GB2505970A

GB2505970A - Safety device particularly for use with an electric boiler, cylinder, thermal store or a lift

Info

Publication number: GB2505970A
Application number: GB1219814.9A
Authority: GB
Inventors: Nicholas Julian Jan Francis Macphail
Original assignee: Individual
Current assignee: Individual
Priority date: 2012-09-12
Filing date: 2012-11-05
Publication date: 2014-03-19
Also published as: GB201219814D0

Abstract

The safety device comprises a detection means arranged to detect at least one hazard signal associated with at least one electrical device, such as a boiler, cylinder, thermal store or a lift. Upon receipt of one or more hazard signals associated with the at least one electrical device, the safety device is arranged to perform at least one of the following: electrically isolate the at least one electrical device; or activate a safety routine. The detection means preferably comprises two hazard sensing devices that cause respective switches 5,6 in a hazard sensing circuit 13 to trip open when a hazard is detected, thereby breaking the hazard sensing circuit. A residual current device (RCD) 2, under volt monitoring relay (11, figure 2, AKA supervising relay) or relay (14, figure 3) may be used to detect a change in voltage across the hazard sensing circuit and actuate an isolating device 1 via actuation wire 9 to cut electrical power to a system load 8 of the electrical device. A redundant protection system may additionally be included by provision of a trip actuation path 12 that is actuated by opening of one or more of the switches to actuate the isolating device.

Description

IMPROVEMENTS IN SAFETY CONTROLS IN

ELECTRIC BOILERS

I, NICHOLAS JULIAN JAN FRANCIS MACPHAIL, a British subject of Mas des Sables, Grandes Rocques, Guernsey of the Channel Islands do hereby declare the invention for which we pray that a patent may be granted to me and the method by which it is to be performed to be particularly described in and by

the following statement:-

THIS INVENTION RELATES TO IMPROVEMENTS IN SAFETY

CONTROLS IN BOILERS AN) OTHER ELECTRICAL SYSTEMS ft is known fixm GB 2456881 that to improve the safety of an electrically powered device such as a heated thermal store or boiler a crowbar circuit or similar system may be used whereby the actuation of overheat thermostat/s or other hazard sensing device may be used to activate a shunt trip causing it to open circuit and shut off the input power to the thermal store or boiler.

The removal of a voltage in a hazard sensing circuit instead of the application ofavoltagefromahazardsensingcircuitisbettertobeusedasthemeansof actuation of any safety shut off. A voltage held on relay contact arranged so that a safety device going open circuit, a break in cabling or a loose connection would cause the relay contacts to open shutting off' power to a boiler is currently used by at least one manufacturer. This system removes the risk of a loose connection or broken cable in a voltage actuated system causing part of the safety chain not failing to safety. While the removal of a voltage can be used to shut off the supply in the event of an overheat thermostat or other hazard sensing device, fix example over and/or under pressure or run dry protection, going "open circuit" to cause a high current relay or relays to open forsafetyitalsocanmeanthatminordmpsinmainsvoltageorpowercutsof even momentary interruption in supply will cause this type of system to open contact causing contact wear fix,m arcing even if there is no safety hazard.

Without care in design this type of system can run the risk, not only of nuisance trips caused by poor relay contact pressure causing arcing and mains spikes, but because this can also cause main isolator trips to actuate could cause, in the case of boiler safety systems tripping out frost damage, flooding to houses and even hypothermia to the frail if there is no one present sufficiently competent to check for safety and reset the mains supply trips to reinstate the heating system.

Indeed one system that is known and in manufacture uses high current power relays that switch high current immersion heaters which are continuously held on by mains voltage while a continuous, and not insignificant, current is consumed by the relay coils. A high coil current is needed to hold in contact the necessarily heavily sprung contacts together against theft contact opening springs continuously awaiting the rare possibility of the failure of no less than three thermostatic protection devices.

