EP3671798A1

EP3671798A1 - A mv switching device of the electromagnetic type

Info

Publication number: EP3671798A1
Application number: EP18215166.2A
Authority: EP
Inventors: Massimiliano Villano; Roberto Penzo
Original assignee: ABB Schweiz AG
Current assignee: ABB Schweiz AG
Priority date: 2018-12-21
Filing date: 2018-12-21
Publication date: 2020-06-24

Abstract

A switching device (1) for medium voltage applications comprising:- one or more electric poles, each comprising a movable contact (11) and a fixed contact (12) adapted to be coupled or uncoupled during a switching operation of said switching device;- an electromagnetic actuator (13) comprising a magnetic core (131), a coil arrangement (132) wound around said magnetic core and a movable plunger (133) operatively coupled to the movable contacts of said electric poles;- a control unit (14) for controlling switching operations of said switching device.Said electromagnetic actuator (13) comprises a conditioning circuit (135) adapted to modify the electric behaviour of said coil arrangement (132) when said conditioning circuit is electrically connected with said coil arrangement.Said conditioning circuit is electrically connected with or disconnected from said coil arrangement, when said movable contact (11) reaches or overruns a reference position (P) during a switching operation of said switching device.

Description

The present invention relates to the field of switching devices for medium voltage applications, such as circuit breakers, contactors, disconnectors, reclosers or the like.
More particularly, the present invention relates to a medium voltage switching device of electromagnetic type.
For the purposes of the present invention, the term medium voltage (MV) identifies voltages higher than 1 kV AC and 1.5 kV DC up to tens of kV, e.g. 72 kV AC and 100 kV DC.
As it is known, a MV switching device of the electromagnetic type comprises an electromagnetic actuator for coupling or uncoupling the electric contacts of the switching device during switching operations.
Generally, the electromagnetic actuator comprises a magnetic core provided with an excitation coil operatively associated to a movable plunger mechanically coupled to the mobile contacts of the switching device.
Typically, during a switching operation, suitably arranged power supply means provide an excitation current to the excitation coil.
The magnetic field, which is induced by the excitation current circulating in the excitation coil, generates a force that operates the movable plunger to carry out a switching operation. Typically, the movable plunger can be reversibly moved between two stable operative positions, each corresponding to a coupling or uncoupling position of the electric contacts and, therefore, to a closing or opening condition of the switching device.
As is known, the actual travelling law of the movable contact during switching operations affects the breaking capabilities of the switching device.
For these reasons, the control unit of the switching device, which controls switching operations, generally needs to obtain data related to the actual position of the movable contact.
In some switching devices of known type, proximity sensors (such as magnetic sensors) are adopted for transmitting sensing signals indicative of the position of the movable contact or the movable plunger to the control unit.
Available proximity sensors capable of providing satisfactory performances in terms of sensing speed are generally quite expensive.
Further, cabling of these sensors is needed, which entails risks in terms of safety (in consideration of the high operating voltages of the live parts of the switching device), increases the overall structural complexity and size and enhances the industrial costs of the switching device.
In other switching devices of known type, micro-switches are adopted to sense the position of the movable plunger. This solution shows drawbacks in term of sensing reliability and wiring complexity and entails high industrial costs as well.
In most advanced switching devices of the state of the art, such as the one disclosed in EP2998977A1 , the actual position of the movable contact is determined in a sensorless manner (i.e. without the arrangement of dedicated position sensors) by suitably processing diagnostic information indicative of the operating status of the electromagnetic actuator of the switching device.
Although these devices perform their functions in a satisfying way, there are some aspects to improve. In particular, these devices have proven to be able to determine the position of the movable contact with a relatively low level of accuracy in certain critical conditions, e.g. during an opening manoeuvre of the switching device, in particular when the movable contact is at a certain distance from the fixed contact (e.g. at a distance higher than 15 mm).
In the state of the art, it is still felt the need for technical solutions capable of overcoming the technical issues described above.
In order to respond to this need, the present invention provides a MV switching device, according to the following claim 1 and the related dependent claims.
In a general definition, the switching device, according to the invention, comprises:
A switching device for medium voltage applications comprising:

one or more electric poles, each comprising a movable contact and a fixed contact adapted to be coupled or uncoupled during a switching operation of said switching device;
an electromagnetic actuator comprising a magnetic core, a coil arrangement wound around said magnetic core and a movable plunger operatively coupled to the movable contacts of said electric poles;
a control unit for controlling switching operations of said switching device.

