GB2513814B

GB2513814B - Electrical safety device

Info

Publication number: GB2513814B
Application number: GB1415542.8A
Authority: GB
Inventors: Pope Matthew; Sheikh Feyaz; E Foley David
Original assignee: Tii Tech Inc
Current assignee: Tii Tech Inc
Priority date: 2012-05-03
Filing date: 2013-05-03
Publication date: 2019-09-11
Anticipated expiration: 2033-05-03
Also published as: GB201207789D0; GB2571679B; GB201415542D0; GB2571679A; GB2513814A; WO2013166388A1; WO2013166388A8; GB201908765D0

Description

ELECTRICAL SAFETY DEVICE

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.K. Provisional Specification Serial No. GB 1207789.7, filed on May 3, 2012, and entitled “ELECTRICAL SAFETY DEVICE”, the disclosure of which is incorporated herein by reference and on which priority is hereby claimed.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an electrical safety device. It has particular application to residual-current devices that operate to interrupt a supply to an electrical circuit in the event that an imbalance between the phase and neutral supply current in an alternating current circuit exceeds a threshold.

Description of Prior Art

Residual-current devices are ubiquitous safety devices in mains electrical installations. The function and operation of residual-current devices is well understood. As with many safety devices, a residual-current device may not have to react to a failure condition for an extended period. Often, many years may pass between failures to which a residual-current device must react. However, it is important that the residual-current device will operate reliably when such a failure does occur. For this reason, residual-current devices are provided with a test control that can be actuated by a user to confirm correct operation of the device. The test control operates by creating a residual testing current within the circuit to which the residual-current device should react.

The intention is that the test control is operated periodically to verify proper operation. However, it is inevitable that this will often be overlooked, and the testing will go undone.

OBJECTS AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide an electrical safety device that functions as a residual-current device that can be tested regularly and conveniently, without excessive expense, and which can provide functionality beyond that of conventional residual-current devices.

It is another object of the present invention to provide a residual-current device that reduces undue wear of the high current-carrying contacts of a power interrupt relay used in the device and premature failure of the device caused thereby.

Tt is still another object of the present invention to provide an electrical safety device that is capable of monitoring the health of electrical equipment situated electrically downstream of the electrical safety device.

It is a further object of the present invention to provide an electrical safety device that monitors and reports on the electrical health of a battery providing auxiliary power to electrical equipment.

It is yet a further object of the present invention to provide an electrical safety device which transmits data from programmed periodic self tests of the device to a remote device or computer.

It is still a further object of the present invention to provide an electrical safety device that includes a foolproof, mechanical indicator which indicates the state of the high current-carrying contacts of a power interrupt relay used in the device.

It is another object of the present invention to provide an electrical safety device having a bypass circuit that ensures that power to electrical equipment situated electrically downstream of the device is not interrupted during periodic self tests of the device.

It is yet another object of the present invention to provide an electrical safety device which includes an ancillary circuit to open the current-carrying contacts of a power interrupt relay associated with the device within a prescribed response time in the event of a fault should there be a delay in the reset or turn-on time of the primary circuit of the device which controls the operation and state of the power interrupt relay associated therewith.

It is still a further object of the present invention to provide an electrical safety device which overcomes the inherent disadvantages of conventional electrical safety devices.

In accordance with the present invention there is provided an electrical safety device comprising a programmable controller, a switching stage operable by the controller to connect or disconnect a load circuit from a source of power, and a residual current detection stage connected to the controller and operative to send a fault signal to the controller in the event of detection of residual currents in the load circuit, the controller operating in accordance with a program to cause the switching stage to disconnect the load in response to the fault signal, and the controller being operable to apply a test signal to the residual current detection stage to simulate presence of a residual current in the load circuit and to monitor the response of the residual current detection stage; wherein the switching stage includes a primary relay circuit, the operation of the primary relay circuit being controlled by the controller, the primary relay circuit being switchable between a first state to disconnect the load circuit from the source of power, and a second state to connect the load circuit to the source of power; and wherein the electrical safety device further comprises a zero cross detector circuit electrically coupled to the controller, the zero cross detector circuit detecting when a zero voltage crossing of the voltage from the source of power provided to the electrical safety circuit occurs and generating a zero cross detection signal in response thereto, the zero cross detection signal being provided to the controller, the controller determining when a substantially zero AC current is flowing through the primary relay circuit based on the zero cross detection signal and causing the primary relay circuit to switch to at least the first state at the time determined when substantially zero AC current is flowing through the primary relay circuit to disconnect the load circuit from the source of power either in response to a fault signal or when the controller is operating in the self-test mode and the test signal is applied to the residual current detection stage.

The invention can thereby provide safety devices that provide the function of a conventional residual-current device, but with the ability to perform testing operations under the control of the programmable controller.

The controller may be programmed to apply a test signal to the residual current detection stage periodically (e.g. at a predetermined time interval).

