WO2013128266A1

WO2013128266A1 - Secure measurement system for current and/or voltage in a high or very high voltage electrical line

Info

Publication number: WO2013128266A1
Application number: PCT/IB2013/000330
Authority: WO
Inventors: Giuseppe Bertolini; Alessandro MAGGI; Fabrizio Lucini
Original assignee: Bertel S.P.A.
Priority date: 2012-03-01
Filing date: 2013-02-21
Publication date: 2013-09-06
Also published as: ITMI20120316A1

Abstract

A system for measuring the electrical quantities in each phase of a medium, high or very high voltage overhead or cabled electrical line, said electrical quantities being the current and/or voltage of said phase, said system comprising means (10), cooperating with said phase, for measuring each electrical quantity, and transfer means (11) to transfer each measurement datum to a control station for the electrical line; the measurement means (10) are associated with a coupling capacitor (1) comprising an internal capacitor (8) to which each measurement datum is transferred, said measurement means being powered via the internal capacitor, the measurement data being sent to the base of said coupling capacitor.

Description

SECURE MEASUREMENT SYSTEM FOR CURRENT AND/OR VOLTAGE IN A HIGH OR VERY HIGH VOLTAGE ELECTRICAL LINE

The present invention relates to a secure measurement system for the electrical quantities of a medium, high or very high voltage electrical line in accordance with the introduction to the main claim.

With reference to said three-phase medium, high or very high voltage electrical lines, for each phase it is known to dispose of means for measuring at least one electrical quantity (current and/or voltage) associated with that phase, in order to maintain the electrical line under control (or rather the line power state), to define the energy circulating therethrough and to verify if temporary distortions in the electrical signal exist which could create problems for the final users connected to the electrical line.

Said control also enables the line to be protected from short circuits or overvoltages which could arise locally and then be transferred along the line. To measure at least one electrical quantity of a high voltage alternating current line, oil or gaseous SF₆ transformers are currently used connected to each phase and earthed via suitable insulated supports specifically provided for this purpose. By way of these supports the measured current and/or voltage datum reaches the transfer means which send it along an electrical connection, for example a cable, connected to a control centre by which the line is kept under control.

EP 1624311 and EP 1624312 describe solutions in which the measurement means are not directly connected to the electrical lines, but measure these latter via a suitable insulator interposed between the line and said measurement means.

A similar solution is described in US 4859925 which describes the measurement of line parameters achieved by members close to (but separated from) a medium voltage electrical line inserted into an insulator structure.

US 4575710 describes an automatic test system for testing t he functionality of units carrying a transmission line which, although using conveyed waves for transmitting measurement data does not describe a system for measuring currents and voltages of a line in a manner completely insulated from earth. However, these transformers present various drawbacks. For example, they can undergo oil leakages or moisture infiltration which can result in a reduction in insulation until its total disappearance, with obvious consequences such as electrical discharges from line to earth and even the explosion of the transformer and its support.

The same can also happen where oil is replaced by gaseous SFe used as insulant (of very high insulation), a use which requires pumps to maintain the gas under pressure; if the pressure falls, the same consequences could arise as in the case of lack of oil in the aforesaid transformers.

US2008/0077336 describes a device for measuring at least one characteristic electrical quantity, i.e. current and/or voltage, of a signal present in each phase of an overhead high or very high voltage electrical line.

This device comprises, connected to that phase, current or voltage measurement means or sensors for measuring the corresponding electrical characteristic; the sensors are connected to measurement transfer means arranged to send the measurement data to a station for monitoring the electrical line feed.

In the aforesaid prior patent, the measurement means and transfer means are physically separated, but are connected remotely via electromagnetic signals which enable the data measured by measurement means or sensors to be sent to the transfer means and from there to the monitoring station. A similar solution is described in WO2010/009413.

However these known devices and correlated operative methods present various drawbacks. Firstly, the electromagnetic signals used to transfer data from the measurement means (associated with the electrical line phase) to the transfer means (positioned on the ground) are sensitive to external radio or electromagnetic signals, preventing correct communication between these means. Moreover, atmospheric agents (such as snow or ice) which accumulate on the ground positioned transfer means (when the known solution is used in impervious, cold territories distant from inhabited centres) interfere with communication via electromagnetic or radio waves between the measurement means and transfer means, with possible prevention of transfer of the measurement data obtained, and hence incorrect control of the overhead line. To this should be added that even the presence of animals between the measurement means and the transfer means or just very low temperatures can negatively influence data transfer between the measurement means and the transfer means.

