"Electric plant"is here to be given a very broad sense and prin- cipally comprises all types of electric circuits, such as transmis- sion and distribution systems for electric power, electric plants within the industry and the like.

The invention is directed to all types of electric switching de- vices, which however have in common that they normally stays in a waiting position and carry out the task they are assigned to only at long time intervals. Such electric switching devices may for example be of the type arranged in a current path for break- ing thereof upon occurrence of fault currents, such as for exam- ple in a switch gear for electricity supply within the industry or in distribution or transmission networks."Electric switching device" comprises also so-called transfer switches through which a cur- rent in a current path may be broken upon occurrence of a fault current in the current path for switching in another current path to a load or the like instead. This electric switching device may

also be of the type that in normal operation of the electric plant is open, i. e. keeps the current path therethrough broken, and only closes when anything particular happens. This"particular" is neither to be anything unpredictable, such as a sudden fault of the electric plant, but the electric switching device could also carry out the task thereof at a predetermined point of time, such as change the position once a month or the like. It may be a question about alternating current as well as direct current.

In common for such electric switching devices normally staying in a waiting position during long periods of time is the need of checking that the state of the electric switching device is satis- fying during these times of waiting, i. e. that it really functions as it is intended to when it is time to work. It is for example ex- tremely important that an electric switching device functioning as any type of protective breaker really carries out the breaking function sufficiently when this is to be done, which could take place at an interval of several years. With respect to especially such electric switching devices the checking of the state has hitherto been carried out by maintenance staff visiting the place for the electric switching device at regular time intervals for taking the electric switching device out of operation for testing the operation thereof between said two closing and breaking po- sitions. Some type of bypassing of the electric switching device is then normally carried out and it is taken out for carrying out the checking of the state, and it is sometimes even taken out physically. A number of time consuming switchings have in any case to take place, and it gets sometimes even necessary to make the electric plant currentless during a short period of time.

Thus, considerable costs are associated with carrying out this condition check, which of course means that there is a high risk that it will not be carried out as often as desired.

SUMMARY OF THE INVENTION The object of the present invention is to provide a method and a device for checking the state of an electric switching device of the type defined in the introduction, which enable a state checking of such electric switching devices being at least in some regard improved.

This object is according to the invention obtained by carrying out the checking in such a method during operation of the electric plant by carrying out the measurement of at least one parameter associated with the condition of the electric switching device without influencing the operation of the electric switching de- vice.

That the electric switching device does not influence the opera- tion means here that the electric switching device is switched in the current path as before in its waiting position and is able to carry out the task thereof. Carrying out for example any by- passing of the electric switching device or in another way re- move the electric switching device from the current path for making the condition check is to be considered as if the opera- tion of the electric plant is influenced. Thus, the operation of the electric plant is to be considered to be uninfluenced if the elec- tric switching device is still switched in so that it may carry out its task.

A number of advantages of carrying out the condition check through such a parameter measurement without influencing the operation through the electric switching device are obtained. An important advantage is that the operation of the electric plant is not disturbed in any way. Another advantage is that time con- suming switchings or even movements of the electric switching device are avoided, so that a checking gets considerably simpler to carry out. Furthermore, there is a possibility that the meas- urement is carried without any need of having any maintenance

staff to get to the electric switching device, so that the condition checks get considerably less expensive than before and may in principle be carried out as often as desired. Accordingly, it gets possible to for example automatically carry out said parameter measurement for condition checks at regular time intervals, such as once a month, once a week or even daily. This means in its turn that possibly degeneration of the condition of the electric switching device may be discovered shortly after they have oc- curred, so that the probability of a good function of the electric switching device when it has to fulfil its object gets very high.

According to a preferred embodiment of the invention at least one parameter describing the state of any part of the electric switching device is calculated on the basis of the result of said measurement. It is advantageous to calculate such a parameter so as to directly get a value of the condition of said part of the electric switching device, even if measured parameters already mentioned may give an indication thereof.

