Voltage Control Techniques for Inverters: It has already been mentioned that Inverter Control providing a variable frequency supply to three phase motors should be capable of providing a variable voltage. This is required to avoid saturation and ensure operation at constant flux density. The Voltage Control Techniques for Inverters can be affected either external to […]
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Power System Protection and Switchgear: Air Blast Circuit Breaker Air Break Circuit Breaker Application of 3 Phase System Arc in Circuit Breaker Arc Interruption Methods in Circuit Breakers Arc Properties Auto Reclosing Scheme Automatic Switch Circuit Breaker Basic Design of Arc Extinction Chamber Basic Elements of Static Relay Basic Ideas of Protection Relay Basic Principle
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Features of Variable Voltage Inverters: The inverter has an impressed dc voltage. The output voltage of the inverter is decided by the firing and duration of the thyristors. The conduction of the thyristors can be either 180° or 120°, depending upon the control employed. In the case of 180° conduction three thyristors conduct at any
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Three Phase Inverter: The variable frequency required for the speed control of three phase ac motors is obtained from a Three Phase Inverter. To avoid magnetic saturation and to obtain constant flux conditions in the machine, the voltage fed to the motor must also be varied. Therefore an inverter feeding a three phase motor must
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Charging a Capacitor in Inverter: Charging a Capacitor in Inverter – Inverters are static power converters for converting dc to ac. By controlling the conducting periods of the thyristors it is possible to obtain variable frequency at the output terminals of the inverter. This variable frequency supply can be used to feed an ac motor,
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Chopper Controlled Resistance: By interrupting the flow of current through a resistance R in a periodic fashion using a switch, the value of resistance can be effectively varied. The interruption of the current can be accomplished by means of a dc chopper connected across the resistance, working as a switching device. When the chopper is
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Selection of Ratings of Devices of a Chopper Converter: Chopper Converter – The waveforms of currents and voltages are useful in deciding the ratings of devices. The main thyristor carries the load current. Superimposed on this there is a current pulse during the recharging process of the capacitor through the resonating circuit. Therefore the peak
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Two Quadrant Chopper: Sometimes a chopper may be required to provide a two quadrant operation by retaining the current direction in both motoring and braking modes. Such a Two Quadrant Chopper is shown in Fig. 3.86, and its waveforms in Fig. 3.87. The chopper permits a change in the polarity of terminal voltage keeping the
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Regenerative Braking: Sometimes the energy of the load may have to be fed to the supply system. A Chopper in this mode is called regenerative. The chopper working as a switch is connected across the load, which is normally a dc machine and the diode is connected in the line. The dc machine works as
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Performance of Chopper in Steady State Condition: Assuming Steady State Condition of the chopper, we have during TON The solution of Eq. 3.89 is where Io is the current at the starting of TON. At TON = aT, the current is when the thyristor is OFF, free wheeling takes place and the operation is described
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