WO2001093405A1 - Schema de protection systeme - Google Patents

Schema de protection systeme Download PDF

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Publication number
WO2001093405A1
WO2001093405A1 PCT/SE2001/001067 SE0101067W WO0193405A1 WO 2001093405 A1 WO2001093405 A1 WO 2001093405A1 SE 0101067 W SE0101067 W SE 0101067W WO 0193405 A1 WO0193405 A1 WO 0193405A1
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WO
WIPO (PCT)
Prior art keywords
system protection
communication
terminals
protection
subset
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PCT/SE2001/001067
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English (en)
Inventor
Per-Anders LÖF
Lars Gertmar
Daniel H. Karlsson
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Abb Ab
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Publication date
Application filed by Abb Ab filed Critical Abb Ab
Priority to AU2001262823A priority Critical patent/AU2001262823A1/en
Publication of WO2001093405A1 publication Critical patent/WO2001093405A1/fr

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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • H02J3/241—The oscillation concerning frequency
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H1/00—Details of emergency protective circuit arrangements
    • H02H1/0061—Details of emergency protective circuit arrangements concerning transmission of signals
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • H02J3/242—Arrangements for preventing or reducing oscillations of power in networks using phasor measuring units [PMU]
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/70—Smart grids as climate change mitigation technology in the energy generation sector
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
    • Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
    • Y04S10/00—Systems supporting electrical power generation, transmission or distribution
    • Y04S10/22—Flexible AC transmission systems [FACTS] or power factor or reactive power compensating or correcting units

Definitions

  • the present invention relates to devices, schemes and methods for network protection of electric power systems, and electric power systems comprising such devices and schemes.
  • Network protection refers to measures in order to avoid or reduce a substantial disturbance in an electric power system.
  • Control and protections in electric power systems are of many different kinds.
  • Single units are often provided with protection devices, which may detect any faults or if the unit is operated outside its limits.
  • Such a protection device typically reduces the operation conditions or disconnects the unit, and is therefore only concerned about the local conditions.
  • power system and “power network” refers solely to electric power, even if not explicitly mentioned.
  • system protection schemes For system disturbances, where the whole or substantial parts of an electric power system are involved, system protection schemes are used, which detects the occurrence or an acute risk for occurrence of a major disturbance and provides measures to reduce the consequences. Such measures may e.g. be the disconnection of certain loads, the division of the power system network into smaller autonomously operating networks, etc.
  • measures may e.g. be the disconnection of certain loads, the division of the power system network into smaller autonomously operating networks, etc.
  • the situation, in which these system protection schemes are activated are emergency or close to emergency situation, and the time for performing the necessary actions is very limited, typically in the order of a part of a second up to half a minute.
  • SPS system protection schemes
  • the defence plans of today against serious disturbances are mainly adapted for transient phenomena in the power network, appearing in the shape of frequency discrepancies as a result of active power imbalance.
  • These types of system protection schemes are mainly concerned with load disconnection, but there are also plans comprising islanding of the network according to predetermined sections between the areas in case of extreme operation conditions.
  • This type of protection scheme partitioning the power system into smaller areas, and thereby having a better opportunity to maintain the operation, are installed in a few places in north-western USA, France and Belgium.
  • the French system is described in the article "Major Incidents on the French Electric System: Potentiality and Curative Measurement” by C. Counan et. al., IEEE Transactions on Power Systems, Vol. 8, No 3, August 1993, pp 879-886.
  • the system is built up in a hierarchic structure, where detection devices are scattered over the network according to a certain configuration.
  • the detection devices are connected to a central analysing unit, determining the risk for disturbances.
  • the detection devices detect voltage beats by monitoring the variations of local voltage.
  • the network is fragmented upon request of the central analysing unit into isolated islands, having one or several detection devices.
  • the French defence scheme is also presented in the research report "Contingencies System against Loss of Synchronism Based on Phase Angle Measurements" by M. Bidet, Electricite de France (EdF) Report 93NR00009, Direction des Etudes etberichts, March 1993.
  • the defence scheme is presented as a last line of defence for countering cases of loss of synchronism, only to be activated in case other protection systems fail to eliminate the disturbance.
  • the system is based on synchronised phase angle measurements sent to a central point in the network, which dispatches e.g. line tripping or load shedding commands if a case of loss of synchronism is detected.
  • the centralised structure is considered as a main characteristic of the proposed defence plan.
  • a network protection system in southern Sweden against voltage collapse has been designed jointly by Svenska Kraftnat, Vattenfall AB and Sydkraft AB and is described in e.g. "Special Protection Scheme against Voltage Collapse in the South Part of the Swedish Grid", by B. Ingelsson et. al., CIGRE Paper 38-105, Paris, August 1996 or "Wide-Area Protection against Voltage Collapse” by B. Ingelsson et. al., IEEE Computer Applications in Power, Vol. 10, No 4, October 1997, pp 30-35.