In one embodiment, programming of the controller can be varied (e.g. by a user or the manufacturer). Such variation may include the number of and/or the frequency of tests to be performed on the switching stage. The variation may include the action in response to a fault signal.

Transient residual current can flow in a circuit as a result of an event that is not a fault. Therefore, the controller may operate to cause the switching stage to reconnect the load circuit following disconnection in response to receipt of a fault signal. Naturally, the controller will cause the switching stage to disconnect the load circuit again in the event that residual currents are again detected. Reconnection may take place after a predetermined delay that may be programmed (e.g. by a user or the manufacturer). The controller may be programmed to attempt reconnection no more than a predetermined number of times.

The controller may operate to cause the switching stage to disconnect or to connect the load circuit in response to conditions other than fault conditions. For example, the controller may operate to cause the switching stage to disconnect or to connect the load circuit at predetermined times, or in response to conditions of operation of the load circuit, such as the magnitude current flowing in it.

Embodiments may further include an input/output module through which the controller can exchange data with external apparatus. For example, the controller may (amongst other things) communicate one or more of the status of the switching stage, the result of a test, the occurrence of a disconnection or reconnection of the load circuit and power flowing in the load circuit to external apparatus. The controller may operate to receive data from external apparatus that causes its programming to be changed or causes the controller to change the state of the switching stage.

These and other objects, features and advantages of the present invention will be apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a block diagram of an electrical safety device in accordance with an embodiment of the invention.

Figure 2 is a schematic diagram of one form of an electrical circuit used in the electrical safety device of the present invention.

Figure 3 is an exploded isometric view of a preferred form of the electrical safety device constructed in accordance with the present invention.

Figure 4 is a side view of the electrical safety device of the present invention shown in Figure 3.

Figure 5 is an isometric view of the electrical safety device of the present invention shown in Figures 3 and 4.

Figure 6 is a longitudinal cross-sectional view of the electrical safety device of the present invention shown in Figures 3-5.

Figure 7 is a flow chart of a battery test subroutine performed by the electrical safety device of the present invention.

Figure 8 is a flow chart of a current draw test subroutine performed by the electrical safety device of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is implemented as a direct replacement for a conventional 2-pole residual-current device. The electrical safety device of the present invention is shaped and dimensioned in accordance with the relevant standards to achieve this compatibility. The device of the present invention is contained within a case that enables it to be mounted in a consumer unit alongside other miniature circuit breakers or by direct screw mounting on a backboard. The preferred overall dimension of the case is 90mm x 85mm x 130mm. Terminals are provided to receive cables of 8mm2 to 25mm2.

As shown in Figure 1, the device includes a power input 20 with phase and neutral conductors 22, 24. Each of these is connected through a respective relay 26, 28 (or respective circuits of a single relay) to a current and fault sense stage 30 from which it passes out to a load circuit 32. These components operate to provide protection of the load circuit 32. In this embodiment, the current and fault sense stage 30 can detect the presence of a residual current and can also measure the total current being delivered to the load circuit 32.

Operation of the device is controlled by a microprocessor 40, which is provided with suitable interface circuitry (see Figure 2). The microprocessor 40 has a relay control output 42 that can open and close each of the relays 26, 28. It also has a test output 44 that can send a test current to the fault sense stage 30 to simulate a fault condition. The microprocessor 40 can send signals to and receive signals from external apparatus through an I/O module 46, for instance by way of a wired or wireless network interface. The I/O module 46 is capable of identifying itself uniquely to the external apparatus, for example using an (e.g. statically-assigned) IP address so that the external apparatus can identify which particular device is sending data. The microprocessor 40 can send signals to and receive signals from a front panel module 48 on which is carried a plurality of indicators 50 and switches 52. From the current and fault sensing stage 30, the microprocessor receives a trip signal input 54 and a current sense input 56. A power supply 60 converts mains power to low-voltage DC to supply power to the controller 40 and other components and circuits of the device.

Under the control of the microprocessor, the device can open and close the relays 26, 28 as and when required. During normal operation of the device, the microprocessor monitors the trip signal input 54. While the trip signal input 54 is at a level indicative of no fault, the microprocessor 40 maintains the relays 26, 28 closed, so energizing the load circuit 32. If the trip signal input 54 is at a level indicative of the presence of fault - that is, a residual current has been detected - the microprocessor 40 causes the relays 26, 28 to open, so removing power from the load circuit 32. In this way, the basic function of a residual-current device is provided by the embodiment of the invention.

The microprocessor 40 can open and close the relays 26, 28 as and when directed by its programming. This can be used to perform a range of additional functions beyond that of serving as a residual-current device.

