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TB 768 B5- Protection requirements on transient response of digital acquisition .

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内容提示: Protection andautomationB5Protection requirements on transient response of digital acquisition chainReference: 768June 2019 TB 768 – Protection requirements on transient response of digital acquisition chain Members J. ZAKONJSEK, Convenor RU T. WERNER, Secretary CH J. BLUMSCHEIN DE J. GALLETERO LOPEZ ES H. GRASSET FR S. HOLST SE L. A KOJOVIC US P. TANTIN FR R. ZHANG GB Corresponding Members M. ACHTERKAMP NL M.A.M. RODRIGUES BR B. PALKI IN H.J. HERRMAN DE L. GANG CN H. MAEHARA JP D....

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Protection andautomationB5Protection requirements on transient response of digital acquisition chainReference: 768June 2019 TB 768 – Protection requirements on transient response of digital acquisition chain Members J. ZAKONJSEK, Convenor RU T. WERNER, Secretary CH J. BLUMSCHEIN DE J. GALLETERO LOPEZ ES H. GRASSET FR S. HOLST SE L. A KOJOVIC US P. TANTIN FR R. ZHANG GB Corresponding Members M. ACHTERKAMP NL M.A.M. RODRIGUES BR B. PALKI IN H.J. HERRMAN DE L. GANG CN H. MAEHARA JP D. MCGINN CA A. SHEVELEV RU F. STEINHAUSER AT V. TERZIJA GB A. BONETTI SE WG B5.24 Copyright © 2019 “All rights to this Technical Brochure are retained by CIGRE. It is strictly prohibited to reproduce or provide this publication in any form or by any means to any third party. Only CIGRE Collective Members companies are allowed to store their copy on their internal intranet or other company network provided access is restricted to their own employees. No part of this publication may be reproduced or utilized without permission from CIGRE”. Disclaimer notice “CIGRE gives no warranty or assurance about the contents of this publication, nor does it accept any responsibility, as to the accuracy or exhaustiveness of the information. All implied warranties and conditions are excluded to the maximum extent permitted by law”. Protection requirements on transient response of digital acquisition chain ISBN : 978-2-85873-470-2 TB 768 – Protection requirements on transient response of digital acquisition chain ISBN : 978-2-85873-470-2 TB 768 – Protection requirements on transient response of digital acquisition chain 5 Executive summary The introduction of Process Bus within international station communication standard IEC 61850-9-2 enables use of different products (primary and secondary) from a number of vendors to form digitized instantaneous value of a measured quantity (voltage and or current) intended for further processing in different protection, control and monitoring algorithms within different IEDs. Static accuracy of a complete measuring chain is well defined by different IEC and other standards while lack in definition of dynamic response represents a potential danger for required high availability of protection and control functions. It is supposed that transient response of conventional instrument transformers is well known and defined by existing international standards. For this reason, it is necessary to determine the minimum requirements on transient response of a complete signal processing chain, including first of all Merging Units (MUs) and Non-Conventional Instrument Transformers (NCITs), named also Low Power Instrument Transformers (LPIT). This work is related to AC systems only. It does not cover installations for existing HVDC installations (lines and HVDC parts of converting stations) nor consider protection, control and monitoring of future HVDC networks. The scope of work has been suggested by SC B5 and approved by CIGRE Technical Council Chairman 2008-12-04 as follows: 1. Study the transient response of different types of Non-conventional InstrumentTransformers (current as well as voltage) on different transients in primary power systems,generally recognized as important for dependable operation of different protectionfunctions as well as for power quality measurement.2. Study the transient response of different transducers intended for potential use in MergingUnits. This includes between others also current and voltage input transformers (ofconventional and non conventional design), passive and active filters used generally beforeA/D converters and the converters themselves.3. Examine also the adequacy of proposals for further use in emerging protectiontechnologies like protection functions based on travelling wave theory, and similar.4. Propose, assuming results obtained by the minimum required transient accuracy of acomplete conversion chain, which can be used as a basis for design of different protection,control and monitoring algorithms within IEDs. The result should consider also the well-known transient response of conventional instrument transformers and should makepossible comparisons with performance of signal conditioning circuits within existingprotective devices.Interoperability requirements on voltage and current digital acquisition and algorithm execution chain are in case of process buss implementation much more demanding than they were for classical combinations of conventional instrument transformers and related protection, control and automation IEDs. CIT brand XCIT brand YIEDbrand AIEDbrand BSecondary currents and voltagesSecondary currents and voltagesBayFigure 1-1: Interoperability between CITs and standard IEDs Today’s interoperability between Conventional Instrument Transformers (CITs) and Secondary (Protection, Control and Monitoring) IEDs results from the standardized outputs of the CITs, see Figure 1-1: • Current Transformers (CTs) secondary outputs are generally standardized to 5A or 1A. TB 768 – Protection requirements on transient response of digital acquisition chain 6 • Voltage Transformers (VTs) secondary outputs are generally rated 100V (phase to phase). Sometimes also 110V, 125V, or 220V. New technologies have appeared with Non Conventional Instrument Transformers (NCITs) that do not have standardized analogue outputs (1A, 5A, 110V, 220V) as the CITs. Furthermore, the process buses that distribute sampled values of measuring quantities via Ethernet network(s), see example on Figure 1-2, needs to be standardized to insure at least the same interoperability as today. In such particular case the MU brand x must be compatible with the protection brand A and C as well as all remaining brands on the same process bus 1. Similar is valid also for MU brand y and protection brands on process bus 2. CIT1 orNCIT 1CIT2 orNCIT 2MUBrand xMUBrand yBayPrimary currents and/or voltagesIEDBrand AIEDBrand BEthernet switchEthernet switchIEDBrand CProcess bus 1 (CITs 1 or NCITs 1)Process bus 2 (CITs 2 or NCITs 2) Figure 1-2: Simple connection with process bus network It is therefore very important to standardize the sampled values characteristics. That is done in the IEC 61850-9-2 standard for steady state currents and voltages but not for transient responses. Obviously, during these transient phenomena that the protection algorithms must operate reliably, which means with both, high security and high dependability. Basic decision: The working group has decided, in order to ease the application of all further conclusions and suggestions to base its further work on the following transfer characteristics: • When the NCITs are used then the IEC 61850-9-2 sampled values should be compared directly to primary voltages and currents and their transients as reference. For Rogowski coil applications, Merging Units should provide both, integrated and non-integrated signals. • When the CITs are used then the IEC 61850-9-2 sampled values should be compared directly to their secondary voltages and currents and their transients as reference. The following elements and especially their transient characteristics have been studied in details in order to determine all the necessary requirements on complete digital acquisition chain: • Primary sources of information, comprising Conventional and Non Conventional Instrument transformers (CITs and NCITs) • Characteristic transients and harmonics in power system • Requirements on applied protection, control and monitoring functionality under different system emergency events • Detailed analysis of different elements within the digital acquisition chain with special concentration on Merging Units (MUs) • Final recommendations are presented at the end of the document. Here it is necessary to expose a requirement on producers of NCITs as well as MUs, to present in mathematical and graphical form the complete Bode diagrams of their products, which have so far not been a practice for conventional protection IEDs. Here it is necessary to mention also that the greatest amount of work has been mainly done at early 2010’s. This means, that some aspects related to NCITs, their experimental use or the publication of relevant parts of IEC 61869 are not taken into account within this Brochure. TB 768 – Protection requirements on transient response of digital acquisition chain 7 Content Executive summary ............................................................................................................. 