This question tests knowledge of electrical power units. In AC circuits, power is categorized into real power, reactive power, and apparent power, each with its specific unit of measurement.
Correct Option: D) Volt-amperes reactive (VAR) is the correct unit for measuring reactive power. This unit specifically designates the power that is exchanged between the source and reactive components (inductors and capacitors) in an AC circuit, which does not result in net energy transfer to the load.
To identify which component primarily contributes to reactive power in an AC circuit, we need to understand the nature of power in AC circuits, specifically real power, reactive power, and apparent power, and how different circuit elements (resistors, inductors, capacitors) interact with AC voltage and current.
Correct Option: B) Inductors and capacitors primarily contribute to reactive power in an AC circuit. Inductors consume lagging reactive power, while capacitors supply leading reactive power (or consume negative reactive power).
The power factor in an AC electrical system is a measure of how effectively electrical power is being used. A low power factor indicates that a significant portion of the current is reactive, meaning it does not perform useful work. Improving the power factor involves reducing this reactive power component, bringing the phase angle between voltage and current closer to zero.
B) Adding capacitors or inductors — Adding capacitors is the most common and effective way to improve a lagging power factor by supplying leading reactive power. While inductors can correct a leading power factor, the general problem of low power factor is usually due to inductive loads, making capacitors the primary solution. Therefore, this option correctly identifies components used for power factor correction.
The question asks about the advantage of a watt-hour meter in measuring energy consumption. To answer this, we need to understand what a watt-hour meter measures and how it differs from other measuring instruments like a wattmeter.
B) Provides a cumulative measure of power consumption over time. A watt-hour meter is designed to integrate power over a period, thereby measuring the total energy consumed. This cumulative measurement is its primary advantage for applications like electricity billing.
To accurately measure power in high-voltage circuits, it's crucial to safely step down the high voltage and high current to levels that standard measuring instruments can handle. This involves using specialized transformers designed for measurement purposes.
Using current transformers (CTs) is crucial for increasing the accuracy of power measurement in high-voltage circuits. CTs step down the high primary current to a safe and measurable secondary current, typically 5 A or 1 A, which can then be fed to the current coil of a wattmeter. They also provide electrical isolation, protecting the instruments and personnel. High-accuracy CTs minimize ratio and phase angle errors, which are vital for precise power calculations.
The question asks to define "active power" in the context of electrical power. Understanding the different types of power in AC circuits (active, reactive, and apparent) is crucial to answer this question.
Correct Option: C) Power that performs work
Active power is the component of electrical power that is converted into useful work (e.g., rotating a motor, lighting a bulb, heating an element). It is the power that is actually consumed by the load.