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  • access - Specific interaction between a subject and an object that is intended to result in the flow of information from one to the other.
  • Access Control - Means of restricting access to objects based on sensitivity (as represented by a label) of the information contained in the object and formal authorization of subjects to access information of such sensitivity.
  • accumulator - An integer value that counts the number of pulses or transitions of a binary input.
  • adaptive relaying - Protection system in which lower-level setpoints, relay logic, and relay action setpoints are adjusted based on data either locally acquired, or provided by the neighboring device on the same level locally or remotely, or sent down from a higher level.
  • addressing - Means to identify the source and sink (recipients) of all information transfers.
  • adjacent substation protection - Protection of power system equipment at one substation based on data measured at others. Examples are line differential protection and teleprotection schemes.
  • agent - Servers that are designed to work with compatible client stubs known as user agents which share the same server protocol. Agents are responsible for picking up and delivering messages between senders and receivers.
  • alarm processing - Alarm analysis procedures to improve presentation of alarm data. It ranges from updating alarm lists and producing group alarms up to more intelligent evaluations.
  • attribute - Represents a property or facility of an object (something that an object knows). It reflects both the problem domain and the system?s responsibilities as some data (state information) for which each object in a class has its own value.
  • automatic reclosing - Automated closing of breakers after the trip by a relay fulfilling some local and/or remote boundary conditions like synchrocheck reclose if applicable.
  • automatic switching sequences - Automatic sequential operation of groups of power system devices to reduce operator workload and/or switching time and to avoid unsuccessful or unnecessary switching attempts.
  • availability of data - State in which data are where the user needs them, when the user needs them, and how the user needs them.

  • BFI - Breaker Failure Initiate.
  • breaker - Device that connects and disconnects energized power circuits, with fault interrupting capability under normal operational conditions (nominal values for current and voltage) and that is capable of interrupting short circuits (synonymous with circuit breaker).
  • breaker (health) monitoring - Automated procedure to measure breaker operating times and accumulated interrupting duty for maintenance scheduling or maintenance on request.
  • breaker failure protection - Backup protection scheme to trip all connected breakers if a breaker fails to trip on a detected fault.
  • broadcast - Simultaneous transmission of data to all destinations on a network.
  • busbar fault isolation - Minimizing propagation of bus and feeder faults. Subset of the general term ? fault isolation (transformer fault, etc.).
  • busbar protection - Scheme to detect busbar faults and trip all breakers attached to the faulted busbar.
  • busbar restoration - Formal procedures for service restoration after busbar trips, very often according to fixed or load dependent priorities (see also ? load shedding).
  • busbar voltage control - a) Automatics to maintain scheduled busbar voltage by any means (tap change, VAr control, etc.). b) Network analysis to determine optimal settings of power system devices to maintain bus voltage.

  • calibrate function - Process of adjusting internal parameters of a measurement unit to reduce errors in its measured values.
  • capacitor bank - Group of capacitors used to adjust power circuit impedance.
  • circuit breaker - Device that connects and disconnects energized power circuits under normal operational conditions (nominal values for current and voltage) and is capable of interrupting short circuits (synonymous with breaker).
  • Client - An IED object that requests information from another (i.e., from the server).
  • Client/Server architecture - An application architecture where one end system (the client) requests another end system (the server) to perform operations and to give back results.
  • Client/Server concept - Communication management scheme in which multiple objects (i.e., the client(s)) can request specified information from one or more other objects (i.e., from the server(s)). Only Clients may issue unsolicited data. Usually data flows primarily from the server to the clients.