According to the invention said electromagnetic actuator comprises a conditioning circuit adapted to modify the electric behaviour of said coil arrangement when said conditioning circuit is electrically connected with said coil arrangement.
According to the invention, said conditioning circuit is electrically connected with or disconnected from said coil arrangement, when said movable contact reaches or overruns a reference position during a switching operation of said switching device.
Preferably, said conditioning circuit is electrically connected with said coil arrangement, when said movable contact reaches or overruns said reference position, during an opening manoeuvre of said switching device.
Preferably, said conditioning circuit is electrically disconnected from said coil arrangement, when said movable contact reaches or overruns said reference position, during a closing manoeuvre of said switching device.
Preferably, said conditioning circuit is adapted to cause variations of the impedance and the inductance values of said coil arrangement with respect to characteristic inductance values of said coil arrangement, when said conditioning circuit is electrically connected with said coil arrangement.
Preferably, said conditioning circuit, consists of a RLC circuit including a conditioning coil, a capacitor and a resistor electrically connected in series.
Preferably, said electromagnetic actuator comprises a micro-mechanical switch actuatable by said movable plunger to electrically connect or electrically disconnect said conditioning circuit with or from said coil arrangement.
Preferably, said micro-mechanical switch electrically connects said conditioning circuit with said coil arrangement, when said movable contact reaches or overruns said reference position during an opening manoeuvre of said switching device.
Preferably, said micro-mechanical switch electrically disconnects said conditioning circuit from said coil arrangement, when said movable contact reaches or overruns said reference position during a closing manoeuvre of said switching device.
Preferably, said electromagnetic actuator comprises an energy discharger circuit that is electrically connectable with or disconnectable from said conditioning circuit.
Preferably, said energy discharger circuit is electrically connected with said conditioning circuit, when said conditioning circuit is electrically disconnected from said coil arrangement. Preferably, said energy discharger circuit is electrically disconnected from said conditioning circuit, when said conditioning circuit is electrically connected with said coil arrangement. Preferably, said micro-mechanical switch is actuatable by said movable plunger to electrically connect or electrically disconnect said energy discharger circuit with or from said conditioning circuit.
Preferably, said micro-mechanical switch electrically disconnects said energy discharger circuit from said conditioning circuit, when said movable contact reaches or overruns said reference position during an opening manoeuvre of said switching device.
Preferably, said micro-mechanical switch electrically connects said energy discharger circuit with said conditioning circuit, when said movable contact reaches or overruns said reference position during a closing manoeuvre of said switching device.
Preferably, said control unit is adapted to carry out a determination method of the position of said mobile contact during an opening operation of said switching device, said determination method comprising the following steps:

measuring the impedance and inductance values of said coil arrangement;
checking whether the measured impedance and inductance values show variations exceeding corresponding threshold values with respect to characteristic impedance and inductance values of said coil arrangement;
determining that said mobile contact has reached or overrun said reference position, if the measured impedance and inductance values show variations exceeding said threshold values;
determining that said mobile contact has not reached said reference position, if the measured impedance and inductance values show no variations exceeding said threshold values.

According to some embodiments of the invention, said control unit may be adapted to carry out a determination method of the position of said mobile contact during a closing operation of said switching device, said determination method comprising the following steps:

measuring the impedance and inductance values of said coil arrangement;
checking whether the measured impedance and inductance values show variations exceeding corresponding threshold values with respect to characteristic impedance and inductance values of said coil arrangement;
determining that said mobile contact has not reached said reference position, if the measured impedance and inductance values show variations exceeding said threshold values;
determining that said mobile contact has reached or overrun said reference position, if the measured impedance and inductance values show no variations exceeding said threshold values.

Further characteristics and advantages of the MV switching device, according to the present invention, will become more apparent from the detailed description of preferred embodiments illustrated only by way of non-limitative example in the accompanying drawings, in which:

Figure 1 is a block diagram that schematically shows the switching device, according to the invention; and
Figures 2-5 schematically show the operation of the switching device, according to the invention; and
Figures 6-9 schematically show the structure and the operation of an electromagnetic actuator included in the switching device, according to an embodiment of the invention; and
Figures 10-13 schematically show the structure and the operation of an electromagnetic actuator included in the switching device, according to another embodiment of the invention; and
Figures 14-15 are block diagrams that schematically show determination methods carried out by a control unit included in the switching device, according to the present invention.