According to another preferred embodiment of the invention the condition check is carried out for an electric switching device comprising an electric actuating member such as an electric motor, arranged to control two contacts movable with respect to each other between said two positions. It is advantageous to carry out the condition check according to the invention of such an electric switching device, since it is very important that it is known that when a determined relative movement of the two contacts is ordered this also will be carried out by the electric actuating member. It is then a need of checking different pa- rameters associated with the function of the electric actuating member, such as the friction between contacts, the energy sup- ply of the actuating member and so on.

According to a preferred embodiment of the invention the condi- tion check of the electric switching device is carried out by checking the function of the electric actuating member by or-

dering a determined relative movement of the two contacts and measuring the result of this order and comparing it with an ex- pected result. It may in this way be ensured that the electric switching device really functions as it shall. It is then possible to discover different defects thereof. The distance for the relative movement may for example be measured through a position detector and a comparison of this distance with an expected distance may be carried out. Would there be a deviation this may for example depend upon a too high friction between the two contacts or a non-satisfying functioning of the energy supply to the electric actuating member. By measuring the distance of a relative movement ordered and the energy consumed by the electric actuating member for achieving this and comparing these values with an expected energy consumption for the movement, it may for example be determined whether the fric- tion against the movement is to high. This may then for example be a result of oxide coatings on the contact surfaces.

The electric actuating member is according to a preferred em- bodiment of the invention adapted to receive energy stored in a capacitor, and the voltage drop across the capacitor is meas- ured and is taken as a value of the energy consumption when carrying out said relative movement. By combining this with a measurement of the current to the electric actuating member the condition of the capacitor may also be tested, i. e. that it can provide the energy required for the control of the electric switching device through the electric actuating member.

According to another preferred embodiment of the invention a detector of the position of the mutual position of the contacts is checked by checking that the position detector delivers a read- ing when simultaneously a movement of a moveable part of the electric actuating member is detected. The good function of the position detector may be directly decisive for a functioning on the hole of electric switching devices of some types, since very accurate co-ordination of movement they have to carry out with

for example the phase position of an alternating current may be required for the correct function of the electric switching device.

According to another preferred embodiment of the invention ap- plied to en electric switching device adapted to be closed and conduct a current therethrough during normal operation of the electric plant, the temperature of at least one of two contacts of the electric switching device and the current through the electric switching device are measured, and these values are compared with expected values therefor so as to determine the condition of the electric switching device with respect to the contact re- sistance thereof. It may by this be determined whether the con- tact resistance of the switching device has become to high, and suitable measures have to be taken for reducing this. Such a too high contact resistance may cause unnecessary power losses and heating of the electric switching device and a possibly dam- age thereof may occur if the temperatures will be too high. An- other way to determine the contact resistance is to measure the voltage between the two contacts of the electric switching de- vice and the current through the electric switching device and compare these values with expected values therefor.

According to another preferred embodiment of the invention ap- plied to an electric switching device adapted to be closed and conduct a current therethrough during normal operation of the electric plant at least one part connected to one of two contacts of the switching device moveable with respect to each other is brought to move while the two contacts maintain their mutual contact. By carrying out such a"small"movement of such a part a very good condition check of the entire electric switching de- vice may be made, without influencing the very operation posi- tion thereof in any way. This may particularly easily be done in the case of an electric actuating member for controlling the movement of this part. Thus, it gets possible to check the posi- tion detector, the contact resistance and the friction of the con- tacts, the energy storage for the actuating member and the good

function thereof through a small movement without the contacts leaving their mutual contact.

According to another preferred embodiment of the invention ap- plied to an electric switching device adapted to keep the current path therethrough broken during normal operation of the electric plant said checking may in a corresponding way take place by carrying out a relative movement of two contacts of the electric switching device while keeping these contacts out of contact with each other and by that preventing current from flowing through the switching device.