  • Client/Server operation - Complete transaction consisting of a request followed by an information delivery of requested information.
  • cold load pickup - Automated procedure to change feeder relay settings to pick up load after an extended outage (special case of adaptive relaying).
  • Cold-Load Pickup Control - Detection of the possibility of cold-load pickup (according to the cold-load pickup time delay) before closing the feeder Breaker refers to the need to either inhibit the instantaneous setting of the OvercurrentProtection, or to raise the Overcurrent settings for a certain period of time when the circuit is energized. By doing so, the protection settings can take into account transient current increases on circuit energization, and the normal fault settings can be adjusted closer to the load profile.
  • communication interface - Serial interface of a device that allows exchange of (physical and logical) information among devices of the same or different functional levels in a hierarchical system. An interface specifies the connection of a communication link, with regard to the mechanical connection as well as to the signal?s physical and functional characteristics. A well known example of an interface is CCITT V.24/V.28 whose American counterpart is EIA RS-232C.
  • configuration data exchange - a) Power system topology exchanges with other, usually neighbor, utilities. b) Exchange of any kind of configurations from power system topology to device setups (parameters, terminals).
  • Critical (synonymous with integrity) - Three levels of data (delivery) criticality are required:
    High, where delivery is essential to operation of the power system (e.g., delivery of a SCADA control command). Examples are settings, commands switchgear states or positions, blocking, releases, trips, synchrocheck detection, and total energy.
    Medium, where later repetition by application of a failed data transfer is acceptable (e.g., delivery of a stored data file) Examples are measured values (measurands) and disturbance recorder data.
    Non-critical, where the recipient can tolerate occasional transfer failures (e.g., delivery of periodically updated data to a data monitoring or averaging process) Examples are repeated continuously polled data and display values.
  • CSOM - Client-Server Object Model.
  • CT - Current Transformer.

  • data - Information with specific physical representation.
  • Data Acquisition Unit (DAU) - General purpose data collector, often used for sensors.
  • data confidentiality - Security service that provides for the protection of data from unauthorized disclosure.
  • data integrity - Security service used to determine if data has been altered or destroyed in transit.
  • Data Object - A Data Object is an abstract element of a real device which is capable of providing (when read) or accepting (when written) or both, a typed data value. A Data Object may represent a single data element (i.e., one measurement point) or a data structure (i.e., a complex set of data elements). The mapping of a Data Object to a real, physical entity in the device is defined by the model of the device being represented, and is outside the scope of this document.
  • data transparency - Data transmission in which there are no restrictions on the bit patterns that user data may have.
  • DataSet - A DataSet is a ordered list of references to Data Objects associated with a specific DataSet Name. A DataSet is a means of grouping data together that is frequently accessed as a group.
  • deadband - The amount by which an analog input must change from the last reported value to be spontaneously reported.
  • Definite Time OvercurrentProtection - The Definite Time OvercurrentProtection corresponds to the definition of IEEE Device Number 62. If there is no intentional time delay, then the Overcurrent ProtectiveDevice corresponds to the definition of the IEEE Instantaneous Overcurrent Device Number 50 and 50N.
  • denial of service - Accidental or intentional actions by a communication network node that disable normal operation of any part of the network and can result in denial of (communication) service to other network users.
  • device - Physical entity connected to the communication network composed of at least one communication element (the network element) which may have a control element and/or a monitoring element (transducer, actuator, etc.).
  • DeviceIdentity - The DeviceIdentity, DI, contains the nameplate information of a device such as make, model, and serial number.
  • Digital Fault Recorder (DFR) - Device that samples and stores analog and related binary sensor data during power system transients for later replay and analysis.
    Directional OvercurrentDirectional overcurrent relaying is necessary for the protection of multiple-source feeders, when it is essential to limit the tripping of faults in only one direction. Fault directional control is possible for faults on each phase, as well as the neutral. Directional current sensing and control requires a voltage, current, or a dual polarizing signal for selective detection of the direction or phase of the fault current. If directional overcurrent control is enabled, the overcurrent protection is inhibited for faults in the non-trip direction.
  • directory - Collection of open systems which cooperate to hold a logical data base of information about a set of objects in the real world (e.g., OSI users and network resources). The directory also provides services for users (people and application processes) to access the information contained in the repository.
  • EDC - Embedded Device Controller.
  • EPRI - Electric Power Research Institute.
  • equipment clock synchronization - Automated procedure to maintain consistent time data throughout the substation or power system, e.g., for time tagging or synchronized sampling.
  • equipment diagnostics - Procedures that monitor the on-line operation of power system devices, perform off-line tests, and provide early warning of potential failures (see also breaker health monitoring). The goal is optimized maintenance scheduling (maintenance on request).
  • Event Report - Event Report is the report generated in the Server by the action of a Transfer Set to be sent to the Client.

