460 ELECTRICAL EQUIPMENT 



to the reactance of the reactor to determine the total apparatus 

 reactance of the circuit. This total reactance, plus the reactance 

 of the line up to the point of short-circuit divided into 100, gives 

 the approximate short-circuit current (the result being expressed 

 in number of times normal). 



Care must be exercised in calculating the possible short-circuit 

 current of a system that the various per cent reactances are on the 

 same basis, i.e., on the same current value. For example, if the 

 reactance for a 6000 Kv.A., three-phase transformer is given as 

 6 per cent but a value is required which corresponds to one of the 

 generators, having a capacity of, say, 4000 Kv.A., three-phase, 



4000 

 the corresponding value would then be 7X6 = 4 per cent. 



Similarly, it must also be remembered that reactance values 

 given for single-phase transformers really refer to a bank of three 

 such transformers. For example, the reactance of a 6000 Kv.A., 

 single-phase transformer is given as 3 per cent. This, then, usually 

 refers to the full-load current from a bank of three such units, i.e., 

 18,000 Kv.A., so that if the reactance were to be converted to the 

 basis of a 6000 Kv.A. generator, its corresponding value would be 



6000 



X3 = l per cent. A careful consideration of the above is of 

 18000 



the greatest importance when reactance values for generators, 

 transformers and transmission lines of different capacities are to 

 be combined. 



For the designation of the rating of a current limiting reactor 

 the following method is generally used: 



" Type ...... Frequency ...... Kv.A ....... Volts Drop ...... 



Amperes ....... Reactor to give ........ per cent reactive drop 



in ...... Kv.A ....... volt ...... phase circuit." 



The type symbols generally used are CLS, CLQ and CLT. 

 The meaning of the symbols is as follows: 

 C.L. Current-limiting reactor. 



S. Single-phase (may apply to any one reactor of a 

 group of two or three for use in two- or three- 

 phase circuits). 

 Q. Two phase (two single-phase reactors mounted 



together). 



T. Three-phase (three single-phase reactors mounted 

 together). 



