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Switchgear Protection Definition of Switchgear A switchgear is a system includes all the switching devices associated with control, metering and regulating of electrical power systems ,thus providing power system protection . The Assembly of such devices in a logical manner forms switchgear . In other words systems used for switching, controlling and protecting the electrical power circuits and different types of electrical equipment are known as switchgear . This is very basic definition of switchgear . Switchgear and Protection We are all familiar with low voltage switches and re-wirable fuses in our home. The switch is used to manually open and close the electrical circuit in our home and electrical fuse is used to protect our household electrical circuit from over current and short circuit faults. In same way every electrical circuit including high voltage electrical power system needs switching and protective devices. But in high voltage and extra high volt...
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Understanding PWM modulation in Electric drives

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Pulse width modulated converter: The voltage source converters are used in electrical drives.These converters utilize capacitors in the DC-link to store temporarily electricalenergy. Switching the power electronic devices allows the DC voltage tobe modulated which can result in a variable voltage and frequency waveform.The purpose of the modulator is to generate the required switching signalsfor these switching devices on the basis of user defined inputs. For this purpose,the voltage–time integral was introduced which in turn is tied tothe average voltage per sample U ( t k) that may be written as U(t)=(1/T s ) ∫ u(t) dt ranging between t k to (t k + T s ) where T s is a given sample interval and u ( t ) represents the instantaneousvoltage across a single-phase of a load.The introduction of the variable T s assumes the use of a fixed sampling frequency which is normally judiciallychosen higher than the fundamental frequency range required to controlelectrical machines.The u...
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