NL2021408B1

NL2021408B1 - Monitoring system of a medium-voltage electric power network, and method thereto

Info

Publication number: NL2021408B1
Application number: NL2021408A
Authority: NL
Inventors: Tillema Johannes; Ginus Richard; Kerstens Wesley
Original assignee: Tryst B V
Priority date: 2018-07-27
Filing date: 2018-07-27
Publication date: 2020-01-31
Also published as: WO2020022875A1; WO2020022875A8; EP3830587A1

Abstract

Monitoring system for monitoring a medium-voltage electric power network, which can be defined as a network on an operating voltage of approximately 3 kV to 25 kV, the system comprising at least one monitoring device and a controller arranged to receive and analyse signals from the at least one monitoring device.

Description

The invention relates to a monitoring system of a medium-voltage electric power network.

A medium-voltage electric power network can be defined as a network on an operating voltage of approximately 3 kV to 25 kV, and can generally serve an area including a group of houses, for example a street of houses, or a single larger building, such as an industrial plant. The mediumvoltage network includes transformer stations where high voltage power is transformed into medium-voltage power, as well as transformer substations or distribution substations of an electric power system, where medium voltage power is transformed into low voltage power which is then supplied to individual users. Grid operators managing a medium-voltage power network can be faced with different types of problems, such as for example short circuits in the medium-voltage power network, which affect a relatively large number of people. Therefore, it is important to be able to detect as soon as possible where the problem has occurred within the network in order to disconnect that part from the rest of the grid. Thereto, medium-voltage transformer substations can for example be provided with load-break switches, fused load-break switches and/or circuit breakers. The load-break switches, which are arranged to deviate current in case of an overload, can for example be provided with a visual indicator, such as a red light, indicating that an error, such as a current with a too high amperage, has passed the load-break switch. When such a problem has occurred on the medium-voltage power network, an employee of the grid operator has to go to one or more of these transformer substation to detect where the problem has occurred before he can intervene and isolate the part of the network that is concerned. This may be a time-consuming process at a moment when a relatively large number of users, houses, and thus people, may be affected by an interruption of power supply. Recently, some of these transformer substations have been equipped with communication means to communicate the occurrence of a problem on the medium-voltage power network to a central grid operator managing system. However, also in this case, the grid operator is only warned of a problem after the problem has occurred, and still has to send an employee to the transformer substation to intervene. Moreover, it has turned out that the installation of such a communication means in a transformer substation may be relatively cumbersome, as these transformer substations may be relatively small with no or only limited access for people, and hardly any space for installing a communication device for example with fiberglass cable connection. It is further known to mount one or more current and/or voltage sensors in a transformer station, but not in transformer or distribution substations, to monitor current and/or voltage of the high-voltage network and give a warning in case of a peak current and/or voltage above a given threshold value. Such sensors can for example be based on the Hall-effect or on the Zeeman-effect, or on any other known concept. However, measurements with, for example, a Hall sensor cannot give a sufficient accuracy because the measured value is very dependent on the distance to the measured current. Moreover, the threshold value of a Hall sensor is not adjustable once the Hall sensor has been mounted. Additionally, as a Hall sensor is mounted around a current conductor, the current on the network needs to be cut-off in order to mount a Hall-sensor into a network, which affects a relatively large number of people and is thus undesirable.

It is an object of the present invention to solve or alleviate one or more of the above-mentioned problems. Particularly, the invention aims at providing a monitoring system of a medium voltage network which can allow to detect possible problems before problems on the medium voltage network arise.