According to a very preferred embodiment of the invention a condition check is intended to take place for an electric switch- ing device for alternating current comprising two branches con- nected in parallel in the current path therethrough, in which a first one of them comprises a first contact member having two movable contacts movable with respect to each other for open- ing and closing and the second one comprises an element with ability to block current therethrough in at least one blocking di- rection and conduct current therethrough in at least one direc- tion, in which a second contact member having two contacts movable with respect to each other for opening and closing is connected in series with said element, in which the switching device is adapted to break the current in the current path by the fact that the first contact member is controlled to open for transferring the current to said element when this is in or going into a conducting state and then the second contact member to open when said element is in a state of blocking current there- through after a zero-crossing of the current, and in which the electric switching device is associated with an electric actuating member adapted to cause a relative movement of the movable contacts, in which the checking is carried out by controlling the electric actuating member to move said contacts with respect to each other without breaking the current through the electric switching device. A function checking of all parameters impor-

tant for the good function of the electric switching device may take place by this without influencing the operation of the elec- tric plant in any way. This has a great importance for this type of electric switchrng devices, since it is important to carry out the breaking in a correct way when fault currents occur so as to keep damages of the surrounding equipment and of parts in- cluded in the electric switching device on a level being as low as possible.

According to a preferred further developments of the embodi- ment last mentioned the moveable contacts of the first contact member may be moved with respect to each other while main- taining a contact therebetween in said checking, but it would also be possible to control the electric actuating member to move the moveable contacts of the first contact member out of engagement with each other in said checking for transferring the current to said member and then move them back for establish- ing contact therebetween again before said element arrives to the blocking state. However, a very short relative movement between the two contacts is probably enough for checking the condition of the electric switching device entirely, but it would also be possible to use the embodiment last mentioned when particular needs are there.

According to another very preferred embodiment of the invention applied on an electric switching device co-ordinated with an electronic unit for control of an electric actuating member ar- ranged for mutual movement of moveable contacts of the elec- tric switching device for bringing this between said two posi- tions, said condition check is controlled by the electronic unit.

Exactly the combination of an electric actuating member for movement of contacts of the electric switching device and an electronic unit for control of the electric actuating member re- sults in extraordinary possibilities to easily carry out condition checks of an electric switching device nearly as often as de- sired. The electronic unit may be"programmed"to carry out

these checkings at regular time intervals or be controlled to do this through signals which may be sent out for example from an operation central being remotely located. The parameters used when carrying'out the checking may then be collected from sig- nals to or in the electronic unit and accordingly be such that the electric unit in any case knows all the time for deciding whether the electric switching device shall be controlled or not.

It is then possible in the case that the condition check results in a determined condition of the electric switching device deviating in any way from the expected condition to call for attention by triggering an alarm or the like, which is then controlled by the electronic unit.

The invention also relates to an apparatus, a computer program and a computer program product according to the corresponding appended claims. It is easily understood that the method ac- cording to the invention defined in the appended set of method claims is well suited to be carried out through program instruc- tions from a processor which may be influenced by a computer program provided with the program steps in question. This is particularly the case in the embodiments with an electronic unit included in the electric switching device, since it is very suitable to program this electronic unit to carry out the condition check.

Although not explicitly expressed in the claims the invention comprises such apparatuses, computer programs and computer program products combined with a method according to any of the appended method claims.

The invention also relates to a device for checking the condition of an electric switching device arranged in the current path of an electric plant, said switching device being controllable between positions for closing and breaking the current path, according to the appended device claims. The function and the advantages of such a device appear without any doubt from the discussion

above of corresponding embodiments of the method according to the invention.

Further advantages as well as advantageous features of the in- vention appear from the following description and the other de- pendent claims.

BRIEF DESCRIPTION OF THE DRAWINGS With reference to the appended drawings, below follows a de- scription of preferred embodiments of the invention cited as ex- amples.

