| 摘要 |
<p>1,076,681. Measurement of condition of high voltage line; current and voltage measurement. ALLIS-CHALMERS MANUFACTURING CO. Feb. 15, 1965 [Feb. 24, 1964], No. 6384/65. Headings G1A and G1U. Apparatus to measure an electrical characteristic of a high voltage line and transmit a generated signal corresponding to this characteristic to a receiver at earth potential includes means producing a variable radiation signal, whose intensity is a function of the generated signal and which is transmitted by a fibre optic dielectric transmission means. The alternating current in a high voltage line (10) is sensed by a current transformer (12) having its secondary inductively coupled to the high voltage conductor which forms the primary to produce a varying signal which is used to modulate an infrared emitting gallium arsenide diode (20). The diode is biased negatively at a constant voltage by the output from a current transformer (27), which is rectified (28) and filtered by a low pass filter (22), giving a quiescent operating point at about the midpoint of its currentlight characteristic. A resistor (23) and capacitor (25) help to establish the selected value of bias current and a diode (24) prevents reverse voltages from appearing across the source (20). The modulated radiation output of the diode thus represents the full sinusoid of the line current waveform. The radiation is transmitted by the fibre optic device, enclosed in a sealed porcelain tube (33) to prevent formation of a conductive layer of moisture on the fibre, which connects the high voltage circuit to the receiving and operating devices at earth potential. The radiation is detected by a photo-multiplier, the output of which is amplified (16) and fed to the operating device (17). The amplifier may only transmit the A. C. component of the photo-multiplier output, thus restoring zero crossings to the signal.</p> |
