Electrical concepts
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This document provides an overview of basic electrical concepts to help readers better understand energy efficiency. It defines key terms like energy, British Thermal Units, the WAGES acronym to remember the main energy sources (water, air, gas, electric, steam), electrical resistance, power distribution in single and three-phase systems, real and reactive power, power factor and how it is calculated, causes of low power factor including displacement and total power factor, load factor calculation, and the power triangle relationship between voltage, current, real power, reactive power and apparent power.
Electrical concepts
- 1. This document will enable the readers to have a better understanding on basic electrical concepts. Amit Kumar Senapati Certified Energy Auditor: Reg. No. EA B.Tech Basic Electrical Concepts This document will enable the readers to have a better understanding on basic electrical concepts. Amit Kumar Senapati Certified Energy Auditor: Reg. No. EA-13771 B.Tech – Electrical, MS – Manufacturing Management This document will enable the readers to have a better understanding on basic electrical concepts.
- 2. Electrical Concepts Purpose of the document : This document will enable the reader to refresher on some of major electrical concepts that we can encounter working on energy efficiency. Energy is the ability to do work. In countries using the US customary measures, energy is often expressed in British Thermal Units. A BTU is the amount of heat required to raise the temperature of one pound of liquid water from 60 to 61 degrees Fahrenheit at a constant pressure of one atmosphere. To fully account for energy, the following should be included water, air, gas, electric and steam. An easy way to remember these is using the acronym W.A.G.E.S. Energy is Compromised of WAGES i) Water includes: a) Domestic portable water. b) Domestic hot water. c) Heating hot water. d) Chilled Water. e) Waste Water. ii) ‘Gas’ refers to natural gas. Gas is often measured by volume, in cubic feet or cubic meters.Liquid fuels like oil and gasoline may also be measured by volume, using gallons or litres. Under the G for Gas in the WAGES acronym, we also include other forms of primary energy, such as coal, oil, gasoline and ethanol. It also includes gasses used in manufacturing processes such as oxygen, argon,CO2 and nitrogen. Liquid fuels like oil and gasoline may also be measured by volume, using gallons or litres. Crude oil is sold in barrels. A barrel of oil is 42 gallons or approximately 159 litres. iii) Resistance determines how much current will flow through a component.Materials with low resistance let electricity flow easily. Materials with higher resistance require more voltage to make the electricity flow. The power equation for electricity is P (watts) = V (volts) x I (amps) Therefore P also = I² R, and P = V²/ R Power Distribution
- 3. In a three-phase system, three circuit conductors carry three currents of the same frequency. The difference is that the three currents experience their peaks at different times. An advantage three-phase power has is it gives constant power transfer over each current cycle. It also enables a rotating magnetic field to occur in an electric motor. This is the sine wave associated with three-phase power. Real and Reactive Power Some types of equipment need reactive power as well as the usual, real power. Real power is used by the equipment to do work. Reactive power may be required to provide a magnetic field. Power factor is a number between 0 and 1 that indicates how efficiently power is being used. A good power factor is 0.9 to 1. 1 is a perfect power factor and while ideal, it rarely occurs. Utility companies can penalize if power factor is lower than their ideal standard (typically lower than 85% or 90%). Any power factor less than 1 can incur a penalty. Kvars are used to reflect a power factor penalty in a utility bill. The Power Triangle This is the power triangle. It shows the relationship of the three components.
- 4. KVA is sometimes called apparent power. The formula for this is the square root of kilowatts squared plus kvar squared kW is sometimes called real power. The formula for real power is kVA times the cosine of the angle And KVAR is called reactive power. The formula for kvar is kVA times the sin of the angle. What Causes Low Power Factor? In an electrical system, volts and amps both ideally have a sinusoidal waveform. If the current and voltage waveforms are aligned, and reach their maximum amplitude at the same time, the current is said to be “in phase” with the voltage and no kvars are present. However if the voltage reaches its maximum amplitude before the current, kvars are said to be “lagging.” On the other hand, if the current reaches its maximum amplitude before the voltage, kvars are said to be “leading.” These leading and lagging cases are based on a phase angle shift between the current and voltage due to an inductive load such as motors or transformers, or a capacitive load such as capacitors or a synchronous motor. There are two types of power factor. They are: a) Displacement power factor b) Total (True) power factor a) Displacement Power Factor is equal to the displacement angle between the current flowing in the load and the supply voltage. It is equal to the cosine of Phi. Capacitors can correct displacement power factor effects.
- 5. b) Total power factor is a measure of kW divided by kVA and includes the effects of distortions known as harmonics. Load Factor Load factor = Actual consumption for period / Consumption at peak demand for period. A low load factor means that occasionally the power usage is very high but at other times it is very low. This will result in a low load factor. A low load factor means that occasionally the power usage is very high but at other times it is very low. This building had a big spike. This makes the green area big, and will result in a low load factor. In a single phase system, power in Watts equals Volts (V) times amps (I). In a three phase system, the power in Watts equals 3 x volts times amps times the power factor References: 1. How to make money by Energy Auditing. Author. Balasubhraminiam. 2. Schneider Energy University.