TRANSACTIONS OF SECTION G. 775 



speed. It is desirable that the mean speed should closely approach the maximum 

 speed. This can only be obtained by using very considerable power, so as to give 

 a great rate of acceleration. Rapid rate of acceleration and great brake-power is 

 all important in i'acilitating trattic. 



Most towns have their older and more important streets arranged radiating 

 from the original centre, market-place or otherwise. This tends to extra 

 congestion near the centre of the town, but it can be relieved by concentric 

 circular roads or boulevards, so that traffic crossing a large town can enter by one 

 radial road, pass the centre by one of these circular roads, then take a radial out 

 again. These concentric roads are much wanted in all towns. Regulation of 

 foot-passengers is as necessary as that of vehicles. Wide footways are needed, 

 but much can be done by passengers always keeping to the right, whether in the 

 footway or roadway. 



MONDAY, SEPTEMBER 14. 

 The following Papers and Report were read : — 



1. Tlie Nature and Quality of some Potable Waters in South-west 

 Lancashire. By Professor J. Campbell Brown. 



2. Protective Devices for High-tension Electrical Systems, 

 By W. B. WooDHOUSE, A.M.I.M.E., A.M.I.E.E. 



The extending use of high tension polyphase transmission is resulting in a 

 gradual standardisation of the methods adopted to protect such systems against 

 breakdown ; but there is still some considerable diversity of opinion shown. The 

 writer proposes to discuss several points in connection with the operation of a 

 high tension polyphase transmission system. 



Nature of System. 



The design of the System should be such that each part is automatically 

 disconnected in the event of a breakdown of that part ; the continuity of supply 

 being of primary importance, all parts should be duplicated. 



Stresses on the System, 



In switching on an unloaded cable a wave of pressure passes along the cable 

 and is reflected ; there may be a rise of pressure to twice the working value. 



In switching on a transformer or an induction motor, or any apparatus with 

 considerable inductance, the full pressure exists for the moment between adjacent 

 coils, the greatest stress falling on the end coils. An inductive circuit has stored 



energy to the amount of -— joules, which must be dissipated when the circuit is 



broken. In a transmission system such as is considered, this energy may be con- 

 verted to the electrostatic form on opening circuit with a resultant rise of pressure ; 



neglecting damping effects the pressure may rise to a value E = ^^ -^ oi" the rise 



of pressure is proportional to the current flowing at the moment of interruption. 

 Pressure rise from resonance is not likely to occur in commercial systems in this 

 country. 



The interval of time between the occurrence of an overload and the opening o^" 

 the circuit should be inversely proportional to the magnitude of the overload; that 

 is to say, on a moderate overload there should be a time-lag of some seconds. 



A little consideration will show that all circuit-breakers on a system should be 

 capable of breaking the whole power which can flow into that part of the system. 



