- Smart Grid - Home
- Smart Grid Introduction
- What is an Electric Grid?
- Electric Grid Evolution
- What is a Smart Grid?
- Smart Grid - Functions
- Smart Grid - Characteristics
- Smart Grid - Advantages
- Smart Grid - Components
- Smart Grid - Challenges
- Smart Grid Technologies
- Smart Energy Resources
- Power System Automation
- Smart Substations
- Substation Automation
- Smart Grid - Feeder Automation
- Energy Management System
- Smart Grid - FACTS
- HVDC Transmission
- Wide Area Monitoring
- SCADA in Smart Grid
- Smart Grid - DMS
- Smart Grid - OMS
- Volt/VAR Control
- Smart Grid - FMSR
- Smart Grid - HEDT
- Phase Shifting Transformers
- Smart Grid - PHEV
- Advanced Metering Infrastructure
- Smart Meters - Introduction
- Smart Meters - AMI
- Smart Meters - AMIS
- Communication Architecture
- Drivers & Benefits
- Phasor Measurement Unit
- Intelligent Electronic Devices
- Power Quality Management
- Power Quality in Smart Grid
- Power Quality Issues
- Power Quality Monitoring Techniques
- Power Quality Conditioners
- Electromagnetic Compatibility (EMC)
- Power Quality Audit
- Smart Grid Communication
- Smart Grid Communication
- Communication Network
- Communication Technologies
- Broadband Over Power Line
- Internet Protocols
- Web Services in Smart Grid
- Cloud Computing
- Multi Agent System Technology
- IP Based Protocols
- Cyber Security
Power Quality in Smart Grid
In electrical power systems, the term Power Quality is not universally accepted but it has become a very important concept in smart grid technology. Other terms are also used to refer the same concept, they are Quality of Power Supply and Voltage Quality. In this chapter, we will understand the concept of power quality with respect to the smart gird. The interest in power quality has recently increased mainly due to the following reasons −
- Modern power system equipment has become more sensitive to voltage disturbances.
- Power electronic devices used to feed loads cause voltage disturbances in the system.
- Increasing need for standardization and performance criteria.
- Increasing harmonic currents and voltage dips, etc.
Power quality is a set of parameters that describes the process of electrical power delivery to the user under normal operating conditions and characterize the supply voltage.
The Concept of Power Quality
In electrical power systems, power quality is a concept that determines the fitness of electrical power delivered to the consumer devices.
In general, synchronization of voltage, frequency, and phases allows electrical power system to function as intended without significant loss in its performance and life. Therefore, the term "power quality" is used to describe electrical power that drives electrical load as in its intended manner. If there is any power quality issue, the device or load may malfunction, fail prematurely, or not operate at all.
It is also important point to understand that the term power quality represents the quality of supply voltage rather than the quality of electrical power. It is because we know that the power is the product of voltage and the current demanded by the load.
Thus, we can simply define the term "power quality" as the quality of voltage and/or the quality of current in the electrical power system.
Why is Power Quality Important?
The modern electronic devices and home appliances are very sensitive to disturbances in the power supply and they require a constant voltage and frequency to operate normally. A voltage greater than the normal voltage can cause these devices to operate inefficiently and may even damage some of the devices. On the other side, a low voltage can also impact in the same way and may cause devices to operate unpredictably or not at all.
As per researches, it has been found that every 1% change in the supply voltage has a corresponding 1% change in the power usage. Consequently, utility companies try to keep the supply voltage within a standard range to maintain the power quality and avoid its consequences.
Why Power Quality is Compromised?
The electrical power system comprises various stages, i.e., power generation, power transmission, and power distribution to the electricity meter installed at the consumers premises. Next, the electrical power moves through the wiring system of the end user until it reaches to the load device.
Thus, the complexity of the electrical system to move the electrical power from the point of generation to the point of consumption associated with variations in weather, generation, demand, and many other factors. Due to all these factors, the quality of power is to be compromised.
Reasons of Poor Power Quality
The following are some important reasons of poor power quality in an electrical power system −
Voltage Sag
Voltage sag is a short-term decrease in the RMS line voltage. It is also referred to as voltage dip. Voltage sag is a condition in which the line voltage decreases by 10% to 90% below the normal value for a short duration, typically 0.5 cycle to 1 minute. The main reason behind the occurrence of voltage sag is a sudden increase in the current demand, for example starting of a large induction motor or utility fault.
