This paper describes the application of a variable-speed drive for the speed-sensing element of a conventional hydro-governor which makes it possible to measure accurately the deflection of the speeder rod for a given speed change from normal. When this characteristic is determined in the field, changes can be made to the control springs if necessary, to make all machines consistent. The device may also be applied to measure directly both the permanent and temporary speed droops of the governor and allow these quantities to be readjusted to the desired values. The advantage of this method of adjustment is that it permits all the work to be carried out with the main machine shutdown. The variable-speed drive consists of a small motor-generator set which supplies direct-current power to a rotary converter, which in turn delivers low-frequency alternating-current power to the speed-sensing motor on the governor. The rotary converter and the motor-generator set are controlled by a system which gives precise control over the speed which is measured by an accurate tachometer.

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