WO2011041843A1

WO2011041843A1 - 3 phase rcbo

Info

Publication number: WO2011041843A1
Application number: PCT/AU2010/001323
Authority: WO
Inventors: Stephen James Woolley
Original assignee: Stephen James Woolley
Priority date: 2009-10-08
Filing date: 2010-10-08
Publication date: 2011-04-14
Also published as: AU2010305324B2; EP2486578A4; EP2486578A1; EP2486578B1; AU2010305324A1

Abstract

A 3 phase RCBO (Residual Current Breaker with Overload) only 3 DIN modules wide as a result of space savings achieved by not switching the neutral circuit and the location of both neutral contacts at one end of the device. A truly mechanical embodiment eliminates issues associated with insulation testing of systems in which it is incorporated.

Description

3 Phase RCBO

FIELD OF THE INVENTION

This invention relates to a 3 phase RCBO (Residual Current Breaker with Overload), in particular a 3 phase RCBO that is only 3 DIN modules wide.

BACKGROUND TO THE INVENTION

Modern electrical installations typically employ both circuit breakers and residual current devices (RCDs) to protect against over-current and earth leakage faults respectively. For 3 phase applications a circuit breaker is typically 3 DIN modules wide and an RCD is 4 DIN modules wide. Together these devices take up a considerable amount of space on switchboard.

Devices combining a circuit breaker together with an RCD have been developed, these are known as Residual Current Breakers with Overload or RCBOs. These RCBOs are invariably 4 DIN modules wide, switching all 3 phases and neutral. Such an arrangement is unsuitable for use in chassis type switchboards as the 3 phase chassis busbar fingers would collide with the neutral input terminal, and the wide casing would make its use unsuitable in some general switchboard installations. A 4 DIN wide module is also not suitable as a drop in replacement for a circuit breaker when the extra protection of an RCD is wanted.

RCBOs can also present problems when insulation testing due to their internal electronics. The electronics give rise to low insulation readings or can even be damaged during the testing procedure. To overcome these problems the electronics in an RCBO need to be isolated by removal or some form of physical isolation during testing. Neither of these options is convenient.

The object of this invention is to provide an RCBO that alleviates the above problems, or at least provides the public with a useful alternative. SUMMARY OF THE INVENTION

Therefore in one form of the invention there is proposed a three phase Residual Current Breaker with Overload, RCBO, comprising a casing with a first end and a second end, the first end including contacts for three phase inputs, the second end including contacts for three phase outputs, a neutral input and a neutral output, wherein the casing is three DIN modules wide.

Preferably the three phase inputs are connected to the three phase outputs via switching contacts and the neutral input is connected to the neutral output without a switching contact. In preference the switching contacts are opened in response to a nonzero net current flowing between the three phase and neutral inputs and the three phase and neutral outputs.

Preferably the contacts for the three phase outputs and the contact for the three phase inputs are interchangeable Preferably the energy to open the contacts is stored in a spring.

In preference the tripping mechanism for opening the contact comprises a magnetic relay

Preferably the RCBO further comprises an actuator lever for turning the RCBO on or off, wherein energy is stored in a spring attached to the actuator lever when it is used to turn the RCBO on.

Preferably the magnetic relay is mechanically linked to components of only one of the phases of the RCBO

In preference energy is transferred via the actuator lever to the magnetic relay via a mechanical linkage when the RCBO is turned off. It should be noted that any one of the aspects mentioned above may include any of the features of any of the other aspects mentioned above and may include any of the features of any of the embodiments described below as appropriate. BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate various implementations of the invention and, together with the description, serve to explain the advantages and principles of the invention. In the drawings:

Figures 1 A and 1 B are front and rear perspective views of an RCBO according to a preferred embodiment of the invention;

Figure 2 is an internal view of an electronic embodiment of the RCBO in the OFF state showing the major components;

Figure 3 is an internal view of an electronic embodiment of the RCBO in the ON state showing the major components;