Voltage Swell
Voltage swell is the opposite phenomenon to voltage sag i.e., when a short-term increase occurs in the RMS line voltage above the normal line voltage, typically 110% to 180%, then it is referred to as voltage swell. The duration of voltage swell is also 0.5 cycle to 1 minute. The main reasons behind the voltage swells are the switching off of heavy loads or fault in the distribution system that cause sudden drop in load or incorrect tap settings in tap changers.
Flicker
When rapid and continuous variations occur in the load current magnitude that cause voltage variations in the system are referred to as flickers. The term flicker is derived from the visible fluctuations in the lighting intensity of lamps. Flickers are mainly caused by arc furnaces and heavy industrial machinery that result voltage fluctuations in utility transmission and distribution systems.
Voltage Imbalance
Voltage imbalance is a condition in three-phase system that occurs when there are variations in the amplitudes of three-phase voltages relative to one another. Voltage imbalance disturbs the operation of three-phase electric motors, overheat them, or result premature failure of system equipment.
Harmonics
Harmonics are sinusoidal voltages or currents having frequencies that are integer multiples of the fundamental frequency of the power system. Harmonics cause distortions in the sinusoidal waveforms of the voltages and currents. The main sources of harmonics are non-linear loads like power electronic components. Harmonics result in overheating of the power system equipment like transformers or motors, and also interfere with the communication systems.
Electrical Noise
Electrical noise is nothing but unwanted electrical signals with broadband spectral content lower than 200 kHz that disturbs the operations of power system equipment. Electrical noise is generally superimposed on the power system voltage or current in phase conductors or found on the neutral conductor or signal lines.
Some common sources of electrical noise include electromagnetic interference or radio-frequency interference from communication lines.
Impulsive Transients
Impulsive transients are short-term, unidirectional, and high-energy variations in the voltages or currents or both in a power line. The main reasons behind the occurrence of impulsive transients are switching of inductive loads, lightning strikes, or faults in power lines. These transients can shut down or damage the equipment if their distribution levels are high enough. The impact of impulsive transients can be reduced by using transient voltage suppressors.
Oscillatory Transients
Oscillatory transients are short-term bidirectional variations in the voltages or currents or both in power lines. These transients are caused by resonance or switching of power factor correction capacitors.
Interruption
Interruptions are defined as the complete loss or below 10% reductions in line voltage or current with respect to the normal voltage level. The durations of interruptions generally not exceed 60 seconds in length. The main causes of interruptions include faults in grid, failure of power system equipment, etc.
Voltage Fluctuations
Voltage fluctuations are the rapid and relatively small, typically less than 5%, variations in the RMS line voltage. Voltage fluctuations are generally caused by power electronic converters, arc furnaces, devices that draw unsynchronized currents with the line frequency, or unstable power supply. These conditions can disturb the operation of the devices like computers or other sensitive electronic devices.
How Does the Smart Grid Improve Power Quality?
Smart grid has several advanced components and technologies that can help utility companies to improve the power quality and deliver better quality power to consumers. The following points explain how the smart grid improve the power quality.
- Advanced Monitoring and Control − Smart grid deploys a number of sensors across the electrical network to provide real-time monitoring and control over the grid parameters.
- Power Conditioning Devices − Smart grid uses several power conditioning devices like harmonic filters, surge protectors, voltage regulators, etc. to improve the power quality.
- Energy Storage Systems − Smart grid integrates different types of energy storage systems like batteries. These devices help in stabilizing the voltage and frequency by absorbing or supplying power in the grid.
- Demand Response Programs − These programs are implemented to reduce loads during peak demand periods and balance supply and demand. This practice significantly improves the power quality.
Conclusion
In conclusion, power quality is one of the key measures for delivering a stable and reliable power supply to the end-users. Power quality can be defined as the electric supply that consistently meets the power supply requirements for reliable and efficient use at consumer end.
In India, home appliances and electronic devices are designed to work within a range of 100 volts to 240 volts of alternating current at 50 Hz. However, these devices work most efficiently at 220 volts, which is the standard for delivered voltage in India.
Utility companies also manage various parameters of power supply to ensure better power quality. For example, frequency that is set at 50 Hz in India and 60 Hz in USA or power factor that determines the amount of useable power delivered to the consumers, etc.