  • the objective of the network protection system is to avoid a voltage collapse after a severe fault in a stressed operation situation.
  • the system can be used to increase the power transfer limits from the northern part of Sweden or to increase the system security or a mixture of both.
  • a number of indicators such as low voltage level, high reactive power generation and generator current limiters hitting limits are used as inputs to a logical decision-making process implemented in the Sydkraft SCADA (Supervisory Control And Data Acquisition) system.
  • Local actions are then ordered from the SCADA system, such as switching of shunt reactors and shunt capacitors, start of gas turbines, request for emergency power from neighbouring areas, disconnection of low priority load and, finally, (non- discriminative) load shedding.
  • the network protection system is designed to have a high level of security, especially for the (non-discriminative) load shedding, as well as a high dependability. Therefore a number of indicators are used to derive the criteria for each action.
  • the logical system is designed in such a way that a faulty indicator neither causes an unwanted operation nor causes a missed operation by the network protection system.
  • a severe disadvantage of the above system is that the response times turned out to be too long and undetermined. Since the ordinary SCADA communication system was used, the data treatment and the transfer times of information and control signals were in fact dependent on the general load of the SCADA system. The SCADA system is, unfortunately, typically particularly heavily loaded at stressed situations. Furthermore, the indicators were for some applications not sufficient to give a good decision support, at least with the simple logics used.
  • PMU Phasor Measurement Unit
  • GPS Global Positioning Satellite
  • Such systems are installed e.g. in north-western USA to record conditions of power systems and are used for a post-evaluation of an emergency situation. See e.g. "Wide Area Measurements of Power System Dynamics - The North American WAMS Project and its Applicability to the Nordic countries” Elforsk Report 99:50, O. Samuelsson, Technical University of Lund, January 2000.
  • An object of the present invention is thus to provide a system protection scheme, being more sensitive to disturbances in the power system.
  • a further object is to make use of time stamped quantities and quantities derived therefrom as a base for protection decisions.
  • Another object of the present invention is to provide a system protection scheme, which has a fast response to indications of disturbances. The response time should preferably be independent of external factors.
  • Yet another object is to provide a system protection scheme, which is reliable with respect to communication links.
  • Arrangements, devices, systems and methods according the enclosed claims achieve the above objects.
  • a number, at least three, of system protection terminals are introduced at suitable locations in the electric power system.
  • the system protection terminals are interconnected by a communication system, using a substantially dedicated communication resource.
  • a number of the system protection terminals are equipped to collect measurement signals associated with characteristic of the power system at that particular location.
  • the measurements preferably comprise complex ac quantities and stability indicators.
  • the signals are processed and data related to the measurements are spread on the dedicated communication resource to the other system protection terminals.
  • a number of the system protection terminals are equipped to evaluate the condition of the local part of the power network and if necessary provide control signals to power system units.
  • the evaluation is based on selected parts of the data available on the communication resource, locally available data and/ or externally entered data.
  • the system protection terminals have local means for storing data.
  • the data comprises the near history of system information as well as older measurements.
  • the storing means are used e.g. at autonomous operation situation, i.e. in situations where the communication fails.
  • the stored data is also preferably used to follow up stressed situations in a post-analysis.
  • the storing means are searchable databases.
  • the substantially dedicated communication resource connecting the system protection terminals is designed with a high capacity.
  • the requirements on the communication time is in the order of fractions of a second, e.g. a few hundred milliseconds for transient angular instability and transient voltage instability, while close to a second might be enough for frequency instability and damping purposes.
  • communication times of up to five seconds are normally acceptable.
  • Each system protection terminal has preferably access to at least two links of the communication system, providing a first degree of redundancy concerning communication failures. Further redundancy is achieved by providing at least two of the system protection terminals with at least three links to the communication system.
  • Each system protection terminal comprises a processor and suitable means for the communication.
  • a local database is provided for each terminal. Not only the measurements, but also the decisions are hereby performed at a local basis. The relevant data is collected from the communication system and the decision algorithms in each system protection terminal can be adjusted to the actual local situation, not subject to any extensive over- all analysis. The decentralised evaluation thus reduces the complexity of each algorithm.
  • the communication is secured by providing dedicated communication resources between the system protection terminals.
  • FIG. 1 is an exemplifying illustration of a power network with a system protection scheme according to the present invention
  • FIG. 2 is an illustration of a defective bus bar fault in the power system of Fig. 1;
  • FIG. 3 is another exemplifying illustration of a power network with a system protection scheme according to the present invention.
  • FIG. 4 is yet another exemplifying illustration of a power network with a system protection scheme according to the present invention.
