FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
A CIRCUIT ARRANGEMENT FOR A RESIDUAL CURRENT DEVICE (RCD);
LARSEN & TOUBRO LIMITED, A COMPANY INCORPORATED UNDER THE COMPANIES ACT, 1956, WHOSE ADDRESS IS L&T HOUSE, BALLARD ESTATE, MUMBAI - 400 001, MAHARASHTRA, INDIA
THE FOLLOWING SPECIFICATION
PARTICULARLY DESCRIBES ThfE
INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

Field of the Invention
The present invention relates to residual current devices.
Background of the Invention
Residual current devices (RCDs) detect earth fault currents, which are also known as residual currents. The principle of operation of RCDs is very well known. The RCDs can be grouped into two broad categories (a) passive residual current devices and (b) active residual current devices.
The passive residual current devices are those which trips in case of an earth leakage and does not trip when supply goes off. It remains in "on" condition unless earth leakage fault happen and residual current detected by the device. Such devices are useful in application like refrigerator; washing machine etc when there is no such need for auto switching of RCD in case of power supply failure.
The active residual current devices are those which trips when supply goes off and one has to switch on again to maintain continuity of supply. In line of passive RCDs, it trips when residual current detected in case of an earth leakage. Such devices are useful in application like machine tools etc. when due to additional safety reasons, we want manual switching to ON in case of power supply failure.

At present known in the art all residual current devices are either passive or active. There is no such mechanism or circuit or device available which combines both active and passive RCDs in order to give high level of flexibility to end user without any complexity and also improves portability. Also, using different devices i.e. active RCDs or passive RCDs at different places leads to increase in the cost.
Therefore, it would be desirable to have one improved and effective device or a circuit or an arrangement or a method is required that can obviate the above-mentioned problems.
Summary of the Invention
An aspect of the present invention is to address at least the above-mentioned problems and/or disadvantages and to provide at least the advantages described below.
Accordingly, an aspect of the present invention is to provide a circuit arrangement comprising: a first circuit for detecting a current imbalance in an AC supply via transformer to a load indicative of a residual current, a relay having contacts in the AC supply to the load, the relay contacts automatically opening if the there is an imbalance current between the terminals, and closing when there is a balance current across the terminals thereby dis-connecting and connecting the load, wherein the imbalance current due to the difference in the voltage across Permanent Magnet Relay (PMR) connected with the transformer and a second

circuit including a charge storage device connected to the AC supply via at teast one rectifying device in parallel with the relay such that, upon application of power from the AC supply, current flows to the charge storage device to charge the latter up, upon power failure, the relay having contacts in the AC supply to the load turned open due to discharge of the charge storage device provides an imbalance voltage across PMR.
In another aspect of the present invention is to provide a circuit arrangement comprising: an inductively acting circuit, a capacitively acting discharge circuit for discharging the current of the circuit, wherein the capacitively acting discharge circuit includes, a four-terminal electrical network (A, B, C, D) including, a first resistor and a third resistor having a known resistance (R1, R3), connected between the network terminals (A) and (C), a second resistor having a known resistance (R2), connected between the network terminals (C) and (D), a second diode (D2) and a third diode (D3) connected in series across the network terminals (C) and (B), a fourth diode (D4) connected between the network terminals (A) and (B), a zener diode (Z1) connected between the network terminals (A) and (D), and a capacitor having a known capacitance (C), connected between the terminals (B) and (D) and means for impressing a source of potential from a supply via a first diode (D1) across the network terminals (A) and (C) leads the capacitor to charge the voltage, and the AC supply connected to a load via CBCT, wherein the inductively acting circuit and the capacitively acting discharge circuit are partially disposed via PMR electrically, wherein the PMR is further coupled to the CBCT, wherein, upon power

failure, the capacitor of the capacitively acting discharge circuit holding the voltage starts discharging and follows the path through diodes D3 and D2 since D4 is in reverse bias which thereby activates the PMR coil.
Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.
Brief description of the drawings
The foregoing aspects and other objects of the invention disclosed herein will be understood from the following detailed description read with reference to the accompanying drawings of one embodiment of the invention. Structures appearing in more than one figure and bearing the- same reference number are to be construed as the same structure. Also, the characteristics and advantages will become better apparent from the following detailed description of preferred but not exclusive embodiments of the invention, illustrated by way of non-limiting example in the accompanying drawings, wherein:
Figure 1 shows a circuit arrangement when switch S1 is open hence acting as passive residual current device, in accordance with one example embodiment of the present invention.

Figure 2 shows a schematic circuit arrangement of passive residual current device before tripping, in accordance with one example embodiment of the present invention.
Figure 3 shows a schematic circuit arrangement of passive residual current device after tripping, in accordance with one example embodiment of the present invention.
Figure 4 shows a schematic circuit arrangement where switch S1 is close hence acting as active residual current device, in accordance with one example embodiment of the present invention.
Figure 5 shows a schematic circuit arrangement of the flow of current in active residual current device, in accordance with one example embodiment of the present invention.
Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure.
Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.