5 1. Introduction .............................................................................................................. 15 1.1 Scope of work .......................................................................................................................................... 15 1.2 Interoperability requirements on voltage and current digital acquisition and algorithm execution chain ......................................................................................................................................................... 15 1.3 Basic decision ......................................................................................................................................... 17 2. Primary sources of information .............................................................................. 19 2.1 Conventional instrument transformers ................................................................................................. 19 2.1.1 Basic operating principle .................................................................................................................... 19 2.1.2 Magnetic (inductive) current transformers .......................................................................................... 20 2.1.3 Magnetic (inductive) voltage transformers ......................................................................................... 26 2.1.4 Capacitive voltage transformers ........................................................................................................ 26 2.2 Electronic magnetic measurement ........................................................................................................ 28 2.2.1 Current measurement ........................................................................................................................ 28 2.2.2 Voltage measurement ........................................................................................................................ 30 2.3 Faraday Effect based NCITs ................................................................................................................... 30 2.3.1 Current measurement ........................................................................................................................ 31 2.3.2 Example of the current measurement system .................................................................................... 31 2.4 Current measurement based on Hall Effect .......................................................................................... 34 2.4.1 Measuring principle ............................................................................................................................ 34 2.4.2 Measurement of operating currents ................................................................................................... 35 2.4.3 Measurement of short circuit currents ................................................................................................ 35 2.4.4 Evaluation of disturbance influences ................................................................................................. 36 2.4.5 Measuring results from a test system ................................................................................................ 37 2.5 Rogowski coil measurement .................................................................................................................. 37 2.5.1 Principles of operation and construction ............................................................................................ 37 2.5.2 Comparison of U-I Characteristics ..................................................................................................... 40 2.5.3 Transient Response ........................................................................................................................... 40 2.5.4 Rogowski coil integrated signal .......................................................................................................... 41 2.5.5 Frequency Response ......................................................................................................................... 43 2.6 Voltage measurement with voltage dividers ......................................................................................... 44 2.6.1 Voltage measurement with RC-Dividers ............................................................................................ 44 2.7 Voltage measurement – Pockels cells ................................................................................................... 47 2.8 Piezo-optic voltage transducer .............................................................................................................. 48 2.9 Conclusion on current and voltage measuring principles ................................................................... 49 3. Characteristic transients and harmonics in power system .................................. 51 3.1 DC current component in AC power system ......................................................................................... 51 3.1.1 Basics, Short-circuit with a constant supply ....................................................................................... 51 3.1.2 Short-circuit close to a generator ....................................................................................................... 52 3.1.3 Pure direct current ............................................................................................................................. 53 3.2 Subharmonic resonance ......................................................................................................................... 54 3.3 Subsynchronous resonance .................................................................................................................. 55 3.4 Inter system oscillations ......................................................................................................................... 55 3.4.1 Oscillations ........................................................................................................................................ 56 3.4.2 Torsional oscillations.......................................................................................................................... 56 3.4.3 Low-frequency oscillations ................................................................................................................. 56 3.4.4 Downwind tower shade or wind barrier effect .................................................................................... 56 3.5 Higher harmonics .................................................................................................................................... 56 3.5.1 Basics, general consideration ............................................................................................................ 56 TB 768 – Protection requirements on transient response of digital acquisition chain 8 3.5.2 Harmonics caused by earth faults ...................................................................................................... 57 3.5.3 Harmonics caused by nonlinear load or power electronics ................................................................ 