As mentioned above; a disadvantage with this prior art is that the brie&st of power cuts or mains voltage drop could cause the mains trip to actuate even though no fhult exists. Such a mains trip could be a major problem for unoccupied buildings leading to frozen/burst pipes with attendant risk of water damage to a property and as mentioned above risk of hypothermia in the frail.

Potential also exists for frost damage to be caused to business premises left unoccupied over a weekend after a simple power cut.

A further disadvantage with this prior art is that most high current relays as used in the above example are not best suited for continuous actuation of theft coils and therefore risk overheating and/or a shortened life in such continuous actuation.

A further disadvantage is that the high current relays have light contact loads compared to a switch or a locked-on shunt trip, due their coil load/contact pressure limits and so high current relays carly an increased risk of contacts arc welding together and not being able to release when they are most needed to release to provide safety isolation.

A further disadvantage with using continuously powered relays instead of a switch or a shunt trip for isolation is that switches or shunt trips are specifically designed for safety isolation use and require little or no hold on current and so arc more energy efficient.

A further example, currently in manufacture, of a control of safety is that of a capillary limit thermostat with heavily sprung contacts to enable the full current used by, in this instance, a flow boiler to be isolated in the event of its water overheating. The disadvantage with this arrangement is that only the hazard of boiler water overheating is protected against. Other hazards such as over or under pressure, lack of water in the boiler, a boiler fire, etc, etc cannot be protected against by this device.

Although for convenience of example water heating, boilers, cylinders, thermal stores, thermal storage boilers, thermal storage combi boilers and the like are described this does not preclude the present invention being used as safety in any other electrically powered or other devices with a need for high safety such as lifts.

It is an aim of thc present invention to overcome or improve on the

disadvantages of the prior art.

According to the present invention there is provided a control of an electric boiler or other device/s having means of detecting one or several hazard sensing/safety devices that open circuit and/or change hazard circuit resistance, circuit voltage or circuit current on hazard sensing in a hazard sensing chain or circuit such as to cause a break and/or change in continuity and/or voltage and/or a current and/or resistance in the said hazard sensing circuit said break and/or change in continuity and/or resistance, voltage or current being sensed by a sensor such as a low current relay and/or a voltage or current or resistance monitoring or supervising relay and/or a residual current device commonly known as an "RCD" being provided balanced resistance feed back and causing the said sensor on its own and/or being an integral part of and/or being mechanically and/or electrically linked to a switch and/or shunt trip to electrically isolate the said electrically supplied device/s and/or activate a

S

safety routine. An extra shunt trip actuation path is able to be provided by utilising a make on hazard contact on at least one of the hazard sensors.

The invention will now be described by way of example with reference to the accompanying drawings in which: Drawing 1 is a diagrammatic illustration of a preferred version of the present invention using a residual current device known as an "RCD" to sense hazard sensing device/s 5 and 6 being tripped to open circuit on the primary hazard circuit 13 while closing contact on the optional secondary hazard circuit 12.

"RCD" devices sense the current flowing into and out of a circuit and trip if a mismatch of current above a certain threshold is sensed.

Drawing 2 is a diagrammatic representation of a frirther preferred form having similarly numbered items except for having a voltage monitoring relay 11 in place of an "RCD". An under volt monitoring relay 11 sometimes known as a supervising relay is used to sense a hazard sensing device 5 and 6 being tripped to open in a hazard sensing circuit. The monitoring relay senses a voltage change in the hazard circuit 13 and trips to actuate a relay which may be linked to a shunt or switch isolator 1 if the voltage in the hazard circuit 13 switches off or drops by a given value. When the voltage is restored by, for example, resetting hazard sensorS andior 6 the monitoring relay may automatically reset.

It should be noted that an optional alternative "volt on" trip actuation path 12 is shown in each drawing and this can be incorporated to give redundancy protection in the "safety chain" circuit if an even greater degree of safety is required. Although only hazard device 5 is shown having a change over contact connected to secondary trip actuation path 12 any or all hazard sensing devices may be connected in this way to secondary actuation path 12.