Detail description of the Invention
The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.
The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.
It is to be understood that the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a component surface" includes reference to one or more of such surfaces.

By the term "substantially" It is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.
Figs. 1 through 5, discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way that would limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged electrical systems. The terms used to describe various embodiments are exemplary. It should be understood that these are provided to merely aid the understanding of the description, and that their use and definitions in no way limit the scope of the invention. Terms first, second, and the like are used to differentiate between objects having the same terminology and are in no way intended to represent a chronological order, unless where explicitly stated otherwise. A set is defined as a non-empty set including at least one element.
Figure 1 shows a circuit arrangement when switch S1 is open hence acting as passive residual current device, in accordance with one example embodiment of the present invention. Referring to figure 1, the switch S1 gives the flexibility to choose the residual current device as an active or passive. In one example operation, when switch S1 is open, the device will act as a passive and when the

switch S1 is close, the device will act as an active, in residual current devices, the difference in the currents is detected by the core balanced current transformer (CBCT), where both phase and neutral are passed through the CBCT. In normal condition, the currents values in phase and neutral are same hence there is no difference in currents. In case of an earth leakage, the difference in current is detected by the CBCT and current starts appearing at the CBCT secondary (S).
As shown in figure 1, the secondary winding (S) is connected across the PMR coil (1 and 2). Here the active/passive selector switch S1 is open hence the device will act as a passive residual current device. Since S1 is open, the electronic components i.e. resistors (R1, R2, R3), diodes (D1, D2, D3, D4), capacitor C1, zener diode Z1 will not take any part in operation of the circuit. Also the voltage level at CBCT secondary is very low (less than 100mV) and it is very much less than the threshold voltage of the silicon diodes D2 and D3.
Figure 2 shows a schematic circuit arrangement of passive residual current device before tripping, in accordance with one example embodiment of the present invention. Figure 2 is the simplified version of figure 1 i.e. passive residual current device is shown in figure 2. Here the complete view of Permanent Magnet Relay (PMR) is shown. In normal case i.e. without leakage, the currents li and I2 are same, hence there is no flow of current in CBCT secondary and no voltage across PMR therefore the PMR will not actuate.
Figure 3 shows a schematic circuit arrangement of passive residual current device after tripping, in accordance with one example embodiment of the present

invention, In case of an earth fault as shown in figure 3, the current l3 is a leakage current. Here the current l2 will be lr-l3 which is less l2 therefore there will be secondary current at CBCT and hence the voltage across the PMR coil (1 and 2). The PMR will actuate and it will give the trip signal to the mechanism. The mechanism will open the contacts.
Figure 4 shows a schematic circuit arrangement where switch S1 is close hence acting as active residual current device, in accordance with one example embodiment of the present invention. The circuit arrangement of figure 4 where the active/passive selector switch S1 is in close condition, hence this is an active residual current device. Here the diode D1 is used for the rectification purpose. It will convert the directional AC supply in unidirectional. The resistors R1 and R2 are forming the voltage divider circuit and voltage V1 is appearing at node (C). The zener diode Z1 will maintain the voltage V22 at node (A) through resistor R3. The values of R1; R2 and the zener diode Z, are selected such that the voltage V, is greater than voltage Vz2. The capacitor C1 is connected across the zener diode Z1 through diode D4. When voltage V22 will appear at node (A), the capacitor C1 will charge to the voltage V22 Hence the voltage V2 at node (B) is equals to V22. The value of resistor R3 is selected such that the current in that branch will not cross the maximum zener current.
Since the voltage V1 is greater than V2, the diodes D2 and D3 will be in reverse bias hence there will be no current in that branch (B-C) or (4-2-1-3). Now if the earth fault comes, the CBCT can directly operate the PMR and mechanism will

open the contact. When supply goes off, which is the case in active residual current device, the voltage V1 will become zero. The capacitor which was holding the voltage V2, will discharge. The only discharging path available is through diodes D3 and D2 since D4 is in reverse bias.
Figure 5 shows a schematic circuit arrangement of the flow of current in active residual current device, in accordance with one example embodiment of the present invention. As shown in figure, the capacitor will discharge through D3 and D4 and the current (I) will flow in branch (B-C) or (4-2-1-3). The current through the PMR coil will activate the PMR. The PMR will give signal to the mechanism and the mechanism will open the contacts. Hence both the conditions in active residual current device i.e. operation in case on leakage current and operation when supply goes off are done with the same circuit, same PMR and same mechanism used in case of an passive residual current device.
The circuit arrangement of the present invention can be used in wiring application like RCD socket, RCD plug, RCD adapter, RCD Inline etc. or any such future applications. The improved (combined) arrangement of both active and passive devices in a single unit with a selective option to select the active or passive gives high level of flexibility to end user without any complexity and afso improves portability. The permanent magnet relay (PMR) which is used in the circuit arrangement requires less power to trip and it do not consume power in normal operation. The present circuit arrangement has less components thereby reducing

the power loss of product and reduce the cost. Moreover, in passive mode, the circuit does not depend on the system voltage, it can be operate on as min. as 1V.
While the invention has been shown and described with particularity in only one of its forms to illustrate the principles of the invention, the invention is not thus limited to the representative embodiment but is susceptible to various changes and modifications that may occur to persons skilled in the art in applying the invention to certain circumstances without departing from the scope of the appended claims. For example, while specific dimensions, materials and processes are described for the representative embodiment, the invention is not limited to the specific example but allows substantial variation of structural features and processes within the range of equivalents that may occur to persons practicing the invention. Further, the numbers and arrangement of the components may be altered.

