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Class A commutation or Resonant Commutation Figure 35 shows the Class A commutation circuit where L and C are commutation components and RL is load resistance. For low value of load resistance, RL, L and C are connected in series as…
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Line Commutation and Forced Commutation Circuits Once thyristors operate in the ON state, carrying forward current, they can only be turned OFF by reducing the current flowing through them to zero for sufficient time to allow the removal…
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Snubber Circuit In most power electronic circuits, protection is necessary against the effects of excessive rate of rise of forward voltage (dv/dt) across the devices, which can otherwise cause unintended breakover, leading to a…
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String Efficiency For series or parallel connected SCRs, it should be ensured that each SCR rating is fully utilized and the system operation is satisfactory. Therefore, string efficiency is a term that is used for measuring the degree…
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Parallel Operation of Thyristors The need to connect thyristors in parallel arises when the current or over current to be handled by the apparatus or equipment exceeds the rating of a single thyristor. Thyristors can be connected…
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Equalising Network Voltage equalisation under these conditions can, however, be achieved by connecting shunt-capacitors as shown in Figure 28. This capacitor removes inequalities in thyristor self-capacitances. Therefore, during turn-off…
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Series Operations of Thyristors If the required voltage rating of the assembly or equipment incorporating thyristors is more than the voltage rating of a single thyristor, then several thyristors have to be united in a series connection.…
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Ratings of SCR All semiconductor devices have definite limits to their capability and exceeding these even for short times will result in failure, loss of control, or irreversible deterioration. All thyristors, therefore, have to be used…
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Overcurrent Protection of SCRs As the thyristors have a restricted overcurrent capacity, special fast-acting fuses and circuit breakers are usually provided for overcurrent protection. As the fault current increases, the fuse opens and…
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Overvoltage Protection of SCRs It is almost always necessary in a power semiconductor equipment to provide a means of limiting transient overvoltages which could otherwise overstress the semiconductor devices. To protect against all…
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