In response to operation by a user of the switches 52, the controller may operate to cause the relays 26, 28 to open or to close (thereby implementing manual on-off operation of the device) or for a test signal to be applied to the current and fault sensing stage 30, thereby implementing a test control. A first additional function is automatic testing operation of the current and fault sense stage 30. Such a test is performed periodically at an interval determined by the manufacturer, user or by regulation. For example, a test may be performed every 90 days. To perform a test, the microprocessor turns on the test output 44, thereby sending an imbalanced current to the current and fault testing stage 30. Simultaneously, the microprocessor 40 monitors the trip signal input 54. If the trip signal input 54 does not present to the microprocessor 40 a signal that indicates a fault condition, then the device is deemed to have failed the test. Otherwise, the test has been passed. In order to avoid interrupting the power supply during testing, in one mode of operation the microprocessor may switch a second set of relays to connect a bypass circuit to maintain the supply to the load.

The findings of the test can be used to influence the further operation of the embodiment. For example, the microprocessor may cause a warning to be indicated by the indicators 50, it may cause the relays 26, 28 to open, or it may send a signal to external apparatus, such as external monitoring systems, through the I/O module 46. The actual behavior will be governed by the programming of the microprocessor 40, and may include one or more of the above actions, and/or alternative actions.

Another additional function is that of power control. The programming of the microprocessor 40 can cause power to be removed from a load circuit 32 under conditions that are determined by a user. For example, a user may wish that all power is removed from apparatus under the control of the device on a predetermined schedule to reduce power use. Alternatively, the microprocessor 40 may be programmed to open the relays on receipt of a specific signal by the I/O module 46. This may be conditional on the state of the load circuit 32. For example, the relays 26, 28 may be opened only once the current and fault sense stage 30 reports that the current flowing in the load circuit 32 has fallen below a predetermined value.

For example, this can be used as a way to reduce power consumption by isolating a network of electrical apparatus. For instance, some or all of the lights in a building could be isolated at night to reduce waste that occurs through lights being left on when the building is unoccupied. A further additional function is power usage monitoring. Data indicative of total current flow can be continuously sampled from the current and fault sense stage 30 and sent through the I/O module 46 to remote monitoring apparatus. In this way, it is possible to determine the total energy being delivered to the load circuit 32, and therefore, the cost of running it. The unique identification provided by the I/O module can be associated with a particular geographical region or a particular set of apparatus.

Another additional function is automatic re-closure. It is well known that certain conditions that are not actual faults can cause residual currents to flow, with the consequence that the load circuit 32 is isolated. Perhaps the most common source of such currents is a lightning strike. The microprocessor 40 can be programmed to close the relays 26, 28 a predetermined interval after a residual current has been detected. The load circuit 32 is then monitored for residual currents as before, and the device will keep the relays 26, 28 closed, or re-open them as appropriate. This can be done one or more times (controlled by the programming) before it is finally determined that there is an actual fault, rather than a transient effect, after which no further attempt at re-closure will be made. These events can be reported to external monitoring systems through the I/O module.

Figure 2 is a schematic diagram of the embodiment of the current invention, with functional blocks labeled according to Figure 1. The AC power input 20 connects to relay 26, 28 (separate single pole, single throw relays may be used, or as shown in Figure 2, relays 26, 28 may be combined as one in a double pole, single throw relay), whose outputs connect to load circuit 32. AC power input 20 passes AC phase and neutral signals respectively on lines 22 and 24 through a current transformer 70 connected to fault sense stage 30. Fault sense stage 30 is comprised of an analog integrated circuit, preferably Part No. M54123L (an earth leakage current detector), manufactured by Mitsubishi Electric, or similar, to detect any current imbalance between the two AC lines. The external circuitry connected to the M54123L circuit is implemented such that current imbalances of a programmed magnitude and time duration cause transistor Q2 to be turned on, driving signal “fault” 76 (also referred to hereinbefore and shown in Figure 1 as trip signal input 54) to a logic low. This signal is monitored by the microcontroller 40, and can also be used to drive the relay contacts open, as described more fully below.

Power input 20 is connected to power supply 60, which generates +24VDC to power the relays 26, 28, and +5VDC to power the microcontroller 40. The power supply 60 is implemented as a non-isolated, low power, high efficiency switching power supply configured as a Buck converter, comprised of an LNK306 integrated circuit manufactured by Power Integrations Inc., or similar. Very little quiescent power is dissipated by this electrical safety device; the primary power requirement is to drive the coils of relays 26, 28, which are switched infrequently. Charge, or current, is stored in capacitor E5 to help facilitate meeting this brief power spike.

In the preferred embodiment, relays 26 and 28 are implemented as a single relay with double poles driven by the same relay coil to ensure that both AC lines are opened or connected simultaneously. The preferred relay embodiment is a magnetically latched relay, enabling zero power dissipation in the coil while open or closed. Furthermore, two separate coils are used; one is driven to open the contacts, and the other is driven to close the contacts. Thus, drive circuitry 71 is greatly simplified, allowing simple high current bipolar NPN transistors Q5, Q6 to change the state of the relays or relay circuits 26, 28 being driven directly by the microcontroller 40.