  • FIG. 5 is an illustration of a combined system protection scheme, composed of the system protection schemes of Figs. 1, 3 and 4;
  • FIG. 6 is an illustration of the different states of operation of an electric power system
  • FIG. 7 is an embodiment of a system protection scheme comprising substantially identical standardised system protection terminals
  • FIG. 8 is a detailed block scheme of a system protection terminal used in the embodiment of Fig. 7; and FIG. 9 is a flow diagram of a system protection method according to the present invention.
  • Power system engineers often distinguish between on one hand unit or equipment protection and on the other hand system protection.
  • One obvious requirement to enable a secure and reliable supply of electric power in a power network is to protect the individual components of a power system against damage, when a fault appears.
  • This protection normally referred to as equipment or unit protection, is typically designed to prevent the current resulting from a fault to cause thermal damage to components.
  • Such component protection typically aims to disconnect the faulty transmission line or equipment.
  • integrity is concerned with the quality or condition of "something" being whole or undivided. In this case it is related to that all, or at least the vital or substantial, parts of a power network are stable and in synchronous operation. This corresponds to that the state of operation (described below) of the power system being either normal or alert. This state of operation can in simplified terms be said to correspond to that the power flow (algebraic) equations are fulfilled, and there is no immediate risk of loss of synchronism in the electric power system. The aim is to prevent widespread interruptions or large area blackouts.
  • SPS System Protection Scheme
  • SPS is designed to detect abnormal system conditions and take predetermined, emergency action to preserve system integrity and provide acceptable system performance.
  • the action is therefore only exceptionally a pure isolation of faulted elements, since such actions normally are provided by equipment protections.
  • SPS action may instead comprise actions like changes in load, generation or system configuration. The object of these changes is to maintain system stability and keep the voltages, active and reactive power flows at acceptable levels.
  • a general power network has different states of operation, depending on the actual situation concerning faults, disturbances, load and generation requests, etc.
  • the basics of defining System Operating States can be found in "Operating under Stress and Strain” by L.H. Fink and K. Carlsen, IEEE Spectrum, Vol. 15, No 3, March 1978, pp 48-53.
  • the general basic ideas are briefly discussed below in connection with the intended area of use of the present invention.
  • a normal operating state 40 the power generation is adequate to supply the existing load demand. No equipment is presently overloaded. All constraints on the power system are satisfied.
  • normal reserve margins are present, which margins are sufficient to provide a certain level of security. These margins are normally designed with respect to the stresses to which the system may be subjected, both regarding generation and transmission.
  • a power system is in the normal operating state 40 during the vast majority of the time. Any deviation from this state is an exception, however, a serious one.
  • alert state 42 If conditions nevertheless are changed 50 in such a manner that the provided security level may be too small, or the probability of disturbances may have increased, the system is in an alert state 42.
  • this alert state 42 all constraints of the system would still be satisfied in an isolated view, i.e. no objects are operated outside its margins. However, the whole system is less secure than in the normal operating state 40. The available margins to cope with disturbances may easily be exceeded even by rather simple and common faults, which then could result in violation of some system constraints. Equipment would be more or less severely overloaded, compared with its rated capabilities.
  • preventive actions 52 can be taken to restore the system back into the normal operating state 40.
  • the term protecting the integrity of an overall power system can as discussed earlier in this context be related to securing the operation of the power system in the normal and, for shorter terms also, in the alert states of operation. If such preventive actions 52 do not take place before another sufficiently severe disturbance, the system is transferred 54 into an emergency state 44. Here, system constraints are violated and the security of the system is breached since there does not exist any security level. The system is however still intact during this emergency state 44 and emergency control actions or "heroic measures" could be initiated in order to restore 56 the system to at least the alert state 42. Emergency control action ' should be directed towards sparing as many pieces of the system as possible and avoid a total collapse. Once a system has entered the emergency state, the deliberate control decisions and actions that are appropriate to the normal 40 and even the alert state 42 are no longer adequate. More immediate action is called for.
  • the system starts to disintegrate 58 into an "in extremis" state 46.
  • system constraints are no longer valid and major portions of the system would not be intact any more and most of the system load would be lost.
  • the collapse is halted 62 before all parts of the system are lost, some remaining equipment will operate within rated capability and the system will enter into a restorative state 48.
  • control actions are taken to pick up lost load and reconnect the system, even if the entire system may not be restored immediately. From this state, the system could transit 66 to the alert state 42 or go back 64 the entire way to the normal operating state 40. The actual path depends on the circumstances of the emergency situation.
  • the present invention mainly comes into operation in the emergency state 44.
  • the aim of the SPS is to sense and identify situations, which normally leads to the "in extremis" state 46, take actions and bring the system back to the alert state 42.
  • the arrow 60 in fig. 6 thus illustrates the action of SPS. If the encountered disturbance is very severe, the transition between states of operation may take place without passing through the intermediate' stages in Fig. 6. Examples are transition directly from the normal state 40 to the emergency state 44 if the encountered disturbance is more severe than the faults described in the design criteria for the power system, and also transition directly from the alert state 42 to the "in extremis" state 46 in case of a very severe disturbance. Irrespectively of the precise path taken during the transition between states of operation, the general aim and purpose of an SPS is the same.
