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Combined Optical Sensor and Capacitor Voltage Divider Arrangement for Voltage Control in Medium Voltage Switchboard Fiber
Available online at www.sciencedirect.com
ScienceDirect Procedia Engineering 168 (2016) 1597 – 1600
30th Eurosensors Conference, EUROSENSORS 2016
Combined optical sensor and capacitor voltage divider arrangement for Voltage control in Medium Voltage Switchboard Fiber Letizia De Mariaa 1, Daniele Bartalesia, Natale Claudio Pistonib a
Department of Technologies for Transmission and Distribution - RSE Research on Energetic System S.p.A, Milan, Italy b Optoelectronics and Fibre Optics Consultant, 20090 Assago, Milan, Italy
Abstract
The integration in a capacitor voltage divider of an optical sensor, based on a double electro-optic crystals and on a standard single mode fiber arrangement, has been proposed as a way to obtain a low cost, accurate and intrinsically safe voltage sensor for an on line control of the voltage parameters in Medium Voltage (MV) switchboard. A compact and miniaturized optical prototype based on a back reflected layout has been previously designed, assembled and characterized on a laboratory mock up. In this work it has been successively inserted in a capacitor voltage divider circuit to preliminary evaluate the feasibility of the whole voltage control system for application to protective equipment. From preliminary electrical characterizations it turns out that the measurement error with the adopted configuration of this voltage device is lower than 3% full scale confirming its suitability for protection and voltage control. © Published by Elsevier Ltd. This © 2016 2016The TheAuthors. Authors. Published by Elsevier Ltd.is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of the 30th Eurosensors Conference. Peer-review under responsibility of the organizing committee of the 30th Eurosensors Conference Keywords: Fibre optic sensor, optical Voltage sensor, distribution network, Medium Voltage equipment; protective voltage transformer.
1. Introduction The availability of real time and capillaries information on the status of electrical equipment will be more and more important to achieve higher flexibility and reliability as required for the development of the new Distribution network[1]. With this aim an innovative approach to the control of electrical components of Medium Voltage (MV) substations is gradually occurring. The development of a new family of “smart” electrical components, with incorporated reliable, safe and cheap sensors with measuring and/or actuation functions, is the first step to achieve 1
* Corresponding author. Tel.: +39-02-39924686; fax: +39-02-39925557. E-mail address: [email protected]
1877-7058 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of the 30th Eurosensors Conference
doi:10.1016/j.proeng.2016.11.469
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Letizia De Maria et al. / Procedia Engineering 168 (2016) 1597 – 1600
distributed information on electrical parameters along the network. Recently novel non-conventional sensors have been proposed for monitoring the operating parameters (voltage, current, phase) in Medium Voltage (MV) switchboard at their energized phase terminals [2]. They are generally based on miniaturized resistive or capacitive s transducers. Alternative optical solutions based on electro-optic materials, which change the polarization of the light passing through them, when they are subjected to electric fields, have been also recently examined [3]. Indeed optical sensors, for their intrinsic high electromagnetic immunity characteristics, can be safely incorporated in MV electrical components. As for non-conventional transducers, optical sensors should be designed to guarantee a high voltage accuracy (i.e. 3% voltage error when used to supply protective equipment), robustness, compactness and they should be also significantly low cost; this last requirement is important in view of a widespread installation of optical sensors in new or in exiting MV switchboards. Recently the Authors reported in [4,5] an optical device based on two electro-optic Lithium Tantalate (LiTO3) crystals, chosen as optical transducers, potentially suitable for an accurate measure of the AC phase voltage of a MV switchboard. Main feature of the proposed optical approach is its simple and modular optical layout, which exploits standard optical components for telecommunications and therefore potentially cheap, reliable and easily available on the market. The layout principle is to convert, in the sensor itself, a change of polarization of an input optical beam, induced by the modulating electric field, into an equivalent variation in the intensity of the optical signal [5]. In this work a back reflected version of the previous optical prototype has been assembled and inserted in a capacitor voltage divider to preliminary evaluate the feasibility of the whole combined voltage system for application to MV protective equipment. 2. Voltage optical sensor 2.1. Optical retracing scheme and assembled optical prototype The scheme of the optical sensor (Figure 1a) has been designed for operating with an input light beam with arbitrary polarization; this layout avoids more expensive polarization maintaining optical fibres and connectors. The standard single mode fibre and the collimator are used to launch the input light, with unknown polarization, toward the sensing bulk optical elements and to collect it back. The sensing region, where the electric field modulates the light intensity, consists of a beam displacer (BD), two Lithium Tantalate (LiTO3) crystals, a Ȝ/8 waveplate and a dielectric mirror, respectively. The two LiTO3 crystals convert the modulating voltage to an optical modulation of the light through the electro-optic (Pockels) effect. The use of Y-cut type crystals allows the adoption of optical transverse configuration, in which the voltage is applied perpendicularly to the direction of the input light through the metallization of two lateral faces of the crystals. This layout allows an easy optimization of the sensitivity of the sensor by properly dimensioning the length of LiTO3 crystals. The two crystals are rotated each other by 90°, in order to compensate for the natural birefringence of LiTaO3, and mainly for preventing environmental disturbances, like temperature variations, found inside the MV switchboard or in the MV substation.
