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A High Current Sensing Method with a Twisted Structure for the Low-Voltage Circuit Breaker

IP.com Disclosure Number: IPCOM000166780D
Published in the IP.com Journal: Volume 8 Issue 2A (2008-02-14)
Included in the Prior Art Database: 2008-Feb-14
Document File: 6 page(s) / 143K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

The Electronic Trip Unit (ETU) of circuit breakers (CB) includes functional blocks such as a current sensor, an electric processing circuit and an actuator. The current sensor is an important element for the ETU because it has to measure the current from the power line in a precise and cost-effective way taking into account the wide range of current. Up to now, a high current transducer with a toroid shape is used in the ETU of the CB. This sensor includes a round or rectangular iron core, a straight copper bar and turns of secondary enameled wire. Another high current transducer used is the Hall current sensor. Both sensors work precisely in the current range from low to medium. However, the output signal quality of the sensor worsens with higher current because of the saturation of the iron core. That is the output signal is not linear regarding to the whole range of current.

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A High Current Sensing Method with a Twisted Structure for the Low-Voltage Circuit Breaker

Idea: Wei Yang, CN-Shanghai; Xiaodong Feng Ph.D., CN-Shanghai; Yue Zhuo Ph.D., CN-Beijing

The Electronic Trip Unit (ETU) of circuit breakers (CB) includes functional blocks such as a current sensor, an electric processing circuit and an actuator. The current sensor is an important element for the ETU because it has to measure the current from the power line in a precise and cost-effective way taking into account the wide range of current.

Up to now, a high current transducer with a toroid shape is used in the ETU of the CB. This sensor includes a round or rectangular iron core, a straight copper bar and turns of secondary enameled wire. Another high current transducer used is the Hall current sensor. Both sensors work precisely in the current range from low to medium. However, the output signal quality of the sensor worsens with higher current because of the saturation of the iron core. That is the output signal is not linear regarding to the whole range of current.

Therefore, a novel sensor is proposed whereby a new twisted bus bar, a Hall element and an iron plate is used. In Figure 1 the exploded view of the proposed solution is depicted. The sensor consists of a plastic housing (7), three one-turn copper bars (8) and three plastic parts (9) which fix the three Hall elements (10). The two iron plates (11) divide the housing into three cavities. The copper bus bars
(8) are connected to the power lines and terminals which are located in the body of the circuit breaker. The three pins of the Hall element are connected to the power source, the ground and the processing circuit respectively. In Figure 2 a sectional view of the proposed solution is presented. The Figure shows the inner structure after complete assembly. The two iron plates (11) divide the housing into three areas which have the same parts and structures with bus bar (8), plastic part (9) and Hall element (10). Thus, the proposed solution allows for an independent measurement of the three phases with less phase-to-phase interference.

The details of one cavity are depicted in Figure 3. The Hall element (10) is fixed in the center of the plastic part (9) which is embedded in the center of the one-turn bus bar (8). The Hall element is sensitive to the magnetic field. The plastic part has a very small magnetic permeability so that its influence on the magnetic field is also small.

In Figures 4 and 5 a more simple structure is depicted which is used in the following to illustrate the working mechanism of the proposed solution. When a current passes for example through the copper bus bar (8), the current flows into the section area (15). Then the current flows out of the section area
(13). Then it flows into the section area (14) and at last it flows out the bus bar...