In the drawings: Fig 1 is a very schematic view illustrating the construction of a device for condition check of an electric switching de- vice and explains a method for such condition check according to a preferred embodiment of the invention, Fig 2 is a simplified view illustrating the construction of an electric switching device for alternating current with a device for condition check connected thereto, Fig 3 and 4 are views corresponding to fig 2 illustrating methods according to two preferred embodiments of the inven- tion for condition check of the electric switching device, Fig 5 and 6 are very simplified views illustrating a method accord- ing to the invention for condition check of an electric switching device of another type than the one illus- trated in fig 2, and

Fig 7-10 are also very simplified views illustrating a method ac- cording to the invention for condition check of an elec- tric switching device of conventional type.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION An electric switching device is indicated at 1 in fig 1. An electric actuating member 2 in the form of an electric motor schemati- cally indicated is co-ordinated with this electric switching device so as to control two contacts 3,4 of the electric switching device moveable with respect to each other between a position closing and breaking the current path 5, in which it is arranged. It is then advantageous that the electric switching device is adapted to be closed and conduct current therethrough during normal operation of the electric plant, but it is also possible that it may instead be arranged to keep the current path broken during nor- mal operation. The electric motor 2 receives electric energy for actuating the electric switching device from an energy storing member 6, which here is constituted by a capacitor. The direct voltage from the capacitor is converted by an inverter 7 to an alternating voltage for operation of the motor 2. An electronic unit 8 is also co-ordinated with the electric switching device for controlling the electric motor 2. A position detector 9 is adapted to detect the position of a moveable contact 4 of the electric switching device and send information thereabout to the elec- tronic unit 8. Furthermore, a member 10 is adapted to measure the current from the inverter 7 to the electric motor 2. A member 11 is adapted to measure the voltage across the capacitor 6 so as to in that way be able to judge how much energy has been tapped therefrom when controlling the electric actuating member 2. Information from the means 9-11 is sent to the electronic unit 8. It is also indicated that a member 12 is adapted to detect the magnitude of the current in the current path 5 and send informa- tion thereabout to the electronic unit 8.

The electronic unit 8 is adapted to take decisions with respect to whether the electric switching device shall be controlled to go from the normal position thereof, i. e. a position closing or breaking the current path, to the other of these two positions, on the basis of information received from the detecting member 12.

However, there is also a possibility to control the switching de- vice by hand to change position by pressing a button not shown.

Signals from the button may then go to the electronic unit through the detecting member.

The electronic unit is adapted to carry out a condition check of the electric switching device 1 at regular time intervals. This may be done by the fact that it controls the inverter 7 to deliver electric energy from the capacitor 6 to the electric actuating member 2 so that the contacts 3,4 of the electric switching de- vice move with respect to each other without changing the influ- ence of the electric switching device upon the electric plant to which it belongs. This means that if the electric switching device normally is adapted to let the current in the current path flow therethrough, this will continue to do so also during the condi- tion check. It is in this way possible to check the condition of the electric switching device through the electronic unit 8, i. e. that it and the actuating circuit thereof function in such a way that the function it has to carry out, breaking or closing, when this is re- quired will function entirely according to the desires. The elec- tronic unit receives through the member 10 information about the current required by the electric motor for carrying out the movement, and the torque required for the movement of the contacts may be calculated through this information. In the case that the contacts bear against each other during said movement this is then a value of the friction between the contacts. Would this be to high for a good function of the electric switching de- vice, which may depend upon a heavy oxide formation on the surfaces of the contacts, the electronic unit may through an alarm unit 13 tell that maintenance of the electric switching de- vice is necessary. However, exactly by carrying out this condi-

tion test at regular time intervals the friction between the con- tacts may be kept down by the fact that oxide layers possibly formed thereon may be scraped off during such a check, so that such a maintenance may be avoided.

The position detector 9 is adapted to send information about the position of the moveable contact 4 to the electronic unit 8 when checking the condition. It may by this be determined whether the position detector functions as it shall. Furthermore, the elec- tronic unit 8 may through information received from the voltage measuring member 11 check that there is sufficient energy in the capacitor 6 for controlling the electric switching device by measuring the voltage drop across the capacitor when actuating the device for said condition check. Thus, it may in this way be checked that when a certain movement is ordered through the electronic unit 8 this is also obtained, i. e. that the actuation of the electric switching device functions as it shall. A measure of the overall condition of the electric switching device may also be obtained by a possibility to determine the contact friction and testing the position detector and the energy storage.

