CLIC is an international study of a future multi-TeV electron-positron linear collider, where the energy of a high-intensity drive beam is extracted and transferred to the main beam via Power Extraction and Transfer Structures (PETS) in the form of rf power. The study of power production is therefore essential for the feasibility of CLIC. Power production in PETS has been studied, and experiments have been performed in the decelerator Test Beam Line in the CLIC Test Facility 3.In particular, the correlation of the power production and the beam position inside the structure has been studied. It is shown that the total produced power is constant when the beam has a position offset through the PETS. In addition, the difference between the measured phases from each side is independent of the beam position, which allows for efficient combination of the fields. However, the ratio of the power on each side of the PETS unexpectedly shows a linear dependence on the horizontal offset, with a correlation value of 0.87. This can potentially affect the power transferred to the main linac, and should be taken into account in the design of the high power rf system.A graphical user interface was developed for the Test Beam Line, and the functionality is described in detail. The program is used in the operation of the Test Beam Line for monitoring, matching, steering and power production experiments, and has interfaces to MAD-X and PLACET. A documentation is also given of the Test Beam Line and the methods of the power measurements.