switch which is employed to protect the resistor from dangerous overheating due to some unusual conditions, such as fan stoppage or blocking of the air-intake door. The fan motor is fed from the main contact tips on the control undervoltage relay and through the control fuses which should give fan operation as long as the control is energized.The resistor is very difficult to protect, as it is essential to trip out the control for a small amount of power in the stack or from a relatively large amount of power in the same length of time. The reason for this is that the resistor is made up of six sections, used in various circuit locations, and each section has a different power rating and time on requirements. A number of different types of thermal switches was tested, and it was found that the switch had to have a best heat response to protect the edgewise resistor units which do not have a great amount of thermal capacity. The next problem was to determine the exact spot where it should be placed in order to protect as many of the sections as possible on the various operating parts. The location of the thermal switch was above the re sistor stack, so that the heat representing large kilowatt dissipation low in the stack would trip the switch. The unit also would function with a relatively low kilo watt dissipation on the top units. The action in the latter case was mainly from radiation from the top units. This switch is entirely waterproof, as it is located where rain could damage it. It is not necessary to remove the thermal switch to take out resistor boxes, as it is mounted on the top of the air baffle. The thermal switch selected protected the resistor sections on most operating points as well as protecting the resistor on a normal operating cycle.

ASSOCIATE AIEE FELLOW AIEE MEMBER AIEET HE general principles employed in the analysis of rectifier circuits have been quite fully covered in the literature and are now well understood. However, there is not available a complete analysis giving the essential formulas in a sys tematic and unified form readily usable by the engineer. It is the purpose of this paper to present such a treatment.A large variety of rectifier circuits has been devised. The analysis of many of the different types of circuits and the determination of their operating character istics are greatly facilitated by the circuit simplifications embodied in the concepts of 1. A rectifying element. 2. Simple, multiple, and cascade rectifiers. 3. Single-way and double-way rectifiers. 4. The reactance factor. 1 By the application of these ideas a stand ardized procedure for the analysis of rectifier circuits has been developed. This method is illustrated by the analysis.In the interest of brevity many parts of the analysis are presented by a state ment of the principles which apply and the expressions which may be derived. In such cases reference is made to stand ard texts for detailed derivation of formulas, discussion of principle, and validity of assumption. General Considerations Procedure.The analysis is divided into three parts in order to simplify the mathematical treatment and show the action more clearly. Wave forms for all three cases are shown on Figure 1.Case I shows the rectifier action with no overlap. The effect of transformer react ance is neglected, and it is assumed that the current transfer from anode to anode takes place instantaneously. The anode current waves are assumed rectangular in form, and the wave forms in this case are generally referred to as the theoretical wave forms. Case II shows the action with overlap and introduces the effect of transformer react ance in modifying the relations developed in case I. Paper 44-11, recommended by the AIEE committee on electronics for presentation at the AIEE summer technical meeting, St. Louis, Mo.. June 26-30, 1944. Manuscript submitted November 10, 1943; made available for printing May 24, 1944. E. F. CHBISTBNSBN is in the power-transformer engineering department. General Electric Company, Pittsneid, Mass.; C. H. WILLIS is professor, de partment of electrical engineering, Princeton Uni versity, Princeton, N. J.; and C. C. HBRSKIND is electrical engineer, power-rectifier department, General Electric Company, Schenectady, N. Y.Case III shows the effect of both phase con trol and overlap upon the rectifier action and characteristics.The analysis is carried through using the delta-double-wye circuit as an ex ample, as this circuit is more widely used and better understood than any other. Also, its analysis involves all of the fea tures found in most rectifier circuits. Mode of Operation.In general, several modes of operation are possible for any rectifier circuit, the various modes differing in the shape of the anode cur rent waves. The mode of operation is determined by the constants ...

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