59 3.6 Traveling waves ....................................................................................................................................... 59 3.6.1 Introduction ........................................................................................................................................ 59 3.6.2 Characteristic features of travelling waves ......................................................................................... 60 3.7 Transients close to HVDC systems and other elements with power electronics .............................. 61 3.7.1 Steady state operation ....................................................................................................................... 61 3.7.2 Dynamics and transients .................................................................................................................... 62 3.8 Switching transients................................................................................................................................ 63 3.8.1 Capacitor banks ................................................................................................................................. 63 3.8.2 Line switching .................................................................................................................................... 65 3.8.3 Transformer inrush ............................................................................................................................ 67 3.8.4 Shunt reactor inrush........................................................................................................................... 70 3.9 Conclusion ............................................................................................................................................... 76 4. Requirements for protection, control, and monitoring ......................................... 79 4.1 Current protection ................................................................................................................................... 79 4.1.1 Overcurrent protection ....................................................................................................................... 79 4.1.2 Overcurrent protection functionality based on symmetrical components ........................................... 80 4.1.3 Overload protection ........................................................................................................................... 80 4.1.4 Current measurement based on harmonic currents ........................................................................... 81 4.2 Voltage measurement ............................................................................................................................. 81 4.2.1 Over – under voltage protection ......................................................................................................... 81 4.2.2 Earth faults and residual voltage measurement ................................................................................. 82 4.2.3 Voltage measurement for complex protection functions .................................................................... 83 4.2.4 Voltage measurement for the needs of SIPS ..................................................................................... 83 4.2.5 Frequency measurement ................................................................................................................... 83 4.3 Distance protection ................................................................................................................................. 84 4.3.1 Time synchronization and general measuring accuracy .................................................................... 85 4.3.2 DC component in short circuit current ................................................................................................ 85 4.3.3 Inrush currents ................................................................................................................................... 85 4.3.4 Switching transients ........................................................................................................................... 85 4.3.5 Higher harmonics in measured currents and voltages ....................................................................... 85 4.3.6 Low frequency oscillations on series compensated and adjacent power lines ................................... 85 4.3.7 Voltage measurement for distance protection .................................................................................... 86 4.4 Protection functions based on superimposed ( ) quantities .............................................................. 87 4.4.1 DPFC distance protection .................................................................................................................. 88 4.4.2 DPFC differential protection ............................................................................................................... 89 4.4.3 DPFC fault detection element ............................................................................................................ 89 4.5 Protection based on traveling waves..................................................................................................... 90 4.6 Differential protection (current, phase), (line, busbar, transformer) ................................................... 93 4.6.1 Transformer current differential protection ......................................................................................... 94 4.6.2 Restricted Earth Fault protection ....................................................................................................... 97 4.6.3 Busbar current differential protection ................................................................................................. 97 4.7 Directional comparison schemes (pilot protection schemes) ............................................................. 99 4.8 High frequency directional E/F protection .......................................................................................... 100 4.8.1 Charging frequency ......................................................................................................................... 101 4.8.2 Charging amplitude .......................................................................................................................... 101 4.8.3 Direction determination principles based on the charging oscillation ............................................... 102 4.9 System integrity protection schemes (SIPS) ...................................................................................... 102 4.9.1 System integrity protection schemes definition ................................................................................ 102 4.9.2 SIPS strategies and technologies .................................................................................................... 103 4.9.3 Synchrophasors and PMU characteristics ....................................................................................... 104 4.9.4 Recommendations ........................................................................................................................... 105 4.10 Sensitive protection schemes .............................................................................................................. 106 4.10.1 Reverse power protection ................................................................................................................ 106 4.10.2 Sensitive earth fault protection ......................................................................................................... 109 TB 768 – Protection requirements on transient response of digital acquisition chain 9 4.11 Protection against resonance during capacitor switching or for topology changes in the network . ................................................................................................................................................................ 112 4.11.1 Introduction ...................................................................................................................................... 112 4.11.2 Resonance phenomenon ................................................................................................................. 