2011 The International Conference on Advanced Power System Automation and Protection

A data exchange method of W AMS based on IEC61970

GUO Jian1, WANG YingTao1, ZHANG DaoNong2, YU YueHai3, XIE XiaoDong4

I China Electric Power Research Institute, Haidian District, Beijing, 100192, China,

2 North China Power Engineering Co., Ltd., Beijing, 100120, China, ;

3 State Grid Electric Power Research Institue, Nanjing, 210061, China,

4 Beijing Sifang Automation Co., Beijing 100085, China

Abstract: With large-scale implementation of smart grid, wide area measurement system (WAMS) based on PMU will become

the basic platform to provide the online power system analysis, real-time monitoring and control. According to the extended

ClM guidelines, a WAMS data model was established in this paper to realize data exchange and sharing between WAMS sys­

tem and other systems. Combined with IEC 61970-404-speed data (HSDA) standard, a scheme of WAMS data exchange in­

cluding data exchange framework, overall design of data exchange and data subscriptions was described in the paper. This

scheme integrates WAMS system with other systems more effectively and makes other applications access WAMS data more

easily.

Keywords: elM, WAMS data model, HSDA, WAMS data exchange

1 Introduction

In recent years, china's power dispatching information has

made great achievements, a state power-dispatching net­

work was built and it has increased real-time data transmis­

sion index significantly. The network gradually integrates

steady-state data of SCADA system, dynamic data of Pha­

sor Measurement System (WAMS), transient data of relay

protection and stability control devices, off-line data of op­

erating modes and DTS together to realize on-line stability analysis, real-time stability analysis, dynamic stability con­

trol. Thereby it enhances the level of security and stability

of power grid and increases transmission capacity to meet

requirements of the electricity market.

Business sectors of power companies have developed

and installed several applications such as WAMS, SCADA /

EMS, DMS, AMR and so on to meet their own specific

needs. These applications have different modeling methods

to solve different aspects of power problems and have their

own communication protocols and data formats that are not

compatible. It causes the complexity of communication

problems, and one system has to do a lot of protocol con­

version to meet other systems requirements unconditionally.

So it is difficult to realize the various subsystems commu­

nicate with each other easily.

To solve the above problems, IEC 61970 [1,21, which uses

common information model and unified application pro­

gram interface, achieves integration of various applications

in control center inside / outside of the system and sharing

the models and operating data.

GUO liall(email: guojiaIl3@epri.sgcc.com.cll)

978-1-4244-9621-1/11/$26.00 ©2011 IEEE

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2 WAMS architecture

PMU in plant side, communication systems and control

system in the dispatching center are elements of WAMS.

WAMS structure shows in Figure 1, of which the master

locates in the dispatching center, sub-stations including the

phase angle and power angle measuring devices, time syn­

chronization devices, communication systems, and industri­

al machine are the monitoring points.

GPS synchronizat ion devices

Detection master

Figure 1 Structure of WAMS

The key of PMU is the measurements of phase angle and

power angle, and the RMS measurement is no different

from traditional device. The phase angle is the angle of bus

voltage or line current relative to the reference axis system.

A generator power angle D is the angle of q-axis relative to

the reference axis. There are two principles of phase angle

measurement: one is zero-crossing detection method and the

other is the Fourier transform method.

APAP2011 www.apap2011.org

2011The International Conference on Advanced Power System Automation and Protection

Currently, compatibility research between WAMS system

and IEC 61970 is rarely done [3]. According to the extended

CIM guidelines, the paper adds WAMS data models by in­

creasing attributes and values to the existing class or inhe­

ritance and association. Then, in order to facilitate the other

systems access PMU data easily, combined with the IEC

61970-404 high-speed data (HSDA), an overall solution of

PMU data exchange is designed in the paper. These are de­

scribed in the next chapters.

3 WAMS data model

Based on the structure and working principle of WAMS,

WAMS data models are created according to the CIM mod­

el specifications. WAMS information model includes the

following: structure of WAMS itself (including connection

information between PMU and grid), various types of mea­

suring devices (including time synchronization devices),

and measurement data obtained by various types of mea­

suring devices, especially the phase angle.

IEC 61970-303 describes the CIM model of SCADA

system. It contains modeling entities for SCADA system,

monitoring and control part for operator controlling equip­

ment, data acquisition part for collection of telemetry data.