Referring to the cited figures, the present invention is related to a switching device 1 for medium voltage applications (here referred to as "MV switching device" or "switching device" for the sake of simplicity).
The MV switching device 1 comprises one or more electric poles, each of which comprises a movable contact 11 and a fixed contact 12, which are electrically connectable to a conductor (e.g. a phase conductor) of a power distribution line (not shown).
The movable contact 11 and the fixed contact 12 are adapted to be coupled or uncoupled respectively during switching operations of the switching device 1.
A switching operation may be a closing manoeuvre (figure 5), in which the contacts 11, 12 are brought from an uncoupled condition to a coupled condition, or an opening manoeuvre (figure 4), in which the contacts 11 and 12 are brought from a coupled condition to an uncoupled condition.
When the contacts 11, 12 are in a coupled or uncoupled condition, the switching device 1 is in a closing condition (figure 3) or in an opening condition (figure 2), respectively.
The switching device 1 comprises an electromagnetic actuator 13 that comprises a magnetic core 131, a coil arrangement 132 wound around the magnetic core 131 and a movable plunger 133 operatively coupled to each movable contact 11 of each electric pole through a corresponding kinematic chain 15.
The coil arrangement of the electromagnetic actuator 13 comprises at least an excitation coil wound around the magnetic core 131.
During a switching operation of the switching device, an excitation current I_E circulates in the coil arrangement 132 (namely in said excitation coil) in order to generate a magnetic flux. The magnetic core 131 properly directs the streamlines of the magnetic flux so generated, in such a way that the movable plunger 133 is operated by a force generated by the magnetic flux enchained with the magnetic core 131 and the movable plunger 133.
According to preferred embodiments of the invention (shown in the cited figures), the above-mentioned coil arrangement 132 includes only said excitation coil.
In this case, said excitation coil may operate as a test coil and it may be supplied also with one or more test signals ST to check the electric behaviour of said coil arrangement, e.g. to measure the impedance values Z_T and inductance values L_T of said coil arrangement. According to alternative embodiments of the invention, the above-mentioned coil arrangement 132 may include a dedicated test coil in addition to said excitation coil. In this case, such a test coil may be supplied also with the test signals ST to measure the impedance values Z_T and inductance values L_T of said coil arrangement.
For the sake of simplicity, without intending to limit the scope of the invention, in the following, specific reference will be made to the embodiments shown in the cited figures, according to which the above-mentioned coil arrangement 132 substantially consists of said excitation coil.
During a switching operation of the switching device 1, the movable plunger 133 is operated between two positions, which correspond to a coupled condition or an uncoupled condition of the electric contacts 11, 12 and, therefore, to a closing condition or an opening condition of the switching device 1.
One or more permanent magnets (not shown) may be conveniently arranged in the proximity of the magnetic core to generate a permanent magnetic force always directed at steadily maintaining the movable plunger 133 in the position reached at the end of its run, when a switching operation is carried out.
Preferably, the switching device 1 comprises power supply means 17 that supply the electric energy needed to generate the excitation current I_E for the coil arrangement 132 during a switching operation.
The switching device 1 comprises control unit 14 for controlling the operation of the switching device 1.
As an example, when a switching operation (i.e. a closing or an opening operation) has to be carried out, the control unit 14 provides control signals to a driving circuit (not shown) to supply the excitation current I_E to the coil arrangement 132 by exploiting electric energy provided by the power supply means 17.
Preferably, the control unit 14 comprises computerised means (not shown) including digital processing resources (such as one or more microprocessors) adapted to execute suitable software instructions to generate command/data signals to manage the operating life of the switching device 1.
Preferably, the control unit 14 comprises said driving circuit (not shown) electrically connected with the coil arrangement 132.
Conveniently, said driving circuit may be directly controlled by the above-mentioned computerised means. As an alternative, it may be controlled by a dedicated control circuit that is in turn controlled by the above-mentioned computerised means.
Preferably, the control unit 14 is capable of providing one or more test signals ST to the coil arrangement 132.
For the sake of clarity, it is evidenced that the test signals ST have a completely different nature with respect to the excitation current I_E provided to the excitation coil 132 to operate the movable plunger 133 during a switching operation of the switching devices 1.
The test signals ST are electric signals (voltage or current signals) having a very small magnitude (amplitude or intensity) and a completely different waveform with respect to the excitation current I_E. As an example, the test signals ST may be pulsed voltage signals having an amplitude of 200 V and a frequency of 100 Hz.
According to the invention, the electromagnetic actuator 13 comprises a conditioning circuit 135 adapted to modify the electric behaviour of the coil arrangement 132, when electrically connected with said coil arrangement.
According to the invention, the conditioning circuit 135 is electrically connected with the coil arrangement 132, when the movable contact 11 reaches or overruns a reference position P, during a switching operation of the switching device 1.
Preferably, the reference position P is set in proximity of position reached by the movable contact 11 when the switching device 1 is in an opening condition. As an example, the reference position P may be set at a distance of 15-20 mm from the fixed contact 12. Preferably, the conditioning circuit 135 is electrically connected with the coil arrangement 132, when the movable contact 11 reaches or overruns the reference position P while moving away from the fixed contact 12, during an opening manoeuvre of the switching device 1 (figure 4). Thus, when the switching device is in an opening condition, the conditioning circuit 135 is electrically connected with the coil arrangement 132 (figure 2).
Preferably, the conditioning circuit 135 is electrically disconnected from the coil arrangement 132, when the movable contact 11 reaches or overruns the reference position P while moving towards the fixed contact 12, during a closing manoeuvre of the switching device 1 (figure 5). Thus, when the switching device is in a closing condition, the conditioning circuit 135 is electrically disconnected with the coil arrangement 132 (figure 3).
Preferably, the electromagnetic actuator 13 comprises a micro-mechanical switch 136 actuatable to electrically connect or electrically disconnect the conditioning circuit 135 with or from said coil arrangement 132.
In general, the micro-mechanical switch 136 is actuated by the movable plunger 133.
The micro-mechanical switch 136 may be directly actuated by the movable plunger 133, for example by means of an actuating element (not shown) coupled with the movable plunger, e.g. an actuating ring or plate or rod solidly fixed with the movable plunger.
As an alternative, the micro-mechanical switch 136 may be indirectly actuated by the movable plunger 133, for example by means of a suitable actuation mechanism operatively coupleable with said movable plunger or by the movable contact 11.
The micro-mechanical switch 136 may be of known type, e.g. a spring micro-switch, and it will not be described in further details for the reasons of brevity.
Preferably, the micro-mechanical switch 136 is actuatable in a first switching position A, at which it electrically connects the conditioning circuit 135 in parallel with the coil arrangement 132, or in a second switching position B, at which it electrically disconnects the conditioning circuit 135 from the coil arrangement 132.
