Variable Ratio Transformer Voltage Regulators.—The principle of operation of this class of regulator is virtually the same as that of the induction type regulator; that is to say, both consist of regulating transformers, but in the variable ratio method the primary or series coil is divided into a number of sections which may be successively cut in or out of the circuit to be regulated, instead of varying the flux through the entire coil, as in the induction type. There are two distinct mechanical forms of variable ratio regulator:
- 1. Drum type;
- 2. Dial type.
Drum Type Regulators.—This form of variable ratio transformer consists essentially of a drum and finger type switch, similar to a railway controller.
There are many contacts, giving a large number of points of regulation, obtained by the use of changing switches and floating coils.
The floating coil is a part of the secondary winding of the regulating transformer which is insulated from the main portion of the winding, and is sub-divided by taps into a number of equal sections.
The sub-divisions of the main secondary winding are much larger, each one being equivalent to the whole of the floating coil.
Fig. 2,434.—Diagram of connections of General Electric high voltage cut out relay (form A) for voltage regulators. Its use in connection with the regulator protects the system from any sudden rise in voltage due to some accident to the regulator which might cause the relay contacts to stick, thus producing full field on the exciter. In construction, the control magnet is connected in series with the alternating current control magnet on the regulator and the contacts are connected in series with the rheostat shunt circuit. Then, should the voltage rise beyond a certain value, predetermined by the setting of the thumb screw supporting the plunger of the control magnet, the contacts of the relay are tripped open which, by inserting all the resistance in the exciter field, reduces the exciter voltage which in turn reduces the alternating current voltage. This relay has to be reset by hand.
Ques. Describe the operation of a drum regulator.