Figure 4 is a schematic diagram of an electronic embodiment of the RCBO;

Figure 5 is a schematic diagram of a mechanical embodiment of the RCBO;

Figure 6 is an internal view of a mechanical embodiment of the RCBO in the OFF state showing the major components; and

Figure 7 is an internal view of an mechanical embodiment of the RCBO in the ON state showing the major components; LIST OF COMPONENTS

10 RCBO

1 1 Electronic RCBO

12 Mechanical RCBO

15 Casing

16 First end (of casing)

17 Second end (of casing)

20 3 phase inputs

21 3 phase outputs 22 Neutral input

23 Neutral output

24 Screw access holes

25 Actuator lever

26 On/Off indicators

28 Test switch

30 Lever pivot

31 Actuator linkage

32 Actuator mechanism

33 Actuator pivot

34 Contacts

36 Trip cam

37 Proximal end (of actuator linkage)

38 Distal end (of actuator linkage)

39 Short circuit solenoid

40 Short circuit solenoid pin

42 Bimetallic strip

43 Overload linkage

46 Calibration screw

50 Trip linkage

52 Sense transformer

53 Secondary winding

54 Bleed resistor

60 Electromechanical circuit (of electronic RCBO)

61 Residual current protection circuit

62 Bridge rectifier

64 IC

66 SCR

67 Capacitors

68 Trip solenoid

70 Trip solenoid pin

80 Electromechanical circuit (of mechanical RCBO)

82 Magnetic relay 86 Magnetic relay reset linkage

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

The following detailed description of the invention refers to the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings and the following description to refer to the same and like parts. Dimensions of certain parts shown in the drawings may have been modified and/or exaggerated for the purposes of clarity or illustration.

The RCBO 10 of the present invention shares many features with prior art RCBOs, circuit breakers and RCDs. These features are well understood by those familiar with the art so are not described in depth in the following description

Figures 1 A and 1 B show front and rear perspective views of an RCBO 10 according to a preferred embodiment of the invention. The RCBO 10 has the physical appearance of a conventional 3 phase circuit breaker, and in particular is 3 DIN modules wide as per a conventional 3 phase circuit breaker. The width of the RCBO 10 distinguishes it from prior art RCBOs which are typically 4 DIN modules wide. This allows the RCBO 10 to be used in switchboards with limited space and is particularly suited as a replacement for a circuit breaker when the added functionality of an RCBO is desired.

The external physical features of the RCBO 10 are a casing 15 with first end 16 and a second end 17. The first end 16 includes 3 phase inputs 20. The second end 17 includes 3 phase outputs 21 , neutral input 22 and neutral output 23. All of the inputs and outputs are of the screw cage clamp variety with access to the screws of the clamps provided by screw access holes 24. The RCBO 10 is turned ON or OFF by actuator lever 25. The state of the RCBO 10 is shown by On/Off indicators 26. The 3 phase inputs 20 and 3 phase outputs 21 can be interchanged between line and load connections as required without affecting the operation of the RCBO.

Unlike conventional RCBOs, the RCBO 10 does not switch the neutral circuit. This abrogates the need for a considerable amount of components, allowing the RCBO 10 to assume its narrow width.

Having both neutral input 22 and neutral output 23 at the same end of the RCBO 10 allows the RCBO to be only 3 DIN modules wide and suitable for use in chassis type switchboards or connected to a 3 phase busbar as the 3 phase chassis busbar fingers would not collide with either of the neutral connections.

The remaining description describes the features of the RCBO 10 according to two separate embodiments, an electronic RCBO 1 1 and a mechanical RCBO 12. Both embodiments have many features in common, in particular the same external configuration as a result of not switching the neutral circuit. The description will cover the electronic RCBO 1 1 in detail followed by the differences in the mechanical embodiment.