To this aim, according to a first aspect of the present invention, there is provided a monitoring system according to the features of claim 1. In particular, the monitoring system for monitoring a medium-voltage electric power network comprises at least one monitoring device including an LC-circuit arranged to measure an amplitude of a current of the mediumvoltage network, an A/D convertor arranged to convert an analog input of the measured amplitude of the current into a digital output corresponding to a current of the medium-voltage network, and a communication interface connected to the A/D convertor and arranged to send a signal to a controller when a current is detected above or below a predetermined threshold of current. The monitoring system further comprises a controller arranged to receive and analyse signals from the at least one monitoring device. As is known to the person skilled in the art, an LC-circuit comprises at least an inductor L and a capacitor C, and may for example also comprise a resistor R, which can stabilize the current measurement. In an inventive way, the LC-circuit can be used to measure an amplitude of a current of the mediumvoltage network, in particular of a current going through a load-break switch in a medium-voltage transformer substation, in that the current induced in the LC-circuit by the magnetic field which is generated by the current in the medium-voltage network is a measure for the amplitude of the current in the medium-voltage network. An inductor of the LC-circuit is used as a pick-up coil for the magnetic field generated by the current in a current conductor of the load-break switch. This is contrary to the normal use of an LC-circuit as a filter, in which application the inductor is generally protected from external magnetic fields. By putting a capacitor in parallel with the inductor, the inductor’s imaginary reactive impedance can be cancelled out, which can increase the energy transfer from the magnetic field and can create an effect of a notch filter rejecting electro-magnetic interference, ensuring in this way that only the current flowing through the current conductor of the load-break switch is measured. Advantageously, the use of an LC-circuit allows a contactless measurement of the current in the medium-voltage network. Moreover, as the LC-circuit in itself does not need to be powered, for example by a battery, to function, the current can be measured continuously instead of a measuring at sampled time intervals. A signal conditioning device or an interpretation circuit, arranged to derive the current in the medium-voltage network from the measured amplitude of current in the LC-circuit, and which device or circuit may for example be part of the A/D-convertor, can function with only a relatively small energy supply. The communication interface can be arranged to send a signal to a controller only when the derived current is above or below a predetermined threshold of current, which threshold may be a programmable value in the communication interface or in the A/D-convertor, and not a feature of the current measuring device, as is the case with a Hall sensor, which is calibrated for a given value of magnetic field strength. The communication interface can for example include a programmable digital comparator to compare the derived value of current in the medium-voltage network based on the measured amplitude of current in the LC-circuit with one or more pre-determined threshold values, for example with a lower threshold and an upper threshold. Alternatively, and preferably, the A/D-convertor can include a programmable analogue comparator to compare said derived value of current with one or more pre-determined current threshold values. This may for example be done at the level of the measured amplitudes of current in the LC-circuit, so before an interpretation circuit can derive the current in the medium-voltage network. In that case, the analogue signal including the derived current in the medium-voltage network can be converted into a digital signal after having compared the value with one or more predetermined threshold values, so for example only when a current value of the medium-voltage network is detected above or below one or more predetermined threshold values. This may be advantageous in terms of energy supply, as the energy consumption for the A/D conversion is higher than the energy consumption of an analogue comparator. An upper threshold can for example be programmed or set at approximately 450 A, which value may be equal to the value at which a load-break switch may react to a peak current, but can also be programmed at a lower value, for example at approximately 100 A, such that a trend of increasing load on the network can be detected before a problem arises, in particular by the controller of the monitoring system, which can analyse the measurements over time, and optionally store the measurements and/or analyses. When a lower threshold is for example set at 0 A, it may be used to detect an interruption of current. The communication interface may be a wired communication device or a wireless communication interface, and is arranged to send real-time signals of the real-time current measurements.

The monitoring device can preferably be arranged to measure current passing through a load-break switch of the medium-voltage electric power network, in particular through a load-break switch which is installed in a medium-voltage transformer substation and is arranged to deviate a current in case of overload. Such load-break switches may also be called switch disconnectors or switch gaps. In this way, the monitoring device can be installed at a relatively accessible location to monitor a medium-voltage network.

Advantageously, the monitoring device may mountable on a loadbreak switch of a medium-voltage electric power network without interruption of power on the network. A load-break switch generally comprises a first part, which may not be touched during maintenance as it is not guaranteed to be safe, and a second part, generally in a different colour to be clearly recognizable, and generally directed to a front side, which may be manipulated with the help of dedicated tools. Said second part at a front side of a load-break switch may therefore include tool connection elements, for example a pair of ridges, to allow connection between the load-break switch and such a dedicated tool. The monitoring device of the present invention can for example also include connection elements which correspond to, and can engage, the tool connection elements on the load-break switch. In this way, the monitoring device may be mounted on a load-break switch of a medium-voltage electric power network without interruption of power on the network. Alternatively, the monitoring device may be fixed on the load-break switch in another known way, such as clamped, glued, screwed or differently, as long as the monitoring device is mounted to the load-break switch at a fixed location.