Moreover, at least some of the aforesaid known solutions mainly enable correct measurement (and hence correct control) of the current flowing in the line, but not of the voltage. This latter measurement is in fact influenced during data transfer by the electromagnetic field present between phase pairs.

Consequently an object of the present invention is to provide a secure and effective system for measuring the electrical quantities of current and voltage in each phase of a medium, high or very high voltage.

A particular object of the invention is to provide a system of the aforesaid type by which current discharges to earth are avoided while at the same time adequately measuring the current and/or voltage in a corresponding phase of the electrical line. A further object is to provide a system the use of which is not influenced by atmospheric conditions, by local electromagnetic interferences or by the presence of animals.

Another object is to provide a system of the stated type which is quickly assembled, is of low cost and enables certain and direct measurement of said electrical quantities.

Another object of the invention is to provide a system of the aforesaid type which does not require particular insulation expedients as it operates at line voltage i.e. is directly connected to it, and is in any event able to operate independently of atmospheric conditions.

These and other objects which will be apparent to the expert of the art are attained by a system in accordance with the accompanying claims.

The present invention will be more apparent from the accompanying drawings, which are provided by way of non-limiting example and in which:

Figure 1 is a front view of the system according to the invention;

Figure 2 is a schematic block diagram of part of the system of Figure 1 ;

Figure 3 is a schematic view of part of the system according to the invention, in a variant thereof.

With reference to said figures, a system according to the invention comprises a usual column-type coupling capacitor 1 connected in any known manner to the phase F of a high voltage overhead electrical line L of three-phase type (of which only one phase is shown in the figures).

This capacitor is of known type and may be commonly used for conveyed wave transmission on the corresponding phase of the line L.

The column-type coupling capacitor 1 comprises, in known manner, a base 2 positioned on a support positioned on the ground under line L and from which an insulator member 3 upwardly extends. On the top or end part of this latter there is a widened portion 4 from which a high voltage terminal 5 projects, connected to the phase F. The insulator member 3 comprises a usual internal capacitor 8 connected to usual electrical members and devices 9 positioned in the base 2 and arranged to also enable transmission of conveyed waves with frequencies between 40 KHz and 1 MHz.

The said column-type capacitor 1 is used as an earthed support member for means 10 for measuring the current and voltage of the phase F of line L or of the electrical signal circulating within it. These measurement means are directly connected to the line L and therefore are at the same voltage as the line. The measurement means are in particular associated with and fixed to the portion 4 of the insulator member 3 and are connected to the internal capacitor 8 in order to be able to transfer to the base 2 of the column-type capacitor 1 via said internal capacitor 8 the data obtained from the voltage and current measurements. Said data are then sent to transfer means 11 which transfer them to a line L control station possibly positioned very far from the place in which the measurement takes place. By means of the internal capacitor 8, the measurement means 10 are also synchronized and powered from earth.

More particularly, the measurement means 10 comprise, for measuring the current in the phase F, at least one device or member 15 directly connected to the high voltage line (and hence without any insulation requirement). This device 15 can be a current transformer, Rogowski cells, anti-inductive resistors or similar members. The means 10 also comprise a device or member 18 for measuring the voltage of the phase F which is also connected to the high voltage line without any interposed insulator. The device 18 can be a voltage transformer, series-connected resistors connected to the phase F of the line L or similar members.

These measurement devices 15 and 18 are directly connected to an analogue/digital converter 19 connected to a microprocessor unit 26. A low pass filter 21 connected to the internal capacitor 8 is positioned between the terminal 5 and the phase F, the voltage measurement device 18 being positioned between the filter 21 and the line L. The filter 21 bars signals from the devices 15 and 18 through the analogue/digital converter 19 and the microprocessor 26 from passing into the line L, these signals relating to measured current and voltage data, which are hence directed towards earth via the internal capacitor 8. This takes place via a band pass filter 40 which connects the microprocessor 26 to the line. The entire aforestated electronic part connected to the measurement devices 15 and 18 is directly connected to these latter and to the high voltage line; this part has no insulation to said line. The filter 21 also bars signals originating from the base and sent to a band pass filter 20.

