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POLARITY DETECTION CIRCUIT FOR CURRENT TRANSFORMER

IP.com Disclosure Number: IPCOM000241281D
Publication Date: 2015-Apr-13
Document File: 6 page(s) / 348K

Publishing Venue

The IP.com Prior Art Database

Abstract

The invention proposes a technique for detecting polarity for current transformers (CT). The technique includes a polarity detection circuit used on an improved electronic trip unit. The transformer secondary includes two connections that are monitored by a monitoring circuit. The monitoring circuit includes polarity detection circuit used on the improved electronic trip unit. If a small known signal is injected into one connection of the transformer, the second connection is used to monitor known signal. The small signal is either alternate current (AC), direct current (DC), or pulsed at a known frequency. The small signal may be present 100% of time or polled periodically. The small signal does not affect performance of the transformer.
The monitoring circuit is able to detect the small signal.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 52% of the total text.

Page 01 of 6

POLARITY DETECTION CIRCUIT FOR CURRENT TRANSFORMER

BACKGROUND

The present invention relates generally to polarity detection circuit and more particularly to a technique for detecting polarity for current transformers.

A polarity detection circuit is widely used in a switching power supply circuit to perform control in accordance with polarity of alternate-current (AC) voltage. The polarity detection circuit detects polarity of the alternate-current (AC) voltage and output a signal that indicates the detected polarity.

A conventional technique includes a current transformer (CT) polarity detection circuit used on an electronic trip unit platform. However, the conventional technique is not efficient in providing immunity to noise. Also the technique does not detect presence of current transformer in the circuit.

It would be desirable to have an efficient technique to detect polarity for current transformers.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 depicts polarity detection circuit used on the improved electronic trip unit.

Figure 2 depicts current transformer (CT) detection circuit.

Figure 3 depicts graphs that show signals on first and second connection when CT is properly connected.

Figure 4 depicts graphs that show signals on first and second connection when CT is properly connected and current is not present on CT.

Figure 5 depicts graphs that show signals on first and second connection when CT is not connected and current is not present on the CT.

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Page 02 of 6

Figure 6 depicts a graph that shows voltage across burden resistor when unit goes into pickup.

DETAILED DESCRIPTION

The invention proposes a technique for detecting polarity for current transformers (CT). The technique includes a polarity detection circuit used on an improved electronic trip unit. Figure 1 depicts polarity detection circuit used on the improved electronic trip unit.

Figure 1

The transformer secondary includes two connections that are monitored by a monitoring circuit. The monitoring circuit includes polarity detection circuit used on the improved electronic trip unit. If a small known signal is injected into one connection of the transformer, the second connection is used to monitor known signal. The small signal is either alternate current (AC), direct current (DC), or pulsed at a known frequency. The small signal may be present 100% of time or polled periodically. The small signal does not affect performance of the transformer.

If the transformer is present, the small signal is passed through the transformer. If transformer is not present, no signal passes through the circuit. Consequently, presence of transformer is detected if under no current/voltage, small signal is detected. When curre...