Recent developments in the renewable energy sector suggest that the wind turbine and photo voltaic as Distributed Generation systems in the distribution network is gaining popularity as a new source of energy. Thus, this interconnected system consistently imposes new challenges in the power system stability. This study investigates the affect of distributed generators on distribution network during fault condition and includes voltage dips, transients and line short circuit fault current. With the increase in power demand, renewable energies such as wind turbines, solar panels and wave power plants have started to play a vital role in the global energy system. The integration of renewable energy into the power system can potentially cause severe challenges for the control and protection of large central generators and the distribution system Despite the capacity of such a complex network, constant disturbances remain in the system which may be dangerous both for the customers and the power electronics equipment in the network.
Advancement in the technology of renewable energy such as wind turbines in the MW range has developed more interest in general and its connection to the distribution network. Today large scale integration of wind turbine is connected to the Grid with high power density and controllability. As the quantity of distribution generation increases, as a result the distribution network becoming more like transmission network and the complexity of the network increases, A fault on such a complex distribution network can have serious consequences on the stability of the power system. A fault in the distribution system creates severe voltage dips and transients which can cause instability. As Distributed resources (DR) or distributed generators (DG)— connected to the distribution systems provides a different type of possibilities for energy conversion and generation compared to large generators connected to the transmission system. For various renewable energy resources like wind turbines, small and micro size wind turbines, conventional diesel generators, internal combustion generators, gas-fired turbines, PV cells and energy storage technologies, converters are required to provide electricity from these resources.
The Power quality is a measure of the voltage, the current and the frequency. Power quality problem may be of different nature which includes interruption, under and over voltages, flickers, harmonics and voltage sags. (The term dip is also used instead of sag).
Distributed generation (DG) is an emerging concept in the electricity sector, which represents good alternatives for electricity supply instead of the traditional centralized power generation concept. The main technical issues for DG connection relate to reliability and quality of supply, protection, metering, and operating protocols for connection and disconnection, islanding and reactive power management. Voltage regulation, voltage flicker, harmonic voltages and DC injection are key quality of supply issues.
Power quality is a measure of how close the voltage at the end user is to being sinusoidal with the rated frequency and the rated voltage magnitude. The cut-in and cut-out of units, especially old wind turbines and large capacitors generate transient voltage variations, also known as switching flicker. Fluctuations in the wind speed cause cyclic voltage fluctuations, also denoted continuous flicker. Frequency converters can generate harmonic currents. The inertia and low negative sequence impedance of induction generators and synchronous generators can, however also contribute to reduction of voltage fluctuations, harmonic currents and imbalance generated by consumers or other generation units.