Electricity: electrical systems and devices – Safety and protection of systems and devices – Feeder protection in distribution networks
Patent
1983-11-21
1988-01-12
Leung, Philip H.
Electricity: electrical systems and devices
Safety and protection of systems and devices
Feeder protection in distribution networks
361 68, 361 91, H02H 722
Patent
active
047195304
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to protective systems against overvoltage for devices for the transmission of binary data through electric lines.
In these devices, the data is conveyed at the sending or receiving end by the opening or closing of a relay. Because the associated installations are then connected to the line, their operation may be seriously damaged if the voltage in said line changes suddenly.
If lightning strikes any point on the line, or even if it strikes nearby, it causes an overvoltage wave which propagates from the point of impact to the two extremities. The connected installations in turn can be affected by this overvoltage and severe damage may be caused.
For this type of installation, ground contacts can be adapted to ensure discharge of the current. This protection remains inadequate, owing to the impedance that these ground contacts always present. When lightning strikes only one of the installations, this may cause a momentary voltage surge in the installation. A voltage differential is then produced between the line and the installation.
To avoid these drawbacks, it is proposed to develop a binary data transmission system using an electric line wherein the tramsitter and the receiver are both sufficiently insulated with respect to the line and to the installations to withstand voltages up to 100,000 volts. Under such conditions, the voltage of the line is immaterial. It may be grounded or not.
SUMMARY OF THE INVENTION
The present invention overcomes the problems in the prior art and provides an insulated device to protect against over-voltage in binary information transmission systems. The new device includes a transmitter as well as a receiver and each including a high insulation transformer that is supplied by an oscillator, the entire assembly being provided in a cylindrical block of insulating synthetic resin. It will be understood that a normal transmission line connects the receiver and transmitter.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a front elevation of my improved device for a transmitter.
FIG. 2 is a vertical section taken through the device of FIG. 1.
FIG. 3 is a front elevation of my improved device for a receiver.
FIG. 4 is a vertical section through the device of FIG. 3.
FIG. 5 is circuit schematic for the transmitter, and
FIG. 6 is circuit schematic for the receiver.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In the transmitter, the presence of a current of a normal voltage of 24 or 48 volts, rectified by diodes 3, if it is alternating, at the input 2 of the transmitter, triggers the operation of an oscillator 4 composed of transistors 5 and 6, and of the coils 7, 8 and 8A of transformer 9. This oscillator provides an alternating voltage of 20 kH frequency which supplies the high insulation transformer 10, having a primary and a secondary.
The rectifier bridge 11 produces direct current from the alternating current present at the secondary of transformer 10. This direct current activates relay 12 whose contact, protected by spark arresters 13 and 14, causes the opening or the short-circuiting of the line.
The transmitter is insulated by the use of ferrite, the insulating characteristics of which are known for the construction of the magnetic circuit of a transformer. On the other hand, the entire transmitter is included in a cylindrical block made of synthetic insulating resin, and the material used in the preferred embodiment of the invention is epoxy resin.
The risk of creepage of the current along the insulator between the input terminals 2 and the output terminals 15A, B, and C is avoided by the length of the cylinder which is longer than the creepage distance, and the wires corresponding to the outputs of transformer 10 are provided accordingly.
Finally, the exterior of the cylinder is provided with grooves designed to extend the path of creepage of the current.
In another embodiment of the invention, an open circuit transformer may be used.
In that case, the magnetic circuit of transformer 10 is replaced by a ferrite rod on
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Leung Philip H.
Wysocki A. Jonathan
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