Wide Area

Measurements in

Power System

Satyendra Pratap Singh, Research Scholar (Power System)

Prof. S. P. Singh

Department of Electrical Engineering, IIT (BHU) Varanasi

Introduction

The Wide Area Measurement System

(WAMS) effort is a strategic effort to meet critical

information needs of the changing power system.

It can be mentioned that a WAMS needs an

infrastructure to perform its tasks. The WAMS

infrastructure consists of people, operating

practices, negotiated sharing arrangements and all

else that are necessary for WAMS facilities to

deliver useful information. WAMS is a new term,

which has been introduced to power system

literatures in late 1980s. Recently, they are

commercially available in power systems for

purposes of monitoring, operation and control.

Need of Wide Area

Measurement in Power System

To be able to monitor, operate and control

power systems in wide geographical area, WAMS

combines the functions of metering devices (i.e.

new and traditional) with the abilities of

communication systems. The overall capability of

this particular combination is that data of the entire

system can be obtained at the same time and the

same place i.e. the control center. This data, which

are obtained from the entire system, can be used by

many WAMS functions, effectively. These facts

indicate that nowadays, WAMS has been a great

opportunity to overcome power systems challenges

related to the restructuring, deregulation and

decentralization.

WAMS Architecture

A generic WAMS architecture can be

depicted as shown in Figure 1. The WAMS

architecture consists of interconnected Phasor

Measurement Units (PMUs) and Phasor Data

Concentrators (PDCs) in different layers of

hierarchy. For applications which require

Figure 1: A generic representation of a WAMS

Architecture

significant amounts of data transfer and low latency,

fiber-optic communication channels are necessary.

For lesser data volumes and slow response times,

other types of communication channels including

telephone circuits, microwave channels or power

line carrier channels may be adequate. In any case,

a communication network is an essential element of

any WAMS architecture.

Synchrophasor Technologies

Monitoring devices called phasor

measurement units (PMUs) measure the

instantaneous voltage, current, and frequency at

specific locations in an electricity transmission

system. These parameters represent the heart-beat

and health of the power system. Voltage and current

are parameters characterizing the delivery of

electric power from generation plants to end-user

loads, while frequency is the key indicator of the

balance between electric load and generation. Thus

frequency that doesnt deviate very much from

60Hz is key to ensuring the proper operation of the

power system and its reliability. When a phasor

measurement is time-stamped, it is called a

synchrophasor.

SCADA v/s PMUs

Attribute SCADA PMUs

Measurement Analogue Digital

Resolution 2-4 samples

per cycle

Up to 60 samples

per cycle

Observability Steady State Dynamic/Transient

Monitoring Local Wide- Area

Phasor Angle

Measurement

No Yes

Conclusion

Wide Area Measurement Systems is a new

opportunity for system operators to monitor,

operate, control and protect power systems in wide

geographical area. The WAMS combines the data

provided by synchrophasor and conventional

measurements with the capability of new

communication systems in order to obtain dynamic

information of the entire system. WAMS

contributes monitoring systems to shift from the

data acquisition systems to the dynamic information systems. Dynamic information of power systems helps power system operators to

overcome generation, operation and planning

challenges that may be resulted from system

restructuring. Furthermore, it has also been shown

that from the big generators to the small home

equipments, WAMS systems are capable of

monitoring and controlling various functions in real

time. It can be concluded that in modern power

systems, WAMS is an essential part of power

system operation and control. As a conclusion, it

can be stated that although the WAMS was firstly

introduced to the power systems in order to obtain

dynamic information of such systems, it can also be

well established in other critical infrastructures (e.g.

natural gas, petroleum, water supply, emergency

services, telecommunication and etc.) to operate,

monitor and control such infrastructures.