An electric switching device in the form of a so-called hybrid breaker for which the method for condition check according to the invention is particularly well suited is schematically illus- trated in fig 2. This electric switching device 1 is switched in in a current path 5 for being able to rapidly break a current there- through by opening it. The electric switching device is intended for alternating current and one such switching device is ar- ranged per phase, so that a three phase network has three such switching devices on one and the same location. The switching device has an inner cylinder 14, which is rotatably arranged around an axle 15 and has a moveable contact 4. A second cyl- inder 16 is arranged outside the cylinder 14 and has four con- tacts 3,3', 3"and 3"'arranged along the movement path of the moveable contact 4 and to form good electric contacts while bearing against the moveable contact 4. The switching device is

switched in in the current path through the two outer contacts 3 and 3"', respectively.

A semiconductor device in the form of a diode 17,18 is con- nected between the two outer contacts and the adjacent inner contact with the conducting direction from the outer to the adja- cent contact. The diodes could just as well be both directed with the conducting direction towards the outer contact.

The switching device has also an electric actuating member 19 adapted to drive the inner cylinder 14 to rotate for movement of the moveable contact 4 with respect to the other contacts 3-3"'.

Members 12 are arranged to measure the current in the current path 5 and send information thereabout to the electronic unit 8 for controlling the electric motor 19 on the basis thereof. The device has also a position detector 20 adapted to detect the actual position of the cylinder 14 and by that also of the move- able contact 4.

The function of a switching device of this type appear more in detail from the Swedish patent application 9904164-2 of the ap- plicant but will here be briefly summarised: when there is a de- sire of breaking the current in the current path 5, for example since the detecting member 12 detects a very high current in the current path 5, which may be caused by a short-circuit there- along, it would then be possible for obtaining the quickest pos- sible breaking to detect the direction of the alternating current and make the rotation direction of the cylinder 14 and by that of the moveable contact 4 depending thereupon. In the closed po- sition according to fig 2 the entire current flows through the switching device between the two outer contacts 3,3'through the moveable contact 4 connecting the former galvanically to each other. We do now assume that a decision is taken to carry out the breaking through rotating the inner cylinder 14 clockwise as seen in fig 2. This shall then preferably be made so that an

opening of the contact member formed by the contacts 3 and 3' is carried out through a zero-crossing of the currents, so that this may take place without the formation of any noticeable arc.

This shall take"place when the diode 17 is going to be forward biased, so that the current then is switched over to this diode instead. When then the voltage across the switching device changes direction no current will flow therethrough, but a volt- age will be built up across the diode 17 then reverse biased and the rotation movement of the moveable contact 4 is now contin- ued in the same direction as before, so that the galvanic con- nection between the contact 3'and the contact 3"'is broken and the breaking of the current is by that made permanent. This breaking may take place arc-free, since no current flow through the contact place.

However, the electronic unit 8 may be adapted to achieve a condition check of this electric switching device during operation of the electric plant in which the current path 5 is a part by con- trolling the electric motor 19 and then carry out measurements of at least one parameter associated with the condition of the electric switching device. It is illustrated in fig 3 how this electric motor 19 for such a condition check controls the moveable con- tact 4 to carry out a sliding movement along the fixed contact 3 while maintaining the contact therewith. The function of the electric switching device and the influence upon the current in the current path 5 is by that not changed at all, but important information about the condition of the electric switching device may be obtained. The position detector 20 may send information to the electric unit 8 about the size of the actual movement taken place. This information may be compared with the ordered movement for checking that the actuation of the electric switch- ing device functions as it shall. Other condition parameters of the electric switching device and the actuating circuit thereof may at the same time be calculated in a way described with ref- erence to fig 1.