The 8 bit microcontroller 40 is preferably Part No. PIC16F677, manufactured by Microchip Technology, or similar, with the operational software program stored in its internal non-volatile memory. Two LED indicators 50 displaying different colors (e.g., blue and yellow) are used to communicate proper operation or fault to the user on the top side of the device. Switches 52 are used to initiate a test or to reset the electrical safety device.

The microcontroller 40 must always know the status of the relay circuits 28, 29, either open or closed, to ensure proper safe operation of the electrical safety device. A line voltage test circuit 73 uses the presence of power at the device output that is connected to load circuit 32 to turn on a photo detector (optocoupler) PCI which creates a logic low in the presence of AC power that is monitored by microcontroller 40.

To generate a current imbalance for self-testing, the microcontroller 40 drives transistor Q3 of circuit 78 on, which draws the specified fault current through a secondary winding of current transformer 70. This is analogous to the controller 40 sending the test current on line 44 to the fault sense stage 30 as described previously in relation to the circuit shown in Figure 1.

An AC line voltage zero cross detector circuit 72 has been implemented using a photo detector (optocoupler) PC2 whose operation is described more fully below.

As mentioned above, the electrical safety device may be programmed to perform automatic self-testing on a periodic basis. Over the life of the product, this self-testing may exercise the current carrying contacts of relays or relay circuits 28, 29 much more frequently than a typical electrical safety device. Therefore, the cumulative effect of the periodic opening and closing of the high current carrying contacts may cause undue wear and premature failure of the device.

In response to a real fault, the device must respond very quickly, opening the relay contacts in 40mS or less to prevent injury or loss of life. For a test initiated by a person pushing one of the switches 52 to perform a test or an automatic self-test performed on a periodic basis, the response time to open the contacts is not time critical as no unsafe condition actually exists. The electrical safety device described herein is designed to take advantage of this fact to minimize contact wear and extend its operational lifetime.

For AC powered devices, it is well understood that the voltage and current waveforms are sinusoidal in nature at a fixed frequency, most commonly 50Hz or 60Hz. It is also well understood that the AC current carried through the device will be positive and negative within each cycle, passing through zero current in between. AC current is exactly in phase with the AC voltage for resistive loads, and will lag the AC voltage slightly in time for most loads which have some inductive component to them. Therefore, the instant the AC voltage passes through zero may be used fairly accurately to estimate when the AC current will pass through zero current.

Referring now to Figure 2, a circuit 72 has been implemented to detect when the AC voltage passes through zero, referred to herein as a zero cross detector. When the AC voltage is zero, the photodiode in optocoupler PC2 will be off, resulting in the phototransistor being off, and the signal “zero cross” 75 will momentarily go to a logic high at that instant in time. The microcontroller 40 may easily determine the time between zero crossing by using an internal timer or similar to measure the time between zero crossings as indicated by circuit 72. For instance, if the AC line frequency is 50Hz, a zero cross will be indicated to microcontroller 40 every lOmS by circuit 72.

Microcontroller 40 may use this zero crossing information, along with empirically measured response times of relays 26 and 28 (the time delay from driving the relay coil to when the contact opens or closes), to optimize the high current carrying contact opening at or near zero AC current flow as follows. If the microcontroller’s programming indicates that it is time to perform a self-test or that a user has pressed a button 52 to initiate a test, the microcontroller is programmed to wait for the zero cross detector 72 to indicate a voltage crossing. Based on this crossing indication and the time between zero crossings, the microcontroller 40 may accurately predict when the next zero crossing will occur. The microcontroller is programmed with the empirically measured response time of relays 26 and 28, and using these two pieces of timing information, it may determine with good accuracy when to optimally drive the relays 26 and 28 open. For instance, if the relay response time delay is 5mS, the microcontroller would use an internal timer or similar means to wait 5mS after the first zero crossing indication and then drive the relays 26 and 28 open. In this manner, contact wear during opening can be dramatically reduced for user initiated or programmed self-tests by always opening the contacts at or near zero AC current flow through the relay contacts.

For real faults, in many instances the microcontroller is also able to optimize relay contact opening as follows. The fault sense stage 30 based on integrated circuit M54123L, or similar, has a specified maximum delay to indicate a fault to the microcontroller 40. Based on this maximum time, the response time of relays or relay circuits 26, 28, and the next predicted zero crossing, the microcontroller 40 can calculate if it is able to wait for the next zero crossing while still meeting specified fault response times. For instance, a typical maximum response time of an electrical safety device such as described here is 40mS. If the maximum delay to indicate a fault for fault sense stage 30 is lOmS, the relay response time is 5mS, and the zero cross occurs every lOmS, it will always be possible to open the relays or relay circuits 26, 28 at the AC current zero cross point while still meeting the overall response time.

Contact closure, or restoration of AC power after a test or reset of a real fault, is never time critical. Therefore, a similar means as described above may be used to ensure that all of the contact closures occur at or near zero AC current to optimally minimize contact wear.

