Overvoltage protection circuits are provided for coupling a subscriber's station to first and second conductors connected to a telephone system or other similar communications source. The overvoltage protection circuits include first circuitry connected between the first and second conductors for conducting current at a first breakdown voltage and for blocking current below the first breakdown voltage; second circuitry for conducting current at a second breakdown voltage and for blocking current below the second breakdown voltage; and circuitry connected in series between the first and second circuitry for filtering voltage signals on the first and second conductors responsive to the second circuitry conducting current. The overvoltage protection circuits are effective for suppressing noise and transient voltage signals occurring above the data signal and do not require a transient voltage signal to exceed the ring signal for operation.

Telephone and data overvoltage protection apparatus

A line protector is provided which includes positive temperature coefficient resistors in the circuit which are thermally coupled to voltage clamping devices which require protection from failures caused by overheating from conducting excessive amounts of current for a time sufficient to cause device breakdown. This may compensate for the performance variability of the positive temperature coefficient resistors so as to improve the likelihood that they will experience a sufficient temperature increase to switch before the voltage clamping device reaches a breakdown temperature. Furthermore, a line protector which may provide protection against current flow to the communications circuit from overvoltage conditions on the circuit side of the line protector or by a ground potential difference between the line protector and the communications circuit is also provided including positive temperature coefficient resistors positioned between the overvoltage line protector circuits and the communications circuit.

Line protector for a communications circuit

Overvoltage protection arrangements are provided for a pair of telephone lines effective for suppressing noise and transient voltage signals occurring above data and voice signals carried on the telephone lines and that avoids current flow between the telephone lines responsive to common mode voltage signals on the lines so that audible hum is avoided. The overvoltage protection arrangements include first voltage clamping circuitry for clamping voltage signals on the lines at a first predetermined voltage potential and second voltage clamping and filter circuitry for clamping voltage signals on the lines at a second predetermined voltage potential and for filtering noise and transient signals from the voltage signals only when the voltage signals exceed the second predetermined voltage potential. The second voltage clamping circuitry substantially avoids current flow between the lines responsive to common mode voltage signals on the lines.

Telephone lines overvoltage protection apparatus

Power for electronic instrumentation on high voltage transmission lines is provided through a high efficiency cascade of ferrite core transformers operating in the superaudio range. An array of tuning capacitors is provided to neutralize the leakage inductance in each transformer primary and thus present a resistive input impedance throughout the cascade. Unequal turns ratios in the transformers may also be utilized to provide constant resistance, and therefore nearly constant voltage and current along the cascade. The transformers in a voltage grading network are optimally enclosed within a cylindrical insulator and a dielectric medium, for example, oil or SF 6 .

Transformer cascade for powering electronics on high voltage transmission lines

An AC line filter having a balun coupled to an AC voltage input and an AC voltage output. The balun includes a first and a second set of windings with a first and a second tap on the first and second set of windings, respectively. A first Y capacitor is connected to a ground and the first tap of the first set of windings of the balun, and a second Y capacitor is connected to the ground and a second tap of the second set of windings of the balun.

AC line filter with tapped balun winding

A capacitive voltage transformer comprises a transformer having its primary winding connected across an intermediate section of a plurality of capacity sections connected in series between a high voltage line and ground to form a voltage divider. The transformer is provided with a protective circuit which serves to switch in a protective damping burden on the transformer in the presence of transient oscillation phenomena, and the circuit connections between the transformer primary and the intermediate capacity section include a choke coil and a low-ohmic blocking coil to improve the transformer for coupling high frequency signals to the line for carrier type communication.

Walter Knoth

Papers

Protective system for capacitive voltage transformers including a circuit for t{d fh-coupling