where R = % resistance drop; X = % reactive drop; P = % power factor of load; W = % wattless factor of load (√1 - P2); D = % resultant secondary drop. For non-inductive loads where P = 100 and W = 0,
D = √X2 + (100 + R)2 - 100.
In the case of leading currents it should be considered negative.
In transformers where there is a great difference in voltage between the primary and secondary windings, however, this remedy has its limitations on account of the great amount of insulation which must necessarily be used between the windings, and which therefore causes the distances between them to become such as to cause considerable leakage of the lines of force.
Ques. How does the regulation vary for different transformers, and what should be the limit?
Ans. Those of large capacity usually have a better regulation than those of small capacity, but in no case should its value exceed 2 per cent.
Fig. 2,858.—Quill drive. This is the proper transmission arrangement substitute for heavy service, requiring large pulleys, sheaves, gears, rotors, etc. It is a hollow shaft supported by independent bearings. The main driving shaft running through the quill is thus relieved of all transverse stresses. The power is transmitted to the quill by means of a friction or jaw clutch. When the clutch is thrown out the pulley or sheave stands idle and the driving shaft revolves freely within the quill. As there is no contact between moving parts there is no wear. Jaw clutches should be used for drives demanding positive angular displacement. They can only be thrown in and out of engagement when at rest. All very large clutch pulleys, sheaves, or gears designed to run loose on the line shaft are preferably mounted on quills. The letters A, B, C, etc., indicate the dimensions to be specified in ordering a quill.
Ques. What advantages have shell type transformers over those of the core type?