Using a microcontroller to control an electrical safety device has many advantages, some of which have been described previously. One important disadvantage is that, upon initial application of AC power, a fault can only be recognized after the DC power supply 60 has stabilized and the microcontroller 40 has come out of reset, initialized itself, and begun program execution. This delay is often too long to meet the specified response time, resulting in risk of injury or potential loss of life. The electrical safety device described here contains a unique design so as to eliminate this delay in the event of a real fault upon application of AC power to meet the specified response time, while still retaining the benefits of a microcontroller.

Fault sense circuit 30 or similar employs an analog integrated circuit directly powered from the AC line. It therefore does not suffer the turn on delay associated with the microcontroller 40, and has a typical response time of less than lOmS. The relay drive circuit 71 is designed such that either the fault sense circuit 30 or the microcontroller 40 can drive the relays and open in the event of a fault. If the microcontroller 40 is powered up and operating normally, it prevents the fault sense circuit 30 from driving the relays open; if the microcontroller 40 is not active, the fault sense circuit can directly drive the relays 26 and 28 open as follows.

In the event of a real fault, fault sense signal 76 pulses logic low at the line frequency. This signal is transformed into a static logic low signal by relay drive control circuit 77, which signal is provided to the base of transistor Q5 of the relay drive circuit 71. If the microcontroller 40 is active and operating normally, it drives the base of transistor Q5 to a logic high to prevent the fault detector signal from driving the relays 26 and 28 open. Subsequently, the microcontroller 40 uses the zero cross detector 72 to optimally time the opening of the contacts to reduce wear as described above. If the microcontroller 40 is not yet out of reset and not running normally, the base of transistor Q5 will be at a logic low and transistor Q5 will be off. This allows fault sense signal 76 to directly drive the relays open using relay drive circuit 71, meeting the specified response time of the device.

Another feature that may be integrated into the electrical safety device in some circumstances is the health monitoring of downstream equipment to verify that current draw after a self-test is approximately the same as the current draw before a self-test. The loss of downstream power may cause sensitive equipment to not restore to their proper operational state after restoration of AC power.

Prior to a programmed self-test, the microcontroller 40 measures the amperage draw from the load before opening the contacts of the relays or relay circuits 26, 28 and then again on closure of the contacts. After 4 minutes, for example, if the amperage difference after the test is completed is greater than, for example, a 2.5 amp loss, then the microcontroller issues an alarm state but remains online. A flow chart of this current draw test subroutine is shown in Figure 8 of the drawings, and reference should also be had to Figure 1. As shown in Figure 1, the electrical safety device of the present invention includes a circuit 63 which may be used to measure the current drawn by the load circuit 32 before opening the contacts of the relays or relay circuits 26, 28 and then again on, or a predetermined time after, closure of the relay contacts. The current measuring circuit 63 may include a current probe or clamp 63 a, as shown in Figure 1, or any other means known in the art to measure AC current. The current measuring circuit 63 provides a signal to the controller 40 which is indicative of the current drawn by the load circuit 32.

The controller 40 conducts a current draw subroutine as shown in Figure 8 (Step 130). First, and prior to conducting a self-test, the controller 40 measures the current drawn by the load circuit 32 before opening the contacts of the relays or relay circuits 26, 28 (Step 132) by monitoring the signal received from the current measuring circuit 63. Then, the controller 40 causes the electrical safety device of the present invention to conduct a self-test by opening the contacts of the relays or relay circuits 26, 28 to interrupt power provided from the source of power 20 to the load circuit 32 and then, subsequently, closing the contacts of the relays or relay circuits 26, 28 to again provide AC power to the load circuit 32 (Step 134).

After the completion of the self-test and after the relays or relay circuits 26, 28 are switched back to their conductive state to reconnect the load circuit 32 to the source of power 20, the controller 40 determines whether a predetermined time (for example, four minutes) has elapsed after the test has been completed (Step 136). If the predetermined period of time has elapsed, the controller 40 will again measure the current drawn by the load circuit 32 (Step 138). This predetermined time could be set to zero so that this second current measurement will be performed immediately following completion of the self-test. The controller 40 then calculates the difference between the current drawn by the load circuit 32 at the first current measurement time taken before the relays or relay circuits 26, 28 are switched to a non-conductive state, and the current drawn by the load circuit 32 at the second current measurement time which occurs after the predetermined time has elapsed following the relays or relay circuits 26, 28 being switched back to a conductive state at the end of the self-test to reconnect the load circuit 32 to the source of power 20, and determines from this calculation a current difference (Step 140). The controller 40 then determines whether this current difference is less than or equal to a predetermined current value, for example, 2.5 amperes, or perhaps zero amperes (i.e., there is no current difference before and after the selftest is performed) (Step 142).

If the calculated current difference between the two current measurements is less than or equal to the predetermined current value, for example, 2.5 amperes, then the controller 40 knows that the self-test did not cause the load circuit 32 to not restore to its proper operational state after AC power was restored. The controller 40 then will end the current test subroutine (Step 144).

