In the center tap full wave rectifier, current flows through the load in the same direction for both half cycles of input AC voltage. The circuit shown in Figure has two diodes D1 and D2 and a center tapped transformer. The diode D1 is forward bias “ON” and diode D2
Month: February 2015
TRIAC are used for the control of power in AC circuits. A TRIAC is equivalent of two reverse parallel-connected SCRs with one common gate. Conduction can be achieved in either direction with an appropriate gate current. A TRIAC is thus a bi-directional gate controlled thyristor with three terminals. Figure 1
A GTO thyristor can be turned on by a single pulse of positive gate current like conventional thyristor, but in addition it can be turned off by a pulse of negative gate current. The gate current therefore controls both ON state and OFF state operation of the device. GTO V-I
The thyristor is the most important type of the power semiconductor devices. They are used in very large scale in power electronic circuits. The thyristor are known also as Silicon Controlled Rectifier (SCR). The thyristor has been invented in 1957 by general electric company in USA. The thyristor consists of
The V-I characteristics of the silicon diode and germanium diode. The icon used to represent the diode is drawn in the upper left corner of the figure, together with the polarity markings used in describing the characteristics. The icon ‘arrow’ itself suggests an intrinsic polarity reflecting the inherent non-linearity of
There are many bad effects of harmonics on the power system components. These bad effects can derated the power system component or it may destroy some devices in severe cases. The following is the harmonic effects on power system components. IN TRANSFORMERS AND REACTORS • The eddy current losses increase
There are several striking features of power electronics, the foremost among them being the extensive use of inductors and capacitors. In many applications of power electronics, an inductor may carry a high current at a high frequency. The implications of operating an inductor in this manner are quite a few,
Rectifiers can be classified as uncontrolled and controlled rectifiers, and the controlled rectifiers can be further divided into semi-controlled and fully controlled rectifiers. Uncontrolled rectifier circuits are built with diodes, and fully controlled rectifier circuits are built with SCRs. Both diodes and SCRs are used in semi-controlled rectifier circuits. There are
Whenever faults occur in power system large currents flow. Especially, if the fault is a dead short circuit at the terminals or bus bars enormous currents flow damaging the equipment and its components. To limit the flow of large currents under these circumstances current limiting reactors are used. These reactors
Knowledge of short circuit current values is necessary for the following reasons. 1. Fault currents which are several times larger than the normal operating currents produce large electro-magnetic forces and torques which may adversely affect the stator end windings. The forces on the end windings depend on both the dc