| 摘要 |
The invention relates to a safety device for vehicles with rubber tyres which are insulated to earth and draw operating current for an electric motor from overhead line contact wires by means of a current collector. If a current-conducting section of a contact wire comes into contact with the body of the vehicle due to a rupture or to a large degree of sagging, the said vehicle body is at a lethal level of voltage for the duration of the contact. The function of the safety device is then automatically to switch off the current immediately in the respective line. For this purpose, the difference in voltage potential between the body of the vehicle which is isolated with respect to earth and an earthed contact strip which is carried on the vehicle but is insulated with respect to the body of the vehicle is continuously measured by means of a voltmeter. When a predetermined value for the difference in voltage potential is exceeded, a transmitter which is fixed to the vehicle is automatically actuated and transmits a switch-off signal to a stationary receiver at a central point, which signal triggers the switching off of the current in the respective line section.
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