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Single-layer Winding It is that winding in which one conductor or one coil side is placed in each armature slot as shown in Fig. 26.27. Such a winding is not much used. Two-layer Winding In this type of winding, there are two conductors or coil sides per slot arranged in two layers. Usually, one side [...]
Written by John on April 29th, 2009 with 6 comments.
Read more articles on Direct Current Machines and Electrical Machines.
Armature Windings The meaning of the following terms used in connection with armature winding should be clearly kept in mind. Pole-pitch It may be variously defined as : i) The periphery of the armature divided by the number of poles of the generator i.e. the distance between two adjacent poles. ii) It is equal to [...]
Written by John on April 29th, 2009 with 8 comments.
Read more articles on Construction of D.C. Machines and Direct Current Machines and Electrical Machines.
Gate circuit should also be protected against overvoltages and over currents. Overvoltages across the gate circuit can cause false triggering of the SCR. Overcurrent may raise junction temperature beyond specified limit leading to its damage. Protection against over-voltages is achieved by connecting a zener diode ZD across the gate circuit. A resistor R2 connected in [...]
Written by John on April 17th, 2009 with 3 comments.
Read more articles on Power Electronics and Thyristor.
As thyristor possesses high surge current capability, it can be used in an electronic crowbar circuit for overcurrent protection of power converters using SCRs. An electronic crowbar protection provides rapid isolation of the power converter before any damage occurs Fig. 4.28 illustrates the basic principle of electronic crowbar protection. A crowbar thyristor is connected across [...]
Written by John on April 17th, 2009 with 1 comment.
Read more articles on Power Electronics and Thyristor.
Thyristors have small thermal time constants. Therefore, if a thyristor is subjected to overcurrent due to faults, short circuits or surge currents ; its junction temperature may exceed the rated value and the device may be damaged. There is thus a need for the overcurrent protection of SCRs. As in other electrical systems, overcurrent protection [...]
Written by John on April 17th, 2009 with no comments.
Read more articles on Power Electronics and Thyristor.
Thyristors are very sensitive to overvoltages just as other semi-conductor devices are. Overvoltage transients are perhaps the main cause of thyristor failure. Transient overvoltages cause either maloperation of the circuit by unwanted turn-on of a thyristor or permanent damage to the device due to reverse breakdown. A thyristor may be subjected to internal or external [...]
Written by John on April 17th, 2009 with 3 comments.
Read more articles on Power Electronics and Thyristor.
A snubber circuit consists of a series combination of resistance Rs and capacitance Cs in parallel with the thyristor as shown in Fig. 4.25. Strictly speaking, a capacitor Cs in parallel with the device is sufficient to prevent unwanted dv/dt triggering of the SCR. When switch S is closed, a sudden voltage appears across the [...]
Written by John on April 17th, 2009 with 4 comments.
Read more articles on Power Electronics and Thyristor.
Reliable operation of a thyristor demands that its specified ratings are not exceeded. In practice, a thyristor may be subjected to overvoltages or overcurrents. During SCR turn-on, di/dt may be prohibitively large. There may be false triggering of SCR by high value of dv/dt. A spurious signal across gate-cathode terminals may lead to unwanted turn-on. [...]
Written by John on April 17th, 2009 with 1 comment.
Read more articles on Power Electronics and Thyristor.
The principle of thyristor operation can be explained with the use of its two-transistor model (or two-transistor analogy). Fig. 4.15 (a) shows schematic diagram of a thyristor. From this figure, two-transistor model is obtained by bisecting the two middle layers, along the dotted line, in two separate halves as shown in Fig. 4.15 (b). In [...]
Written by John on April 14th, 2009 with no comments.
Read more articles on Power Electronics and Thyristor.
The forward gate characteristics of a thyristor are shown in Fig. 4.9 in the form of a graph between gate voltage and gate current. Here positive gate to cathode voltage Vg and positive gate to cathode current Ig represent dc values. As gate-cathode circuit of a thyristor is a p-n junction, gate characteristics of the [...]
Written by John on April 13th, 2009 with 4 comments.
Read more articles on Power Electronics and Thyristor.
Static and switching characteristics of thyristors are always taken into consideration for economical and reliable design of converter equipment. Static characteristics of a thyristor have already been examined. In this part of the section; switching, dynamic or transient, characteristics of thyristors are discussed. During turn-on and turn-off processes, a thyristor is subjected to different voltages [...]
Written by John on April 9th, 2009 with no comments.
Read more articles on Power Electronics and Thyristor.
Static and switching characteristics of thyristors are always taken into consideration for economical and reliable design of converter equipment. Static characteristics of a thyristor have already been examined. In this part of the section; switching, dynamic or transient, characteristics of thyristors are discussed. During turn-on and turn-off processes, a thyristor is subjected to different voltages [...]
Written by John on April 9th, 2009 with no comments.
Read more articles on Power Electronics and Thyristor.