Cycloconverters find extensive use in high power systems like locomotive drives, cement and sugar mills etc. Cycloconverters works on the principle of converting single fixed frequency AC signal to Variable frequency AC signal. This is achieved by using a center tap transformer. Four different SCRs used. Appropriate snubber circuits protect these SCRs. Volt meter and Current meters for the measurement of voltage and current within the circuit. PHASE CONTROL CIRCUITS Why phase control?
Power systems using Thristors often exert control of load power by control of the time of firing during the AC cycle. This implies delaying conduction of the thyristor so that only a selectable portion of the AC cycle is available for the load. The non-sinusoidal voltage and current wave applied to the load has operational, measurement, analytic, and harmonic interference not encountered with straight DC or with AC sine-wave power. However, such phase-control circuits are relatively simple, efficient, and very convenient. Efficiency is high because turn on is extremely fast, and turn off is reasonably fast. Also conductive losses tend to be low because of the volt or so dropped across these devices. A good thing about using thyristor for phase controlled power is the self commutating feature, wherein turn off automatically obtains when the current wave goes through zero. The phase control can be achieved either on a full or half wave basis. A single SCR yields a half wave circuit, whereas TRIACS enable full wave operation from a single wave operation from a single device. Several relationships pertaining to phae controlled proper are often overlooked or become the sources of confusion. Best thing is to experiment and see your self what is right or for that matter why is it right. AC regulator works on the principle of converting fixed AC voltage to a variable AC voltage operating at the same frequency. This principle is used in speed control of AC drives, pumps, illumination control, temperature control of ovens etc. The devices used for such a control are THYRISTORS. This trainer contains a THYRISTOR, necessary firing circuit, and power supply, test points for observing waveforms. |
