Protective Circuit for a Current Transformer and Current Transformer with a Protection Circuit

Patent metadata

Field	Value
Publication number	US-2015333509-A1
Application number	US-201314442886-A
Country	US
Kind code	A1
Filing date	Nov 7, 2013
Priority date	Nov 16, 2012
Publication date	Nov 19, 2015
Grant date	—

Abstract

A protective circuit for a current transformer for preventing a secondary voltage on a secondary circuit of the current transformer from exceeding a secondary voltage threshold. A protective circuit input can be coupled to the secondary circuit of the current transformer such that the secondary voltage is applied to the protective circuit input. A control unit is connected to the protective circuit input. A switch unit is connected to the protective circuit input and is operatively connected to the control unit. The control unit is adapted to provide a control signal to the switch unit in response to the secondary voltage exceeding the secondary voltage threshold. The switch unit is adapted to short-circuit the protective circuit input in response to the control signal provided by the control unit. The switch unit is implemented as a semiconductor circuit.

First claim

1 . A protective circuit for a current transformer for preventing a secondary voltage on a secondary circuit of the current transformer from exceeding a secondary voltage threshold, comprising:
a protective circuit input which can be coupled to the secondary circuit of the current transformer such that the secondary voltage is applied to the protective circuit input; a control unit connected to the protective circuit input; and a switch unit connected to the protective circuit input and operatively connected to the control unit;
wherein
the control unit is adapted to provide a control signal to the switch unit in response to the secondary voltage exceeding the secondary voltage threshold;
the switch unit is adapted to short-circuit the protective circuit input in response to the control signal supplied from the control unit; and
the switch unit is implemented as a semiconductor circuit.

2 . The protective circuit as claimed in claim 1 , exhibiting at least one of the following features:
the control unit is connected directly or immediately to the protective circuit input; the switch unit is connected directly or immediately to the protective circuit input; the protective circuit comprises a limiting unit connected to the protective circuit input, for overvoltage protection.

3 . The protective circuit as claimed in any of claim 1 , wherein the control unit comprises one or more of the following components:
a comparator unit which is adapted to provide the control signal to the switch unit if an input voltage of the comparator unit exceeds a threshold; a rectifier connected to the protective circuit input for providing a preferably pulsating direct current voltage depending on an amplitude of the secondary voltage, as an input voltage for the comparator unit.

4 . The protective circuit as claimed in claim 1 , wherein the comparator unit comprises one or more of the following components:
a comparator having a positive input, a negative input on which a voltage of approximately the level of the input voltage of the comparator unit is applied, and an output which provides the control signal; a voltage divider, wherein the positive input is connected to the input voltage of the comparator unit via the voltage divider; a Zener diode which is connected to the negative input, for limiting a voltage applied to the negative input; a capacitor which is connected to the positive input.

5 . The protective circuit as claimed in claim 1 , wherein the switch unit comprises one or more of the following components:
at least one MOSFET; two MOSFETs arranged in a back-to-back circuit; a solid-state relay (SSR) with (i) a MOSFET, or (ii) a plurality of MOSFETs arranged in parallel; a TRIAC; an opto-isolator for introducing the control signal.

6 . The protective circuit as claimed in claim 1 , wherein the limiting unit comprises one or more of the following components:
a transient voltage suppression diode; a varistor; a gas discharge tube.

7 . A current transformer comprising a protective circuit as claimed in claim 1 .

8 . The current transformer as claimed in claim 7 , wherein the protective circuit is accommodated in the housing of the current transformer, in particular in the secondary terminal box thereof.

Assignees

• Phoenix Contact Gmbh & Co

Inventors

• Jankowski Martin

Classifications

• H01F2027/408

  Association with diode or rectifier · CPC title

• H02H7/042

  for current transformers · CPC title

• H01F27/402

  Association of measuring or protective means · CPC title

• G01R15/183

  using transformers with a magnetic core · CPC title

• H02H9/043 Primary

  Protection of over-voltage protection device by short-circuiting · CPC title