(a)
(b)
Fig. 1. (a) Back reflected scheme of the optical sensor ; b) picture of the assembled optical prototype
Letizia De Maria et al. / Procedia Engineering 168 (2016) 1597 – 1600
1599
The beam displacer BD3 with the mirror M are in charge to eliminate any noise due to the state of polarization of the input optical beam, and, at the same time, to translate the electric field variation to intensity changes of the light beam. The Ȝ/8 waveplate introduces a proper bias in order to center the sensor output at the middle of the total dynamical range [5,6]. All the optical components must be carefully aligned among themselves to guarantee the correct functionality of the device and the maximum rejection to polarization disturbances. Figure 1b shows the assembly and testing phases of the optical prototype, based on the described retracing scheme. For a practical implementation of the sensor, LiTaO3 crystals with lateral dimensions (3mm x 3mm) equals to those of the beam displacer, of the Ȝ/8 waveplate and of the mirror ones, have been chosen to improve the easy assembling and the compactness of the whole sensing device. LiTiO3 crystals lengths have been dimensioned to ensure the operation of the same in all normal operating condition of the power network. These crystal dimensions also guarantee a high protection from any possible electrical breakdown for the maximum applied voltage value. 2.2. Voltage optical sensor in a capacitor voltage divider Figure 2a shows the experimental set-up used for testing performances of the whole Voltage transducer consisting of the optical sensor coupled to the Capacitor Voltage divider. A standard Capacitor Voltage divider, normally found in MV substations (12/20 kV), has been used for this preliminary feasibility assessment. The test mock-up consists of a function generator coupled to a high voltage amplifier, a high voltage 1000:1 probe (Tektronix P6015A), a digital oscilloscope (Hewlet - Packard Infinium) and a dedicated electro-optic unit (EOU) for detecting the back-reflected optical signal coming out from the sensor prototype. It consists of a power stabilized 1550nm laser source, a photodetector and transimpedance amplifier (200kHz bandwidth). The high voltage amplifier amplifies signals till 3kVrms at frequencies from 20Hz to 3kHz to drive the capacitor divider/optical sensor. It is well known, that equipment and apparatus such as power inverters connected along the electric lines, or failures due unpredictable external events, may substantially affect the amplitude, the frequency, the waveform and the phase relationships values of the MV electric board voltages, introducing also high harmonics and noise. The assembled testing mock-up, thanks to the function generator and the high voltage amplifier, is able to simulate some of these events. The high voltage power supply is connected to the hot point of the capacitive divider and the optical sensor is placed across the capacitive divider and ground. To preliminary evaluate performances of the combined voltage sensor, the optical sensor has been inserted in the metal support of the capacitor divider and coupled to it (Figure 2b). This assembly guarantees minimum lengths of connecting wires with an adequate electromagnetic shielding for the wires themselves, avoiding the coupling of disturbances to the optical sensor. The connecting optical fibre is physically immune to these disturbances.
(a) (b) Fig. 2. Experimental setup: a) laboratory test mock-up, b) layout of the optical voltage sensor combined with the capacitor voltage divider
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Letizia De Maria et al. / Procedia Engineering 168 (2016) 1597 – 1600
3. Experimental results Figure 3a shows 50Hz time traces of the HV probe (magenta) and of the combined voltage sensor (green) recorded by the oscilloscope for two applied voltage values (amplitude equal to 50Vrms and 100Vrms respectively). The optical signal reproduces faithfully and with high signal to noise ratio the applied voltage changes. High stability of the optical voltage output has been recorded on short and medium term ( tens of minutes ) with variations of the DC level less than 0.5%. In Figure 3b the measured Transfer function of Optical voltage device the is plotted versus the Voltage applied to the capacitive divider (Vpp) showing a good linear response of the assembled voltage device at all the tested frequencies, up to 1.6kHz. The measurement error is always less than 3% in the linear area of the sensor transfer function, as required for application associated with protective equipment. ϰϭϯϬ,nj
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Fig.3 a) AC Measurements: time traces of the High Voltage Probe (magenta) and of the combined Optical Voltage Sensor (green) under applied 50Hz voltage amplitudes of 50Vrms and 100Vrms respectively; b) Measured Transfer function of the combined Optical Voltage Sensor.