Whilst the RCBO 10, in both of its embodiments, is intended for three phase operation it will operate equally as well with only a single phase present. Where convenient the figures only show items associated with one of the phases and items shared amongst the three phases. The operation of each of the three phases is to all intents and purposes identical. As with conventional 3 phase devices, the three phases are mechanically interlocked so that they operate in unison. The actuator lever 25 for instance operates on all three phases. Likewise the trip mechanisms for each phase are interlocked. A fault detected on any phase will cause all 3 phases to trip.

Figures 2 and 3 show cut-away views of an electronic RCBO 1 1 in the OFF state and ON state respectively, whilst figure 4 shows a schematic diagram of the electromechanical circuit 60 of the RCBO 1 1 . The RCBO 1 1 comprises an actuator lever 25 pivotally mounted on a lever pivot 30 and an actuator mechanism 32 in conjunction with a trip cam 36 pivotally mounted on an actuator pivot 33. As the actuator lever 25 is moved from the OFF position (as in figure 2) to the ON position (as in figure 3) an actuator linkage 32 connected to the actuator lever 25 pushes the actuator mechanism 32 about the actuator pivot 33, bringing contacts 34 together thus making an electrical circuit between a phase input 20 and a phase output 21 .

In moving from the actuator lever 25 from the OFF position to the ON position the actuator linkage 31 works against a torsion spring (not shown). The spring is arranged such that when the proximal end 37 of the actuator linkage 31 is above the line between the lever pivot 30 and the distal end 38 of the actuator linkage 31 the spring will keep actuator linkage 31 in the ON position and when proximal end 37 moves below the line the spring will return the actuator linkage 31 to the OFF position. As the proximal end 37 is only a very small distance above the line, any small movement of the actuator mechanism 32 or the trip cam 36 will trip the mechanism thus returning it to the OFF position and break the electrical circuit between the phase input 20 and the phase output 21 . The first protection provided by the RCBO 1 1 is overload protection (also known as thermal protection) provided by a bi-metallic strip 42 which deforms with an increase in temperature resultant from the current flow through it. The bi-metallic strip operates the trip cam 36 through overload linkage 43, thus resetting the RCBO 1 1 . Calibration screw 48 provides adjustment for the current required to activate the overload protection.

The RCBO 1 1 also provides short circuit protection (also known as magnetic trip protection) via short circuit solenoid 39. Part of the electrical circuit between the phase input 20 and the phase output 21 makes up the coil of the short circuit solenoid 39. In response to a short circuit current the short circuit solenoid 39 will fire a pin 40 that operates the trip cam 36, thus resetting the RCBO 1 1 . The third form of protection provided by the RCBO 1 1 is Residual Current Protection (also known as Earth Leakage Protection) via residual current protection circuit (RCPC) 61 . The RCPC 61 incorporates a sense transformer 52 comprising a toroidal coil through which the neutral and 3 phase circuits pass to form a primary winding. The transformer detects the net three phase current in the circuits which is reflected in a secondary winding 53. Under normal operational circumstances, the net three phase current of all the conductors will equal OA. The current flowing in a conductor in one direction will return back through the other conductors, thereby creating a cancelling effect to the overall sensed current values. The circuitry will detect no out of balance currents because no current will be induced into the sense transformer 52.

If there is an instance of residual current (or earth leakage current), the current flows through a phase then returns through another path (Earth Return etc.) and does not return back through the sense transformer 52. The current in the secondary winding 53 of the sense transformer 52 will then be a measure of the earth fault current. This current is monitored by an IC 64 and if the fault current exceeds a threshold of 30mA the IC 64 will turn on SCR 66 and activate trip solenoid 68, firing a pin 40 that operates the trip cam 36, thus resetting the RCBO 1 1 .

DC power for the RCPC 61 is derived from the 3 phase circuits via bridge rectifier 62, only one phase needs to be present to provide power. Optional electrical isolation from the 3 phase is achieved by the use of capacitors 67 connected in series with the bridge rectifier 62 and trip solenoids 68.