  • SPS System Protection Scheme
  • the proposed System Protection Scheme focuses on system protection. Emergency protection devices/ schemes are dealing with incidents with a relatively low probability and enormous consequences. The risk, defined as the product of probability and consequence, for such events is therefore hard to derive. But due to the ever-increasing dependency of modern society of a reliable power supply, the proposed System Protection Scheme will serve a very important role. Strategies for reducing the risk and effects of major disturbances in the power system are a major concern for power utilities - both regarding planning and operational aspects.
  • the operation of power systems can be characterised by three objectives: quality, security and economy.
  • quality quality
  • security economy
  • the overall operational objective for power systems is to find a satisfactory compromise between the two conflicting objectives of security and economy.
  • Economic considerations are in many power systems today, partly due to the on-going deregulation of power markets, the major influencing factor of these two objectives.
  • the aim of actions taken by SPS is to provide uninterrupted power supply by use of sometimes rather ruthless methods, i.e. by taking actions that could be referred to as measures of last resort (and which would not be used during normal operational conditions).
  • the objective of SPS is to retain power system operational security.
  • Fig. 1 illustrates an electric power system 1 network with a system protection scheme according to the present invention.
  • the power network comprises a number of nodes 10 connected by power lines 16. (Only one of each item is provided with a reference number, unless specifically referred to.)
  • the nodes could be connected to generators 12 and/or loads 14.
  • System protection terminals 18 are provided at selected nodes, connected by measurement obtaining connections 20 to the nodes.
  • a communication network 22, having at least one substantially dedicated communication resource connects the system protection terminals to each other.
  • the nodes connected to the loads 14-A, 14-B and 14-C are provided with system protection terminals 18.
  • the illustrated electric power system 1 has in its left part high capacity generators 12 and in its right part many loads 14.
  • the general transmission situation is therefore normally that the left part generates power, which is transmitted to the loads in the right part.
  • Two main power lines connect the right and left parts of the power system.
  • the node 10-A in fig. 1 is illustrated in more detail in fig. 2.
  • the node is an interlocking installation and bus bars 24-A, 24-B are here used for connecting the different objects 12-A and power lines 16-A, 16-B and 16-C.
  • the power lines and objects are connected to the respective bus bars 24-A, 24-B via circuit breakers 28.
  • a circuit breaker 28- A is also provided at the interconnection 26 between the bus bars 24-A, 24-B.
  • the power system 1 has lost the generator 12-A and the power lines 16-A, 16-B and 16-C.
  • the generated power may perhaps be compensated by other generators in the power system, but all power now has to be transmitted by the single power line 16-D.
  • the power system is subject to enter a state of voltage instability, and perhaps an overload of the 16-D line.
  • the system equipment might however still be within permitted limits, and no further object/ equipment protection is activated.
  • Voltage stability problems can, however, within a time period of less than a minute cause a general breakdown of the electric power system 1, due to the low voltage level in the load area, load recovery, further voltage reduction, trip of overloaded equipment, and so on. A chain of events will thus lead to a breakdown.
  • the system protection terminals 18 will now come into action and save the power network.
  • the system protection terminals are in this example provided with means for obtaining time stamped voltage values, corresponding to the respective node. These time stamped voltage values are processed to give so called complex ac quantities. These complex ac quantities are communicated in the communication network 22 in order to spread the information within the system protection arrangement.
  • Each one of the system protection terminals 18 is in this example also provided with control signals providing means, which in turn comprises means for detecting serious risk for voltage instability. This detection means detects the risk of instability in the electric power system and provides control signals as a respond on the instability risk, e.g. when two of the nodes present voltage values are below 90% of the nominal values.
  • the control signals are sent to the respective nodes, in order to instruct a reduction of the magnitude of each of the loads 14-A, 14-B and 14-C.
  • line 16-D might be the critical one. To keep the integrity of the system it is very important not to trip this line. Therefore, load shedding of a fraction of the total load in the load area (preferably low priority load) might be enough to save the whole system. If no action is taken, the total of the right part of the power system, i.e. the load area, will probably experience a blackout.
  • fig. 3 a similar power network to the one illustrated in fig. 1 is shown.
  • five system protection terminals 18 are connected mainly to nodes in the left, high generating capacity part, of the electric power system 1.
  • One system protection terminal 18 is also present in the right, load area. Assume the same scenario of fault as in the above example.
  • each system protection terminal comprises a phasor measurement unit (PMU), characterising the dynamical evolution of the state in respective node.
  • PMU phasor measurement unit
  • the system protection terminals connected to nodes controlling a generator 12-B, 12-C, 12-D, 12-E, and 12-F are further equipped with means for recognising power oscillations.