4. Conclusions A combined system based on a standard capacitor Voltage divider and on a simple optical sensor layout has been assembled for the AC phase voltage control in Medium Voltage (MV) switchboards. Its functionality has been preliminary checked by means of an ad hoc designed laboratory mock-up. The measurement error is always less than 3% in the linear area of the combined voltage sensor transfer function, confirming the potential application of this type of the optical assembly for the control of the rated voltage in the MV equipment. Acknowledgements This work has been financed by the Research Fund for the Italian Electrical System under the Contract Agreement between RSE and the Ministry of Economic Development-General Directorate for Energy and Mining Resources stipulated on 29 July 2009 in compliance with the Decree of 19 March 2009. References [1] Nano Markets Markets for Sensors for the Smart Grid-2014 Nano-731, LC August 2014 [2] I. Gentilini R. Calone F. Giammanco, G. Bolcato, J. Weichold, M. Stalder, “The Smart Termination: An Innovative Component To Enable Smart Grids Development” CIRED 2013 22nd Conf. on Electricity Distribution, Stockholm, 10-13 June 2013, Paper 0598. [3] Feng Pan, Xia Xiao, Yan Xu and Shiyan Ren An Optical AC Voltage Sensor Based on the Transverse Pockels Effect Sensors 2011, 11, 65936602. [4] L.De Maria, N.C.Pistoni “An optical approach for monitoring electrical parameters in a distribution network” AISEM A2015 XVIII , DOI:10.1109_ AISEM.2015.7066792. [5] L. De Maria, N. C. Pistoni, D. Bartalesi, “An optical device for an automated temporization of diagnostic tools for medium voltage substation”, V European Workshop on Optical Fibre Sensors, Krakow, Proc. of SPIE Vol. 8794 ,879444-1,2013.
ScienceDirect Procedia Engineering 168 (2016) 1597 – 1600
30th Eurosensors Conference, EUROSENSORS 2016
Combined optical sensor and capacitor voltage divider arrangement for Voltage control in Medium Voltage Switchboard Fiber Letizia De Mariaa 1, Daniele Bartalesia, Natale Claudio Pistonib a
Department of Technologies for Transmission and Distribution - RSE Research on Energetic System S.p.A, Milan, Italy b Optoelectronics and Fibre Optics Consultant, 20090 Assago, Milan, Italy
Abstract
The integration in a capacitor voltage divider of an optical sensor, based on a double electro-optic crystals and on a standard single mode fiber arrangement, has been proposed as a way to obtain a low cost, accurate and intrinsically safe voltage sensor for an on line control of the voltage parameters in Medium Voltage (MV) switchboard. A compact and miniaturized optical prototype based on a back reflected layout has been previously designed, assembled and characterized on a laboratory mock up. In this work it has been successively inserted in a capacitor voltage divider circuit to preliminary evaluate the feasibility of the whole voltage control system for application to protective equipment. From preliminary electrical characterizations it turns out that the measurement error with the adopted configuration of this voltage device is lower than 3% full scale confirming its suitability for protection and voltage control. © Published by Elsevier Ltd. This © 2016 2016The TheAuthors. Authors. Published by Elsevier Ltd.is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of the 30th Eurosensors Conference. Peer-review under responsibility of the organizing committee of the 30th Eurosensors Conference Keywords: Fibre optic sensor, optical Voltage sensor, distribution network, Medium Voltage equipment; protective voltage transformer.