Preferably, the micro-mechanical switch 136 is actuated in the switching position A when the movable contact 11 reaches or overruns the reference position P, while moving away from the fixed contact 12, during an opening manoeuvre of the switching device 1 (figure 4). Preferably, the micro-mechanical switch 136 is actuated in the switching position B when the movable contact 11 reaches or overruns the reference position P, while moving towards the fixed contact 12, during a closing manoeuvre of the switching device 1 (figure 5).
As mentioned above, the conditioning circuit 135 is adapted to modify the electric behaviour of the coil arrangement 132, when it is electrically connected (preferably in parallel) with this latter.
Preferably, the conditioning circuit 135, when electrically connected in parallel with the coil arrangement 132, is adapted to cause variations Δ_Z and Δ_L of the impedance values and inductance values of said coil arrangement with respect to its characteristic impedance values Z_TC and characteristic inductance values L_TC.
For the sake of clarity, it is specified that the term "characteristic impedance values" and "characteristic inductance values" intend respectively the impedance values Z_TC and the inductance values L_TC, which are measured in response to the application of a test signal with given voltage and operating frequency and expected for the coil arrangement 132 in absence of the conditioning circuit 135.
Preferably, the conditioning circuit 135 comprises a conditioning coil 1350 wound around the magnetic core 131 in parallel with the coil arrangement 132.
More particularly, the conditioning circuit 135 is formed by a RLC circuit including the conditioning coil 1350, a capacitor 1352 and a resistor 1351 electrically connected in series with the conditioning coil 1350.
The arrangement of the RLC circuit is quite advantageous as it allows a suitable control of the overall impedance shown by the conditioning circuit 135 when an AC test voltage V_L (at a given operating frequency) is applied at its terminals.
Additionally, the capacitor 1352 allows interrupting or limiting the flow of currents in case of failures (safety self-healing) whereas the resistor 1351 allows limiting the current circulating along the conditioning coil 1350.
Conveniently, the conditioning circuit 135 (namely the RLC circuit thereof) is designed in such a way to cause relevant variations Δ_Z and Δ_L of impedance and inductance values of the coil arrangement 132 (i.e. variations Δ_Z and Δ_L exceeding given corresponding threshold values Z_TH and L_TH) in such a way to be easily detectable when an AC test voltage V_L (at a given operating frequency) is applied to said coil arrangement.
Figures 8, 9 schematically represent the electric behaviour of the coil arrangement 132 and the conditioning circuit 135 for different switching positions A, B of the micro-mechanical switch 136.
When the micro-mechanical switch 136 is in the switching position A, the conditioning circuit 135 is electrically connected in parallel with the coil arrangement 132.
When a test voltage V_L is applied, a current I_L flows along the coil arrangement 132 and a current I_L3 flows along the conditioning circuit 135. In this case, the conditioning circuit 135 causes a variation of the characteristic impedance and inductance values Z_TC and L_TC of the coil arrangement 132.
When the micro-mechanical switch 136 is in the switching position B, the conditioning circuit 135 is electrically disconnected from the coil arrangement 132.
When a test voltage V_L is applied, a current I_L flows along the coil arrangement 132 whereas no currents flow along the conditioning circuit 135. In this case, the conditioning circuit 135 does not cause any variation of the characteristic impedance and inductance values Z_TC and L_TC of the coil arrangement 132.
According to some embodiments (figures 10-13), the electromagnetic actuator 13 comprises an energy discharger circuit 137 adapted to be electrically connected with or disconnected from the conditioning circuit 135.
Conveniently, the energy discharger circuit 137 is electrically connected (preferably in parallel) with the conditioning circuit 135, when this latter is electrically disconnected from the coil arrangement 132.
Preferably, the energy discharger circuit 137 is adapted to form a closed loop circuit in cooperation with the conditioning circuit 135, when it is electrically connected in parallel with this latter.
In this way, the conditioning coil 1350 and the capacitor 1352 included in the conditioning circuit 135 may be suitably discharged after having been excited (when the conditioning circuit 135 is electrically connected in parallel with the coil arrangement 132).
The energy discharger circuit 137 may be of known type. As an example, it may include one or more shunt resistors.
Preferably, the micro-mechanical switch 136 is actuatable by the movable plunger 133 to electrically connect or disconnect the energy discharger circuit 137 with or from the conditioning circuit 135.
Preferably, the micro-mechanical switch 136 electrically disconnects the energy discharger circuit 137 from the conditioning circuit 135, when it is actuated in the first switching position A, i.e. when the movable contact 11 reaches or overruns the reference position P, while moving away from the fixed contact 12, during an opening manoeuvre of the switching device 1 (figures 4, 12).
Preferably, the micro-mechanical switch 136 electrically connects the energy discharger circuit 137 with the conditioning circuit 135, when it is actuated in the first switching position B, i.e. when the movable contact 11 reaches or overruns the reference position P, while moving away from the fixed contact 12, during an opening manoeuvre of the switching device 1 (figures 5, 13).
Figures 12, 13 schematically represent the electric behaviour of the coil arrangement 132, the conditioning circuit 135 and the energy discharger circuit 137 for different switching positions of the micro-mechanical switch 136.
When the micro-mechanical switch 136 is in the switching position A, the conditioning circuit 135 is electrically connected in parallel with the coil arrangement 132 whereas the energy discharger circuit 137 is electrically disconnected from the conditioning circuit 135.
When a voltage V_L is applied, a current I_L flows along the coil arrangement 132 and a current I_L3 flows along the conditioning circuit 135. Instead, no currents flow along the energy discharger circuit 137.
In this case, the conditioning circuit 135 causes a variation of the characteristic impedance and inductance values of the coil arrangement 132, as discussed above, whereas the energy discharger circuit 137 does not impact of the operation of the conditioning circuit 135 and the coil arrangement 132.
When the micro-mechanical switch 136 is in the switching position B, the conditioning circuit 135 is electrically disconnected from with the coil arrangement 132 and it is electrically in parallel with the energy discharger circuit 137 to form a closed loop circuit in cooperation with this latter. A transient discharge current I_D thus temporarily flows along the conditioning circuit 135, in particular along the conditioning coil 1350 and the capacitor 1352. Conveniently, the energy discharger circuit 137 is designed to allow the discharge current I_D to flow and dissipate the energy stored in the conditioning coil 1350. In this way, the conditioning circuit 135 will not influence the next opening manoeuvre of the switching device.
Thus, when a voltage V_L is applied, a current I_L flows only along the coil arrangement 132 and the conditioning circuit 135 does not cause any appreciable variations of the characteristic impedance and inductance of said coil arrangement.
The arrangement of the conditioning circuit 135, which is electrically connectable (preferably in parallel) with the coil arrangement 132 when the movable contact reaches or overruns a reference position P, conveniently allows the control unit 14 to carry out determination methods 100, 101 of the position of the mobile contact 11 during a switching operation of the switching device.
In a practical implementation of the invention, the control uni 14 are adapted to execute suitable software instructions to execute the determination methods 100, 101.
Preferably, the control unit 14 is adapted to carry out a determination method 100 of the position of said mobile contact 11, during an opening operation of said switching device. Preferably, the determination method 100 comprises the following steps:

