Application of a Grid Data Language for Power System Data Base Definition and Query

Copyright © I FAC Power Systems Modelling and Control Applications, Brussels, Belgium 1988

APPLICATION OF A GRID DATA LANGUAGE FOR POWER SYSTEM DATA BASE DEFINITION AND QUERY D. Rumpel, U. Post and R. Zaluk Duisburg L'nil'enity, FRG

Abstract.Electrical Energy systems - as seen by operation - consist of objects. The objects have properties and can assume states. On the one hand the objects, by hierarchical aggregation, form larger units as bays switchyards or substations; on the other hand, a subset of the objects is topologically linked and meshed. Starting from that view, a combined network/hierarchical-data base was developed. This data base is defined and filled using a source-language which is capable of expressing the stock of objects and its topological linkage in format free a-text. The present paper further describes a newly developed query language and the related query and state setting system, applied in simulation and software test mode. For accessing the DB-contents and convenient formulation of queries, the automatic design and production of a functional keyboard was developed. Keywords. Data handling; hierarchical systems; powersystem control; on-line operation; process control

This application is in further development at Duishurg University. On the base of the data language, a query language was developed. This query language is used to set and inquire object states in training, system development and test, but can also be applied for general process inquires during operation. For convenient formulations of queries, a function-keyboard is plotted and put on a digipad. This keyboard is automatically derived and dimensioned from the data base and its contenta.

INTRODUCTION

The computer aided operation of power systems requires a data base (DB), which among other data contains a data model. This data model has to map the full stock of objects present in the power system as well as the geographical, topological and functional relations between objects. Further, the actual states of all objects have to be administered in the model. Compared to other DB-applications, power system data models require a rather unique combination of properties : -they have to administer a considerable number of single objects (several 10 thousands to a few 100 thousands), composed from a considerable variety of object classes (several ten to a few hundred) • -they have to provide extremely fast access (in the I1sec-range) to the state of the objects. -they have to provide easy facilities to amend the stock of objects, as well as the linkage between objects, in accordance to more or less continous construction work and equipment chanie going on in the network. -the amendment must not require process interuption.

SCXJRCE LANGUAGE

Object Descriptor An object is identified by a hierachical descriptor, also used as a primary key, consisting of four names: - a 1D8.X. 5 character name ("Local" abbr. "L") - a 1D8.X. 5 character number ("Nuneral" abbr. "N") - a 1D8.X. 8 character name ("Partial" abbr. "P") - a 1D8.X. 8 character name ("Species" abbr. "S")

The following notation is used for the descriptor:

Starting with these requirements in mind, a combined hierarchical/network DB-system was developed. The system provides DB-definition from the source data, as well as forward/backward translation from source to DB-code and vice versa during amendment. It features a grid data language described by Rumpel (1983) and Rumpel, ReiBig (1984) which allows a very efficient editable source description of the stock of objects including the (potential) topology of the network in abbreviated operator's terms. Thus, it combines readabili ty by man and computer. The efficient source code is also of advantage in describing the different networks to be handeled in stand alone training simulators.

"'L' 'N'P[S]

(1 )

The hierarchical rank of a name is expressed by the number of preceding apostrophs. The primary key is not semantically confined and can asSt.llle different meanings depending on the situation. (see fig. 1)

73

74

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ploiting this fact, the grid data language expresses linkage wi thin bays by the syntax of the chained object enuoeration, cormections within a switchyard by short references, and only the remaining 10-2~ of topological links require references carrying the full object descriptor to the next cormected object. The syntax is capable of mapping a tree structure of any dimension. References are attached to the objects (in source language as well as in the data element of the DB). In that way the text of fig . 2 includes also the full description of the topological linkage of the substation.

Semantic Use of the Descriptor

The first three names in most cases define the location, and the fourth name the kind of the object. Stock Description by chaining The description of a grid becomes very effective by "chaining" . This implies that a hierarchical name written in the text remains valid, until it is replaced by a name of the same rank or superseded by a name of higher hierarchical rank. Fig . 2 shows an example of a small substation ; the equipment is described in chained fashion, e. g. The numeral ntmber "20 for 20KV objects remains valid for all objects until it is replaced by the numeral number "2 for transformers etc .• Dictionary and Attribute assignment The chained description of fig. 2 defines the number and kinds (species) of objects existing in the substation. Species have properties and can assume states. Vice versa, one species (repeating in different objects under different locations) is defined by the fact that its properties and potential states are always the same. Species are defined via a dictionary which for each species contains: -the species name -the species number -a data-element definition -a set of potential states -a data frame -topological or operational properties -a common processing assignment -database storage information -application markers -a lOI1il name -whether it is an absolute or relative species -a cooment The potential states in their turn are assigned names ("attributes") via an "attribute list". Dictionary and attribute list are central parts of the data base as well as of the application system. Topology Description
DATA-BASE FILLING AND

