Some Researches about the Safety of the Underground Communication Cables

Abstract

The author made some studies about the safety of induction radio's lines which are used in coal mines.
The carrier waves which have been taken up in this research are the kilocycles of between 100 and 250 per second.
Results obtained till now are following:
i) In the case of ignition against methane mixture.
a) Ignitions occur at the sparking power of 3.5VA, when the line is broken during the carrier wave is being transmitted.
b) Ignitions occur at the sparking power of 0.78VA, when the line is disconnected by an occident during the modulation wave is being transmitted in the cable.
c) Ignitions, occur at the sparking power of 9.8VA, when induction wire line is being earthed in some occidents.
ii) a) lgnition power may be 28.8VA, when the wire cables connecting to the detonators are earthed, that are placed paralell with the induction systam.
b) Detonators ignite when the power comes up to 33.8VA, at the terminal of the transmitter. This is the case when the current has been originated in the cable of connecting to the detonators by inductive action of the paralell placed trans mitten line.
c) The minimum electric power what is able to ignite methane mixture or detonators is affected by impedance of the terminals, frequencies of carrier waves and the length of the induction line.
It is necessary that these conditions must be satisfied in order to keep the safety from methane mixture or detonator ignition, if we use the induction lines in the underground of coal mine.
1) Frequencies of the carrier waves must be between 160 and, 200kc/s.
2) Impedance of the high frequency terminal is to be below 150Ω.
3) Out-put of the transmitters does not exceed 5VA.