09-11-2016, 09:29 AM
1467198716-paper.docx (Size: 77.05 KB / Downloads: 6)
Introduction
To have sustainable growth and social progress, it is necessary to meet the energy need by using renewable energy resources like wind, biomass, hydro etc. It is very costly to store electrical power. Hence, the power produced by generating station must be consumed by the load. Power balance is very compulsory between generating plant and the load demand. The power imbalance can affect the frequency of the system which can lead to loss of synchronism in certain cases. Power imbalance between generating and load plants is the big problem in wind power generation due to the unpredictable nature of wind. The integration of wind energy into existing systems presents technical challenges like voltage regulation, stability and power quality problems. Integration of wind power into the grid affects the performance of the system and wind energy system also faces the problem of fluctuating voltage due to the nature of wind .
Power quality problems
Power quality
Power quality problem in any power problem presented in voltage , current, or frequency deviation that results in malfunctioning and failure of customer equipments. The main demand of consumers of electricity is the reliability of supply, we can define reliability is the continuity of supply. The distribution lines faces mainly two problems, first is power quality and second is power reliability. Due to the first problem the problems can exists are harmonic distortion, impulses and swells and second group consists of voltage sags and outages. Voltage sag is very serious problem and can lead to large amount of damage. Both the quality of power and power reliability is equally important .
Causes and consequences of power quality issues
Poor power quality causes trouble in transmission eqipmentsand electronic equipment malfunctions or failure. Power quality is a common problem for electric power suppliers and users, it is very difficult to find the cause of poor power supply quality at supplier’s systemand or at user’s system. Power disturbance can be classified into the following categories:
• Power imbalance
• Power outages
• Voltage variations
• Harmonics
• Flickers
Power Imbalance
Wind energy conversion system output depends on the wind speeds and the speed of wind cannot be forecasted with high accuracy over daily periods and the wind often deviates from minute to minute and hour to hour. This variations in the output of wind energy conversion system may increase the operating costs of the system. This variability and the unpredictability of the wind power can cause a power imbalance on the grid so their output power may not be available to meet the load demand when needed or there can be excess power when the demand of load is very low, this can upset the grid.
Power outage
Outages of power are the total interruptions of electric supply and there are various causes of power interruptions like ice storms, lightning, equipment failure. Due to these causes there is a complete disruption of operation
Voltage variations
The voltage variation is directly connected to real and reactive power variations. The wind velocity and generator torque results in voltage variations. The voltage variations are classified as:
• Voltage sags
• Voltage swells
• Short interruptions
Flickering , variation, harmonics of voltage results in malfunctioning of equipments. It can also leads to the tripping of protective devices. There are various causes of voltage variations like sudden change in load, large equipments start up or shut down
Flickers
Sometimes the wind generators produce oscillatory output power which can cause flickers in the power system network. The fluctuations caused by tower shadow effect can cause flickering. The wind turbine can cause two type of voltage variations
• Continuous operation
• Switching operation
The voltage variations because of continuous operation results from the variations of active and reactive power due to variations in wind speeds. Voltage variations due to the switching operations are due to fast changes of power from one level to another which is due to switching between wind generators
The effects of flickers is almost negligible in variable wind speed generators because they have ability to damp out fluctuations frpm switching operation
Harmonics
Harmonics are present at both the generation and consumer end. At the consumer end harmonics are present due to the non linear loads such as television, personal computers, compact fluorescent lamps etc and at the generation end the causes of harmonics are the FACTS(flexible Alternating Current transmission system) such as reactive power compensators. These can also cause voltage and current harmonics. Due to harmonics losses can increase and can cause excessive heating of equipments which can give effect on the lifetime of equipments