Otis Singleton
Volt-ampere reactive (VAR) is a unit of measurement of reactive power in electric power transmission and distribution. It is used to indicate the difference between real power and reactive power when there is a phase difference between voltage and current. In other words, VARs are used to measure the extra power that is borrowed from a power company and later returned when a magnetic field collapses and the energy stored in it is converted back into power.
| Characteristics | Values |
|---|---|
| Definition | A var or volt-ampere reactive is a unit of measurement used to describe the reactive power in an AC circuit. |
| Symbol | The symbol for var is "VAR" or "var". |
| Base Unit | 1 VAR = 1 Watt = 1 Volt x 1 Ampere |
| Reactive Power | VARS represent the reactive power component of AC circuits, which is distinct from real power (watts). |
| Phase Difference | In a pure reactive load, the voltage and current waveforms are out of phase by 90 degrees. |
| Inductive and Capacitive Loads | Inductive loads (motors, transformers) consume reactive power (VARS), while capacitive loads (capacitors) can generate reactive power and are used to correct power factor. |
| Power Factor Correction | VARS are used to improve power factor by compensating for reactive power, ensuring efficient energy use and reducing losses in transmission and distribution systems. |
| Measurement | VARS can be measured using power analyzers or by calculating the phase difference and magnitude of voltage and current waveforms. |
| Unit Multiples | Like watts, VARS also use multiples like kilovars (kVAR), megavars (MVAR), and gigavars (GVAR) for larger systems. |
| Application | VARS are commonly used in electrical engineering, power system analysis, and design to ensure proper sizing, efficiency, and performance of electrical equipment and grids. |
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What You'll Learn
Volt-Amp Reactive (VAR) is a unit of measurement for reactive power
In electric power transmission and distribution, VARs are specifically employed to quantify reactive power. Reactive power comes into play in an AC circuit when the current and voltage are not in phase. This type of power is distinct from the power that is actually consumed by a load, which is reflected in conventional kW-only power meters. However, modern electronic power meters can display both kW and kVAR power drawn by a load.
The term "var" was introduced in 1930 by the IEC in Stockholm and has since been adopted as the standard unit for reactive power. Interestingly, the International System of Units (SI) allows the use of "var" as a unit, even though it represents a form of power. According to EU directive 80/181/EEC, the correct symbol for the unit is "var" in lowercase, although variations such as "Var," "VAr," and "VAR" are also commonly used, with "VAR" being prevalent in the power industry.
Understanding VARs is crucial, especially for power plant operators. While some operators may have a basic understanding, the concept can be challenging to explain without delving into complex mathematical equations involving trigonometry, phase angles, and other intricate elements. However, visual analogies, such as the Wheelbarrow Analogy, can help provide a simpler understanding of the basics of reactive power and VARs.
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VAR power is 'borrowed' and returned by power companies
VAR, or Volt-Amperes Reactive, is a type of power that is borrowed and returned by power companies. It is considered "reactive" because it is used to build up a magnetic field during one part of the power cycle, which then collapses during another part of the cycle, at which point the energy is converted back into power and returned to the power company. This type of power is used by inductive loads, such as motors, transformers, and classic-style fluorescent lighting ballasts, and it bounces back and forth between the power company generator and the loads.
While VAR power is not consumed by the load, it does cause larger currents to flow through the power company's generators and distribution systems, which can be problematic. As a result, power companies may need to install more robust generators and distribution equipment to handle the extra current.
To compensate for high-VAR inductive loads, capacitors can be installed in parallel with the loads. Capacitors store energy in an electric field instead of a magnetic field, and when installed with the correct amount of capacitance, the extra reactive power needed can cycle back and forth between the capacitor and the inductive loads, reducing the reactive power seen by the power company.
By understanding and managing VAR power, power companies can optimize their systems and reduce the need for costly upgrades to generators and distribution equipment. This involves carefully matching the value of capacitance to the value of load inductance to minimize the reactive power drawn from the power company. Overall, the concept of VAR power and its management is an important aspect of power systems and building automation, ensuring efficient energy usage and distribution.