It should be noted that for clarity the contacts of the sensors and shunt trip in the safety chain circuit are shown open in the primary hazard circuit 13 although in their normal hazardless operating condition they would be closed.

Only live and neutral are shown, earth being omitted for clarity.

It should further be noted that for clarity of understanding the said electrically supplied device/s are exampled by a boiler, cylinder, thermal store, thermal storage boiler or thermal storage combi boiler (not shown) although the present invention may be used in any other application where a break in a safety sensing chain or circuit is required to be used to trip off to safety any device or system or actuate a safety routine. Although in the following description only two hazard sensors 5 and 6 opening contacts under hazard conditions are shown any number of hazard sensors may be incorporated. Hazard sensor 5 and/or 6 may advantageously have change over contacts that provide an extra shunt trip safety path 12 to be used to apply voltage to actuate a shunt trip isolator 1 or othcr mcans of isolation.

Although drawings 1 and 2 shows safety isolation being performed by an isolator I being actuated by an "RCD" 2 or monitoring relay II it should be understood that where the "RCD" 2 or monitoring relay 11 is electrically suitable and has sufficient switching capacity it may act as the isolator alone or be linked mechanically or electrically to a switch (not shown) to perform safety isolation as well as or instead of the shunt trip 1. "RCD" 2 or monitoring relay II may also incorporate an isolator 1, resistors 3 and 4 and/or means mechanical or electrical to link to other isolating devices in a form that may conveniently be din rail mountable.

Although a single switch or shunt trip isolator I is shown being actuated by the hazard sensor/s 5 and 6 in conjunction with the disparity sensor or "RCD" 2 or monitoring relay 11 multiple switches or shunts serving multiple circuits may be actuated.

Isolating device 1 is actuated to off by the hazard sensor/s 5 and 6 via "RCD" 2, monitoring relay 11 or relay 14. When a hazard exists said isolation device I is actuated to off by a voltage, continuity or current mismatch sensing device 2, 11 or 14 such as a residual current device known as an "RCD" 2 or monitoring relay 11 or relay 14 which is actuated if one or more hazard sensor/s S and 6 located in a hazard chain circuit 13 so that their opening contacts cause/s a mismatch in the "RCD" 2 of outgoing current compared to its ingoing current or a drop in voltage or current or change in resistance in monitoring relay 11 or cause low current 14 to de-energise and close contacts shown energized open.

The outgoing current and ingoing current in the "RCD" 2 are kept tiny by matched resistors 3 and 4 the accuracy of their match being dictated by the sensitivity of the "RCD" 2.

By running a resisted circuit from thc live output of an "RCD" 2 back to its neutral input and running a circuit with a similar resistance from its neutral output to its live input a very low current balance can be maintained in the "RCD" 2. If hazard sensing devices 5 and/or 6 go open circuit or change their resistance are introduced into either the live or neutral resisted circuit then when a hazard is sensed it will cause a sensor to open circuit and currents at the "RCD" 2 will no longer be balanced and the "RCD" 2 will trip off Should a break or loose contact or miss wire occur in the hazard sensing circuit 13 then again a lack of balance in current will occur and the "RCD" 2 will trip off.