measuring the impedance values Z_T and the inductance values L_T of the coil arrangement 132;
checking whether the measured impedance values Z_T and inductance values L_T show relevant variations with respect to the characteristic impedance values Z_TC and inductance values L_TC of the coil arrangement 132;
determining that the mobile contact 11 has reached or overrun said reference position P, if the measured impedance values Z_T and inductance values L_T show relevant variations Δ_Z and Δ_L with respect to characteristic impedance values Z_TC and inductance values L_TC of said coil arrangement, respectively; or
determining that the mobile contact 11 has not reached said reference position P, if the measured impedance values Z_T and inductance values L_T show no relevant variations Δ_Z and Δ_L with respect to characteristic impedance values Z_TC and inductance values L_TC of said coil arrangement, respectively.

For the sake of clarity, it is specified that the term "relevant variations" intends variations values Δ_Z, Δ_L, which exceed predetermined threshold values Z_TH and L_TH, i.e. variation values Δ_Z = |Z_T - Z_TC| >= Z_TH and Δ_L = |L_T - L_TC| >= L_TH, where Z_T, Z_TC are respectively the measured impedance values and the characteristic values of the coil arrangement 132 and L_T, L_TC are respectively the measured inductance values and the characteristic values of the coil arrangement 132.
If no relevant variations of the measured impedance values Z_T and inductance values L_T with respect to characteristic impedance values Z_TC and inductance values L_TC of the coil arrangement 132 are detected, this means that the mobile contact 11 has not reached the reference position P while moving away from the fixed contact 12. In this case, the actual position of the mobile contact 11 may be estimated or determined in a known manner.
If relevant variations of the measured impedance values Z_T and inductance values L_T with respect to characteristic impedance values Z_TC and inductance values L_TC of the coil arrangement 132 are detected, this means that the mobile contact 11 has reached or overrun the reference position P while away from the fixed contact 12.
It is evident from the above, the actual position of the mobile contact 11 may thus be determined, even if no dedicated position sensors are arranged. To this aim, it is sufficient to properly set the reference position P. As an example, by setting the reference position P in proximity of position reached by the movable contact 11 when the switching device 1 is in an opening condition, the determination method 100 allows exactly determining when the movable contact 11 is almost at the end of its run and the switching device 1 is close to an opening condition.
Preferably, the step of measuring the impedance values Z_T and inductance values L_T of the coil arrangement 132 comprises the following sub-steps:

providing a test signal ST to the coil arrangement 132 for an observation period of time T_O;
obtaining measuring data M indicative of the voltage V_L at the terminals of the coil arrangement 132 and indicative of the current I_L circulating along the coil arrangement 132 in response to the application of the test signal ST during the observation period T_O;
calculating the impedance values Z_T and inductance values L_T of the coil arrangement 132 basing on said measuring data M.