It is illustrated in fig 4 how it principally would be possible to continue the movement of the moveable contact 4 for said con- dition check of the electric switching device so that the contacts 3,4 of the first contact member are moved out of engagement with each other, so that the current is transferred to the member 17, but it would then be necessary that the electric motor 19 is controlled to move the contact 4 back for establishing contact with the contact 3 again before the member 17 arrives to the blocking state.

It is illustrated in fig 5 and 6 how a method according to the in- vention may be applied on another type of electric switching de- vice 1 for condition check thereof. Parts having correspondence in the device according to fig 1 have here been provided with the same reference numerals. The two contacts 3,4 of the elec- tric switching device are adapted to bear under pretension against each other through a spring member 21 schematically indicated in normal operation of the electric switching device.

The electric motor 2 is adapted to control the moveable contact 4 to such a movement for said condition check that the spring member is allowed to release a determined amount of potential energy being below the level required for a separation of the contacts, so that for example the position according to fig 6 is obtained. It may through the position detector 9 be checked that the movement ordered by the electronic unit has really taken place.

It is illustrated in fig 7-10 how a method according to the inven- tion may be applied to an electric switching device 1 of conven- tional type with a rectilinear relative movement of the two con- tacts. Parts having correspondence in the device according to fig 1 have here been provided with the same reference numer- als. The case in which the electric switching device is adapted to be closed and conduct current therethrough during normal operation (fig 7) of the electric plant is illustrated in fig 7 and 8.

The electric motor 2 is for said condition check adapted to con-

trol the moveable contact 4 to such a movement that the electric switching device remains closed, such as to the position ac- cording to fig 8. Any of the parameters discussed above is si- multaneously measured for the condition check. The case of the arrangement of the electric switching device to keep the current path therethrough broken during normal operation (fig 9) of the electric plant is illustrated in fig 9 and 10. The condition check here takes place by moving the moveable contact 4 towards the contact 3 without closing the breaker, such as to the position shown in fig 10.

The electronic unit 8 is preferably through a suitable program- ming adapted to entirely autonomously control the condition check of the electric switching device 1. It may be designed to do this automatically at predetermined points of time, so that possible faults of the function of the electric switching device, i. e. actually the actuating circuit thereof, may be discovered before the electric switching device shall carry out the task it is intended for, which may be expected to take place at very long time intervals. When then any maintenance really has to be car- ried out on the electric switching device and the actuating circuit thereof the electric unit sends information thereabout to for ex- ample an operation centra through an alarm system. However, this means that no maintenance has to be carried out before this is stated by the electronic unit, so that considerable mainte- nance time may be saved and at the same time the degree of utilisation of the electric switching device may be increased, since it has not to be taken out of operation for the checks.

The invention also relates to such a condition check of an elec- tric switching device which may take place without any move- ment between the two contacts moveable with respect to each other. It is then for example possible to measure the contact re- sistance between two contacts of the switching device by meas- uring the current through the switching device and the voltage between the contacts. Another possibility is to measure the tem-

perature of the contacts and the current therethrough. The tem- perature at a given current magnitude is also a measure of the contact resistance.

The invention is of course not in any way restricted to the pre- ferred embodiments described above, but an amount of possi- bilities to modifications thereof would be apparent to a person with skill in the art, without departing from the basic idea of the invention as defined in the appended claims.

The invention is applicable to electric switching devices in- tended for all conceivable levels of voltages and currents, even if it is particularly well suited for condition check of electric switching devices in a current path in switch gears for electricity supply within industry, distribution or transmission networks having a voltage in the current path on intermediate and high voltage level, i. e. between 1 and 800 kV. Furthermore, the in- vention is particularly applicable to electric switching devices adapted to be able to take an operation current of 1 kA, prefer- able 4 kA.

That the contacts of the electric switching device are moveable with respect to each other is in this disclosure to be interpreted in its broadest sense, i. e. one of them may be stationary while the other is moveable or both may be moveable. They could even move in the same direction but with different speeds.