However, if the current difference calculated by the controller 40 is greater than the predetermined current value, then the controller 40 knows that the load circuit 32 is not in the same power state after the self-test as the power state it was in prior to the self-test. The controller 40 will then issue an alarm or send a message indicating such through the input/output module 46 (Step 146). RCDs are often installed in battery-backed systems, such as outdoor telecommunications equipment cabinets. The electrical safety device may contain a feature that leaves the contacts open for a specified period of time during a programmed periodic self-test cycle. During this time, the microcontroller 40 of the electrical safety device monitors the DC battery voltage to measure the battery discharge time to reach a 20% charged state or similar. The AC power is then restored, and the time required to restore the batteries to full charge is measured. This information is used by the microcontroller or communicated via I/O module 46 to an external device to raise an alarm if the battery/ batteries require replacing. The microcontroller 40 may also communicate with an external voltage monitoring device to facilitate battery testing. In this case, the microcontroller 40 would indicate to the external device when it has opened the relay contacts, and the external device would indicate back to the microcontroller when the relay contacts should be closed based on the discharge state of the battery or batteries.

More specifically, and as shown in Figure 1 of the drawings, a battery (or batteries) 61 provides auxiliary, back-up power to the load circuit 32 in the event of a power failure. Oftentimes, these batteries need to be tested to determine their battery life or status, and may need to be replaced. The electrical safety device of the present invention is designed to perform a test on the auxiliary battery 61 to determine its status and whether it needs to be replaced.

As shown in the flow chart of Figure 7, and as shown in the block diagram of Figure 1, the controller 40 of the electrical safety device of the present invention receives a state-of-charge signal indicative of the DC voltage of the battery 61 providing auxiliary power to the load circuit 32. This state-of-charge signal may be realized by feedback signals carried on lines connected directly to the positive and negative output terminals of the battery 61 and provided on inputs of the controller 40 (see Figure 1).

The controller 40 may start the battery test subroutine (Step 100) at predetermined times automatically set by the controller. Initially, the controller 40 measures the voltage on battery 61 and determines whether it is within acceptable limits (Step 102). If the battery voltage is not within acceptable limits, then the controller 40 stores in memory or transmits through the input/output module 46 an error condition (Step 104), and terminates the battery test subroutine (Step 106).

However, if the controller 40 determines that the battery voltage is within acceptable specified limits, then the controller 40 conducts battery discharge and charge tests. First, the controller 40 causes the relays or relay circuits 26, 28 to open, which interrupts power provided by power input 20 to the load circuit 32 (Step 108), so that the load circuit 32 is now powered by the auxiliary battery or batteries 61. Then, the controller 40 monitors and records the battery voltage while the battery 61 is discharging (Step 110). More specifically, the controller 40 measures the time it takes the battery 61 to discharge from a specified first voltage (for example, the battery voltage when fully charged) to a specified second voltage (for example, where the battery 61 is at ten percent charge). The controller 40 determines whether the battery has reached this predetermined discharge voltage level (Step 112) while continuing to measure the battery discharge time (or rate).

When the battery voltage has reached the specified discharge voltage, as measured by the controller 40, the controller will calculate and store the battery discharge time and will then close the relay contacts so that power from power source 20 is provided through the relays or relay circuits 26, 28 to the load circuit 32 (step 114).

When load circuit 32 has an auxiliary battery or batteries 61 associated therewith, there is most often a battery charging circuit (not shown) associated with the load circuit 32 for charging the battery 61. The battery charging circuit is normally powered by the AC power provided to the load circuit 32, and when powered, recharges the battery 61 or maintains the battery 61 at a fully charged state.

Now that the electrical safety device of the present invention has discharged the auxiliary battery 61 to a predetermined voltage level, and the controller 40 has now closed the relay circuits 26, 28 so that AC power is provided to the load circuit 32 and its associated battery charge circuit, the auxiliary battery 61 will now start charging. The controller 40 monitors and records the voltage on battery 61 while the battery is charging, and measures the time it takes to recharge the battery to the specified first voltage, for example, the battery voltage when the battery is fully charged (Step 116). The controller 40 determines whether the battery 61 has now reached this specified first voltage (for example, the voltage when the battery is fully recharged) (Step 118). When the battery 61 has reached its fully charged state, that is, the specified first voltage, the controller 40 calculates the time it takes the battery 61 to recharge from the specified second voltage (for example, the ten percent charge remaining voltage) to the specified first voltage (for example, the voltage when the battery is fully charged), or calculates the rate of charge, and stores this information in its memory or transmits the results of this test through the input/output module 46 to a remote computer or device (Step 120). The battery test subroutine performed by the controller 40 is now complete (Step 122), and the controller will run this subroutine again at a later, predetermined time.