Preferably, the test signal ST has a waveform capable of exciting the magnetic circuit 131, 132, 133 of the electromagnetic actuator 13 to generate a magnetic flux.
Preferably, the test signal ST is a signal having a pulsed waveform. In this case, the frequency, duty-cycle and amplitude of the pulses of the test signal ST are advantageously selected on the base of the magnetic characteristics of the magnetic circuit 131, 132, 133. Preferably, the test signal ST is a voltage signal applied at the terminals of the coil arrangement 132.
The transmission of the test signal ST causes the application of an AC test voltage V_L (having the same frequency of the test signal ST) at the terminals of the coil arrangement 132, thereby causing the circulation of a current I_L (having the same frequency of the test signal ST) along this latter.
As mentioned above, when the conditioning circuit 135 is electrically connected in parallel with the coil arrangement 132, a current I_L3 (having the same frequency of the test signal ST) circulates along the conditioning circuit 135. However, such a current does not need to be measured as its basic function is to excite the conditioning coil 1350 and determine relevant variations of the overall inductance seen at the terminals of the coil arrangement 132.
The coil arrangement 132 is constantly fed with the test signal ST during the observation period of time T_O, which may be, as an example, of 20 ms.
Preferably, the switching device 1 comprises sensing means 16 operatively coupled with the control unit 14 and adapted to acquire the measuring data M.
Such sensing means may comprise a current sensor and/or a voltage sensor configured to provide suitable sensing signals to the computerised means of the control unit 14.
The sensing signals provided by the current and voltage sensors are respectively indicative the sum of the current I_L circulating in the coil arrangement 132 and the current I_L3 circulating in the conditioning circuit 135 and indicative of the voltage V_L actually applied at the terminals of the coil arrangement 132 in response to the transmission of the test signal ST.
The control unit 14 is adapted to receive the sensing signals transmitted by the sensing means 16 and obtain the measuring data M by processing the sensing signals received from the sensing means 16.
Preferably, the measuring data M are obtained at a plurality of subsequent sampling instants comprised in the observation period T_O, which have a sampling period T_S (e.g. 0.1 ms) set by the computerised means of the control unit 14
The calculation of the impedance values Z_T and inductance values L_T of the coil arrangement 132, basing on said measuring data M, may conveniently employ calculation algorithms of known type.
Preferably, the step of checking whether the measured the impedance values Z_T and inductance values L_T show relevant variations with respect to the characteristic impedance values Z_TC and inductance values L_TC of the coil arrangement 132 comprises comparing the measured the impedance values Z_T and inductance values L_T with the characteristic impedance values Z_TC and inductance values L_TC, which may be stored in a memory.
In order to carry out such a comparison step, suitable look-up tables may be used or processed by the control unit 14.
Preferably, the control unit 14 is adapted to carry out a determination method 101 of the position of said mobile contact 11, during a closing operation of said switching device. Preferably, the determination method 101 comprises the following steps:

measuring the impedance values Z_T and the inductance values L_T of the coil arrangement 132;
checking whether the measured impedance values Z_T and inductance values L_T show relevant variations with respect to the characteristic impedance values Z_TC and inductance values L_TC of the coil arrangement 132;
determining that the mobile contact 11 has not reached said reference position P, if the measured impedance values Z_T and inductance values L_T show relevant variations Δ_Z and Δ_L with respect to characteristic impedance values Z_TC and inductance values L_TC of said coil arrangement, respectively; or
determining that the mobile contact 11 has reached or overrun said reference position P, if the measured impedance values Z_T and inductance values L_T show no relevant variations Δ_Z and Δ_L with respect to characteristic impedance values Z_TC and inductance values L_TC of said coil arrangement, respectively.