~

Translation of source language to DB-Contents/ Cartridges In source language, a complete description of a power system to be automated consists of several 10 to a few 100 "local-packages" of the kind contained in fig. 2. Further a dictionary and an attribute-list is provided. Each local package is translated into a DB-unit called cartridge by a reversible algorithm; the name of the cartridge is identical with the local name. The translation itself usually is done with "void" state frames , thus, no attribute list is required for this process. The translation maintains the structure of the source description as well as the a-names of the location. Species are assigned a data element, bearing the speciesnumber, a state-frame and references (if required) . Thus, the translation process is reversible and transparent to the selected type of topology description. For fast access the translation further establishes address-pointers to the numeral and partial packages in the cartridges and includes this pointer-system into the cartridge. Cartridges have a variable length depending on the size of, for instance, the substation they are describing; a typical size is 1-3 k-words. The cartridge contains: Name of the cartridge - Place (region-file) in the data base - Displacement-pointer to the cartridge-end - The above metioned pointer system - Contents A trailer finiahing the cartridge and providing for checks of completeness and correctness. Structure of the Data Base Fig. 3 ahows the general DB structure. The first tier in the data base hierarchy is a section. One section may serve for the power system data roodel, others are designed for containiI1il remote control coupliI1il lists, or formats for graphical displays on a monitor. Each section is divided into max. 15 regions. A region comprises a region table and a region file into which pregenerated cartridges are loaded. DB-head, section-heads and region-heads define the overall structure of the DB and remain practically fixed during the lifetime of the control system. Cartridge-heads and the filling of the regianfiles are subject to change by the 8IIIeI'ldment system.

75

Application of a Grid Data Language

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•roH)N [ACCPHIB. DlJI':MY*R. WARN •SWSQRUN •RECl'IFFr , SUPFT •PRaI'CHK. RCUFT I "20 ·roH)N[ACCPHIB,SF6WARN,FUSETRP.PROTCHK) ·BUSl[JUN1/V(·BAYA-BSEL1'BAYB-BSEL1·OOUPL-BSEL1'OOUPL-BSELA'BAYT-BSEL1),ACCPHIB.VOLT) 'BUS2[JUNl/V( 'BAYA-BSEL2'BAYB-BSEL2'00UPL-BSEL2'00UPL-BSELB'BAYT-BSEL2) ,ACCPHIB,VOLT] ·BAYA[BSEL1/Jl*R.BSEL2/J2*R.GRNDB/*R,BRK*R.GRNDL/*R.ISL,PEC/Q('·'STAT2·'$·BAYX[PEC/Q)).ACCPHIB. GRNDFT.RECLOSE*R,DIST.CURR) ·BAYB[BSEL1/Jl*R.BSEL2/J2*R,GRNDB/*R.BRK*R.GRNDL/*R.ISL.PEC/Q(··'STAT3' "'BAYX[PEC/Q]) ,ACCPHIB, GRNDFT.RECLOSE*R.DIST.CURR] ·00UPL[BSEL1/Jl*R,BSEL2/J2*R,GRND1/*R,BRK*R,GRND2/*R.BSELA/Jl*R,BSELB/J2*R.DIST] ·BAYT[BSEL1/Jl*R,BSEL2/J2*R,GRNDB/*R.BRK*R,GRNDT/*R. ISL,PEC/Q('··.·'2·TRAFQl[PEC/Q)),ACCPHIB.CURR) • '2

·TRAFOl[PEC1/Q(···.··20·BAYT[PEC/Q]l,TRDAT.PEC2/Q(···.·'l'CUSTOMER[PEC/Q)),TRAFTEMP.AUTOREG, R:eITlOO] "3

•AUDI~[SUPFT 1 LEVELFI' I "4 IC~[AALARM,BALAllMl

Ft,. 2 Description of a Substation

D. Rumpel. L. Post and R. Zaluk

76

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Fig .3 Structure of The Data-Base Organisation Application programs start their access in the region table (fig.3). The desired cartridge can be found by successive comparison of the name until the matc hing one is found . An average access process up to this point has to pass about 100 assembler commands which takes about ZOO ~sec on a Siemens R30 mini-computer for the network example c haracte rized in the conclusion. Within the cartridge an ave rage access to a single object takes about 150 ~sec. Usually, as, an entering of new measurement states or retracting of switch states f or a diagram, a plurality of data from one cartridge is involved. Such accesses requi re between 10 to 150 ~s per sequential data, depending on the alignment between the data in the cartridge and the search requirement. Data amendment Data amendment starts with the editing of a backward translated cartridge. All modifications concerning the local can be entered on a-level (e. g. a new transformer in a substation). The altered local is forward-translated again and inserted into the reserve space of the region file marked "new". The activation of the new cartridge can be executed at any proper time. A program compares the new and the old cartridge, informs the operator on the discrepancies, and prepares a correspondence list to achieve a fast transfer of all actual states from the active cartridge to the new one. During this transfer which takes about 20 ms (+possible external memory transfer time ) the access to the region file has to be disabled. This fast amendment procedure doesn't disturb normal DB-operation. RELATIONALLY