Data from programmed periodic self-tests may be transmitted to an external device via I/O module 46. Alternatively, the results of these tests may be stored locally in a nonvolatile memory for interrogation via a USB, wireless, or similar means by a field technician. Another possibility is that a mechanical counter wheel (not shown) is incremented each time a periodic self-test completes successfully to allow simple visual inspection by a technician.

For personnel safety reasons, electrical safety devices must provide foolproof visual indication of the state of the contacts. This presents a challenge to electronically controlled devices, such as the preferred embodiment described here, when AC power input 20 is lost.

Figures 3-6 illustrate a mechanical indicator that accomplishes this requirement. The indicator 80 is displayed through a clear window 84 (lens 158 in Figure 3) in the top side of the device. It has two states, each indicated by different indicia, such as writing or color, for example, red and green.

Indicator 80 is attached to indicator arm 81, which in turn is attached to the moving contact 85 of the relay circuits 26, 28 at attachment point 82.

As the relay center contact 85 moves between its two states, open and closed, the indicator arm 81 at the attachment pin 82 moves along with it. As the attachment pin moves, the indicator 80 is forced to move in a semi-circular manner due to the constraint at pivot point 83. The indicator 80 has a slightly convex shape so as to allow it to move without hitting the clear viewing window 84.

In this manner, a mechanical indicator is provided that is assured to always be a proper visual indication of the state of the electrical safety device’s electrical contacts.

In some applications, interruption of power to the load circuit 32, even during a brief test, is unacceptable. The electrical safety device described here may contain a second pair of relays 26a, 28a, having pole circuits which are connected respectively in parallel with the pole circuits of relays 26, 28. The contacts of relays 26a, 28a make a secondary electrical connection from power input 20 to load circuit 32 prior to self-test. During test, the primary relays 26, 28 are opened to verify proper functionality, but power to the load is never interrupted, as power is provided to the load through secondary relays 26a, 28a. When the test is complete, relays 26, 28 are closed, and the secondary relays 26a, 28a are opened.

Figures 3-6 illustrate a preferred form of the electrical safety device of the present invention. The power input phase and neutral conductors 22, 24, and comparable output conductors providing power to equipment and devices electrically downstream of the electrical safety device of the present invention, are connected on opposite lateral sides 90 of the case or housing 92 of the device using screw-type clamping connectors 160, 161, with the heads of the screws 94 being accessible through openings 95 in the top side 96 of the housing 92. The housing 92 defines an internal cavity 97 in which the electrical circuit of the device shown in Figures 1 and 2 is situated.

The indicator arm 81, which is attached to and pivotable on the attachment pin 82, includes an arcuate indicator surface 80 on which is preferably painted transversely across it a green stripe and a red stripe. The arcuate indicator surface 80 of the indicator arm 81 is positioned in close proximity to the window 84 situated on the top side 96 of the housing 92 of the device such that, the red stripe is positioned in alignment with and viewable through the clear window 84 when the pole circuits of the relays or relay circuits 26, 28 are in an open position, and the green stripe on the arcuate indicator surface 80 of the indicator arm 81 is in alignment with and viewable through the window 84 of the housing 92 when the relay or relay circuits 26, 28 are in a closed position to provide power through the electrical safety circuit from the AC power input 20 to the electrical equipment and devices situated electrically downstream of the electrical safety device.

Figure 3 is an exploded view of a preferred form of the electrical safety device of the present invention. The housing 92 basically includes two sections, that is, a top housing section 154 and a bottom housing section 155, which mate and may be held together by mounting screws 163. The top side 96 of the housing 92 includes a pair of round LED lenses 153 mounted through corresponding openings formed through the thickness of the top housing section 154. Situated below the respective lenses 153 are the blue LED and the yellow LED (see Figure 2), which are used to communicate proper operation of the safety device or a fault to the user. The lenses 153 may be colored, such as in blue or yellow, or alternatively, the LEDs may emit light of different colors through clear (uncolored) lenses 153.

Two push buttons 159, one for “test” and the other for “reset” (see circuit 52 in Figure 2), are mounted through openings formed through the thickness of the top housing section 154 and are situated in alignment with the reset and test push button switches 52a, 52b mounted on a section of a printed circuit board 165 which is situated within the housing 92. The printed circuit board 165 contains most, if not all, of the electrical circuitry of the safety device shown in Figure 2 of the drawings. A clear lens 158 is also mounted in an opening formed in the top housing section 154 so that the curved indicator 80 and the indicia or colored stripes thereon may be viewable through the lens 158.

Mounted on the bottom housing section 155 is a relay assembly 151, as described previously, which includes the indicator 80 and indicator arm 81. Indicator 80 preferably has an arcuate surface, as mentioned previously. Indicator arm 81 passes through an opening 150 formed through the thickness of the printed circuit board 165 so that the indicator 80 will be positioned in proximity to and be viewable through the lens 158 situated on the top housing section 4. The relay assembly 151 includes the primary relays or relay circuits 26, 28, and may further include the secondary relays or relay circuits 26a, 28a.