This band pass filter 20 is connected to the coupling capacitor 8 and to the microprocessor 26; the filter 20 is also connected to a feed member 50 for the entire measurement means 10. The member 50, for example, is an electrical circuit comprising capacitors, rectifiers and equivalent elements arranged to feed the members of the means 10 at the correct voltage. By way of the internal capacitor 8 and the band pass filter 20, each element of the measurement means 10 (i.e.: the measuring devices 15, 18; the converter 19; the microprocessor 26; the filters 21 and 40) is remotely powered electrically, i.e. powered at a distance from the ground, by the transfer means 11. As in the case of data exchange, this powering is achieved via the internal capacitor 8 physically present in the capacitor 1 , in a protected position within this latter. The filter 20 receives from the means 11 a signal at a frequency Fi which is used to power the means 10 and to provide a synchronization signal to the microprocessor 26. In contrast, the band pass filter 40 generates a signal at a frequency F₂ which conveys the measurement data, measured by the members 15 and 18, to the means 11.

Advantageously, the column-type coupling capacitor 1 can support two measurement means of identical conformation, the first measurement means 10N operating as usual (or "normal") measurement means, the second measurement means 10R operating as "reserve". As shown in Figure 3, the (remote) feed to the measurement means 10N and 10R is common to both at phase F of the line L, whereas in proximity to this latter there is a change-over switch 25 which can selectively connect the means 10N and 10R to the transmission means 11 positioned in the base 2 of the capacitor 1 , these means 11 being advantageously split into normal transmission means 11 N and reserve transmission means 11 R. At these latter, a change-over switch 30 enables the signals originating selectively from the transmission means 11 N or 11 R to be received simultaneously by means 10N and 10R.

In Figure 3, the measurement means 10N and 10R are defined by way of example as two components, 80 and 81. The first acts as a transmitter modulator and the second as a receiver demodulator. Each component 81 receives the signal at frequency Fi emitted by the means 11 , while each component 80 generates the signal at frequency F₂. These components are not indicated in Figure 2 in the scheme of the means 10 for simplicity and clarity. Similar components 82 and 83 (transmitter modulator and receiver demodulator) are shown schematically in the means 11 N and 11 R. Each component 82 receives the signal at frequency F-i , while each component 83 is able to receive the signal at frequency F₂.

The aforedescribed "split" solution makes direct measurement of the circulating current and voltage present in and on phase F of the line L more secure in that, in the case of a fault in one of the measurement means 10 or in one of the transmission means 11 , the other measurement means or transmission means can come into operation.

As stated, the transmission means 11 (or 11 N and 11 R) comprise a high frequency signal transmitter modulator 82 connected to the internal capacitor 8 to generate the power and synchronization signals (of frequency Fi) for the measurement means 10. These latter generate a signal at frequency F₂ with the data from the measurements carried out, which are received by the receiver demodulator 83. These data, addressed to the demodulator 83 are addressed via a network 37 such as a LAN or fibre optic, to a remote control station. The connection can take place preferably with IEC61850 protocol.

By virtue of the invention, correct operation of the measurement means 10 can be maintained (powered even if line L voltage or current is lacking), together with secure data transfer to the remote control station. In this respect, the existing connections between the means 10 and 11 via the internal capacitor 8 are internal to the capacitor 1 ; moreover the transfer means 11 can be located in a protected position close to the base 2 or in an individual protected position close to or distant from the base 2. As signal transmission from and to the measurement means takes place via the internal capacitor 8, the system of the invention is not influenced by atmospheric agents (such as snow or ice), or by the possible presence of wild animals, and does not require human intervention on site for its operation.

The signals transferred by the means 11 can also contain a time reference (time mark) which enables the measurements to be sampled with time precision. By virtue of the fact that the system of the invention uses a coupling capacitor, as these latter are usually utilized along medium, high and very high voltage lines, implementation of the invention is simplified and of low cost.