If the "RCD" 2 or monitoring relay II has insufficient switching capacity and/or it cannot be mechanically linked to a switch or shunt trip the "RCD" 2 or monitoring relay II or a contactor or switch (not shown) linked to the actuation of the "RCD" 2 or monitoring relay 11 may on its own or by a linked relay (not shown) pass an actuating signal via actuation signal carrying wire 9 or mechanical link (not shown) to the shunt trip or other mains isolation device I causing the shunt trip and/or other mains isolation device I to open circuit to safety shutting off for example heat input to a boiler, cylinder, thermal store, thermal storage boiler or thermal storage combi boiler (not shown) or any other application wherc a break in the safety sensing chain is required to be used to trip off to safety any device or system. Heat input primary control with, for example, primary thermostat/s heater control etc. is represented by 7 and a system load, whether electrical or other, is represented by 8. Should there be a reduction of mains voltage or a power cut at the mains input 10 the current flowing into and out of the "RCD" 2 or voltage difference in monitoring relay 11 remains balanced and so will not trip off the shunt trip and/or isolator 1. As only when one or more hazard sensing device/s 5 and 6 goes open contact, or a hazard circuit break by, for example, a loose connection causing a change is detected by the "RCD" 2 or monitoring relay 11 or relay 14 this causes a shut off at the shunt trip or other isolation device 1. A ifirther safety feature of the above described invention is that should a wiring error or loose connection occur in the hazard sensing chain 13 this will also cause a change to be detected at the "RCD" 2 or voltage difference in monitoring relay 11 or relay 14 causing actuation of the shunt trip or other isolating device ito safety until the fault is corrected and the shunt trip is reset.

The "RCD" 2 or monitoring relay ii or relay 14 or other hazard sensing device and switch or contactor (not shown) may be separate to or integral with the isolating device or shunt trip 1. Other electrical safety hazards such as over current, short circuit, earth leak etc. may be met by the said shunt trip and/or other devices (not shown) also inteally or separately and may conveniently be in a din rail mounting form Although the present invention is described for clarity and simplicity as being an electromechanical system using shunts, trips, "RCD"s, monitoring relays, switches, thermostats and pressure switches, it should be understood that any or all of these devices may be substituted by solid state components such as thyristor switches, triacs, thermistors, pressure transducers, current andlor voltagc comparator operational amplifiers and thc like. Advantageously solid state temperature sensing devices like thermistors may be used as hazard scnsors and havc thcir circuitry incorporatcd into thc monitoring relay 11 or "RCD" 2 together with hazard circuit 13 and shunt trip I as a unified safety device conveniently din rail mountable or other suitable housing.

Although for clarity a current mismatch and voltage difference or current off means of sensing open contactts of hazard sensor/s are described, it should be understood that other suitable means of detecting open contacts of the hazard With an "RCD" dcvicc tripping with lcss than lOmA mismatch of input to output current the resistors 3 and 4 can be in the order of 23k Ohms to ensure that, whcn a scnsor gocs opcn circuit, sufficient mismatch at thc "RCD" cxists to cnsurc a trip occurs while reducing any current drawn to a minimum acccptaNc leveL Solid state componcnts wifl enable thc tiny current consumed by the present invention safety system to be reduced still ifirther as the current drain of FET operational amplifier current and voltage comparators and the like arc disappearingly small.

Although only two hazard scnsors 5 and 6 arc shown, any numbcr and typc of sensor may be incorporated in the sensor chain circuit to suit the type and number of hazards needing protection against and more than one "RCD" 2 or monitoring relay 11 or other sensor detector may be used with multiple hazard sense circuits.

Drawing 5 is diagrammatic representation of a preferred form of the present invention having control and/or hazard sensors 5 and 6 which may be manually or automatically re-settable in a relay coil control line to high current relay 15 where, as outlined before, any or all of the hazard sensors may have a change over contact where the break in hazard, in this example, breaks the relay 15 coil supply causing the relay/s contact's to open isolating element/s 8 load/s while make on hazard contact/s exampled at hazard sensor 5 cause an electrical and/or mechanical actuation of the shunt isolator/switch 1 thus providing more than one hazard isolating means to improve safety. High current relay/s 15 and load/s 8 are shown which can be single or when needed multiple relay/s and load/s and incorporate time delay/s 16 to delay sequential relays being actuated to on. This is to reduce high instantaneous load switching from causing spikes that risk nuisance tripping.

It should bc undcrstood that hazard scnsors 5 and 6 are located on the hazard sensing chain or circuit which is not numbered said hazard sensing chain or circuit may conveniently also incorporate normal temperature control thermostats.