The predetermined threshold is preferably adjustable. Thereto, the communication interface or the A/D convertor can for example include a programmable analogue or digital comparator, such that the predetermined threshold can be adjustable through programming or dedicated software. In this way, the threshold can for example be adjusted once a first threshold has been reached regularly, for example when part of the network is increasingly loaded over time.

The monitoring device may further advantageously comprise a fluxgate magnetic sensor. The magnetic flux-sensor can detect a magnetic field which is generated by the current in a current conductor of the medium-voltage electric power network, for example by the current in a load-break switch. Current measurements by such a magnetic flux-sensor are relatively accurate, and can provide additional information over the measurements by the LC-circuit, such as for example an absolute value of current in the medium-voltage network. The magnetic flux-sensor may further be arranged to provide an analogue output which is proportional to the current generating the detected magnetic field, for example through the flux-sensor being provided with a compensation circuit. In order to save energy, the magnetic flux-sensor may be arranged to do measurements only at pre-determined time intervals rather than measuring continuously. The combination of continuous measurements by the LC-circuit with interval measurements, which may be more accurate, can provide valuable information on a status of a medium-voltage electric power network and can allow precautionary actions to be taken, for example when part of the network shows an increasing load over time, rather than only allowing to intervene after a problem, such as a short-circuit due to an overload, has taken place and been reported by a known monitoring system. Alternatively, a Hall-sensor may be used, although measurements of a Hall-sensor are not substantially linear with respect to the current to be measured, as is the case for a fluxgate magnetic sensor.

The monitoring device may preferably further comprise a voltage sensor. The voltage sensor can for example include two conducting plates, for example copper plates, arranged around a current conductor of the medium-voltage network, each plate at a slightly different distance to the current conductor, between which plates a voltage difference generated by a current in said current conductor may be measured. This measured voltage difference, due to a different ratio of the distance between the conductor and the ground relative to the distance between the plates, may give an indication of the voltage on the current conductor. As a voltage occurring in a conductor of a medium-voltage network may be approximately 10 kV or more or less, such a voltage sensor is preferably configured to detect such relatively high voltage values, which is not necessarily the case for known voltage sensors. In this way, the voltage sensor can detect a voltage of a medium-voltage network at a distance of a current conductor. Such a contact-free measurement can allow a relatively safe installation of the sensor in spite of the presence of a medium-voltage network.

Monitoring system comprising a plurality of monitoring devices, wherein the monitoring devices are mounted at various locations within the medium-voltage electric power network during use. Different mediumvoltage transformer substations may for example be provided with one or more monitoring devices, preferably one monitoring device for every loadbreak switch, which devices may all be connected to a same controller. In this way, a comprehensive monitoring of a medium-voltage power network may be carried out, which monitoring allows precautionary actions to be taken on the network to prevent problems rather than repair the network after a problem has occurred. As such, the monitoring system can significantly reduce maintenance cost of the network as well as interruptions of power supply to the customers because of this maintenance.

According to a further aspect of the invention, there is provided a method for monitoring a medium-voltage electric power network having the features of claims 8-11. Such a method can provide one or more of the abovementioned advantages.

According to still a further aspect of the invention, there is provided a retro-fittable monitoring device having the features of claim 12 for a monitoring system of a medium-voltage electric power network. In this way, existing transformer substations of a medium-voltage electric power network can be provided with one or more of the monitoring devices in a relatively easy and economical way.

According to still a further aspect of the invention, there is provided a load-break switch for a medium-voltage electric power network, having the features of claim 13 comprising a monitoring device of a monitoring system. In case of building new transformer substations of a medium-voltage electric power network substation, the monitoring device can relatively easily be integrated into a load-break switch of such a new transformer substation.

According to still a further aspect of the invention, there is provided a use of a monitoring system in a medium-voltage electric power network substation having the features of claim 14. Such a use can provide one or more of the above-mentioned advantages.

The present invention will be further elucidated with reference to figures of exemplary embodiments. Corresponding elements are designated with corresponding reference signs.

Figures la shows a perspective view on a load-break switch provided with an embodiment in an exploded view of a monitoring device according to the invention in a transformer substation of a medium-voltage electric power network shown in Figure lb;

Figure 2 shows a perspective view on the load-break switch of Figure la provided with an embodiment of a monitoring device according to the invention;

Figure 3 shows a schematic circuit of an embodiment of a monitoring device of a monitoring system according to the invention.

