S0627. Electric Transformers. 139 







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50631. 1:12. 



Electric Transformers 



for obtaining Direct Current in places where the Electricity Works supply Three Phase, Two Phase 



or Monophase Alternating Current. 



The majority of electrical apparatus for experimental purposes require direct current, the 

 tj direct employment of alternating or three phase currents being only seldom possible. If, therefore, 

 only alternating or 3-phase current is available, arrangements must be pro vided for transforming this 

 into direct current. 



CD 



i A motor generator is best suited for this purpose. Electrolytic or Koch rectifiers necessitate 



(1) the installation of a large battery of accumulators, and (2) they are more difficult to manipulate 



and keep in order. Such a motor generator consists of an electric motor for 3-phase or single phase 



< alternating current with a continuous current dynamo coupled directly to it. Both machines are 



mounted on a massive iron base plate. A foundation is desirable but not absolutely necessary. For 



the small types especially it is sufficient to erect on a wood support. 

 M 



x The motor must, in conformity with the rules of a number of electricity works, be provided 



^ with a slip ring rotor, to allow of its being started without causing lanre current rushes. Since the motor 

 can in the case in point start light, there is no objection, especially with the smaller types, to using 

 the much cheaper motors having a short circuited rotor and connected in the star-delta method. 



The dynamo is compound wound as a rule, and the compound winding can be switched out. 

 The pressure best suited for general experimental purposes is 65 volts: it is e. g., sufficient for working 

 a large arc lamp and for operating an induction coil in conjunction with a Wehnelt interrupter. If de- 

 sired, however, the transformers are also supplied with voltages up to 300, at the same prices and with 

 the same wattage. 



An experimental switchboard (preferably a board of the Ai type, Xo. 50,471) is connected up 

 direct to the terminals of the dynamo. With the aid of this switchboard it is not only possible to take 

 off all desired current strengths, but also low voltages. Under the. experimental switchboard are placed 

 the switch and fuses for the motor in addition to the shunt regulator for the dynamo. There is also 

 the starter in the case of motors with a slip ring armature. The starting of the motor and regulation 

 of the dynamo can in this manner be conveniently carried out from the switchboard while the trans- 

 former itself is installed in another room. 



If desired, the transformers are also supplied with Shunt Wound Dynamos for increased pres- 

 sure regulation, e. g.. for 5 65 volts, in accordance with the special table contained on p. 141. In this 

 case, a contact resistance and a voltmeter and ammeter can be used instead of the experimental switch- 

 board. It is strongly recommended that even in these cases an experimental switchboard be employed. 



Should it be desired to be able to take alternating or three phase current from the dynamo 

 in addition to Direct Current, the dynamos are provided with 4 slip rings at the extra prices shown 

 in the table. In this case, in the transformers with compound winding, the compound winding must 

 be cut out. As regards piessure, 46 volts can be taken off in the case of alternating and 40 volts 

 in the case of three phase current. 



Cl. 5364. 



