WO2009155661A1

WO2009155661A1 - A bypass device for safety switch testing

Info

Publication number: WO2009155661A1
Application number: PCT/AU2009/000826
Authority: WO
Inventors: Robert Norman Reynolds; Thomas William Bunworth
Original assignee: Easytest Pty Ltd
Priority date: 2008-06-26
Filing date: 2009-06-26
Publication date: 2009-12-30
Also published as: NZ589818A; AU2009262363A1; AU2009262363B2

Abstract

Residual Current Devices (RCDs), or "safety switches", require routine checking in which they are tripped. This leads to a loss in power to their load circuits which can cause significant inconvenience to commercial premises or households. The present invention relates to a bypass device for use when testing a circuit breaker connected to an electrical load circuit having at least an active circuit and a neutral circuit, the bypass device characterised by a means of ensuring power is maintained through the electrical load circuit downstream of the circuit breaker after it has been tripped so that no interruption is noticed by the electrical load circuit.

Description

A bypass device for safety switch testing

The present invention relates to an electric bypass device and, in particular, to a device for bypassing a Residual Current Device (RCD), otherwise known as a Residual Current Circuit Breaker (RCCB) or "safety switch", after it has been test tripped so that no interruption is noticed by the electrical load circuit.

BACKGROUND OF THE INVENTION

Residual current circuit breakers operate to disconnect their circuit when they detect that current leaking out of the circuit, such as current leaking to earth through a ground fault for example, exceeds safety limits. Such devices are intended to operate quickly so that when a person contacts a live wire, the circuit is isolated before electric shock can drive the heart into ventricular fibrillation, the most common cause of death in such circumstances. Most RCD 's are designed to trip when a current of 30 mA (milliamps) over 300 ms (milliseconds) is detected.

Because RCD's are important in saving people's lives, their integrity is required to be tested on a regular basis. Typically, RCD's have inbuilt testing circuits. These generally require that a user push and hold a button on the RCD which bleeds off 30 mA either over the period of time the button is pressed or until the circuit is tripped. In Australia, RCD manufacturers typically require that this "push-button" test be performed monthly in the case of fixed equipment and in the case of portable equipment, each time the equipment is used. Australian Occupational Health and Safety (OH&S) Regulations recommend that the "push-button" test be performed every 6 months. In other jurisdictions around the world, recommendations and regulations may differ.

The present Applicant is the owner of International Patent Application No. PCT/AU2006/000734 directed towards an improved apparatus and method of testing circuit breakers. The apparatus is adapted to be connected to a circuit having a circuit breaker, and includes a means of performing a first, second and third test on the associated safety switch. The first and second tests are performed in sequence and are used to determine whether the safety switch will trip when a first and second predetermined current is leaked from active to earth respectively. The apparatus includes an additional test, being to determine the actual tripping current required to trip the circuit breaker when the actual tripping current is leaked from active to earth. The apparatus of the abovementioned international patent application is being widely used and is successful in testing circuit breakers. The Applicant has however identified a new problem.

When RCD's are tripped during testing, power downstream of the RCD is lost. This is why it is normal practice to have all electrical appliances which are connected to the electrical load circuit to be switched off until the trip tests are complete. This however can cause considerable disturbance to a home or workplace, particularly those which are highly dependent on the use of mains power for day-to-day operations. For example, some commercial premises need to be able to source mains power at all times to remain operational, and even a loss of power for some 20-30 seconds of testing can impact greatly on operational efficiency. There is therefore a real need for an RCD test operator to be able to enter a premises, and perform the necessary tests on the safety switch without affecting the power supply downstream.

It is therefore an object of the present invention to overcome at least some of the aforementioned problems or provides the public with a useful alternative.

It is a further object of the present invention to provide a means of testing the operation of an RCD without losing power downstream in the electrical load circuit.

SUMMARY OF THE INVENTION

Therefore in one form of the invention there is proposed a bypass device for use when testing a circuit breaker connected to an electrical load circuit having at least an active circuit and a neutral circuit, said bypass device characterised by a means of ensuring power is maintained through the electrical load circuit downstream of the circuit breaker after it has been tripped so that no interruption is noticed by the electrical load circuit.

Preferably said means of ensuring power downstream of the circuit breaker is in the form of a transformer configured such that when said circuit breaker is not tripped, no current flowing through the load circuit flows through the transformer, and when the circuit breaker is tripped, all current flows through the transformer.

