They do not require synchronizing and have mechanical characteristics that are

They do not require synchronizing and have mechanical

This preview shows page 10 - 12 out of 15 pages.

small, grid-connected generation, primarily because they are relatively inexpensive. They do not require synchronizing and have mechanical characteristics that are appealing for some applications (wind, for example). They also absorb reactive power rather than generate it, and are not controllable. If the output from the generator fluctuates (as wind does), the reactive demand of the generator fluctuates as well, compounding voltage-control problems for the transmission system. Induction generators can be compensated with static capacitors, but this strategy does not address the fluctuation problem or provide How reactive power is helpful to maintain a system healthy | EEP ... 10 of 15 2/11/2015 9:10 AM
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controlled voltage support. Many distributed generation resources are now being coupled to the grid through solid-state power electronics to allow the prime mover’s speed to vary independently of the power-system frequency. For wind, this use of solid-state electronics can improve the energy capture. . For gas-fired micro turbines, power electronics equipment allows them to operate at very high speeds. Photovoltaic’s generate direct current and require inverters to couple them to the power system. Energy- storage devices (e.g., batteries, flywheels, and superconducting magnetic-energy storage devices) are often distributed as well and require solid-state inverters to interface with the grid. This increased use of a solid-state interface between the devices and the power system has the added benefit of providing full reactive-power control, similar to that of a STATCOM. . In fact, most devices do not have to be providing active power for the full range of reactive control to be available. The generation prime mover, e.g. turbine, can be out of service while the reactive component is fully functional. This technological development (solid-state power electronics) has turned a potential problem into a benefit, allowing distributed resources to contribute to voltage control. Top Transmission side Unavoidable consequence of loads operation is presence of reactive power, associated with phase shifting between voltage and current. . Some portion of this power is compensated on customer side, while the rest is loading the network. The supply contracts do not require a cosφ equal to one. The reactive power is also used by the transmission lines owner for controlling the voltages. . Reactive component of current adds to the loads current and increases the voltage drops across network impedances. Adjusting the reactive power flow the operator change voltage drops in lines and in this way the voltage at customer connection point. The voltage on customer side depends on everything what happens on the way from generator to customer loads. All nodes, connation points of other transmission lines, distribution station and other equipment contribute to reactive power flow.
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