We Claim:
1. A circuit arrangement comprising:
a first circuit for detecting a current imbalance in an AC supply via transformer to a load indicative of a residual current;
a relay having contacts in the AC supply to the load, the relay contacts automatically opening if there is an imbalance current between terminals, and closing when there is a balance current across the terminals thereby dis-connecting and connecting the load, wherein the imbalance current due to difference in voltage across Permanent Magnet Relay (PMR) connected with the transformer; and
a second circuit including a charge storage device connected to the AC supply via at least one rectifying device in parallel with the relay such that, upon application of power from the AC supply, current flows to the charge storage device to charge the latter up,
upon power failure, the relay having contacts in the AC supply to the load turned open due to discharge of the charge storage device provides an imbalance voltage across PMR.
2. The circuit of claim 1, wherein the first circuit is a passive residual current device and the second circuit is an active residual current device.

3. The circuit of claim 1, further comprising:
a switch (S) for selecting the residual current device as an active or passive device.
4. The circuit of claim 1, wherein the first circuit includes the PMR coil, the transformer (e.g. Core Balanced Current Transformer CBCT) and a triggering mechanism for closing and opening of contacts across supply.
5. The circuit of claim 1, wherein the second circuit includes diodes, zener diodes, resistors, PMR coil, capacitor, transformer (e.g. Core Balanced Current Transformer CBCT) and a triggering mechanism for closing and opening of contacts across supply.
6. A circuit arrangement comprising:
an inductively acting circuit;
a capacitively acting discharge circuit for discharging the current of the circuit, wherein the capacitively acting discharge circuit includes,
a four-terminal electrical network (A, B, C, D) including, a first resistor and a third resistor having a known resistance (R1, R3), connected between the network terminals (A) and (C), a second resistor having a known

resistance (R2), connected between the network terminals (C) and (D), a second diode (D2) and a third diode (D3) connected in series across the network terminals (C) and (B), a fourth diode (D4) connected between the network terminals (A) and (B), a zener diode (Z1) connected between the network terminals (A) and (D), and a capacitor having a known capacitance (C), connected between the terminals (B) and (D); and
means for impressing a source of potential from a supply via a first diode (D1) across the network terminals (A) and (C) leads the capacitor to charge the voltage;
and
the AC supply connected to a load via CBCT, wherein the inductively acting circuit and the capacitively acting discharge circuit are partially disposed via PMR electrically, wherein the PMR is further coupled to the CBCT,
wherein, upon power failure, the capacitor of the capacitively acting discharge circuit holding the voltage starts discharging and follows the path through diodes D3 and D2 since D4 is in reverse bias which thereby activates the PMR coil.
7. The circuit of claim 6, further comprising:
means for detecting voltage developed across a PMR coil connected between the terminals (B) and (C), the detecting means includes first and second contacts and a latching mechanism operated by an actuated member.

8. The circuit of claim 6, wherein the diode D1 is used for rectification to convert the directional AC supply in unidirectional DC, wherein the resistors R1 and R2 form the voltage divider circuit thereby enabling voltage V1 to appear at the terminal (C).
9. The circuit of claim 6, wherein the zener diode Z1 between the network terminals (A) and (D) will maintain the voltage Vz at terminal (A) through resistor R3.
10. The circuit of claim 6, wherein the values of resistor R1, resistor R2 and the zener diode Z1 are selected such that the voltage V1 (appearing at the terminal (C)) is greater than voltage Vz.
11. The circuit of claim 6, wherein if the earth fault appears, the CBCT can directly operate the PMR, wherein the PMR further triggers a mechanism to open the contact, and wherein when supply goes off, the voltage V1 will become zero thereby leading the capacitor to discharge which was holding the voltage V2, the discharge path available is through diodes D3 and D4 as D4 is in reverse bias, since the voltage V1 is greater than V2.

12. The circuit of claim 11, wherein the capacitor discharges through D3 and D4 and the current flows through the PMR coil thereby activating the PMR, wherein the PMR will give signal to the mechanism and the mechanism will open the contacts, thereby achieving both the conditions in active residual current device i.e. operation in case of leakage current and operation when supply goes off are achieved with the same circuit, same PMR and same mechanism that are used in case of a passive residual current device.