In a further form of the invention said means of ensuring power downstream of the circuit breaker is in the form of an active bypass circuit configured such that when said circuit breaker is not tripped, no current flows through the active circuit, and when the circuit is tripped, all current flows through the active circuit. In preference said bypass device further includes: a means of measuring current in the active bypass circuit; a means of eliminating current flowing through the neutral circuit through the circuit breaker; a means of measuring a difference in current between the active bypass current and the neutral circuit current; and a means of adjusting the neutral circuit current in accordance with said measured difference so as to minimise the difference.

In a still further form of the invention, said means of ensuring power downstream of the circuit breaker includes: a means of producing an active supply voltage to the load circuit downstream of the circuit breaker; a means of detecting when the circuit breaker has tripped; a means of switching source of power to the load circuit downstream of the circuit breaker between output from the circuit breaker when no trip is detected and output from the means of producing an active supply voltage when the circuit breaker is tripped.

Preferably the supply voltage produced by the bypass device is phase synchronised with mains supply voltage to the electrical load circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

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

Figure 1 illustrates a circuit diagram of an RCD and a bypass device for safety switch testing in accordance with a first embodiment of the present invention;

Figure 2 illustrates a circuit diagram of an RCD and a bypass device for safety switch testing in accordance with a second embodiment of the present invention;

Figure 3 illustrates a circuit diagram for the power supply block of the second embodiment of the present invention;

Figure 4 illustrates a circuit diagram for a pre-amplifier stage of the second embodiment of the present invention; Figure 5 illustrates a circuit diagram for a pre-amplifier stage of the second embodiment of the present invention;

Figure 6 illustrates a circuit diagram for the level detector block of the second embodiment of the present invention;

Figure 7 illustrates a circuit diagram for the power amplifier block of the second embodiment of the present invention;

Figure 8 illustrates a circuit diagram of an RCD and a bypass device for safety switch testing in accordance with a third embodiment of the present invention;

Figure 9 illustrates schematic details of the third embodiment of the present invention; and

Figure 10 illustrates the present invention in use during RCD testing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following detailed description of the invention refers to the accompanying drawings. Although the description includes exemplary embodiments, other embodiments are possible, and changes may be made to the embodiments described without departing from the spirit and scope of the invention. Wherever possible, the same reference numbers will be used throughout the embodiments and the following description to refer to the same and like parts.

The present invention relates to a device 10a/ 10b/ 10c adapted to be used during the testing of the operation of a Residual Current Device (RCD) or safety switch 12, to ensure that power to a load 13 downstream of the RCD 12 is not lost. It is to be understood that the invention is not intended to be limited to any one embodiment.

When tripped, an RCD isolates the electrical circuit and prevents the person at risk from being electrocuted. An example in which this may occur is where a person contacts a live wire downstream of the RCD. The majority of RCD' s used today are commercial, single phase, single pole RCD's and the present invention is intended for use during the testing of these RCD's. However, it is to be understood that the invention is not intended to be limited to such use, as it could equally well be used when testing commercial, double pole RCD's for example.

An electrical circuit 14a is illustrated in Figure 1, and illustrates an RCD 12 and how a device 10a, in accordance with a first embodiment of the present invention interacts with.the input and output of the RCD 12 in order to ensure that power downstream is not lost when the

RCD is tripped during testing.

The RCD 12 includes a switch 15 which during normal operation is in a closed position, and when the RCD 12 is tripped moves to an open position, as known in the art. The device 10a works by isolating the input and output of the RCD 12 through an isolation transformer 16, which has 5 Volts higher output than input. In the example shown, the input is 240 Volts and the output is 245 Volts. A pair of 6 Volt Zener Diodes 18 are connected back to back in series with the isolation transformer 16.

The 5 Volt drop across the Zener is needed or there would be 5 Volts difference between the two outputs, which would cause circulating currents and destroy the isolation transformer 16.

When the switch 15 is in the closed position, the mains Voltage is 1 Volt higher than what it would be through the transformer 16. When the switch is opened during the trip test, there is no voltage from the mains so all current flows through the transformer 16. Therefore, even when the RCD switch 15 is open, the isolation transformer ensures that power is not lost downstream of the RCD 12.

