Claims:We claim:

1. A toroidal Rogowski coil with air gapped magnetic core, the toroidal Rogowski coil comprising:
a cavity/circular sleeve made up with nonmagnetic material;
a magnetic core formed by a plurality of magnetic pieces arranged symmetrically within the cavity/circular sleeve forming air gaps in magnetic core path, the plurality of magnetic pieces are insulated by putting insulating material therebetween; and
a secondary winding wound over the cavity/circular sleeve, wherein the cavity/circular sleeve with the plurality of magnetic pieces therein forms a central opening for accommodating primary current carrying conductor of which current is to be measured.

2. The toroidal Rogowski coil as claimed in claim 1, wherein the nonmagnetic material of the cavity/circular sleeve is air permeable.

3. The toroidal Rogowski coil as claimed in claim 1, wherein the secondary winding is made of conductive material.

4. The toroidal Rogowski coil as claimed in claim 1, wherein insulating material for insulating the plurality of magnetic pieces is selected from any one of resin, and insulating tape.

5. The toroidal Rogowski coil as claimed in claim 1, wherein the half of the cavity/circular sleeve is made of non magnetic material having the plurality of magnetic pieces arranged symmetrically therein and other half is made up of magnetic material piece.

6. The toroidal Rogowski coil as claimed in claim 1, wherein the half of the cavity/circular sleeve made of non magnetic material is fitted to the other half of the magnetic material by any one of click fit, insert fit and dovetail arrangement.

7. The toroidal Rogowski coil as claimed in claim 1, wherein cavity/circular itself acts as insulating means.
, Description:Field of the invention

The present invention relates to a circuit breaker, and more particularly, the present invention relates to a current measurement coil used in circuit breaker for sensing the current in the circuit breaker.

Background of the invention

Circuit Breaker is a mechanical switching device capable of making, carrying and breaking currents. Under normal circuit conditions, the circuit breaker make the circuit, carry current for a specified time and break the circuit under specified abnormal circuit conditions. The circuit breakers are employed for current interruption. More particularly, the circuit breakers are utilized to protect instruments from damage during adverse conditions prevailing during the operation of the circuit in which circuit breaker is employed. During adverse conditions like short circuit, the current rises to an alarmingly high level. This high current may cause damage to the parts in the electrical system. Hence, during these conditions, the circuit has to be opened to protect the system.

The circuit breaker can be manually opened and closed, as well as automatically opened to protect conductors or equipments from damage caused by excessive heating due to over current in abnormal conditions such as overload or short-circuit.

Switching devices like molded case circuit breaker (MCCB) operating on the current limiting principle typically have a pair of solid stationary electrical contacts joined by a solid moving electrical contact, which provides a path to carry the electrical current in the network.
The MCCB employing electronic trip unit uses current sensor which typically consist of a power up coil and a sensing coil. The energy supplied by the sensor’s power up coil is utilized for electronic card functioning and the power up the device called Flux Shift Device (FSD) which converts electrical signal into mechanical signal.

Specifically, Rogowski coil acts as sensing coil which functions to generate a signal proportional to current in the line. The generated signal may be anyone of the analog voltage, current or even digital output. The signal is then utilized to display the measured current in an ammeter or can be stored for further analysis in a data acquisition system or can be utilized for control purpose.

Specifically, US Patent No. 7078888 discloses a Rogowski type current measuring device. The Rogowski type current measuring device as shown in figure 1 comprises at least three coils electrically connected in series and forming a closed polygon outline designed to surround a conductor to perform current measurement. The local inductance of at least one of the ends of said coils is greater than the local inductance towards the central part of said coils.

Another US Patent No. 7227441 discloses an improved Rogowski coil is formed on a toroidal core made of a thermoplastic or other moldable material as shown in figure 2. The core is made preferably continuous groove or grooves extending around the core. The grooves correspond in size to magnet wire which registers within the grooves, thus controlling the specific location of the wires. The grooving may be helical. A return loop can be provided for return path cancellation, or a reverse winding can be added in a direction opposite to the direction of advancement of the main coil.

Yet another Indian patent application is 1204/MUM/2014 as shown in figure 3-5 discloses a compact self-powered co-axial current sensor. The current sensor comprises a power coil to power up electronic card and sensing coil for generating a signal equivalent to current in a power line. Both coils are enclosed in two enclosures as shown in figure 3 having a bus bar opening of substantially round shape extending longitudinally there through. Here, Toroidal Rogowski coil shown in figures 4-5 consist core of insulating material whose permeability is equal to air permeability. This type of sensing coil used to generate sensing signal at low current.

In general, in the prior art, the module spaces are constrained by volume for compact products such as MCCB. Hence, it becomes difficult to make toroidal Rogowski with desired output for low current range within given space. To
obtain required output at low primary current may increase secondary number of turns within given space which calls for winding wire with small diameter. This may lead to manufacturing process difficulty in terms of wire
breakage, assembly handling, and the like. These factors can increase manufacturing process time, hence it becomes difficult to industrialize. In addition, in air core Rogowski, secondary output at low current becomes more prone to external field disturbances which makes output signal noisy hence difficulty in sensing.

