ODM Data Structure & Relationship

Introduction

It is our goal to capture all key data relationships found in the existing, commonly used, data formats, including IEEE CDF, PSS/E and UCTE. It has been observed that although these data formats are quite different at individual record and field level, they have common underlying data entity/object relationships. After all the data formats are intended to create nodal Y-matrix for performing power system analysis.

Please Note: Eclipse IDE is used to create and maintain the schema. The schema is currently hosted at GitHub, open and freely accessible.

Record

Most power system simulation algorithms are developed on the network nodal admittance Y-matrix. The most basic relationship, a power system simulation data file describing, is a set of bus records and branch records, with the branch records "connecting" to two or more bus records to form a power simulation network.

There is also an underlying sequence assumption that the last record in the record set will win. For example, if there are two records in a data file, trying to set the same bus voltage:

set voltage at bus 00001 to 1.01 pu

....

set voltage at bus 00001 to 1.02 pu

The bus voltage shall be set to 1.02.

Name Tag

Every data object in the ODM in general has a name and optional a description.

Base Record

By examining the existing power system simulation data formats, the smallest unit of information could be described by a record, sometime called entity. The records have certain common attributes, such as name, description, status ... We use the BaseReacordXmlType to describe attributes common to all records. Please note, all attributes defined are optional.

It is impossible to create a Schema, which will cover all possible situations. The BaseReacordXmlType has a name value pair list, where any extra attribute could be defined. For example, one might add the following name-value pair:

<pss:nvPairList>

<pss:nvPair>

<pss:name>Most Important ODM Feature</pss:name>

<pss:value>Open, Extensible, created and maintained by Open-Source Groups</pss:value>

</pss:nvPair>

</pss:nvPairList>

Another extension point is the extension element, where you can attached a Xml document of any type. This is an advanced feature. It is intended for software vendors to add features which might be difficult to define using the existing schema.

The BaseReacordXmlType is the parent of all record types in the ODM schema.

ID Record

Records, for example, a bus record or branch record, are identified by an unique Id. The IDRecordXmlType is for defining records with an unique id. The XML schema data type ID will make sure that the field is unique within an XML document.

ID Reference Record

Some records are referencing certain record in the model. For example, a generator data record might reference to a bus record, where the generator is connected. The IDRefRecrodXmlType is for defining reference records. The XML schema data type IDREF will make sure that the field is referencing an ID field defined in the XML document.

Study Case

We use the Study Case concept to represent a unit of simulation data for exchange purpose. Normally a study case is stored in a data file. By analysis of the existing power system simulation data file formats, three key concepts are very obvious: (1) base case; (2) modification to the base case and (3) A set of study scenarios.

Power System Simulation Network

The baseCase attribute is of the type PSSNetworXmlType, which, among other things, contains a list of bus records and branch records, plus other records. The bus records are connected (referenced) by the branch records to form a power network for simulation purpose.

Bus Record

A bus record is an ID record with a base voltage, plus other fields. It represents a logical node in power networks. The bus record will be extended to describe more complex data structure for Loadflow study, short circuit analysis and other type of analysis.

Branch Record

A branch record is an ID record with a fromBus ID reference record, referencing to the from bus record and a toBus ID reference record. The tertiaryBus, which is optional, is for modeling 3-winding transformer, The circuitId (optional) is for describing multiple parallel branches between two buses.

Network Record

A power system simulation network is represented by the PSSNetworkXmlType. At most basic level, it consists of a set of bus records and a set of branch records. The following is a simple XML document describing a simple two buses and one branch network.

(Todo, a sample Xml doc)

One might ask why we are doing this. This is much complex than the IEEE CDF. The reason is that the XML document, confirming the OMD Scheme, could be easily processed by any W3C standard based XML processing tools.

Modification

(Todo ...)

Scenario

(Todo ...)

Modifications could apply at each scenario level to create a study case scenario. For example, for N-1 analysis, the modification might be open a line.