  • This recognising means makes use of the data that is available at the communication system for detecting a power oscillation and to determine that the oscillation in this case is poorly damped.
  • the control signal means of the system protection terminals provides suitable control signals to the standard power system stabilisers (PSS) of the generators.
  • PPS power system stabilisers
  • damping means such as governor-boosting or breaking resistors to achieve satisfactory damping of the oscillations.
  • a similar power system is illustrated.
  • seven system protection terminals are introduced at locations all over the power system.
  • the system protection terminals are connected with a communication system 22, which in this example is meshed in order to provide back-up possibilities for malfunctions in certain communication links.
  • the evolving angular instability situation might be counteracted and the two parts of the system could be kept together - to the price of a comparably small amount of load shedding.
  • the best measuring criterion is probably based on the voltage phase angle difference between the two ends of the remaining transmission line 16- D, connecting the two areas.
  • the three examples above comprise system protection terminals in different configurations. In order to provide for a better total protection, the system protection terminal configurations may be combined. In fig. 5, only the system protection arrangement is illustrated, comprising terminals corresponding to the three above examples.
  • a common communication network 22 connects all of the system protection terminals.
  • each of the three examples above are provided as more or less separate systems, in that the communication of the measured characteristics of the power system are communicated in one resource each, over the common communication system.
  • the communication resources are of such capability that the data of all examples are possible to distribute within a certain satisfactory predetermined time.
  • the system protection terminals select which data is of interest for its own purposes.
  • the system protection scheme can therefore be built in a very modular manner, allowing for future adaptations to new operation conditions or to new network characterising equipment installed. Modes of the system, which are not influenced by the changes, may also be unchanged in the system protection scheme, and only the relevant parts have to be updated.
  • the communication system is one of the most important components in the present invention, it is preferred to provide a communication system which is as safe and reliable as possible.
  • One way to provide the reliability is to provide redundancy in the communication system.
  • Centralised protection schemes are typically based on communication systems built in a star-like or radial fashion, where the central unit communicates with the different peripheral units. For a centralised configuration, such designs are easy to implement.
  • the system protection terminals are provided as more or less identical protection units, which can be connected by a communication networks to operate anywhere in a power network as parts of a composed system protection scheme.
  • the system protection terminals 18 are here illustrated as exchangeable units comprising identical means and are only distinguished in the configuration of the software of each terminal.
  • an electric power system 1 comprises six system protection terminals 18, which are interconnected by a communication network 22.
  • Each system protection terminal 18 is connected to a control system 70 for input 72 of measured power system characteristics and for output 74 of control information to power network objects.
  • the system protection terminals 18 of this embodiment are further equipped with an GPS interface 76 and an operator interface 78.
  • the illustration of the communication network 22 in fig. 7 should be regarded as a general representation of a communication network of any configuration. As mentioned above, the network may in practise be formed e.g. as a loop or a meshed structure.
  • FIG. 8 A more detailed illustration of a system protection terminal 18 according to the embodiment of Fig. 7 is shown in Fig. 8.
  • Inputs 72 of measured power system quantities are received in the substation control system 70 by means of power system transducers and measurement devices 80.
  • the measurement signals are transferred into internal measurement signals in a measurement signal unit 82. These local signals are communicated to an input interface 88 of the system protection terminal 18.
  • a GPS time synchronisation unit 90 uses GPS signals 76 to create a time reference for the measured data. This time reference is connected to the input interface 88 to create a time stamp of the received measurements.
  • the time stamped measurements are further provided to a power system variable database 93.
  • the power system variable database 93 is in turn connected bi-directionally to a high speed communication interface 96, which handles the communication on the communication network 22 to other system protection terminals 18.
  • the data in the power system variable database 93 will in this way contain information, not only about the power network variables of units connected directly to the system protection terminal 18 in question, but through the communication network 22 also about power network variables associated with other system protection terminals.
  • the power system variable database 93 may therefore have, for its own purposes, a complete set of updated power system information.
  • This information is available for a decision making logic unit 92, which is also supplied with an appropriate time reference from the GPS time synchronisation unit 90.
  • the decision making logic unit 92 is the heart of the local part of the system protection scheme.
  • the decision making logic unit 92 interprets the available data and decides if any emergency actions have to be performed.
  • the decision making logic unit 92 uses an output interface 91 to send internal control signals to a control signal unit 86 in the control system 70.
  • a power system actuator unit 84 transfers the internal control signals into relevant control signals 74 acting on the associated objects in the electric power system 1.
  • the basic idea of this embodiment is thus that each system protection terminal 18 is responsible for measurements as well as emergency control signals to a number of objects in the power system. The decisions are made locally and may therefore more easily reach a sufficiently short reaction time on instabilities or disturbances. The design with local decisions for actions also improves the overall protection system reliability.