112 4.11.3 Resonance detection algorithm ....................................................................................................... 113 4.11.4 Recorded Data ................................................................................................................................. 114 4.12 Disturbance recording .......................................................................................................................... 114 4.12.1 General requirements ...................................................................................................................... 114 4.12.2 Functional requirements .................................................................................................................. 115 4.12.3 Performance requirements .............................................................................................................. 115 4.12.4 DR functions with MU ...................................................................................................................... 116 4.13 Conclusions ........................................................................................................................................... 116 5. Voltage and current digital acquisition chain (merging units) ............................119 5.1 General on complete digital acquisition chain ................................................................................... 119 5.2 Conventional current and voltage input transformers ...................................................................... 120 5.3 Anti aliasing filters................................................................................................................................. 120 5.3.1 AD converters which are sampling with the “final sampling rate” ..................................................... 122 5.3.2 Sigma-Delta converters which are using the over-sampling technology .......................................... 122 5.4 A/D converters ....................................................................................................................................... 123 5.5 Basic signal processing ........................................................................................................................ 123 5.5.1 Resampling: ..................................................................................................................................... 124 5.6 Time synchronization ............................................................................................................................ 124 5.6.1 Jitter ................................................................................................................................................. 125 5.6.2 Constant time delay ......................................................................................................................... 126 5.6.3 Drifting delay .................................................................................................................................... 126 5.6.4 Loss of synchronization ................................................................................................................... 127 5.6.5 Time synchronization methods ........................................................................................................ 127 5.6.6 Time synchronization impact on transients ...................................................................................... 128 5.7 Some issues, which will require additional work in near future ........................................................ 129 5.7.1 Behavior of the subscribing function towards missed samples ........................................................ 129 5.7.2 MU failure declaring synchronized samples while the MU is not synchronized ............................... 130 5.7.3 Behavior of the subscribing protection function at different quality declaration from the MU to the published samples ...................................................................................................................................... 130 5.7.4 Behavior of the subscribing protection function if samples are received after 3 ms from when they have been taken ......................................................................................................................................... 130 6. Testing .....................................................................................................................131 6.1 Testing and identification of sensors .................................................................................................. 131 6.1.1 Identification of the Sensor's Equivalent Circuit ............................................................................... 131 6.1.2 Small signal behavior ....................................................................................................................... 131 6.1.3 Large signal behavior....................................................................................................................... 132 6.2 Testing and identification of merging units ........................................................................................ 132 6.2.1 Testing concepts .............................................................................................................................. 133 6.2.2 Merging units with inputs for conventional CTs and PTs ................................................................. 133 6.2.3 Merging units with low level inputs ................................................................................................... 134 6.2.4 Merging units with Rogowski Coil inputs .......................................................................................... 134 6.2.5 Merging units with custom inputs for non conventional sensors ...................................................... 134 6.3 Testing and identification of the complete signal processing chain ................................................ 135 6.3.1 Small signal behavior ....................................................................................................................... 135 6.3.2 Large signal test – impulse response............................................................................................... 135 7. Recommendations and conclusions .....................................................................137 7.1 Bode diagram ......................................................................................................................................... 137 7.1.1 H1(s) Transfer function of the sensor............................................................................................... 138 7.1.2 H2(s) Transfer function of the ant-aliasing filter ............................................................................... 139 7.1.3 H3(s) Transfer function of decimation filter of ADC .......................................................................... 139 7.1.4 H4(s) Transfer function of used filter in the processing .................................................................... 140 TB 768 – Protection requirements on transient response of digital acquisition chain 10 7.1.5 H(s) Total transfer function of data acquisition system plus sensor ................................................. 141 7.1.6 Conclusion on Bode diagram: .......................................................................................................... 142 7.2 Dynamic range and related functionality ............................................................................................. 143 7.2.1 Frequency range .............................................................................................................................. 143 7.2.2 Sampling rate ................................................................................................................................... 143 7.2.3 Initial filtering of analog signals ........................................................................................................ 143 ...

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