GB2392029A

GB2392029A - Phase failure relay for detecting multiple faults

Info

Publication number: GB2392029A
Application number: GB0219196A
Authority: GB
Inventors: Jeffery William Rodbard
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-08-16
Filing date: 2002-08-16
Publication date: 2004-02-18
Also published as: GB0219196D0

Abstract

A phase failure relay comprising: a base unit for connection to a three phase supply 1, 2, 3 to be monitored, three voltage sensing units A, B, C, each housed separately and being releasably connected to the base unit, connected to the three phase supply 1, 2, 3 in a delta configuration,and an output from the base unit connected to the switch contacts of the three units A, B, C in such a way that this output represents the status of the majority of the units.

Description

( PHASE FAILURE RELAY

This invention relates to a phase failure relay.

A phase failure relay is an electrical device which can be connected an electrical 5 power supply, and will then g ive an indication to other equipment as to whether this supply is available, and whether the amount of power is within pre-set criteria or not. Primarily the device is used primarily to detect failure or presence of power, and to initiate an automatic replacement of the power supply from an alternative source accordingly, by means of internal volt-free contacts within the relay.

10 It follows that if a failure of the circuitry within the relay occurs it is likely that indication is given to other equipment that the supply being monitored has failed, when, in actual fact, it has not. In this case, the resultant switching of power to an alternative source will cause a break in the continuity of the supply, and this can have serious and costly effects where a supply is critical, such as when used to operate l.T. or hospital 15 equipment, passenger lifts and many other items.

It is also the case that, where a three phase mains supply is to be monitored, known phase failure relays receive all three phases of voltage, with some 41 5V potential between them, and contain a small transformer and many electronic components inside a case of limited dimensions, thereby causing the devices to become hot. This makes 20 reliable operation difficult when the phase failure relays are energised for prolonger periods, a situation common to most units. In addition, most of these relays unnecessarily monitor phase sequence and frequency, which add further to the complexity of the device and the problems described above.

The present invention therefore aims to provide a phase failure relay which 25 overcomes these problems, and greatly increases reliability compared with known phase failure relays.

According to the present invention, there is provided a phase failure relay comprising: a base unit for connection to a three phase supply to be monitored; 30 three voltage sensing units, each unit housed separately and being releasably connected to the base unit, connected to the three phase supply in a delta configuration, each unit having at least two volt- free output contacts; and an output from the base unit connected to the contacts of the three units in such a way that this output represents the status of the majority of the units.

35 Thus, if all three units are in the same state, the output is indicative of this common state and in the case of any non-similarity of status, it represents the status of the two units that concur.

Furthermore no transformers or other wound components are used, except for D.C. operated output relays.

Thus the phase failure relay of the present invention will generate a signal that the monitored supply is failed only if two or more of the units detect such a loss. Similarly, a 5 signal is generated that the supply is returned, only if two or more of the units detect such a return. The present invention thereby avoids the situation where one failure of a circuit within the device causes an indication of supply failure, when there is no problem in fact, and similarly will still indicate the event of a true loss of supply even if one unit fails to open on the power loss.

10 The three voltage sensing units used are each housed separately, and reisasably connected to a base unit, the output from this base unit being connected to the contacts of the three units in such a way that it always represents the status of two or more of the units. Thus in the event of one unit being in a different state than the other two, or even removed completely, the output represents the state of the concurring two units.

15 A further advantage is that, because three identical circuits are used, each connected between a different pair of phases in delta formation, each has only a two-wire input rather than a three phase input. This enables the total number of components, and the amount of heat dissipated, to be far lower than in a conventional phase failure relay.

Parameters such as frequency and phase sequence are not monitored. As 20 regards phase sequence, this is because the phase sequence is verified when a building is first commissioned. If power is removed for some major works, it is standard procedure to check for correct sequence by other means before connecting, so that this function is unnecessary in a phase failure relay. Regarding frequency, the mains supply cannot vary without huge consequences to the transformers and other equipment, and even a 25 generator supply is self-monitoring, and will disconnect if frequency is outside normal limits. The output from the base unit is derived from the contacts in the individual relays within the voltage sensing units; for normally open contacts, and referring to the relays as A, B & C, this is preferably achieved by connecting one contact of relay A in series with 30 one contact of relay B. also one contact of relay B in series with one contact of relay C, and one contact of relay C in series with one contact of relay A. These three pairs of series-connected contacts are preferably interconnected in parallel. This arrangement causes the overall status at the output terminals to represent the status of any two relays that agree, and ignore the one that is in a differing state.

35 For normally closed contacts connected in series, the arrangement is exactly the same. It is preferable to provide both types, using one common contact, and in this case one of the contacts in each relay can be a change-over type.

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( The threshold voltage below which the three circuits release is normally arranged to be between 320 and 380 volts, but can be set as desired by component choice. Thus, if the monitored supply fails, a volt- free contact output is given from the base unit in the normal manner. If one of the three phases of a monitored supply of 415v fails, then the 5 input voltage of two of the circuits will reduce to approximately 250v or 207v, depending on whether the failed phase is earthed or disconnected. This will cause these two units to indicate failure.

