Fig. 2,431.—Westinghouse drum type variable transformer voltage regulator. It consists of a drum and finger type switch. A preventive resistance is used between the different contacts, making it unnecessary to open the circuit when moving from one tap of the regulating transformer to the next tap. A spring actuated, quick moving, central stopping mechanism is used to prevent burning the resistances. The regulator is arranged to give 40 points of regulation. In many cases this large number of points is not absolutely necessary, but it is desirable to use them because the voltage per step is thus reduced to a small value, and a corresponding increase in the life of the contacts results because of the reduced sparking at the lower voltage. Two drums are employed. The first drum has ten contacts and a corresponding number of fingers, the latter being mounted upon an insulated bar. These fingers are connected to the floating coils of the regulating transformer, and as the drum is rotated, the finger connected to the line is brought into contact successively with each of the ten taps. The second drum is of similar construction and consists of a changing and reversing switch. It connects the two floating coils to the various taps on the main secondary coil of the regulating transformer at the proper time, and also reverses the transformer so that the total winding can be used for either raising or lowering the voltage. All the points of regulation are obtained by a continuous motion of the handle, the various connections produced in the manner are shown in the diagram, fig. 2,433. The top and base of the regulator are made of cast iron and the top is supported by steel bars, two of which are insulated, and used to support the metallic bases finger to which the cable leads are attached. The drums consist of metal castings mounted upon insulated shafts. The first drum, which is the only one upon which arcing can take place, is provided with removable copper contact tips. The main castings are made of aluminum to secure low inertia of the drum. A sheet iron cover is used to enclose the regulator, and the leads are brought out through the bottom of the controller.
A non-inductive resistance placed in parallel with each coil of the secondary relay, takes current approximately in phase with the current in the main coil of the primary relay, and of proper strength to make the number of ampere turns in the auxiliary coil three-fourths per cent. of the number in the main coil. The resistances have the additional effect of absorbing the "discharge" from the main coils of the secondary relay when the contacts are broken, thereby obviating sparking at the primary contact points.
Fig. 2,432.—Diagram showing connections of the Stillwell regulator.
Fig. 2,433.—Diagram showing position of the floating coil on different steps of Westinghouse drum type variable ratio transformer regulator. The upper half of the diagram shows the connections of the various coils for each position of the regulator handle. This arrangement applies to a regulator used in connection with an independent regulating transformer. When regulators are used in connection with large power transformers, the regulating transformer can be omitted and auxiliary coils can be placed on the main transformer to provide the necessary taps for regulating purposes. The lower half of the diagram shows the connections used when auxiliary coils are added to a large transformer. The diagram shows connections for a single phase regulator. Where polyphase regulators are required, the connections consist essentially of two sets of single phase connection, and the controller is extended in length so as to contain double sets of drum and contact.