Thus, it should already be apparent how the present invention provides for testing of RCD's without affecting the load downstream. In this particular case, the means of ensuring power downstream of the circμit breaker is in the form of a transformer configured such that when the circuit breaker is not tripped, no current flowing through the load circuit flows through the transformer, and when the circuit breaker is tripped, all current flows through the transformer.

Figure 2 illustrates an electrical circuit 14b including an RCD 12, and how a device 10b in accordance with a second embodiment of the present invention, interacts with the input and output of the RCD 12 in order to ensure that power downstream of the RCD is not lost when it is tripped. Figures 3-7 illustrate associated circuit diagrams.

The device 10b is used to bypass the "active" leg of the RCD 12 with a circuit that senses the current used by the electrical load. Then, using this signal, the device provides a current through the "neutral" leg, of equal magnitude but opposite phase, to thereby "null" the current so that the RCD 12 can be reset. Turning now to the individual components, the device 10b includes Zener diodes 100, a current level sensor 20, a current balance sensor 22, pre-amplifiers 24 and 26, a level detector 32summing and power amplifier 30, and a power supply 36.

The Zener diodes ensures that the device 10b only acts to bypass the RCD when the RCD switch 15 is open.

The current level sensor 20 is a "Hall Effect" sensor, used to detect the amount of current drawn by the load. The output of the sensor 20 is an AC voltage directly proportional to the current drawn.

The current balance sensor 22 is a "Hall Effect" sensor detecting the imbalance between the load current and the output of the bridge amplifier 30. The output is an AC voltage proportional to the difference current.

The pre-amplifiers 24 and 26 are responsible for conditioning the two outputs mentioned above.

The level detector 32 provides a point for metering the load current while comparing this value to a preset level, to switch the summing and power amplifier 30 on or off as required via the switching logic 34. The level detector consists of rectifier 82 and a comparator 84. The level control signal 86 turns the amplifiers off when the current through the current level sensor 20 is below 15 mA.

The summing and power amplifier 30 is comprised of an input level adjustment 70, control circuit 34, summer 72, offset control and feedback 78 and a power amplifier 80.

The control circuit 30 is used to ground the input of the following summer 72 in order to turn off the output of the device.

The summer 28 is an instrumentation amplifier that combines the two current signals in the correct phase and magnitude to be sent to the power amplifier. The offset control and feedback 78 is also configured as an instrumentation amplifier. It combines the output of the summer with an offset control signal 76 to ensure there is no DC offset in the output 110 of the Power Amplifier 80. A feedback signal 74 helps reduce crossover distortion. The power amplifier 80 incorporates FETs 81 to handle the high current requirements. Thermistors 83 are connected to the FETs 81 to provide them with temperature compensation.

Finally, the power supply 36 is used to supply power to the circuit as required. The power supply consists of transformers, bridge rectifiers and linear regulators as is known in the art. The power supply also includes batteries 90 and 92 to provide high current capabilities to the power amplifier 80. The power supply provides current limited recharging capability for the batteries.

The skilled addressee would realise that device 10b therefore produces the same useful result as that of device 10a, that is, ensuring that testing of the RCD 12 does not affect the load 13 downstream. It achieves this through use of an active bypass circuit configured such that when the circuit breaker is not tripped, no current flows through the active circuit, and when the circuit is tripped, all current flows through the active circuit. The device 10b therefore includes a means of measuring current in the active bypass circuit, a means of eliminating current flowing through the neutral circuit through the circuit breaker, a means of measuring a difference in current between the active bypass current and the neutral circuit current, and a means of adjusting the neutral circuit current in accordance with the measured difference so as to minimise this difference.

Figure 8 illustrates an electrical circuit 14c including an RCD 12, and how a device 10c in accordance with a third embodiment of the present invention, interacts with the input and output of the RCD 12 in order to ensure that power downstream of the RCD is not lost when it is tripped. Figure 9 illustrates the associated circuitry.

The device 10c works by detecting the absence of the power signal 40 from the RCD and replacing it with a replica signal.

Turning now to the individual sections, the device 10b includes a step down transformer 42, a power supply 44, a comparator 46, a relay supply 48, a microcontroller 50, a filter and buffer 52, a power amplifier 54 and a relay 56.

The step down transformer 42 is to isolate the device from the mains and lower the internal working voltage. The internal power supply 44 provides split rails for the analog circuitry as well as +5V for the microcontroller. The power is derived from batteries 61 and 62 to enable a high power output.