One embodiment of the invention has been described. Others are possible such as that in which the means 10 and 11 are duplicated (as in the solutions of Figure 3) and in which both always operate during current and voltage measurement, the means 11 being able to receive the measurement data from any one of these means 10 by simply switching the position of the switches 25 and 30.

Other solutions are possible while remaining within the scope of the following claims.

Claims

1. A system for measuring the electrical quantities, namely current and/or voltage, of a signal present in each phase of a medium, high or very high voltage overhead or cabled electrical line, said system comprising means (10), cooperating with said phase, for measuring each electrical quantity, and transfer means (11 ) for transferring each measurement datum to a control station for the electrical line, the measurement means (10) and the transfer means (11) being associated with a column-type coupling capacitor (1 ), an internal capacitor (8) being present within this latter, characterised in that said measurement means (10) are directly connected to the respective phase (F) of the electrical line (L), without interposing insulating members or structures, said measurement means (10) and said transfer means (11 ) being connected together via said internal capacitor (8), the measurement data relative to said current and said voltage being transferred along said connections from the measurement means (10) to the transfer means (11), said measurement means being remotely powered and synchronized via the same internal capacitor (8).

2. A system as claimed in claim 1 , characterised in that said transfer means (11 ) are associated with a base of the coupling capacitor.

3. A system as claimed in claim 1 , characterised in that the transfer means are separated from the column-type coupling capacitor (1 ) but are electrically in contact with said measurement means (10).

4. A system as claimed in claim 1 , characterised in that said measurement means (10) comprise a member (15) for measuring the current circulating within the line and a member (18) for measuring the voltage in the line (L), said members (15, 18) being directly connected to the corresponding phase (F) of said line (L).

5. A system as claimed in claim 4, characterised in that the electric current measuring member (15) is chosen from a resistive element, preferably of anti- inductive type, a current transformer with a magnetic core, a Rogowski coil, an electromagnetic field sensor, or a similar measurement member.

6. A system as claimed in claim 4, characterised in that the voltage measuring member (18) is chosen from a voltage transformer, series-connected resistors connected to the phase (F) of the electrical line (L), or similar measurement members.

7. A system as claimed in claim 1 , characterised by comprising two measurement means (10N, 10R) positioned on each phase (F) of the overhead line (L) and corresponding transfer means (11 N, 11 R), said measurement means (10N, 10R) being always both powered, but only the data of one of said measurement means being sent to the transfer means (11 N, 11 R).

8. A system as claimed in claim 1 or 7, characterised in that the measurement means (10) are associated with an end part of the column-type coupling capacitor (1) close to the electrical line (L) such as to be directly connected to this latter.

9. A system as claimed in claims 1 and 4, characterised in that the measurement means (10) comprise a band pass filter (20) connected to the internal capacitor (8) of the column-type coupling capacitor (1) and receiving a signal at a first frequency (F-i) from the transfer means (11 ), said filter (20) being positioned between said internal capacitor (8) and a microprocessor unit (26), and a feed member (50) arranged to power the measurement means (10) via said first frequency signal generated by the transfer means (11 ), said microprocessor unit being connected to an analogue/digital converter (26) connected to said current (15) and voltage (18) measurement members, the voltage measurement member (18) being connected to a band pass filter (21 ), said microprocessor unit being connected to a band pass filter through which a signal at a second frequency (F2) containing the measurement data is sent to the transfer means (11 ).

10. A system as claimed in claim 1 , characterised in that the transfer means (11 ) comprise a high frequency signal generator/transmitter (82) to feed and synchronize the measurement means (10) via the signal at first frequency (F-i).

11. A system as claimed in claim 1 , characterised in that the transfer means (11 ) comprise a receiver demodulator (83) arranged to receive the measurement data sent by the measurement means (10) and to transfer them to a network (37) connected to the control station.

12. A system as claimed in claim 1 , characterised in that the measurement means (10) comprise a transmitter modulator (80) arranged to send the obtained current and voltage measurement data to the transfer means (11 ) with the signal at the second frequency (F₂).

13. A system as claimed in claim 1 , characterised in that the measurement means (10) comprise a receiver demodulator (81 ) arranged to receive the signal at first frequency (F-i) generated by the transfer means (11) with which these latter feed and synchronize said measurement means (10).