It also supports alarm notification. A large part of classes

and properties in SCADA package is also applicable for

WAMS, for example, Current Transformer class and Voltage Transformer class. Therefore, this paper designed Time

Sync class, PMU class, Phase Angle class, the relationship

between classes shown in Figure 2.

Figure 2 Relationship between WAMS classes

3.1 Time Sync class

Time Sync class refers to the time synchronization device,

which is designed to represent synchronization information

of each measurement value, for example, the reference

phase and information of reference point. The most critical

technology to achieve simultaneous monitoring full network

is obtaining absolute precision time. Obtaining absolute

precision time is not only the basis of describing the beha-

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vior of system, but also the basic guarantee of synchroniza­

tion of observational data at different locations, so it is im­

portant to describe the time synchronization.

In Time Sync properties, acquisitionTime refers to the time of collecting data; baesPhasePosition represents the

position of phase reference point. At a certain time point,

one or more PMU provide data, at the same time, a PMU

device collects data at different time points. Although each

PMU base station are synchronized with GPS, it should take

into account all of the time delay, such as input delay, data

processing time (DFT), centralized data, communication

link propagation delay, the amount of data transmission as

well as some random delays, so it is necessary to set proper­

ties Timeosffet to indicate the time offset. Attributes of class

show in Table 1.

Table 1 Attributes of Time Sync

Attribute Type

PowerSystemResourceName Name

AliasName String

PowerSystemResourceDescription Description

acquisitionTime DateTime

basePhasePosition Address

TimeOffset Bits

3.2 PMU class

PMU class is designed to represent the basic information

and connection information of the PMU, which two

attributes that name and description inherit from PowerSys­

temResource class of the Core package. In addition, ob­

jectPosition represents PMU installation address, control­

CenterPosition represents monitoring center address which

refers to the central station processor address in dispatching control center. PMU attributes described in Table 2.

Table 2 Attributes of PMU

Attribute

PowerSystemResourceName

AliasName

PowerSystemResourceDescription

objectPosition

pmuType

pmuProtocol

controlCenterPosition

3.3 PhaseAngle class

Type

Name

String

Description

Address

String

Name

Address

According to the principle of PMU, the measurement me­

thod of RMS equivalent is no different from conventional's,

so CurrentTransformer class and VoltageTransformer class

of WAMS are similar with SCADA's. Current transformer

which reduces primary current value to rating value (e.g.,

4A) is used by rely protection and measuring devices, so the

2011The International Conference on Advanced Power System Automation and Protection

same to the voltage transformer. In addition, in order to ex­

press the measurement device of phase angle, PhaseAngle

class is designed to obtain phase angle information from the

unit side or the bus. Classes like CurrentTransformer, Vol­

tageTransformer, and PhaseAngle are not exactly the same

to the actual power measurement device but the abstract

representation. Class attributes shows in Table 3

Table 3 Attributes of Phase Angle

Attribute Type

Name String

AliasName String

Description String

4 WAMS data exchange

Here IEC 61970-404 high-speed data access interface (High

Speed Data Access HSDA) standard is used to achieve

real-time exchange of WAMS data [4].

4.1 High-speed data access interface (HSDA)

As an important part of IEC 61970 CIS, high-speed data

access (HSDA) refers to the data access (DA) section of

industry standard data access system (DAIS) of object

management group (OMG). There are two types of inter­

faces in OMG DAIS data access (DAIS DA) [5] that

browsing interface and data access interfaces. Browsing

interface is used for mining objects and properties industrial

process supported by DAIS servers which are organized and

named in a hierarchy way. Data access interface is used for

accessing the object properties of the industrial process

(usually real-time data). The reason why OMG DAIS sup­

ports high-speed data access is that data access interface

adopts order mechanism to locate variable memory space

quickly in the server and client. In addition to the general

request-response data exchange mode API, order mechan­

ism also supports subscription, customers can subscribe data

concern to the server only when data are available or up­

dated, and the server will pass the relevant data to custom­

ers. Data exchange services of DASI include the following

three cases:

(1) Reading data: customer can read data from DASI

server cache; and can obtain latest data from devices;

(2) Writing data: command and updated data can be writ­ten to the device according to release method of DASI;

(3) Subscription: based on data exchange service of order,

when data is updated, DASI server sends the latest industri­

al process data to the client.

SubscribelRelease is the most important data exchange

method of DAIS, which achieves efficient exchange of large

amounts of data. An order (group) is a set of order items

(group Entity), including life-cycle, order name, subscrip­

tion status, callback object, update rate, activity status, order

item has four items identifier like pathname, client_handle,

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server_handle to record order information.