  • a supervision unit 94 for supervision, service, maintenance and updates communicates with the power system variables database 93 and the decision making logic unit 92.
  • This supervision unit 94 monitors and evaluates the operation of the system protection terminal 18 based on the information which was available in the power system variables database 93.
  • the supervision unit 94 comprises or is connected to a database of historic power system state information. Such a database may be used for post- analysis of stressed situations or as a temporary source of locally control information if the communication with other system protection terminals is broken.
  • the supervision unit 94 is bi-directionally connected to a low speed communication interface 97, for enabling communication with an operator via an operator interface 78. The operator is thereby allowed to monitor and influence the operation of the system protection terminal 18.
  • the low speed communication interface 97 is also connected to a parameter setting database 95, which in turn is readable by the decision making logic unit 92.
  • the parameter setting database 95 comprises parameters used by the decision making logic unit 92 in its operation. The operator thus has a possibility to manually tune the decision logics during operation, i.e. without taking the SPS out of service. .
  • the system protection terminal 18 may be necessary for emergency control of some power system objects, but no corresponding measurements are required.
  • the system protection terminal 18 may in such cases lack the units for measurement input, i.e. units 80, 82 and 88.
  • the entire information on which the decision is based is in such cases received by the communication network 22 from other system protection terminals 18.
  • the emergency control action decision is, however, made locally.
  • system protection terminal 18 acts as an administrative system for measurement input, and decision logics and associated units may be omitted.
  • the system protection scheme comprises a set of system protection terminals.
  • a first subset of terminals comprises means for measurement handling. This first subset may contain all terminals in the set or less. The first subset should, however, comprise at least two terminals, since the overall system concept otherwise would make no sense.
  • a second subset of terminals comprises means for emergency control. This second subset may contain all terminals in the entire set or less. It may also be identical to the first subset, if all terminals comprise both functions, or have a number of common terminals. The second subset should by the same reasons as for the first subset comprise at least two terminals.
  • a second subset of only one terminal would correspond to a centralised decision structure, which is one of the features that the present invention intends to avoid, due to the obvious disadvantages.
  • a neighbouring terminal may then effectuate the operation of such emergency control, by providing a connection between the output interface 91 and the high-speed communication interface 96.
  • the decision making logic unit 92 effects not only the decisions concerned with its own associated power system object, but also with power system objects associated with a neighbouring terminal. If a control action on such neighbour object is determined, the internal control signal is provided to the high-speed communication interface 96 for further delivery to the neighbouring terminal. In the neighbouring terminal, which basically lacks the decision logics, the control signal is received in the high-speed communication interface 96 and is forwarded directly to the output interface 91.
  • Such solutions are, however, not suitable when the time aspects are critical, since it involves additional communication steps.
  • Fig. 9 shows a flow diagram of a general method for system protection according to the present invention.
  • the process starts in step 200.
  • step 202 measurement signals corresponding to power system characteristics are collected in terminals comprised in a first subset of terminals. Data associated with the measurements are communicated to terminals comprised in a second subset of terminals in step 204. The communication takes place via a substantially dedicated communication resource.
  • step 206 the terminals of the second subset processes available data for evaluating system stability and disturbance situation.
  • the method according to the present invention may be implemented as software, hardware, or a combination thereof.
  • a computer program product implementing the method or a part thereof comprises a software or a computer program run on a general purpose or specially adapted computer, processor or microprocessor.
  • the software includes computer program code elements or software code portions that make the computer perform the method using at least one of the steps previously described in fig. 9.
  • the program may be stored in whole or part, on, or in, one or more suitable computer readable media or data storage means such as a magnetic disk, CD-ROM or DVD disk, hard disk, magneto-optical memory storage means, in RAM or volatile memory, in ROM or flash memory, as firmware, or on a data server.
  • Suitable primary power system quantities that can be measured and used as inputs to the system protection terminals are e.g. voltage, current, status of power system high voltage equipment, status of power system control and protection equipment, such as start and trip signals, and positions or actual values for control functions.
  • the magnitude, phase angle and frequency are the most interesting features when measuring voltages and currents.
  • Power system high voltage equipment comprises equipment such as transformers, circuit-breakers, disconnecting switches, capacitor banks, reactors and power system control and protection equipment comprises e.g. voltage regulators, speed-governor controls, valve actuators, relays as well as HVDC and FACTS controllers. Also other quantities may be used.
  • the quantities are preferably time stamped.
  • phasor quantities From time stamped measures, complex ac quantities, so called phasor quantities, are derivable.
  • the quantities may be communicated as measured or may be pre-processed before being communicated to other terminals. Based on these quantities a large number of related quantities can be derived, such as frequency, derivatives of the quantities, active and reactive power. Also sums, differences, maximum and minimum values are easily derivable. Also relation quantities such as thresholds, "larger than”, “smaller than”, etc., can be computed and used.