Accordingly, there exists a need to provide a current measurement coil i.e. a Rogowski coil, which overcomes abovementioned drawbacks.

Objects of the invention

An object of the present invention is to achieve desired secondary output with small secondary number of turns in a Rogowski coil, even if at very low primary current.

Another object of the present invention is to make output signal of the Rogowski coil current sensor less noisy which reduces difficulty in sensing.

Yet another object of the present invention is to reduce number of secondary turns in a Rogowski coil which gives advantages in cost, manufacturing and industrialization.

Summary of the invention

Accordingly, the present invention provides a toroidal Rogowski coil with air gapped magnetic core. The toroidal Rogowski coil comprises a cavity/circular sleeve made up with nonmagnetic material, and a magnetic core having a plurality of magnetic pieces arranged symmetrically within cavity/circular sleeve forming air gaps in a magnetic core path. The plurality of magnetic pieces are insulated by putting insulating material therebetween. The toroidal Rogowski coil further comprises a secondary winding wound over the cavity/circular sleeve. Specifically, the cavity/circular sleeve with the plurality of magnetic pieces therein forms a central opening for accommodating primary current carrying conductor of which current is to be measured.

In an embodiment, half of the cavity/circular sleeve is made of non magnetic material having the plurality of magnetic pieces arranged symmetrically therein and other half is made up of magnetic material piece. Specifically, the half of the cavity/circular sleeve made of non magnetic material is fitted to the other half of the magnetic material by any one of click fit, insert fit and dovetail arrangement.

In another embodiment, the number of magnetic pieces of the plurality of magnetic pieces to form the magnetic core is decided by the current range of the sensor.

Brief description of the drawings

Figure 1-5 shows various current sensors, in accordance with the prior art;

Figure 6 shows a toroidal Rogowski coil with air gapped magnetic core, in accordance with the present invention;

Figure 7 shows a cross sectional view of the toroidal Rogowski coil of figure 6 with secondary winding and carrying conductor placed at center;

Figure 8 shows a toroidal Rogowski coil with air gapped magnetic core, in accordance with an embodiment of the present invention;

Figure 9 shows a toroidal Rogowski coil with air gapped magnetic core, in accordance with another embodiment of the present invention;

Figure 10 shows a cross sectional view toroidal Rogowski coil of figure 9, wherein the secondary winding is wound over the core assembly and primary current carrying conductor is placed at center;

Figure 11 shows a core assembly in which magnetic material piece placed in cavity of housing made of insulating material;

Figure 12 shows the toroidal Rogowski assembly of figures 6, 7 and 8 terminated with pair of wires.

Figure 13 shows the toroidal Rogowski assembly of figures 6, 7 and 8 accommodating in housing;

Figure 14 shows a current sensor used in molded case circuit breaker (MCCB) in which power coil and sensing coil enclosed in top housing and bottom housing and both coils wires connected to connector; and

Figure 15 shows a cross sectional view of the full current sensor used in molded case circuit breaker of figure 14 assembly in which links arrangement is shown which forms primary conductor to current sensor and facilitates MCCB connections respectively.

Detailed description of the invention

The foregoing objects of the present invention are accomplished and the problems and shortcomings associated with the prior art, techniques and approaches are overcome by the present invention as described below in the preferred embodiment.

The present invention provides a toroidal Rogowski coil with air gapped magnetic core. The toroidal Rogowski coil with air gapped magnetic core helps in reducing secondary number of turns as compared to air core Rogowski to achieve required secondary output for a specific primary current. Specifically, reduced secondary number of turns is advantageous to ease manufacturing process by reducing winding time, makes coil compact and less complex compared to air core Rogowski which benefits in space constraint issues. Further, the toroidal Rogowski coil with air gapped magnetic core generates strong secondary output signal which becomes less sensitive to external disturbances at low currents hence better sensing. The magnetic core and air gap in-between can be varied in sizes to produce different sensing coils for different current levels to achieve specific secondary output voltage.

Referring now to figure 6, 7 and 8, there is shown a toroidal Rogowski coil with air gapped magnetic core (100) (hereinafter ‘the Rogowski coil (100)’) in accordance with the present invention. A Rogowski coil (100) comprises a cavity/circular sleeve (10), a magnetic core (20) and a secondary winding (30).

The cavity/circular sleeve (10) made up with nonmagnetic material. In an embodiment, the nonmagnetic material of the cavity/circular sleeve (10) is air permeable.

Further, the magnetic core (20) is formed by the plurality of magnetic pieces (12) arranged symmetrically within the cavity/circular sleeve (20) forming air gaps in magnetic core path. Though the exemplary embodiment of figure 6 shows four magnetic pieces (12), it is evident to those skilled in the art that the number of magnetic pieces may vary based on current range required of the sensor. Specifically, figure 8 shows typical arrangement of magnetic core (20) with eight magnetic material pieces (12a) placed in cavities/circular sleeve (10) of nonmagnetic material spaced equally to form air gaps in between. This configuration can be used to enable measuring for different current range. As discussed earlier, the number of magnetic cores can be varied depending on the current range. Specifically, the magnetic core (20) needs at least three magnetic pieces to form the core

The plurality of magnetic pieces, for example the four magnetic pieces (12) as shown in figure 6, and the eight magnetic material pieces (12a) as shown in figure 8, placed in cavities/circular sleeve (10) are insulated by putting insulating material therebetween. In an embodiment, the insulating material for insulating the plurality of magnetic pieces (12, 12a) is selected from any one of resin, and insulating tape.

