power measurement is simple and involves using a voltmeter and an ammeter. The power is calculated by multiplying the voltage (V) and current (I), i.e., P = V * I.

What should be considered when measuring power in a DC circuit with a voltmeter and ammeter?

When measuring power in a DC circuit, the voltage drop across the load (V) must be considered. In some cases, the voltage drop is small enough to be neglected, but it should be accounted for if significant.

How is AC power measurement different from DC power measurement?

In AC circuits, the power measurement is based on the effective values of voltage and current (also known as RMS values). The power is calculated using the formula P = V_eff * I_eff * cos(θ), where cos(θ) is the power factor, representing the phase difference between voltage and current.

What does the effective value of AC voltage and current mean?

The effective value (RMS value) of AC voltage or current represents the equivalent value of DC that would produce the same amount of heat in a resistor. It is the value that can be sensed or felt in practical applications.

What is the importance of the phase difference in AC circuits?

The phase difference between voltage and current in AC circuits is important because it affects the power factor. If the current and voltage are perfectly in phase, the power factor is 1, meaning all the energy is effectively used. A phase difference causes a reduction in the effective power, which is accounted for by the cos(θ) term.

How do inductive and capacitive loads affect the phase relationship in AC circuits?

In inductive loads, the current lags behind the voltage (lagging phase). In capacitive loads, the current leads the voltage (leading phase). This difference in phase affects the power factor and the overall power calculation.

What is the role of the power factor in AC power measurement?

The power factor (cos(θ)) represents the ratio of the real power to the apparent power in an AC circuit. It indicates how efficiently the electrical energy is being used. A low power factor means more energy is wasted.

How is the power measured in a three-phase system?

In a three-phase system, the power can be measured using a wattmeter or voltmeter and ammeter. It involves measuring the voltage and current of each phase. The total power is calculated by summing the power in each phase.

What is the method for measuring power in a three-phase system using current and voltage transformers?

In a three-phase system, power is often measured using current transformers (CTs) and voltage transformers (VTs). These transformers step down the high current and voltage levels to safer, measurable values. The measurements are then calibrated to determine the total power.

What is the significance of using a wattmeter in a three-phase system?

A wattmeter in a three-phase system is used to directly measure the real power in the system. For accurate readings, multiple wattmeters are used depending on the configuration of the system, such as a single wattmeter for a balanced load or three wattmeters for an unbalanced load.