4.2 Data Exchange Framework

After establishment of WAMS data model, it is possible to

integrate WAMS system to the enterprise information bus to

exchange information in a unified information model. Ac­

cording to the high-speed data access (High Speed Data

Access HSDA) interface specification [5, 6], a power ap­

plications framework is designed based on message mid­

dleware, shown in Figure 3.

Figure 3 Integration framework of power applications

WAMS systems and other electrical applications (such as:

SCADA, DMS.) exchange data through the messaging mid­

dleware, so it does not consider the data models difference

between applications and realizes data share.

4.3 Data exchange overall design

WAMS system has been applied more than a decade, and

has proprietary format. To compatible with existing WAMS,

data format is packaged based on the original standard [7] to

facilitate data exchange with the outside, the overall design

shows in Figure 4.

WAMS data

exchange in

real-time

WAMS

,----� CIMOB (class,

property, ins

tance)

aCQuisi lion

system

DAIS service,

DAIS DB

Figure 4 design of data exchange

There are two main processes in the data exchange:

User

(1) Through WAMS database mapping with CIMDB,

WAMS data collected is converted to the data which It's

format is compliance with CIM and be stored to CIMDB;

(2) CIMDB initiates DAIS data update, the CIM format

data is converted to DAIS format data, which is released by

the DAIS service components. While these two processes

are bi-directional conversion when user takes the initiative

to update DAIS data, CIMDB is also responsible for con­

verting data gotten from DAIS update service into proprie­

tary data format, which is compliance with WAMS system.

4.4 WAMS data subscription

4.4.1 Create WAMS Order

Orders [8] are created by the order factory that DAIS: Da­

taAcess:: GrouP:: IHome. Order factory object can be

created by group_home 0 method of session. The steps

2011The International Conference on Advanced Power System Automation and Protection

creating new WAMS order are as follows:

(1) Order factory in the server side calls create_group 0

method to create an empty order, and obtains management

object of order which is added to the order management

containers in the server side;

(2) create a new order item, and configure path­

name/ItemID, client_handle of each item;

(3) calls create_entries 0 method to add organized order

items in the client side to the order, and get Result object

returned from the server which includes server_handle and

client_handle of each item;

(4) set the active status of orders and order items;

(5) Subscribe (unsubscribe) orders.

4.4.2 Release WAMS data

After CIMDB updating DAIS data, DAIS data service agent

performs the following steps to release WAMS data:

(1) Get groupVec object of order management container.

Lock the source of group Vec data to avoid changing the

order at the time of updating orders.

(2) Read each order management object of group Vec,

traverse all items of the order, and filter out the active items

of active order.

(3) Create ItemStates. Find the real-time data in the

DAIS database through order item named server_handle.

Obtain quality, time stamp and measured values of item to

constitute ItemState with client_handle of item, customers

can identify data easily through the client_handle.

(4) DAIS server triggers callback object Callback::

on_data _change 0 to release the latest ItemSates in the

server side, users accept and store these data in their own

data structure. Unlock group Vec after sending data, so re­

sources are available by other requests. The publication is

completed

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5 Conclusion

Based on IEC6197, WAMS common information model

was created, and properties of its several key classes were

described. Combined with IEC 61970-404-speed data

(HSDA) standard, a scheme of WAMS data exchange in­

cluding framework, overall design of data exchange and

data subscription was designed. WAMS applications be­

come open, componential and integrate with other applica­

tions effectively. As CIM itself is still evolving, further

study is improving WAMS common information model.

IEC 61970: Energy management system application program inter­

face (EMS-API)-Part301: Common information model (CIM) base

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Model of Wide Area Measurement System Based on CIM [J]. Pro­

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Interface (EMS-API) -Part303: Common Information Model (CIM ) SCADA [ S ].2002,Revision 4

4 IEC 61970 Energy management system application program interface

(EMSAPI)-Part 404: high speed data access (HSDA)[S].2007.

5 IEC, draft IEC61970:Energy Management system Application pro­

gram Interface (EMS-API)-Part402:Common Data Access Facility,

Revision4 •

6 Draft IEC6I 970:Energy management system application Program in­

terface(EMS-API)-Part450:CIS Information Exchange Model Speci­

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INFORMATION INTEGRATION BASED ON MULTI-AGENT

SYSTEM TECHNOLOGY [J]. Proceedings of the CSEE,

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