1. Introduction The availability of real time and capillaries information on the status of electrical equipment will be more and more important to achieve higher flexibility and reliability as required for the development of the new Distribution network[1]. With this aim an innovative approach to the control of electrical components of Medium Voltage (MV) substations is gradually occurring. The development of a new family of “smart” electrical components, with incorporated reliable, safe and cheap sensors with measuring and/or actuation functions, is the first step to achieve 1
* Corresponding author. Tel.: +39-02-39924686; fax: +39-02-39925557. E-mail address: [email protected]
1877-7058 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of the 30th Eurosensors Conference
doi:10.1016/j.proeng.2016.11.469
1598
Letizia De Maria et al. / Procedia Engineering 168 (2016) 1597 – 1600
distributed information on electrical parameters along the network. Recently novel non-conventional sensors have been proposed for monitoring the operating parameters (voltage, current, phase) in Medium Voltage (MV) switchboard at their energized phase terminals [2]. They are generally based on miniaturized resistive or capacitive s transducers. Alternative optical solutions based on electro-optic materials, which change the polarization of the light passing through them, when they are subjected to electric fields, have been also recently examined [3]. Indeed optical sensors, for their intrinsic high electromagnetic immunity characteristics, can be safely incorporated in MV electrical components. As for non-conventional transducers, optical sensors should be designed to guarantee a high voltage accuracy (i.e. 3% voltage error when used to supply protective equipment), robustness, compactness and they should be also significantly low cost; this last requirement is important in view of a widespread installation of optical sensors in new or in exiting MV switchboards. Recently the Authors reported in [4,5] an optical device based on two electro-optic Lithium Tantalate (LiTO3) crystals, chosen as optical transducers, potentially suitable for an accurate measure of the AC phase voltage of a MV switchboard. Main feature of the proposed optical approach is its simple and modular optical layout, which exploits standard optical components for telecommunications and therefore potentially cheap, reliable and easily available on the market. The layout principle is to convert, in the sensor itself, a change of polarization of an input optical beam, induced by the modulating electric field, into an equivalent variation in the intensity of the optical signal [5]. In this work a back reflected version of the previous optical prototype has been assembled and inserted in a capacitor voltage divider to preliminary evaluate the feasibility of the whole combined voltage system for application to MV protective equipment. 2. Voltage optical sensor 2.1. Optical retracing scheme and assembled optical prototype The scheme of the optical sensor (Figure 1a) has been designed for operating with an input light beam with arbitrary polarization; this layout avoids more expensive polarization maintaining optical fibres and connectors. The standard single mode fibre and the collimator are used to launch the input light, with unknown polarization, toward the sensing bulk optical elements and to collect it back. The sensing region, where the electric field modulates the light intensity, consists of a beam displacer (BD), two Lithium Tantalate (LiTO3) crystals, a Ȝ/8 waveplate and a dielectric mirror, respectively. The two LiTO3 crystals convert the modulating voltage to an optical modulation of the light through the electro-optic (Pockels) effect. The use of Y-cut type crystals allows the adoption of optical transverse configuration, in which the voltage is applied perpendicularly to the direction of the input light through the metallization of two lateral faces of the crystals. This layout allows an easy optimization of the sensitivity of the sensor by properly dimensioning the length of LiTO3 crystals. The two crystals are rotated each other by 90°, in order to compensate for the natural birefringence of LiTaO3, and mainly for preventing environmental disturbances, like temperature variations, found inside the MV switchboard or in the MV substation.
(a)
(b)
Fig. 1. (a) Back reflected scheme of the optical sensor ; b) picture of the assembled optical prototype
Letizia De Maria et al. / Procedia Engineering 168 (2016) 1597 – 1600
1599
The beam displacer BD3 with the mirror M are in charge to eliminate any noise due to the state of polarization of the input optical beam, and, at the same time, to translate the electric field variation to intensity changes of the light beam. The Ȝ/8 waveplate introduces a proper bias in order to center the sensor output at the middle of the total dynamical range [5,6]. All the optical components must be carefully aligned among themselves to guarantee the correct functionality of the device and the maximum rejection to polarization disturbances. Figure 1b shows the assembly and testing phases of the optical prototype, based on the described retracing scheme. For a practical implementation of the sensor, LiTaO3 crystals with lateral dimensions (3mm x 3mm) equals to those of the beam displacer, of the Ȝ/8 waveplate and of the mirror ones, have been chosen to improve the easy assembling and the compactness of the whole sensing device. LiTiO3 crystals lengths have been dimensioned to ensure the operation of the same in all normal operating condition of the power network. These crystal dimensions also guarantee a high protection from any possible electrical breakdown for the maximum applied voltage value. 