Figures la and 2 show a perspective view on a load-break switch 1 provided with an embodiment of a monitoring device 2 of a monitoring system according to the invention. The monitoring device 2 is arranged to measure current passing through the load-break switch 1 of the mediumvoltage electric power network. Such a load-break switch 1 can for example be found in a transformer substation 3 of a medium-voltage electric power network, as shown for example in Figure lb. Such a transformer substation 3 of a medium-voltage electric power network can for example be situated in an industrial plant transforming medium voltage power into low voltage power and providing electric power to the entire plant. Such a substation 3 can also be situated near a group of houses, supplying electric power to for example all houses in a given street or area. These transformer substations 3 are generally equipped with load-break switches 1, fused load-break switches and/or circuit breakers and may further comprise other secondary equipment. In the embodiment of a transformer substation 3 as shown in Figure lb, there are for example nine load-break switches 1, in groups of three, each load-break switch 1 of a group of three being for one phase of the three-phase current. The load-break switch 1 can deviate current and/or isolate part of the network in case of a failure, such as an overload current. The load-break switches 1 can for example be provided with a visual indicator 4, such as a red light, indicating that an error, such as a current with a too high amperage, has passed the load-break switch 1. The loadbreak switch 1 generally includes a dark coloured part 5 which may not be touched as this part is not guaranteed safe when in operation, and a light coloured front part 6 into which a dedicated tool can be clamped to remove the load-break switch 1 from the network if necessary. Thereto, the lightcoloured front part 6 can for example include two flanges 7 which are spaced-apart and between which a tool receiving space 8 is formed. The shape of the flanges 7, for example an inversed L-shape, or any other suitable shape, can be such that a tool can be clamped in between said two flanges. As these flanges 7, or any other tool clamping system, is usually provided on a load-break switch, the invention can make use of the existing clamping system to mount a monitoring device 2 of a monitoring system to the load-break switch 1. The system can for example comprise two mounting plates 9 which can be clamped in the existing clamping system, for example in the flanges 7, and onto which the monitoring device 2 can be fixated, for example by screws 10 or bolts or any other suitable fixating means. For other types of load-break switches, or other types of tool clamping systems on the front part 6 of the load-break switch, other mounting systems may be developed, as long as in this way, the monitoring device 2 is mountable on a fixed location on the load-break switch 1 of a medium-voltage electric power network without interruption of power on the network. The light-coloured front part 6 or panel can for example also comprise the visual indicator 4, which may then be covered by the monitoring device 2. The monitoring device 2 itself may comprise a housing 11 enclosing a printed circuit board

12.

Figure 3 shows a schematic circuit of an embodiment of a monitoring device 2 of a monitoring system according to the invention. The circuit can for example be implemented on a printed circuit board 12, as shown in Figure la. The monitoring device 2 at least includes an LC-circuit

13, an A/D convertor 14, and a communication interface. The LC-circuit 13 includes an inductor L and an capacitor C. The LC-circuit 13 may further comprise a resistance R, connected in parallel with the inductor L and the capacitor C, which can make the LC-circuit more stable. Between the LCcircuit 13 and the A/D convertor 14, a diode 15 may be present to direct the current towards the A/D convertor 14 while preventing current from flowing back towards the LC-circuit 13. The A/D convertor 14 may include, or may be connected to, a micro-controller 16. Communication between the A/D convertor 14 and the micro-controller 16 may for example be arranged via an inter-integrated circuit 12C (or I²C) computer bus 17 and -protocol. The micro-controller 16 can preferably remain in a low power mode, unless a signal from the A/D convertor 14 activates the micro-controller 16. After activation of the micro-controller 16 by the A/D convertor 14, the microcontroller 16 can be arranged to send a signal to a controller (not shown) of the monitoring system when a current is detected above or below a predetermined threshold of current. As such, the micro-controller 16 can be considered as being the communication interface of the monitoring device 2, or can include the communication interface of the monitoring device 2. The predetermined threshold of current can be adjustable, as the threshold may be programmed on the micro-controller or on the A/D convertor, or programmed in a cloud and sent to the micro-controller. There may be a single threshold, for example an upper threshold of current, above which a signal needs to be sent to a controller, or there may be an upper and a lower threshold, the lower threshold for example being set close to zero, in order to send a signal to the controller also in case of no current detection at all. All the elements shown in the circuit which is represented in Figure 3 may be part of an integrated circuit, for example on a printed circuit board 12. The controller, which is part of the monitoring system, but not part of the monitoring device 2, may be spaced-apart from the at least one monitoring device 2. Such a controller may for example be a computer, and is arranged to receive and analyse signals from the at least one monitoring device 2.