  • Fault Identification and Location - This is logic that determines the type of fault, e.g., phase-to-phase, etc., the distance to the fault, and the impedance of the fault.
  • fault isolating - Minimizing the impact of a fault on a power network device (transformer, busbar, Switchgear, etc.).
  • fault recording - Procedures for collection, storage, and analysis of power system fault data.
  • feeder fault isolation - Automated procedure to operate feeder sectionalizing switches (isolators) to bypass a faulted feeder section.
  • feeder fault location estimation - Procedure to locate feeder faults to minimize service restoration time.
  • feeder monitoring - Display of feeder breaker and connectivity status.
  • feeder switching - Automated procedure to manage feeder connectivity changes (see also automatic switching sequences).
  • freeze - To copy the current value of an accumulator to another memory location.
  • functional block - An autonomous function, such as auto-reclosing, operational units, breaker failure protection, disturbance recording, etc., which might be implemented in separate hardware.
  • gateway - Processor providing communication protocol conversion services to permit communications between dissimilar data systems.
  • generator protection - Schemes to protect generators from fault conditions such as loss-of-field, motoring, and from all other potentially damaging conditions.
  • Global Positioning System (GPS) Receiver - Device that acquires precision time and position data from the U.S. Department of Defense system of a constellation of low-orbit satellites for position determination world-wide. For substations it is used as time receiver for equipment clock synchronization.
  • GMT - Greenwich Mean Time.

  • High Impedance Fault (HiZ) Detection - HiZ detection reports possible high impedance arcing fault conditions on the feeder. A high impedance fault is characterized as having an impedance sufficiently high that it is not detected by conventional OvercurrentProtection. To date, this has been commercially applied to distribution feeder ProtectiveDevices, and is mostly used in the monitoring and alarm mode.
  • IEC - International Electrotechnical Commission.
  • IEC TC 57 - International Electrotechnical Commission Technical Committee 57.
  • instance of (when instantiated) - Phrase used to denote that an abstraction (class-object) takes on a real-world form and behavior of a person, place or thing that it represents. An instance of is usually denoted by an attribute identifier that it inherits from the parent or is an attribute of the class-object instantiated.
  • integrity - Immunity requirements to the network of data transfer errors due to accidental or intentional interference. Three levels are defined:
    High, where a vanishingly small probability of undetected error must be achieved.
    Medium, where inherent data redundancy provides adequate error immunity.
    Low, where errors are merely a nuisance to the data recipient.
  • Intelligent Electronic Device (IED) - Programmable monitoring, control, protection, or data processing device with at least one serial communication interface.
  • interchangeability - Two IEDs are interchangeable when one can replace the other without changing external functionality or performances.
  • interoperability - Two IEDs are interoperable when able to exchange information needed for their on-line operation. This is normally achieved by using only published standard data and object definitions, standard commands and standard protocols at all relevant layers of the OSI Reference Model.
  • Inverse Time Overcurrent - This device determines whether a fault exists in its associated power apparatus by comparing a current (Ampere) measurement against a threshold (trip setting) value. However, the trip setting is determined (characterized) by a settings curve (time versus measured current). The curves are characterized by varying degrees of the inverse relationships of current to time duration. If the measured current exceeds the trip setting for the corresponding time on the settings curve, a fault is indicated.
    The Inverse Time OvercurrentProtection corresponds to the definition of the IEEE Inverse Time Overcurrent Device Number 51 and 51N.
  • ISO - International Organization for Standardization.
  • isolator - Device that connects and disconnects de-energized power circuits.
  • journalin - Means to maintain an audit trail of all control activities.
  • kb - Kilobytes.
  • line fault location - Procedure to locate line faults to minimize service restoration time.
  • line load monitoring - Automated supervision procedure to support line operation close to limits.
  • line protection - Scheme to detect line faults and trip all breakers attached to the faulted line.
  • load flow control - Procedure to manage transmission or distribution line loading.
  • load tap changer (LTC) - A power switch integral to a LTC transformer or step-voltage regulator that accommodates adjustment of the voltage ratio while operating under load.
  • Load tap changer (LTC) control - Electronic device which receives scaled system voltage, current or other signals, compares existing operating conditions to that desired and accordingly commands load tap changer action.
  • Load tap changer controller relay - Device that manages the operation of a load tap changer on a transformer or step-voltage regulator. Synonymous with voltage regulating relay when used for control of the system voltage.