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Capacitors can compensate for high-VAR inductive loads
VAR, or Volt-Amperes Reactive, is a type of power that does not show up on a conventional kW-only power meter. It refers to the extra power that is "borrowed" from the power company by inductive loads. This power is temporarily stored in a magnetic field before being returned to the power company when the field collapses.
The use of capacitors to compensate for high-VAR inductive loads has several benefits. Firstly, it eliminates the losses that occur due to the extra reactive current drawn by inductive loads, improving the efficiency of the circuit. Secondly, it reduces the total amount of current taken from the source supply, which can result in significant savings for the utility company. Finally, capacitors can improve the power factor of a circuit, reducing the supply current and minimizing losses.
It is important to note that the correct amount of capacitance must be installed in parallel with the inductive load for this compensation method to be effective. If the capacitance is too low, the capacitor may not be able to provide enough reactive power to compensate for the inductive load. On the other hand, if the capacitance is too high, the capacitor may provide more reactive power than is needed, which can also be inefficient.
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VAR is less well-understood than kW
VAR, or kVAR, stands for "kilo-Volt-Amperes Reactive". It is a measure of reactive power in AC electrical systems. Unlike active power (measured in kW), which performs actual work, reactive power maintains voltage levels and supports inductive loads such as motors and transformers.
KW is a more familiar term for those involved in building automation as it is the rate at which a building consumes energy from the power company. However, VAR is a less well-understood concept. This may be because VAR power is not visible on a conventional kW-only power meter. A kW meter only shows power that is consumed by the load. VAR power, on the other hand, is "borrowed" by inductive loads from the power company and then returned when the magnetic field collapses and the energy is converted back into power.
Despite not being consumed, VAR power does have an impact on the power company's systems. The extra VAR power causes larger currents to flow through the generators and distribution equipment. This means that power companies must install more robust generators and equipment to handle the extra current.
To address high VAR inductive loads, capacitors can be installed. Capacitors store energy in an electric field and release it at the opposite times to an inductive load. This means that the extra reactive power can cycle back and forth between the capacitor and inductive load, and the power company does not see the reactive power on their system.
VAR management is crucial for industrial and commercial operations as utilities often penalize low power factors. By using power factor correction with capacitors, kVAR demand can be minimized, lowering energy costs and improving system capacity.
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VAR was introduced in 1930 by the IEC in Stockholm
Volt-Amperes Reactive (VAR) power, or kVAR, is a term used to describe reactive power in electrical engineering. It was introduced in 1930 by the IEC in Stockholm.
The IEC, or International Electrotechnical Commission, is the world's leading organization for the preparation and publication of international standards for electrical, electronic, and related technologies. The introduction of the VAR term was an important development in the field of electrical engineering, as it provided a way to measure and understand reactive power, which was not previously accounted for in conventional kW-only power meters.
Reactive power is the extra power that is "borrowed" from the power company by inductive loads. This power is not consumed by the load but is instead temporarily stored in the magnetic field created by the current flowing through the load. At a later point in the power cycle, this magnetic field collapses, and the energy stored in it is converted back into power and returned to the power company.
By introducing the VAR term, the IEC provided a way to measure and compensate for this reactive power. This is important because high-VAR inductive loads can impact the efficiency and stability of power systems. By installing capacitors in parallel with inductive loads, the reactive power can be cycled between the capacitor and the load, reducing the impact on the power company's system.
Today, many modern electronic power meters can display both kW and kVAR power, providing a more accurate understanding of a building's energy consumption and allowing for better management and optimization of power systems.
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Frequently asked questions
VAR stands for Volt-Amp Reactive or Volt-Ampere Reactive.
VAR is a unit of measurement of reactive power. It indicates the difference between real power and reactive power.
The term VAR was proposed by Romanian electrical engineer Constantin Budeanu and introduced in 1930 by the IEC in Stockholm.
VAR is important because it helps to understand and manage reactive power, which is a form of power that exists when there is a phase difference between voltage and current.
With inductive loads, extra power is "borrowed" from the power company and later returned when the magnetic field collapses. This power is called reactive power or VAR power. By installing capacitors, the extra reactive power can be stored and released at the appropriate times, reducing the burden on the power company.