2.2. Voltage optical sensor in a capacitor voltage divider Figure 2a shows the experimental set-up used for testing performances of the whole Voltage transducer consisting of the optical sensor coupled to the Capacitor Voltage divider. A standard Capacitor Voltage divider, normally found in MV substations (12/20 kV), has been used for this preliminary feasibility assessment. The test mock-up consists of a function generator coupled to a high voltage amplifier, a high voltage 1000:1 probe (Tektronix P6015A), a digital oscilloscope (Hewlet - Packard Infinium) and a dedicated electro-optic unit (EOU) for detecting the back-reflected optical signal coming out from the sensor prototype. It consists of a power stabilized 1550nm laser source, a photodetector and transimpedance amplifier (200kHz bandwidth). The high voltage amplifier amplifies signals till 3kVrms at frequencies from 20Hz to 3kHz to drive the capacitor divider/optical sensor. It is well known, that equipment and apparatus such as power inverters connected along the electric lines, or failures due unpredictable external events, may substantially affect the amplitude, the frequency, the waveform and the phase relationships values of the MV electric board voltages, introducing also high harmonics and noise. The assembled testing mock-up, thanks to the function generator and the high voltage amplifier, is able to simulate some of these events. The high voltage power supply is connected to the hot point of the capacitive divider and the optical sensor is placed across the capacitive divider and ground. To preliminary evaluate performances of the combined voltage sensor, the optical sensor has been inserted in the metal support of the capacitor divider and coupled to it (Figure 2b). This assembly guarantees minimum lengths of connecting wires with an adequate electromagnetic shielding for the wires themselves, avoiding the coupling of disturbances to the optical sensor. The connecting optical fibre is physically immune to these disturbances.
(a) (b) Fig. 2. Experimental setup: a) laboratory test mock-up, b) layout of the optical voltage sensor combined with the capacitor voltage divider
1600
Letizia De Maria et al. / Procedia Engineering 168 (2016) 1597 – 1600
3. Experimental results Figure 3a shows 50Hz time traces of the HV probe (magenta) and of the combined voltage sensor (green) recorded by the oscilloscope for two applied voltage values (amplitude equal to 50Vrms and 100Vrms respectively). The optical signal reproduces faithfully and with high signal to noise ratio the applied voltage changes. High stability of the optical voltage output has been recorded on short and medium term ( tens of minutes ) with variations of the DC level less than 0.5%. In Figure 3b the measured Transfer function of Optical voltage device the is plotted versus the Voltage applied to the capacitive divider (Vpp) showing a good linear response of the assembled voltage device at all the tested frequencies, up to 1.6kHz. The measurement error is always less than 3% in the linear area of the sensor transfer function, as required for application associated with protective equipment. ϰϭϯϬ,nj
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Fig.3 a) AC Measurements: time traces of the High Voltage Probe (magenta) and of the combined Optical Voltage Sensor (green) under applied 50Hz voltage amplitudes of 50Vrms and 100Vrms respectively; b) Measured Transfer function of the combined Optical Voltage Sensor.
4. Conclusions A combined system based on a standard capacitor Voltage divider and on a simple optical sensor layout has been assembled for the AC phase voltage control in Medium Voltage (MV) switchboards. Its functionality has been preliminary checked by means of an ad hoc designed laboratory mock-up. The measurement error is always less than 3% in the linear area of the combined voltage sensor transfer function, confirming the potential application of this type of the optical assembly for the control of the rated voltage in the MV equipment. Acknowledgements This work has been financed by the Research Fund for the Italian Electrical System under the Contract Agreement between RSE and the Ministry of Economic Development-General Directorate for Energy and Mining Resources stipulated on 29 July 2009 in compliance with the Decree of 19 March 2009. References [1] Nano Markets Markets for Sensors for the Smart Grid-2014 Nano-731, LC August 2014 [2] I. Gentilini R. Calone F. Giammanco, G. Bolcato, J. Weichold, M. Stalder, “The Smart Termination: An Innovative Component To Enable Smart Grids Development” CIRED 2013 22nd Conf. on Electricity Distribution, Stockholm, 10-13 June 2013, Paper 0598. [3] Feng Pan, Xia Xiao, Yan Xu and Shiyan Ren An Optical AC Voltage Sensor Based on the Transverse Pockels Effect Sensors 2011, 11, 65936602. [4] L.De Maria, N.C.Pistoni “An optical approach for monitoring electrical parameters in a distribution network” AISEM A2015 XVIII , DOI:10.1109_ AISEM.2015.7066792. [5] L. De Maria, N. C. Pistoni, D. Bartalesi, “An optical device for an automated temporization of diagnostic tools for medium voltage substation”, V European Workshop on Optical Fibre Sensors, Krakow, Proc. of SPIE Vol. 8794 ,879444-1,2013.