BASED QUERY TOJLS

Codd (1971) introduced the relational algebra as a yardstick of selective pLwer of a data be.se system. The relational algebra provides the following operations on relations: restriction, join and projection. A tupel is a set of usually one "primary key" and several "attributes". The term relation means a tabular matrix of tupels; primary key and attributes are entered in a fixed order, so, that attributes of the same kind form rows. When applied to power system description, the be.sic relations of a relational DB consist of a set of tables where one table contains all objects belonging to one species. In each tupel the primary key identifies the object; the attributes identify the actual states of the object; this arrangement is described by Lehmann and Mattioni (1983). The primary key may consist of a hierarchical key, as given in (I), or a serial object number is applied. In this case the hierarchical structure can be expressed in further relations.

A restriction selects tupels from one relation according to a comparison (>, <, ~, ~, =, =) of different attributes in a relation or attributes and a constant. Equality restrictions require matching of the attribute in search and in the DB. They can be used for both , a and numerical attributes. Unequality restrictions usuall y make sense only with numerical attributes. Verbal examples are:" select tupels (objects) of relation (A) whose attribute of kind (a) is larger than 123" or "larger than the argunent in their attribute kind (b)". The result is a relation of the same row arrangement as (A), but wi th a reduced nt.lllber of lines. In power system application this might e.g. ask f or "all transfonners having a higher tapsetting than .... ". A join links tupels of different relations according to a comparison c riteria . Often tupels are joined when their primary key is equal. In the resulting tupel one primary key is superfluoues and can be omitted (natural join). Verbal examples are: "Combine tupels of relation (A) and relation (B), whic h have the same primary key" or " ... the same argument in attribute kind (a) and kind (b) respectively". The result is a relation, the r ow number of whi ch is usually equal to the sum to the number of rows in (A) and (B). In power system application this might e.g. ask f or the collective listing of object attributes, wh ich are scattered over different relations, or (possibly after restricting the isolator- and breaker-relations to one bay) :" Is there a breaker in the same state as an isolator?" . By a projection a group of a ttributes can be eliminated from one r e lation. The result is a relation, which keeps only the attributes prescribed (+the primary key). In power systems this might be applied, if only one state or attribute of a kind of objects is of interest. The terms defined are required for comparisons in the following. DATA-LANGUAGE

BASED QUERy TOJLS

Single Access A single access to the DB of fig. 3 is formulated by just stating a full object descriptor: "'STATl' 'ZO'BAYT[BRK=CLl

(2)

Applied to the data-be.se this can be understood in two ways: l.enter state "closed" for the circuit breaker of "BAYT", voltage level 20 KV in substation "STATl" 2 . check , i f the circuit breaker of "BAYT" , voltage level 20 KV in "STATl" is closed. The distinction between an entry (1.) and a query (Z.) is given by an additional designation, preceding the descriptor: QQQ for databe.se query and EEE for data-be.se entry. Introduction of the Universal Quantifier "?" Introducing a universal quantifier which can take the position of any name, the descriptor (1) is made more general. There are 30 possibilities to arrange one, two,

Application of a Grid Data Language three, four or five universal quantifiers in the descriptor, as shown in the following examples; ,t

'?' '?'?[?=?]

(3)

addresses the entire DB. Read as a data-basequery, it causes the enumeration of all objects with their actual states. An expression with four universal quantifiers can have the fonn: "'?"?'TR101[?=?]

(4 )

and addresses all objects in the grid which have

partial names "TR101". Three universal quantifiers can be arranged as follows: "'?"?'?[CB=CL]

( 5)

77

Search and output In the DB structure of fig. 3 the search process required is essentially the same for all inquiries (2) to (8): Once go through the power system model part of the DB, and jllllp over the segments which are not coincident with the names present in the query-deseriptor. The higher ranking the names, the bigger the first junpe.. In the implemented program system all objects fulfilling the requirements are p..It out, listed one per line with all their states in alphanumeric fonn, until the search process has ended or the CRT is filled. In the latter case the program can be continued to deliver a new CRTfilling. Due to the data-structure, the objects appear in the order of the network hierarchy which is roughly comparable to a natural join over larger network sections.