  • management information base - The set of managed objects in a system, together with their attributes, constitutes that system's management information base. It is a conceptual repository of management information at each system.
  • management information library - A document containing the specification of all defined managed objects and a complete description of their behavior. Development of this library is currently being proposed by groups such as the NIST OSI Implementers' Workshop Group.
  • master - The remote client that requests information or a control operation from an RTU. Usually referred to in the singular, but there may be more than one.
  • Master/Slave - Communication management scheme called polling in which one IED (the Master) requests a specified one of a group of IEDs (Slaves) to deliver specified information. Only Masters, not Slaves, may issue unsolicited data or commands. Used where data flows primarily between the Slaves and the Master. Quiescent reporting schemes use an implied initial data request solicitation by the Master.
  • MB - Megabyte.
  • meter - Device that uses sensor data to calculate real and reactive power and energy.
  • method - Specific behavior that an object is responsible for exhibiting. The central issue in defining services is to define required behavior classified as follows: 1) on the basis of immediate causation, 2) on similarity or evolutionary history change over time, and 3) on the similarity of function. A service also defines the necessary communication between objects.
  • MMI - Man-machine interface.
  • MMS - Manufacturing Message Specification.
  • modem - Modulator/Demodulator; electronic device that enables digital data to be sent over analog transmission facilities.
  • ms, msec - millisecond.
  • multicast - Simultaneous transmission of data to a defined group of destinations on a network.
  • Negative Sequence Overcurrent Protection - Negative sequence instantaneous and time overcurrent is used to increase sensitivity in the detection of unbalanced load and fault conditions, e.g., in the unbalanced loading of a generator, or unsymmetrical types of faults on a feeder. The negative sequence settings can be set below load current levels since normal, balanced load currents do not generate negative sequence current. This relay monitors the negative sequence current of each phase.
  • NegativeSequence - OvercurrentProtection corresponds to the IEEE Device number 46
  • non-repudiation - Method by which the sender of data is provided with proof of delivery and the recipient is assured of the sender?s identity, so that neither can later deny having processed the data.

  • OSI - Open Systems Interconnection.
  • out-of-step protection - Automated detection of potential generator phase slip to avoid generator damage, to manage power network islanding, and to prevent undesired line relay action in the event of a stable power swing.
  • peer-to-peer - Ability of arbitrary pairs of network nodes to manage communication mutual information in contrast to the master/slave communication.
  • phase shifter control - Procedure to control the load tap changer of phase shifting transformers to manage phase angles and load flows.
  • Phasor Measurement Unit (PMU) - Device that extracts line-frequency phase angle and magnitude data from sensor signals.
  • pilot channel monitoring - Automated procedure that reports detected failures of protective relaying signaling channels.
  • PLC - Programmable Logic Controller.
  • point - Physical input/output hardware, or the data describing that hardware.
  • power flow control - Automated procedure to manage power transfers through power transmission and distribution networks.
  • power quality monitoring - Procedures for collection, storage, and analysis of power quality data at subtransmission and distribution load points.
  • priority - Ability of the communication network to support several levels of message priority. Higher priority messages are given access to communication resources before lower priority messages.
  • protection facilities - Manual support of protection system operations.
  • Quality of Service (QOS) - A parameter specifying the level of performance needed for communications, such as transit delay, priority, accuracy, or reliability.
  • RCB - Report Control Block.
  • RCL - Relay Control Logic.
  • reactor/capacitor protection - Scheme for detailed monitoring of reactive devices to detect internal faults and to trip all breakers connected to the faulted reactor/capacitor.
  • recloser - Special purpose breaker with integral relaying that automatically trips and recloses to minimize service restoration time after temporary faults.
  • recloser control - Automated procedure to manage the setpoints of reclosers to minimize service restoration time.
  • regulator - Abbreviated form for step-voltage regulator. Often incorrectly used when load tap changer controller relay is intended.
  • relay - Device that uses sensor data to protect major power system equipment items.
  • relay setting control - Procedure to manage the adjustment of setpoints in protective relaying equipment.
  • relay setting update - Procedures that report existing setpoints of protective relays and support the delivery of revised settings.
  • relay testing - Procedures that support testing of protective relay equipment.
  • Remote Terminal Unit (RTU) - A device that concentrates sensor data for transfer to, and accepts power system device control commands from, an external SCADA system.
  • Report By Exception (RBE) Criteria - RBE Criteria are the values against which Data Objects in a DataSet will be checked to determine if an event condition has occurred. When an event condition occurs, then specified Data Objects in the DataSet are collected to be transmitted to the designated Client.
  • Report Control Block (RCB) - A data structure which describes the criteria for the Server to initiate Unsolicited Data transfers by time and/or event. The data transmitted will either be the complete Data Object or DataSet (no RBE), or it will be only the changed values within a Data Object or DataSet (if RBE is specified).
  • Report-By-Exception (RBE) - Mode of operation in which an end system (e.g., RTU or IED) only reports information that has changed since data was last transmitted.
  • response time - Time between the request and the response for a network transaction.
  • RLC - Reactive Line Component.
  • RTU - Remote Terminal Unit