  • the measurements can be derived from many different transducers in the power system.
  • Non-limiting examples are e.g. voltage transformers, current transformers, binary signals from relays, active and reactive power transducers, generator speed transducers and temperature transducers.
  • More specific transducers such as phasor measurement units (PMUs), voltage instability predictors (VIPs) as well as transducers sensitive to frequency instability, poorly damped power oscillations and transient instabilities, can also be used.
  • PMUs phasor measurement units
  • VIPs voltage instability predictors
  • transducers sensitive to frequency instability, poorly damped power oscillations and transient instabilities can also be used.
  • a phasor measurement unit provides continuous or sampled phasor measurements in real time. Synchronised phasor measurements are e.g. described in "Synchronized Phasor Measurements in Power Systems" by A.G. Phadke in IEEE Computer Applications in Power, Vol. 6, No 2, April 1993, pp 10- 15. Such equipment is commercially available from several different suppliers, e.g. PMU model 1690 from Macrodyne, Inc. This PMU unit has an effective sample rate of more than 2 kHz and is time synchronised using GSP time to an accuracy of 1 ⁇ s.
  • VIP voltage instability predictor
  • Predictors sensitive to frequency instability, thermal violations having an impact on stability properties, poorly damped power oscillations and transient instabilities may in the same manner be utilised in the system protection scheme. They may be implemented as separate units operating only on local measurements, or may be implemented as a part of the system protection terminal decision logics.
  • the emergency control actions are sent as orders to objects in the power system.
  • Suitable, but non-limiting examples could be generator governors, generator AVRs (Automatic Voltage Regulators), HVDC (High Voltage Direct Current) controllers, SVC/FACTS (Static Var Compensator/ Flexible AC Transmission Systems) controllers, transformer OLTCs (On- Load Tap- Changers) and circuit breakers for e.g. load shedding, generator rejection, shunt capacitors and shunt reactors.
  • Most conventional controllable objects may be used to perform required emergency control actions according to the decisions made by the system protection terminal.
  • the communication system is an important part of the present invention. Since the system protection scheme operates in the emergency state of operation of a power system, the time is an important factor. Data has to be communicated between the different system protection terminals in such a fast manner that emergency actions still may have the intended effect. Using ordinary communication systems, sharing the communication resources gives an unacceptable uncertainty of the communication speed.
  • the communication system of the present invention thus requires a substantially dedicated communication resource for the communication between the system protection terminals.
  • Such dedication ensures that the transmission times within the communication network can be estimated and all data can be available at all terminals within a predetermined time.
  • the value of this time depends on the transmission capacity of the communication resource, the amount of data to be communicated and the communication network configuration.
  • the requirements on the predetermined maximum communication time is in the order of fractions of a second. A few hundred milliseconds are needed for transient angular instability and transient voltage instability. Time limits of a second might be enough for frequency instability and damping purposes. For protection against longer-term voltage instability, communication times of up to five seconds are normally acceptable.
  • the capacity of the communication resource has to be adapted thereafter, stressing the importance of fixed (or at least predictable) delays in the communications system.
  • communication resource is in this document referring to any limited, allocable communication resource. Examples could be time slots or frequency bands in radio transmitted communication systems, or even separate physical links, such as dedicated fibres or wires. The important feature is that the capacity of the resource is permanently allocated to the system protection scheme communication and not influenced by competing traffic.
  • the power system can be modelled with one set of differential and one set of algebraic equations, i.e. a differential-algebraic system of equations or a DAE model.
  • a general form for a DAE model can be written as:
  • x is a vector of dynamic system states, sometimes called state variables
  • y is a vector of algebraic, power flow
  • states i.e. system variables associated with the nonlinear algebraic constraints
  • p is a vector of parameter values.
  • inequality constraints can for example represent system variables, such as currents and voltages, which must not exceed maximum levels representing the limitations of physical equipment.
  • the inequality constraints if necessary could be split into one set of strict inequalities and one set of inequalities greater or equal than zero; i.e. 0 > Hl[x,y,p) and 0 ⁇ H2 ⁇ x,y,p). In most instances, it is possible to re-write all types of inequality constraints into strict inequalities.
  • the states of operation can be based on the above basic DAE model augmented with a security margin giving the distance to defined insecure state.
  • margins for transmission as well as for generation must be sufficient to provide an adequate level of security with respect to the stresses to which the system may be subjected. If a disturbance according to the design criteria applicable to the studied power system would result in a violation of some inequality (or even worse equality) constraints, the margin for this case would be considered insufficient (negative). The equipment would e.g. be overloaded more or less severely above its rated capabilities
  • the states of operation to be defined are mainly aimed at power system operation, e.g. in control centres, where the main parts of studies, today, are performed in a static or at least a quasi-static environment.
