COOPERATIVE WORK ON JOINT USE OF POLES 237 



laboratory where 20,000 kv-a. of generating capacity was available. 

 The tests showed the dependability that could be placed upon the 

 various fuses for interrupting voltages of the range from 2300 to 13,200 

 volts. They show^ed under what conditions the fuses could be de- 

 pended upon and the ranges where the available type of fuses could not 

 be depended upon for safe operation. 



A number of the experimental models showed considerable promise 

 of improvement over existing models, and this work will be carried 

 further to determine what improvements can be made in the operating 

 characteristics of fuses. 



The next phase of the problem taken up included a study of the 

 operating characteristics of various types of overvoltage protectors 

 suitable for use on communication circuits. The experimental work 

 covered breakdown with direct current, 60-cycle alternating current 

 and a complete study with a cathode ray oscillograph of the behavior 

 under steep wave fronts for carbon block protectors, neon and vacuum 

 tubes. 



These tests showed that the carbon block protector has a breakdown 

 point with all types of applied wave fronts which is sufficiently fast 

 and low to protect the insulation that is now used in the communica- 

 tion plant, as shown by similar tests on condenser and cable paper. 

 The shortcomings of these blocks lie in their tendency to permanently 

 ground the circuit when carrying current for any appreciable length of 

 time. 



The tests with steep wave fronts were carried to a rate of rise of 

 36,500 volts per microsecond, and it was determined by tests of 

 propagation of steep wave front voltages through telephone cable that 

 it was practically impossible to subject the plant to voltages with any 

 faster rate of rise than those used in the protector tests. 



The problem of adequate protection of the telephone plant in joint 

 use, obviously, cannot be solved by the development of the telephone 

 protective devices alone. The protective devices in the power system 

 are equally important. 



One of the important functions of the power system protective de- 

 vices is that of clearing power system faults in a reasonable time inter- 

 val. Obviously, telephone protective equipment cannot be expected 

 to prevent damage to telephone plant in case of contact between the 

 wire circuits of the two utilities when power system protective devices 

 fail to operate and the physical contact of the circuits is maintained over 

 an indefinite period of time. 



One problem in the development and research work is the fixing of 

 the part that the protective devices on each system must play in abnor- 