  • SBO - Select Before Operate.
  • SCADA - Supervisory Control and Data Acquisition.
  • scale - Multiplier used to convert a value from the measured value to the appropriate units.
  • Scan group - RTU/SCADA term for a data set
  • security - Immunity of network resources to accidental or intentional unauthorized access. Three levels are defined:
    High, where access is limited to predefined and validated Clients.
    Medium, where access is granted to any Client meeting simple criteria.
    Low, where access (usually read-only) is granted to any Client.
  • Select Before Operate (SBO) - Is a sequence of control services consisting of the Select service and the Control/Operate service. The Select service is used to arm an Select Before Operate (SBO device prior to operation. The Control service is used to carry out a control command after a Select has succeeded. This sequence has the effect that a client can lock-out other clients from operating a point for a pre-determined period of time so that it is the only client that can operate the point.
    sensorSensing device for physical variables such as ac and dc Voltage and Current, Switch Status, Temperature, Humidity, etc.
  • Sequence of Events (SOESequence Of Events) - An ordered, timestamped log of the state changes of binary inputs (also known as status inputs). Used to recreate or analyze the behavior of a power system over a period of time.
  • Sequence of Events (SOE) Recorder - Device that samples and stores all events like contact status changes, trips, limit violations, etc., for later replay and analysis. The events are time-tagged at the source.
  • Sequence-of-Events Monitoring - Procedure to manage the collection, analysis, and presentation of SOE data.
  • server - Object that provides information to another (i.e., to the Client). Typical examples of servers are station computers and bay control/protection units. In substation applications servers have real-time requirements and are running with real-time operating systems.
  • SQL - Sequential Query Language.
  • step-voltage regulator - Device used in the power circuit to regulate the system voltage, usually to within +/-10% of its input voltage level.
  • supervisory control - Arrangement for operator control and supervision of remotely located apparatus using multiplexing techniques over a relatively small number of interconnecting channels.
  • switch - Common denominator for circuit breakers and isolators (i.e., for the switching elements in the power network).
  • synchro check - Automatic procedure to check if frequency, voltage and phase match when interconnecting energized portions of the power network.
  • synchronization - Automatic procedure to reach frequency, voltage and phase match when interconnecting energized portions of the power network by active means (excitation, etc.).
  • syntax - Grammar or structure rules which must be adhered to by a language (e.g., transfer syntax).
  • TAL - Time-Allowed-to-Live.
  • Tap changer - In general, may refer to a load tap changer or a deenergized tap changer. Will be used as an abbreviated form for load tap changer in the context of this document.
  • tap changer controller - Device that manages the operation of load tap changers or voltage regulators for control of voltage level (synonymous with voltage regulation relay in the context of this document).
  • tie tripping - Procedures to separate and reconnect the two parts of a split bus to minimize fault propagation through the power network.
  • timestamping - Message contains a field that tells the age of the information that it carries.
  • transformer - Device that links power system circuits at different ac voltage levels.
  • transformer circulating reactive current control - Automated procedure to detect and reduce excessive circulating reactive currents as may result from the parallel operation of non-identical LTC transformers.
  • transformer protection - Scheme to detect transformer internal faults and to trip all breakers connected to a faulted transformer.
  • UCA - Utility Communications Architecture.
  • UF - Under Frequency.
  • UMS - Utility Message Specification.
  • unit tripping - Automatic disconnection of a faulted generator unit.
  • unsolicited message - Message transmitted in response to a locally occurring event, rather than an explicit remote request.
  • VAr controller - Device that manages the operation of banks of capacitors and/or inductors for control of reactive power flow.
  • virtual device - Class of power system substation devices.
  • volt and VAr control - Procedures to manage bus voltages and VAr flows throughout the transmission or distribution network.
  • voltage regulating relay - Device that manages the operation of a load tap changer on a transformer or step-voltage regulator when applied for the purpose of controlling system voltage.
  • voltage regulator - Abbreviated form for step-voltage regulator. Often incorrectly used when load tap changer controller relay is intended.
  • VT - Voltage transformer.

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