  • power system dynamics can be divided into electromagnetic, electromechanical and longer- term phenomena. This division is based on the time-scale in which different phenomena exert their main influence. All electromagnetic and electromechanical dynamics of generators as well as all dynamics of network and loads are in the following discussion considered to be at steady-state, i.e. the corresponding state variables are at equilibrium values.
  • An equilibrium point is asymptotically stable if all nearby solutions not only stay nearby, but also tend to this equilibrium point as time goes to infinity.
  • the operating point of the studied system of state variables will after the last switching operation, i.e. for the post-fault condition, lie in the region of attraction of the post-fault equilibrium point which is an asymptotically stable equilibrium point, if such a point exists. If this assumption is severely violated, it will also manifest itself in the equality and inequality constraints.
  • the differential set describes the physical laws governing the dynamic behavior of the system's components.
  • the two algebraic sets comprise "equality constraints" and "inequality constraints”.
  • the equality constraints refer to the system's total load and total generation.
  • the inequality constraints state that some system variables, such as currents and voltages, must not exceed maximum levels or fall below minimum levels. Maximum levels can e.g. represent limitations due to thermal stress of physical equipment.
  • M M ⁇ 0 . If M is positive, M > 0 , then the security margin is sufficient with respect to design criteria for the power system, i.e. dimensioning rules. The equality and inequality constraints are either considered “ok” if they are fulfilled or “violated” if they are not fulfilled, while the margin is considered “ok” if it is positive and “violated” if it is negative.
  • H ok i.e. H(x,y,p) ⁇ 0

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Remote Monitoring And Control Of Power-Distribution Networks (AREA)
  • Supply And Distribution Of Alternating Current (AREA)

Abstract

La présente invention concerne un schéma de protection système comprenant au moins trois bornes de protection système (18), introduites en des emplacements adaptés d'un réseau d'énergie électrique (1). Les bornes de protection système (18) sont interconnectées par un système de communication (22) à l'aide d'une ressource de communication sensiblement spécialisée. Au moins deux des bornes de protection système (18) sont équipées de façon à pouvoir collecter des signaux de mesure (72) associés à des caractéristiques du réseau électrique en cet emplacement particulier. Les mesures, de préférence, comprennent des quantités ca complexes et des indicateurs de stabilité. Les signaux sont traités et les données relatives aux mesures sont distribuées aux autres bornes de protection système (18) au niveau de la ressource de communication spécialisée. Au moins deux des bornes de protection système (18) sont équipées de façon à pouvoir évaluer l'état de la partie associée du réseau électrique et, si besoin, fournissent des signaux de commande (74) à des unités de réseau électrique. L'évaluation est basée sur des parties sélectionnées des données disponibles au niveau de la ressource de communication et des données localement disponibles.
PCT/SE2001/001067 2000-05-31 2001-05-16 Schema de protection systeme WO2001093405A1 (fr)

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SE0002050A SE517963C2 (sv) 2000-05-31 2000-05-31 Nätvärnssystem för skydd av ett totalt elkraftsystems integritet, elkraftsystem innefattande ett nätvärn, systemskyddsförfarande, systemskyddsterminal samt datorprogramprodukt

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Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2005088802A1 (fr) * 2004-03-08 2005-09-22 A. Eberle Gmbh & Co. Kg Dispositif de prevention de grandes pannes dans des reseaux d'alimentation electrique
EP2124311A1 (fr) * 2008-05-23 2009-11-25 ABB Research LTD Compensation de temporisation dans le contrôle d'un système d'alimentation
WO2009141297A1 (fr) * 2008-05-23 2009-11-26 Abb Research Ltd Compensation des retards dans la commande des systèmes électriques
CN102099982A (zh) * 2008-05-23 2011-06-15 Abb研究有限公司 电力系统控制中的时延补偿
US8497602B2 (en) 2008-05-23 2013-07-30 Abb Research Ltd Time delay compensation in power system control
CN102355055A (zh) * 2011-09-09 2012-02-15 航天科工深圳（集团）有限公司 一种实现数据同步的配网采集终端
CN102394742A (zh) * 2011-09-09 2012-03-28 航天科工深圳（集团）有限公司 一种配网采集终端数据同步的方法和装置
WO2015164292A1 (fr) * 2014-04-22 2015-10-29 Siemens Aktiengesellschaft Architecture de commande flexible pour l'élasticité d'un microréseau
US10116164B2 (en) 2014-04-22 2018-10-30 Siemens Aktiengesellschaft Flexible control architecture for microgrid resiliency
CN104898606A (zh) * 2015-04-10 2015-09-09 航天科工深圳（集团）有限公司 智能环网柜及其监控单元系统和监控方法
US10983150B2 (en) 2017-08-28 2021-04-20 General Electric Technology Gmbh Systems and methods for detecting and evaluating oscillations in an electrical power grid

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