The residual current protection can be tested by pressing test switch 28. Pressing switch 28 completes a circuit through bleed resistor 54 in which the current bypasses sense transformer 52. This results in a net 3 phase current through sense transformer 52 thus simulating a residual current fault which should be detected by the RCPC 61 resulting in the resetting of the RCBO 1 1 . In a second preferred embodiment of the invention there is a mechanical RCBO 12 employing electromechanical means as opposed to electronic means to implement RCD functionality. The general construction and operation of the electronic RCB012 is the same as the electronic RCBO 1 1 . The following discussion will largely focus on where the two embodiments differ from each other.

Figure 5 is a schematic of the electromechanical circuit 80 of a mechanical RCBO 12. The circuit is similar to the electromechanical circuit 60 of the electronic RCBO 1 1 as shown in figure 4. Figures 6 and 7 show cut-away views of the mechanical RCBO 1 2 in the OFF state and ON state respectively,

As per the electronic RCBO 1 1 , an earth fault current is detected from the net three phase current passing through sense transformer 52.

However, in contrast to the electronic RCBO 1 1 , the secondary winding 53 of the transformer 52 is not connected to an electronic sensing circuit, but to an electromechanical actuator in the form of a magnetic relay 82. The power induced by an earth fault current in the secondary winding 53 is enough to trigger the magnetic relay 82 which pushes the trip linkage 50 which in turn pushes the overload linkage 43 to operate the trip cam 36, thus resetting the RCBO 12.

In the mechanical RCBO 12 no internal connection to the supply phases or neutral is necessary, as the energy required to operate the trip components is provided by stored energy in the magnetic relay 82 in the form of springs, and released with an electrical signal provided by the secondary winding 53 of the transformer 52.

The energy required to reset the magnetic relay 82 is provided by the energy stored in the off return spring of the actuator lever 25 when the RCBO 12 is switched from the OFF state to the ON state. The energy is transferred to the magnetic relay 82 via magnetic relay reset linkage 86 and trip linkage 50 when the RCBO switches from the ON state to the OFF state. The reader will now appreciate the advantages offered by the present invention in both its embodiments, namely providing an RCBO only 3 DIN modules wide. The mechanical embodiment provides further advantages in being free of electronic components that interfere with or are damaged by insulation testing.

Further advantages and improvements may very well be made to the present invention without deviating from its scope. Although the invention has been shown and described in what is conceived to be the most practical and preferred embodiment, it is recognized that departures may be made therefrom within the scope and spirit of the invention, which is not to be limited to the details disclosed herein but is to be accorded the full scope of the claims so as to embrace any and all equivalent devices and apparatus. Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of the common general knowledge in this field.

In the summary of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprising" is used in the sense of "including", i.e. the features specified may be associated with further features in various embodiments of the invention.

Claims

1 . A three phase Residual Current Breaker with Overload, RCBO,

comprising a casing with a first end and a second end, the first end including contacts for three phase inputs, the second end including contacts for three phase outputs, a neutral input and a neutral output, wherein the casing is three DIN modules wide.

2. An RCBO as in claim 1 , wherein the three phase inputs are

connected to the three phase outputs via switching contacts and the neutral input is connected to the neutral output without a switching contact.

3. An RCBO as in claim 2, wherein the switching contacts are opened in response to a non-zero net current flowing between the three phase and neutral inputs and the three phase and neutral outputs.

4. An RCBO as in claim 2, wherein the contacts for the three phase outputs and the contact for the three phase inputs are

interchangeable

5. An RCBO as in claim 3, wherein the energy to open the contacts is stored in a spring.

6. An RCBO as in claim 3, wherein the tripping mechanism for opening the contact comprises a magnetic relay.

7. An RCBO as in claim 3, further comprising an actuator lever for

turning the RCBO on or off, wherein energy is stored in a spring attached to the actuator lever when it is used to turn the RCBO on.

8. An RCBO as in claim 6, wherein the magnetic relay is mechanically linked to components of only one of the phases of the RCBO

9. An RCBO as in claim 7 wherein energy is transferred via the actuator lever to the magnetic relay via a mechanical linkage when the RCBO is turned off.