If relevant variations of the measured impedance values Z_T and inductance values L_T with respect to characteristic impedance values Z_TC and inductance values L_TC of the coil arrangement 132 are detected, this means that the mobile contact 11 has not reached the reference position P while moving towards the fixed contact 12. In this case, the actual position of the mobile contact 11 may be estimated or determined in a known manner.
If no relevant variations of the measured impedance values Z_T and inductance values L_T with respect to characteristic impedance values Z_TC and inductance values L_TC of the coil arrangement 132 are detected, this means that the mobile contact 11 has reached or overrun the reference position P while towards the fixed contact 12.
Also in this case, the actual position of the mobile contact 11 may thus be determined, even if no dedicated position sensors are arranged. To this aim, it is sufficient to properly set the reference position P.
Conveniently, the various steps of determination method 101 may be carried out by the control unit 14 in a similar way with respect to the steps of the above-described determination step 100.
According to preferred embodiments, the control unit 14 is adapted to carry out at least the above-described determination method 100 of the position of said mobile contact 11, during an opening operation of said switching device.
Other embodiments of the invention may however provide that the control unit 14 is adapted to carry out the determination method 101 of the position of said mobile contact 11, during a closing operation of said switching device.
An example of operation of the switching device is briefly described in the following.
The switching device 1 is initially supposed to be in a closing condition (figure 3).
The micro-mechanical switch 136 is in the switching position B and the conditioning circuit 135 is electrically disconnected from the coil arrangement 132.
If an energy discharger circuit 137 is present, this latter is electrically connected in parallel with the conditioning circuit 135.
During an opening manoeuvre of the switching device 1 (figure 4), the control unit 14 can execute the determination process 100.
Until the movable contact 11 reaches the reference position P, the micro-mechanical switch 136 remains in the switching position B and the conditioning circuit 135 remains electrically disconnected from the coil arrangement 132.
If an energy discharger circuit 137 is present, this latter remains electrically connected in parallel with the conditioning circuit 135.
The conditioning circuit 135 does not cause any variations of the electric behaviour of the coil arrangement 132. In this case, the impedance values Z_T and the inductance values L_T of the coil arrangement 132, which are measured by the control unit 14, do not show relevant variations with respect to characteristic values Z_TC and L_TC of said coil arrangement.
The control unit 14 thus determines that the movable contact 11 has not reached the reference position P while moving away from the fixed contact 12.
When the movable contact 11 reaches the reference position P, it actuates the micro-mechanical switch 136 that switches in the switching position A.
The conditioning circuit 135 is electrically connected in parallel with the coil arrangement 132.
If an energy discharger circuit 137 is present, this latter is electrically disconnected from the conditioning circuit 135.
The conditioning circuit 135 is now capable of modifying the electric behaviour of the coil arrangement 132.
In this case, the impedance values Z_T and inductance values L_T of the coil arrangement 132, which are continuously measured by the control unit 14, show relevant variations with respect to the characteristic values Z_TC and L_TC.
The control unit 14 thus determines that the movable contact 11 has reached (and possibly overrun) the reference position P while moving away from the fixed contact 12. Conveniently, the conditioning circuit 135 remains electrically connected in parallel with the coil arrangement 132 up to the completion of the opening manoeuvre and while the switching device 1 is in the opening condition (figure 2).
If an energy discharger circuit 137 is present, this latter remains electrically disconnected from the conditioning circuit 135.
The switching device 1 is now supposed to be in an opening condition (figure 2).
The micro-mechanical switch 136 is in the switching position A and the conditioning circuit 135 is electrically connected with the coil arrangement 132.
If an energy discharger circuit 137 is present, this latter is electrically disconnected from the conditioning circuit 135.
When a closing manoeuvre is carried out (figure 5), the mobile contact 11 will necessarily pass again through the reference position P while moving towards the fixed contact 12. When the movable contact 11 reaches or overruns the reference position P, the micro-mechanical switch 136 switches in the switching position B.
The conditioning circuit 135 electrically disconnects from the coil arrangement 132 and it remains in this switching position B.
If an energy discharger circuit 137 is present, this latter electrically connects in parallel with the conditioning circuit 135 and it remains in this condition.
In this case, the energy discharger circuit 137 suitably facilitates the transient discharging process of the conditioning coil 1350 and of the capacitor 1352 included in the conditioning circuit 135.
During the closing manoeuvre of the switching device 1, the control unit 100 may execute the determination process 101.
If the impedance values Z_T and the inductance values L_T of the coil arrangement 132, which are measured by the control unit 14, show relevant variations with respect to characteristic values Z_TC and L_TC of said coil arrangement, the control unit 14 determines that the movable contact 11 has not reached the reference position P while moving towards the fixed contact 12.
If the impedance values Z_T and the inductance values L_T of the coil arrangement 132, which are measured by the control unit 14, show no relevant variations with respect to characteristic values L_TC of said coil arrangement, the control unit 14 determines that the movable contact 11 has reached or overrun the reference position P while moving towards the fixed contact 12. The switching device, according to the present invention, provides relevant advantages with respect to the state of the art.
Thanks to the arrangement of the conditioning circuit 135, the position of the mobile contact 11 may be determined with a high level of accuracy even in critical operating, e.g. during an opening manoeuvre when the mobile contact 11 is at a large distance from the fixed contact. The conditioning circuit 135 allows determining the position of the mobile contact 11 in the above-mentioned critical conditions without adopting dedicated position sensors.
The determination methods 100, 101 of the position of the movable contact 11 can be easily implemented in practice and they require relative small calculation resources for being carried out by the processing unit 14.
The conditioning circuit 135 has a compact structure that and it may be produced at industrial level at competitive costs.
Th switching device 1 is thus relatively simple and cheap to produce at industrial level with respect to similar devices of the state of the art.

