Method of AC Voltage Control
When the load on the supply system changes, the voltage at the consumer’s terminals also changes. hence, as per requirement of load voltage. its necessary to control the AC voltage at load. system voltage is changed in according with the load to obtain constant voltage at the consumer’s end. which is getting by voltage control. there are various method of AC voltage control are following,
- Auto-transformer tap changing
- Booster transformer
- By synchronous condense
- By using tap changing transformers
- Induction regulators
- By excitation control
Auto-transformer tap changing:-
Auto-transformer tap changing shown in figure.
Here, a mid-tapped auto-transformer or reactor is used. One of the lines is connected to its mid-tapping. A switch is remains in the closed position under normal operation. which is A short-circuiting switch S is connected across the auto-transformer. This Reactor transformer is connected to a series of switches across the odd tappings. The other end X is connected to switches across even tappings. during normal operation there is no inductive voltage drop across the auto transformer. therefore, different tappings are provide on the secondary side of the auto Xmer.
According to figure is we connect tapping no. 4 then minimum winding turn come in circuit. hence, the secondary voltage is minimum. as we connect the tapping no. 1 then maximum no of winding turn are came in circuit. hence, the voltage rating at secondary side is maximum. When connected tap chnging at no. 4 then voltage is lowest. if we want to rais in output voltage the connect tapping with the 3 no. stud. when it is connected on 4th. short circuit switch is open. but during the tap changing that short circuit switch need to close. By this way we can tap changing without interrupting the supply voltage.
When during the tap changing , short circuit switch is open. the load current flows through one-half of the reactor coil, so that there is a voltage drop across the reactor. in this condition heavy current flow through the tapping and its causes of sparking during the tap changing. so equipment may be can damage because of that sparking and may chances to failure of insulation. When switch 3 is closed, the turns between points 3 and 4 are connected through the whole reactor winding. A circulating current flows through this local circuit, but it is limited to a low value due to high reactance of the reactor.
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