Read as a data-base entry, this expression

changes all states of the circuit breakers with name "CB" to "CL" . Entries like this are useful for program or graphic tests. As a query, the expression would cause the outp..lt of all circuit breakers with name "CB" which are in the closed position. A similar expression with only one universal quantifier can restrict the set of objects to all "CB" of voltage level 115 in substation "STAT1": "'STAT1"115'?[CB=OP]

(6)

Matching of names in part Names of operational objects are oftenly fonned in a regular fashion, as e.g. "all transfonnernames start with TR" or "all busbar-names start with BUS". Where this is the case in a utility, the feature can be exploited for formulations as: "'?"?'TR?[COOLING=RUN]

( 7)

with the agreement that the universal quantifier, in the third name, covers the remaining letters or signs of all possible names. The chance that a "nontransfonner" with initial TR (e. g. a transfonner bays) presented in the outp..lt, is almost excluded by the further request for COOLING, which is quite transfonnerspecific. Matching in part was implemented for partial names, because in this rank most of the interesting regularities are found. Inequality restriction Inequality restrictions with a constant were implemented only on attribute level, e.g. in the fonn "'?"110'BUS?[VOLT~115kv]

(8)

asking for any busbar on 110 KV, which has a voltage measurement above 115 KV. Projection Object attributes which are not under query could be obli terated by a projection of the search descriptor on the descriptor of a found object. This feature was not implemented; the found objects are p..It out with all states actually present. In power systems, the objects usually have only a small m.mber of attributes which can apply at the same time, further, additional attributes as "handset" or "improper value" might be quite necassary to correctly interpret the attribute asked for. P.s.-o

Comparison to relational procedures In a relational database, the search process depends on the relations prepared. If access tools standardized according to the relational algebra are applied, and if only the basic set of species ordered relations with hierarchical key is available, the search process requires a restriction operation perfonned one-by-one over all tupels of all relations, except where the species name is available. If the hierarchical dependences are described by additional relations, the number of speciesrelations to be processed can be reduced by initial restriction/natural join operations. The reduction achieved would depend on the mix of species present at the substation, voltage-level or bay in search. Outp..ltting the objects in the order of the network hierarchy would require sorting or multiple processing of species relations. GENERATION OF A ruNCTIONAL KEYBOARD

For convenient use of the query language, a function keyboard is automatically contrived from the DB-contents. The keywords are selected from the DB in a hierarchical way. Starting with the local-names, a program collects all names and p..Its them out. The user can add additional names or obliterate names not wanted. All key words which are present only in a non selected local, are neglected in further selections. The same procedure is repeated with the Numerals, Partials, Species and Attributes. Obliteration of names only decrease comfort, as they still can be imput via the a-keyboard. In addition to these five groups of keybuttons so called "Modi"-keys can be added • They serve for coding certain f\.U'lCtions like "QQQ" for DBquery or "EEE" for DB-entry. In addition to the six variable groups the keyboard comprises 2 fixed groups: alphalll.meric keys and comparison keys. According to this infonnation the program designs the keyboard, assigns names to the "p..I8hbuttons" and links their coordinates to the system. The keyboard is drawn by a plotter (see fig. 4 and fig. 5) • The plotted keyboard is fixed on a digipad and operated by usina a stylus or a mouse The keyboard can also serve for other purposes in grid control. Its flexibility makes it especially helpful for a trainina simulator.

78

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Application of a Grid Data Language OONCWSION

To test the definition-capabilities of the grid data language 3 different real power systems were described: -Transmission level grid with 180 bays, 62 lines, 56 transformers -Municipal level network with 236 bays, 61 lines, 53 transformers -Rural network with 283 bays, 331 unitsubstations, 436 line se!!JDents on distribution level and 32 substations on subtransmission level. The latter network was used as a test system in the present sttrlies. The size of the generated data model is about 40 k 16-bit-words. It contains about 40 cartridges on a disk. The dictionary defines about 300 species and is divided into a 4 K words main memory resident part (HDIRT) and a 10 k words part (EDIRT) on disk. The set of queries which can be fonnulated by the query language derived above, is far from being relationally complete, but we are pretty confident to cover the main part of questions (and settings) required in grid operation and simulation in concise and functional form. Further extensions are possible, if the practical necessi ty appears. Worst case response time to a query effecting a one-by-one search through the DB and including 41 disk accesses requires 3 s on a Siemens R 30 minicomputer.

A major part of the work reported here was sponsored by the research fund of the state Nordrhein-Westfalen, for which the authors want to express their gratitude.

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