01-01-2011, 11:48 AM
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DYNAMIC VOLTAGE RESTORER
Power Quality (PQ) is an important measure of an electrical power system. The term PQ means to maintain purely sinusoidal current wave form in phase with a purely sinusoidal voltage wave form. The power generated at the generating station is purely sinusoidal in nature. The deteriorating quality of electric power is mainly because of current and voltage harmonics due to wide spread application of static power electronics converters, zero and negative sequence components originated by the use of single phase and unbalanced loads, reactive power, voltage sag, voltage swell,flicker, voltage interruption etc. To improve the power quality traditional compensation methods such as passive filters, synchronous capacitors, phase advancers, etc. were employed. However traditional controllers include many disadvantages such as fixed compensation, bulkiness, electromagnetic interference, possible resonance etc.. These disadvantages urged power system and power electronic engineers to develop adjustable and dynamic solutions using custom power devices.
Custom power devices are power conditioning equipments using static power electronic converters to improve the power quality of distribution system customers. These include APF, dynamic voltage restorer (DVR) and Unified Power Quality etc.
Series voltage controller
[Dynamic Voltage Restorer, (DVR)]
The series voltage controller is connected in series with the protected load. Usually the connection is made via a transformer, but configurations with direct connection via power electronics also exist. The resulting voltage at the load bus bar equals the sum of the grid voltage and the injected voltage from the DVR. The converter generates the reactive power needed while the active power is taken from the energy storage. The energy storage can be different depending on the needs of compensating.
DVR can compensate voltage at both transmission and distribution sides. Usually a DVR is installed on a critical load feeder. During the normal operating condition (without sag condition) DVR operates in a low loss standby mode During this condition the DVR is said to be in steady state. When a disturbance occurs (abnormal condition) and supply voltage deviates from nominal value, DVR supplies voltage for compensation of sag and is said to be in transient state.