Further, the secondary winding (30) is wound over the cavity/circular sleeve (20). The secondary winding (30) is made of conductive material.

The cavity/circular sleeve (10) with the plurality of magnetic pieces (12) as shown in figure 7 forms a central opening for accommodating primary current carrying conductor (40) of which current is to be measured.

In another aspect, the present invention provides a toroidal Rogowski coil (200). As shown in figure 9, the toroidal Rogowski coil (200) includes a half cavity/circular sleeve (110) made of non magnetic material. The half cavity/circular sleeve (110) includes a plurality of magnetic pieces (112) arranged symmetrically therein to form a magnetic core with air gaps therebetween. However, it may be evident those skilled in the art that the number of magnetic pieces (112) may vary depending upon current range required of the sensor. The other half (120) of the toroidal Rogowski coil (200) is made up of magnetic material piece. In an embodiment, the half cavity/circular sleeve (110) of non magnetic material is made insulating. Here, the insulating material serves the purpose of closing the core loop by means of air gap.

Specifically, the half cavity/circular sleeve (110) made of non magnetic material is fitted to the other half (120) of the magnetic material by any one of click fit, insert fit and dovetail arrangement.

Specifically, figure 9 shows the half cavity/circular sleeve (110) with at six magnetic pieces (112). Here also, the six magnetic material pieces (112) are insulated by putting insulating material therebetween. In an embodiment, the insulating material for insulating the magnetic pieces (112) is selected from any one of resin, and insulating tape. Further, the toroidal Rogowski coil (200) includes a secondary winding (130) wound thereon i.e. over the half cavity/circular sleeve (110) and other half (120) of magnetic material as shown in figure 10. There is also shown a central opening for accommodating primary current carrying conductor (140) of which current is to be measured.

Referring now to Figure 11, there is shown a toroidal Rogowski coil (300). The toroidal Rogowski coil (300) provides alternative arrangement for the core assembly as compared to arrangement shown in figure 10. The toroidal Rogowski coil (300) includes a circular housing (210). The housing (210) is made of insulating material. The toroidal Rogowski coil (300) also includes a plurality of magnetic material pieces (220) forming a core placed in the cavity (212) created in housing (210). The toroidal Rogowski coil (300) also includes a secondary winding (not shown) wound thereon. Here the housing (210) itself act as insulation between secondary winding and magnetic core (220). This type of arrangement is advantageous in ease of core assembly and winding.

Referring now to figure 12, there is shown a start and end of winding of a toroidal Rogowski coil of the present invention. For the purpose of explanation, the figure 12 is described with reference to figure 6, and 7. Figure 12 shows start and end of winding (30) of the toroidal Rogowski coil (100) terminated with a pair of insulating wires (32). In an embodiment, the insulating wires (32) are selected from anyone of PTFE, PVC and the like. The pair of insulating wires (32) further used to make connection of Rogowski to electronic card.

Similarly, figure 13 is also described with reference to figure 6, and 7 for the For the purpose of explanation. Figure 13 shows the toroidal Rogowski coil (100) placed in housing (100A) with opening window (40a) at center through which primary conductor passes whose current needs to be measured. The arrangement is made such that Rogowski coil (100) is centered with the conductor passing through the window (40a).

Figure 14 shows a current sensor in molded case circuit breaker MCCB (not shown) in which the toroidal Rogowski coil (100) of the present invention is combined with a power coil which is enclosed with two housings i.e. top housing (7) and bottom housing (8). Specifically, termination wire of the power coil and the sensing coils are connected to a connector (9) which is used to make connection with electronic circuit. Figure 15 shows cross sectional view of the current sensor of figure 14.

Here, arrangement of links (3, 40, 5) are made such that the link (40 ) acts as primary conductor for current sensor and the link (3) and (5) can be used for MCCB connections.

Advantages of the invention

1. The Rogowski coil (100) facilitates secondary number of turn reduction for low primary currents.
2. The Rogowski coil (100) requires low secondary number of turns which benefits to ease in manufacturing process and reduces manufacturing time as well
3. The Rogowski coil (100) provides overall volume reduction of current sensing coil.
4. By varying air gap in sizes and shapes, different coil configurations can also be made for different low current ranges.
5. In the Rogowski coil (100), noise in the secondary output is minimized due to magnetic material permeability plays role to generate signal, thus signal becomes less sensitive to external fields compared to air core Rogowski coil hence improves the measurement even if at primary current is low.

The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, and to thereby enable others skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omissions and substitutions of equivalents are contemplated as circumstances may suggest or render expedient, but such omissions and substitutions are intended to cover the application or implementation without departing from the spirit or scope of the claims of the present invention.