Such a controller may for example be provided in a transformer substation 3, where the controller may be connected with the micro-controller 16 in a wired or in a wireless manner. Preferably, the controller may be provided outside a transformer substation 3, for example at a central monitoring location, where the controller may be arranged to receive and analyse signals from a plurality of monitoring devices 2 in one or more transformer substations 3. In order to improve the monitoring device 2, the circuit shown in Figure 3 may additionally comprise a fluxgate magnetic sensor and/or a voltage sensor, preferably integrated on the same printed circuit board 12.

For the purpose of clarity and a concise description, features are described herein as part of the same or separate embodiments, however, it will be appreciated that the scope of the invention may include embodiments having combinations of all or some of the features described. It may be understood that the embodiments shown have the same or similar components, apart from where they are described as being different.

In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word ‘comprising’ does not exclude the presence of other features or steps than those listed in a claim. Furthermore, the words ‘a’ and ‘an’ shall not be construed as limited to ‘only one’, but instead are used to mean ‘at least one’, and do not exclude a plurality. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to an advantage. Many variants will be apparent to the person skilled in the art. All variants are understood to be comprised within the scope of the invention defined in the following claims.

Claims

Conclusions

A monitoring system to monitor an electric medium voltage network, the system comprising:

- comprising at least one monitoring device

- an LC circuit adapted to measure an amplitude of a current of the medium voltage network;

- an A / D converter adapted to convert an analog input of the measured amplitude of the current to a digital output corresponding to a current of the medium voltage network;

- a communication interface connected to the A / D converter and adapted to send a signal to a control device when a current is detected above or below a predetermined threshold of current;

- a control device adapted to receive and analyze signals from the at least one monitor device.

The monitor system of claim 1, wherein the monitor device is adapted to measure current passing through a load-break switch of the medium-voltage electrical network.

A monitor system according to any one of the preceding claims, wherein the monitor device is mountable on a load break switch of an electric medium voltage network without interruption of current on the network.

A monitoring system according to any one of the preceding claims, wherein the predetermined threshold is adjustable.

The monitor system of any one of the preceding claims, wherein the monitor device further comprises a magnetic fluxgate sensor.

The monitor system of any one of the preceding claims, wherein the monitor device further comprises a voltage sensor.

A monitor system according to any one of the preceding claims, comprising a plurality of monitor devices, wherein the monitor devices are mounted at different locations within the medium voltage electrical network during use.

A method for monitoring an electric medium voltage network comprising the steps of

- providing at least one load-break switch in a transformer sub-station of the medium-voltage electrical network with a monitor device of a monitor system, for example a monitor system according to any one of the preceding claims, wherein the monitor device is adapted to measure at least one current flowing through the at least one load-break switch flows;

- setting a current threshold;

- continuously measuring the current flowing through the at least one load break switch;

- sending a signal to a control device of the monitoring system when a current above or below the predetermined current threshold is detected.

The method of claim 8, wherein the current flowing through the at least one load break switch is continuously measured by an LC circuit.

The method of claim 9, wherein the current flowing through the at least one load break switch is further measured by a fluxgate sensor at predetermined time intervals.

A method according to any one of the preceding claims 8-10, wherein the step of providing at least one load break switch in a transformer sub-station of the medium-voltage electrical network with the monitoring device of the monitoring system, for example a monitoring system according to any of the preceding claims 1-7, wherein the monitor device is adapted to staple at least one current flowing through the at least one load break switch, without interrupting current through the load break switch.

A retro-buildable monitor device for a monitor system according to any of the preceding claims 1-7, wherein the monitor device is mountable on a load break switch of a medium-voltage electrical network without interruption of current on the network.

A load break switch for a medium voltage electrical network, comprising a monitor device for a monitor system according to any one of the preceding claims 1-7, wherein the monitor device is integrated in the load break switch.

Use of a monitoring system according to any of the preceding claims 1-7 in an electric medium voltage network substation.