In addition, it is also preferable to provide a further contact in each unit to enable remote monitoring to detect if any one of the three units has operated to a "fail" status.

10 This can be achieved in one of two ways. Firstly, to indicate that one unit has changed to "fail" status by breaking a circuit, then the contacts in each unit are of the normally open type, and are connected in series. By this means, when all relays are energised, i.e. power supply present, then the monitoring circuit is closed. If one or more units drop out, the circuit is broken, indication that at least one unit has moved to "failed 15 status. This same indication will be given for a real supply failure, when all three units drop out.

Alternatively to indicate that one unit has changed to "fail" status by making a circuit, then the contacts in each units are of the normally closed type, and are connected in parallel. Thus when all units are energised, (supply present) then the monitoring circuit 20 is open. If one or more relays drop out, the circuit is made, indication that at least one unit has moved to "failed" status. Again this same indication will be given for a real supply failure, when all three units drop out.

Examples of the present invention will now be described with reference to the accompanying drawings, in which: 25 Figure 1 is a schematic view of the arrangement of the relays in the present invention; Figure 2 is a schematic arrangement showing one example of the connections between the terminals and the switch contacts in the present invention; Figures 3A and 3B show different examples of a monitoring circuit for use with the 30 present invention; and Figure 4 shows a typical circuit for use in a voltage sensing unit.

As can been seen from Figure 1, a three phase supply having red 1, yellow 2 and blue 3 phases is connected in a delta arrangement to relays A, B and C. In this delta arrangement, each relay A, B. C sees only two of the three phases and therefore each 35 acts as a single phase voltage loss detector working at typically 415 volts. Thus, if a phase is lost, then the two relays using that phase become connected only to the other two phases in series and see a voltage substantially below the expected voltage, and -3

therefore drop out. At this time, an alternative power supply, such as auxiliary generators, is then activated to provide the necessary electrical supply.

The three phases 1, 2, 3 are provided to a base unit (not shown) to which each of the relays A, B. C are connected in a simple "plug in" fashion such that they can be easily 5 changed if a failure of an individual relay occurs.

The base unit is also provided with output terminals 11, 12, 14, as can been seen in Figure 2. Terminal 11 is a common terminal and is connected to switches A,, B. and C,, terminal 14 is a normally open terminal and terminal 12 is a normally closed terminal.

In this example, each relay A, B. C has a minimum of two contacts A,, A2, B., B2, 10 C,, C2, either both normally closed, or both normally open A,, As, B., B3 Cl, C3. In the case of normally open contacts, these will be closed when the relay senses voltage live, and the circuit will not be broken even if one relay incorrectly opens, or fails to sense the monitored voltage as healthy. If one relay stays closed incorrectly when the other two open, the circuit is still broken, still giving a correct indication of failure of the monitored 15 supply. In the case of normally closed contacts, the same logic applies, but in this case the circuit is made if the monitored voltage fails, and opened if it is healthy. In the broadest form, it is necessary only to have either of these arrangements, using teminals 1 1 and 12 for normally closed contacts, of terminals 1 1 and 14 for normally open contacts.

However, by including both sets of switches and both output terminals, the operator of the 20 phase failure relay can select either or both arrangements depending upon the desired usage In this way, the present invention ensures that the signal at the output is only indicated as a fail if more than one relay fails. Such a fail would indicate that the alternative power supply, such as auxiliary generators, needed to be brought on line.

Each relay is preferably provided with at least one additional contact A4, B4, C4 25 which can be used to indicate that a relay has actually failed and the additional contacts are brought out, via the base unit, to additional output contacts 20, 21 as shown in Figures 3A and 3B.

Figure 3A shows the arrangement in which the switches A4, B4, and C4 are connected via the normally open contact in series so that with the power "on" they are all 30 closed and if a failure of one plug in relay only occurs, i.e. not an actual power failure, then the circuit is broken, given an indication that the relay has failed.

Figure 3B shows the arrangement in which the switches A4, B4 and C4 are connected via the normally closed contacts in parallel so that with the power "on" they are all open and if a failure of one relay only occurs, i. e. not an actual power failure, then the 35 circuit is made, giving an indication of a relay failure.

Figure 4 shows a simplified example of a circuit which could be used as a voltage monitoring unit as part of the present invention.

Claims

1. A phase failure relay comprising: a base unit for connection to a three phase supply to be monitored; 5 three voltage sensing units, each unit housed separately and being releasably connected to the base unit, connected to the three phase supply in a delta configuration, each unit having at least two volt-free output contacts; and an output from the base unit connected to the switch contacts of the three units in such a way that this output represents the status of the majority of the units.

2. A relay according to claim 1, wherein the output comprises a common terminal and one of a normally open terminal and a normally closed terminal.

3. A relay according to claim 1, wherein the output comprises a common terminal, 15 a normally open terminal and normally closed terminal.

4. A relay according to any one of the preceding claims, wherein each of the relays comprises a further contact connected to further output terminals to provide an indication that one of the relays has failed.

5. A relay according to claim 4, wherein the further contacts are connected in parallel via the normally closed contacts.

6. A relay according to claim 4, wherein the further contacts are connected in series 25 via the normally open contacts.

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