3 34 of the transformer 3 may be neglected the nominal inductance l n must be able to handle a current i n for instance during continued operation for this the following applies if only insulations with lesser capacitance values are to be tested having a value of for instance c k a higher frequency f is required this variation of the testing frequency is the immediate result of the above equations by replacing l by l n there follows equ3 whereby f n nominal frequency compare this with fig4 if for instance c n 25 u00b7 c k then f 5 u00b7 f n which is five times greater than such frequency f n needed for the highest insulation to be tested the current of the choke l n used in this connection always remains below the permissible current load in spite of this excess frequency whereby it changes in consideration of the last two equations as follows equ4 if for instance c n 25c then i i n 5 in this connection compare fig4 it follows from the above that even with insulations with relatively low capacitances the chokes are well loaded by the current the acceptor circuit with its variable frequency proves to be particularly advantageous in case capacitors which are much higher than c n must be tested whenever the.