Claims

A switching device (1) for medium voltage applications comprising:
- one or more electric poles, each comprising a movable contact (11) and a fixed contact (12) adapted to be coupled or uncoupled during a switching operation of said switching device;

- an electromagnetic actuator (13) comprising a magnetic core (131), a coil arrangement (132) wound around said magnetic core and a movable plunger (133) operatively coupled to the movable contacts of said electric poles;

- a control unit (14) for controlling switching operations of said switching device;
characterised in that said electromagnetic actuator (13) comprises a conditioning circuit (135) adapted to modify the electric behaviour of said coil arrangement (132) when said conditioning circuit is electrically connected with said coil arrangement, said conditioning circuit being electrically connected with or disconnected from said coil arrangement, when said movable contact (11) reaches or overruns a reference position (P) during a switching operation of said switching device.
A switching device, according to claim 1, characterised in that said conditioning circuit (135) is electrically connected with said coil arrangement (132), when said movable contact (11) reaches or overruns said reference position (P), during an opening manoeuvre of said switching device.
A switching device, according to one of the previous claims, characterised in that said conditioning circuit (135) is electrically disconnected from said coil arrangement (132), when said movable contact (11) reaches or overruns said reference position (P), during a closing manoeuvre of said switching device.
A switching device, according to one of the previous claims, characterised in that said conditioning circuit (135) is adapted to cause variations of impedance and inductance values (Z_T, L_T) of said coil arrangement (132) with respect to characteristic impedance and inductance values (Z_TC, L_TC) of said coil arrangement, when said conditioning circuit is electrically connected with said coil arrangement.
A switching device, according to claim 4, characterised in that said conditioning circuit (135) consists of a RLC circuit including a conditioning coil (1350), a resistor (1351) and a capacitor (1352) electrically connected in series.
A switching device, according to one of the previous claims, characterised in that said electromagnetic actuator (13) comprises a micro-mechanical switch (136) actuatable by said movable plunger (133) to electrically connect or electrically disconnect said conditioning circuit (135) with or from said coil arrangement (132).
A switching device, according to claim 6 characterised in that said micro-mechanical switch (136) electrically connects said conditioning circuit (135) with said coil arrangement (132), when said movable contact (11) reaches or overruns said reference position (P) during an opening manoeuvre of said switching device.
A switching device, according to claim 6 or 7 characterised in that said micro-mechanical switch (136) electrically disconnects said conditioning circuit (135) from said coil arrangement (132), when said movable contact (11) reaches or overruns said reference position (P) during a closing manoeuvre of said switching device.
A switching device, according to one of the previous claims, characterised in that said electromagnetic actuator (13) comprises an energy discharger circuit (137) electrically connectable with or disconnectable from said conditioning circuit (135).
A switching device, according to claims 9, characterised in that said energy discharger circuit (137) is electrically connected with said conditioning circuit (135), when said conditioning circuit is electrically disconnected from said coil arrangement (132).
A switching device, according to claim 6 and one of the claims from 9 to 10, characterised in that said micro-mechanical switch (136) is actuatable by said movable plunger (133) to electrically connect or electrically disconnect said energy discharger circuit (137) with or from said conditioning circuit (135).
A switching device, according to claim 11 characterised in that said micro-mechanical switch (136) electrically disconnects said energy discharger circuit (137) from said conditioning circuit (135), when said movable contact (11) reaches or overruns said reference position (P) during an opening manoeuvre of said switching device.
A switching device, according to claim 11 or 12 characterised in that said micro-mechanical switch (136) electrically connects said energy discharger circuit (137) with said conditioning circuit (135), when said movable contact (11) reaches or overruns said reference position (P) during a closing manoeuvre of said switching device.
A switching device, according to one or more of the previous claims, characterised in that said control unit (14) is adapted to carry out a determination method (100) of the position of said mobile contact (11) during an opening operation of said switching device, said determination method comprising the following steps:
- measuring impedance and inductance values (Z_T, L_T) of said coil arrangement (132);

- checking whether the measured impedance and inductance values (Z_T, L_T) show variations (Δ_Z, Δ_L) exceeding corresponding threshold values (Z_TH L_TH) with respect to characteristic impedance and inductance values (Z_TC, L_TC) of said coil arrangement;

- determining that said mobile contact (11) has reached or overrun said reference position (P), if the measured impedance and inductance values (Z_T, L_T) show variations (Δ_Z, Δ_L) exceeding said corresponding threshold values (Z_TH L_TH);

- determining that said mobile contact (11) has not reached said reference position (P), if the measured impedance and inductance values (Z_T, L_T) show no variations (Δ_Z, Δ_L) exceeding said corresponding threshold values (Z_TH L_TH).
A switching device, according to one or more of the previous claims, characterised in that said control unit (14) is adapted to carry out a determination method (101) of the position of said mobile contact (11) during a closing operation of said switching device, said determination method comprising the following steps:
- measuring impedance and inductance values (Z_T, L_T) of said coil arrangement (132);

- checking whether the measured impedance and inductance values (Z_T, L_T) show variations (Δ_Z, Δ_L) exceeding corresponding threshold values (Z_TH L_TH) with respect to characteristic impedance and inductance values (Z_TC, L_TC) of said coil arrangement;

- determining that said mobile contact (11) has reached or overrun said reference position (P), if the measured impedance and inductance values (Z_T, L_T) show no variations (Δ_Z, Δ_L) exceeding said corresponding threshold values (Z_TH L_TH);

- determining that said mobile contact (11) has not reached said reference position (P), if the measured impedance and inductance values (Z_T, L_T) show variations (Δ_Z, Δ_L) exceeding said corresponding threshold values (Z_TH L_TH).