Two openings 172 are formed in each of the two opposite lateral side walls of the top housing section 4. These openings 172 are provided to receive the load wires connecting the load circuit 32 to the safety device, and the line wires connecting the source of AC power 20 to the safety device. Screw-type clamping terminals 160, 161 are provided within the housing 92 and are situated in alignment with the openings 172 for receiving the load and line wires. The screws 94 are adjustable through openings 95 formed in the thickness of the top side 96 of the top housing section 154 so that they may be tightened to cause the terminals to clamp onto the ends of the load and line wires. The clamp terminals 160, 161 include terminal blocks 162 which receive the stripped ends of the load and line wires. A load wire stop piece 156 and a line wire stop piece 157 are inserted between the load and line screw-type clamp terminals 161, 162 and the printed circuit board 165 to prevent the load and line conductors from being inserted too far into the openings 172 and terminals 160, 161 so that the conductors do not contact the circuit board 165 and the circuitry thereon. A mounting clip 152 is provided for mounting the electrical safety device in place within a junction box or other electrical equipment.

Although illustrative embodiments of the present invention have been described herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments and that various other changes and modifications may be effected herein by one skilled in the art without departing from the scope or spirit of the invention.

Claims

What is Claimed is:

1. An electrical safety device comprising a programmable controller, a switching stage operable by the controller to connect or disconnect a load circuit from a source of power, and a residual current detection stage connected to the controller and operative to send a fault signal to the controller in the event of detection of residual currents in the load circuit, the controller operating in accordance with a program to cause the switching stage to disconnect the load in response to the fault signal, and the controller being operable in a selftest mode to apply a test signal to the residual current detection stage to simulate presence of a residual current in the load circuit and to monitor the response of the residual current detection stage, wherein the switching stage includes a primary relay circuit, the operation of the primary relay circuit being controlled by the controller, the primary relay circuit being switchable between a first state to disconnect the load circuit from the source of power, and a second state to connect the load circuit to the source of power; and wherein the electrical safety device further comprises a zero cross detector circuit electrically coupled to the controller, the zero cross detector circuit detecting when a zero voltage crossing of the voltage from the source of power provided to the electrical safety circuit occurs and generating a zero cross detection signal in response thereto, the zero cross detection signal being provided to the controller, the controller determining when a substantially zero AC current is flowing through the primary relay circuit based on the zero cross detection signal and causing the primary relay circuit to switch to at least the first state at the time determined when substantially zero AC current is flowing through the primary relay circuit to disconnect the load circuit from the source of power either in response to a fault signal or when the controller is operating in the self-test mode and the test signal is applied to the residual current detection stage.

2. An electrical safety device according to claim 1 in which the controller is programmed to apply a test signal to the residual current detection stage periodically.

3. An electrical safety device according to claim 1 in which programming of the controller can be varied.

4. An electrical safety device according to claim 3 in which variation includes the number of and/or the frequency of tests to be performed on the switching stage.

5. An electrical safety device according to claim 3 in which variation includes the action to be taken in response to a fault signal.

6. An electrical safety device according to claim 1 in which the controller operates to cause the switching stage to reconnect the load circuit following disconnection in response to receipt of a fault signal.

7. An electrical safety device according to claim 6 in which the controller operates to cause reconnection to take place after a predetermined delay.

8. An electrical safety device according to claim 6 in which the delay is programmable.

9. An electrical safety device according to claim 6 in which the controller operates to cause reconnection to take place no more than a predetermined number of times.

10. An electrical safety device according to claim 9 in which the number of times is programmable.

11. An electrical safety device according to claim 1 in which the controller operates to cause the switching stage to disconnect or to connect the load circuit in response to conditions other than fault conditions.

12. An electrical safety device according to claim 11 in which the controller operates to cause the switching stage to disconnect or to connect the load circuit at predetermined times.

13. An electrical safety device according to claim 11 in which the controller operates to cause the switching stage to disconnect or to connect the load circuit in response to conditions of operation of the load circuit.

14. An electrical safety device according to claim 1 further including an input/output module through which the controller can exchange data with external apparatus.

15. An electrical safety device according to claim 14 in which the input/output module includes a wired or wireless network interface.

16. An electrical safety device according to claim 14 in which the controller operates to communicate one or more of the status of the switching stage, the result of a test, the occurrence of a disconnection or reconnection of the load circuit and power flowing in the load circuit to external apparatus.

17. An electrical safety device according to claim 13 in which the controller operates to receive data from external apparatus that causes its programming to be changed or causes the controller to change the state of the switching stage.

18. An electrical safety device according to claim 1, wherein the controller causes the primary relay circuit to switch to the second state at the time determined when substantially zero AC current will be flowing through the primary relay circuit to reconnect the load circuit to the source of power.

19. An electrical safety device according to claim 1, wherein the primary relay circuit includes a dual coil, magnetic latching relay, the dual coil, magnetic latching relay dissipating minimal or no power in either the first state or the second state.