The comparator 46 produces a square wave signal 58 representing the input power signal 40.

The microcontroller 50 produces two sine wave signals 56 and 58 of opposite phase. The microcontroller uses the comparator signal 50 to synchronise the sine wave signals to the power signal 4O.The sine wave signals 56 and 58 pass through the filter and buffer 52 and then to the power amplifier 54 consisting of a bridge amplifier and step up transformer.

The output 64 of the power amplifier together with the power input 40 are inputs to a relay 56. The output 66 of the relay is the final output of the device 10c. The relay supply 48 is powered from the power input 40 via the transformer 42 in a manner such that when the power input 40 is present it is connected to the output 66 and when it is not present the output 66 is connected to the power amplifier output 64.

The output 66 thus always has a source of power. In summary, the third embodiment teaches a means of ensuring power downstream of the circuit breaker by providing a means of producing an active supply voltage to the load circuit downstream of the circuit breaker, a means of detecting when the circuit breaker has tripped, and a means of switching source of power to the load circuit downstream of the circuit breaker between the output from the circuit breaker (when no trip is detected), and the output from the means of producing the active supply voltage (when the circuit breaker is tripped). In preference, the supply voltage produced by the bypass device is phase synchronised with mains supply voltage to the electrical load circuit.

It is to be understood that consideration must be given to reaction time to switch off the bypass circuit after a reset, versus the time required to re-trigger a "trip" of the RCD.

All of the above embodiments include a logic section which ensures that all connections are made, that the connections are not across 415 Volts, and that the RCD is already open.

Those skilled in the art should now appreciate the benefits in using the devices lOa/lOb/lOc of the present invention. The apparatus 10 does away with the need for all appliances downstream of an RCD being tested to be switched off. Figure 10 illustrates the device 10 in use in an RCD testing scenario. It is envisaged that this device 10 can easily be carried by an RCD test operator 17 so that once they arrive on site, they may simply attach the device 10 to the input and output wiring of the RCD 12, and then proceed with the usual operational tests on the RCD without requiring all personnel on site to stop using mains power. It is also envisaged that RCD's will be manufactured to include an input which does not require the operator to find and tap into the input and output wiring of the. RCD 12, but which requires simply the plugging in of a cable. The bypass device is intended for particular use in association with trip test equipment 11 developed by the present Applicant, however, is not intended to be limited to such use. Furthermore, although not shown, the trip test equipment which includes analogue and digital displays, etc, could be incorporated into the bypass device to form single unit which the operator can simply carry around from job to job.

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.

In any claims that follow and 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 bypass device for use when testing a circuit breaker connected to an electrical load circuit having at least an active circuit and a neutral circuit, said bypass device characterised by a means of ensuring power is maintained through the electrical load circuit downstream of the circuit breaker after it has been tripped so that no interruption is noticed by the electrical load circuit.

2. A bypass device as characterised in claim 1 wherein said means of ensuring power downstream of the circuit breaker is in the form of a transformer configured such that when said circuit breaker is not tripped, no current flowing through the load circuit flows through the transformer, and when the circuit breaker is tripped, all current flows through the transformer.

3. A bypass device as characterised in claim 1 wherein said means of ensuring power downstream of the circuit breaker is in the form of an active bypass circuit configured such that when said circuit breaker is not tripped, no current flows through the active circuit, and when the circuit is tripped, all current flows through the active circuit.

4. A bypass device as characterised in claim 3 wherein said bypass device further includes: a means of measuring current in the active bypass circuit; a means of eliminating current flowing through the neutral circuit through the circuit breaker; a means of measuring a difference in current between the active bypass current and the neutral circuit current; and a means of adjusting the neutral circuit current in accordance with said measured difference so as to minimise the difference.

5. A bypass device as characterised in claim 1 wherein said means of ensuring power downstream of the circuit breaker includes: a means of producing an active supply voltage to the load circuit downstream of the circuit breaker; a means of detecting when the circuit breaker has tripped; a means of switching source of power to the load circuit downstream of the circuit breaker between output from the circuit breaker when no trip is detected and output from the means of producing an active supply voltage when the circuit breaker is tripped.

6. A bypass device as characterised in claim 5 wherein the supply voltage produced by the bypass device is phase synchronised with mains supply voltage to the electrical load circuit.