An Overview of Wide Area Measurement System and Its Application in Modern Power Systems

Introduction

Wide area measurement systems (WAMS) are measurement systems that are based on the transmission of analogue and/or digital information using telecommunication systems and allowing synchronization (time stamping) of the measurements using a common time reference. The devices that are used for measuring by WAMS have their own clocks synchronized with the common time reference using synchronizing devices. This concept has been used for radio signals as well. Supervisory Control and Data Acquisition (SCADA) also depend on the accuracy time reference of transmitters. An example of a transmitter is the DCF77, which produces signals that are used for synchronization (Machowski et al., 1988). There are many communication channels for use with WAMS such as GPS, optic fiber, telephone lines, power lines and microwave links. The most important factor to consider when using WAMS is the delay associated with the communication channel. The delay gives the time that is taken before a control or protection action is taken. These delays must be included in power system design and simulations in order to stabilize the grid in practical applications. WAMS assists power systems operators by providing real time measurements that are used in maintaining/fixing stability of a power system/network. The WAMS using Phasor Measurement Unit gather data from system. Data is communicated to the control centre, processed for control protection, and monitoring.

The following are some of the factors that have driven the need to use WAMS:

• •

  Optimum utilisation of the grid to meet economical and technical demands.

• •

  Increase in interconnections of grids within regions and continents.

• •

  Improvements in technology for measurement, control and protection.

• •

  Mixed sources of power i.e. wind, hydro and solar and independent power providers now involved.

• •

  Sufficient Research on the power system phenomena causing widespread blackouts,

The old technologies like SCADA posed some challenges hence the need was found for improved technology. The challenges like delays in data acquisition using SCADA makes it difficult to have real time picture of the power system. The data sources used by SCADA, which are traditional relay, IEDs and meters, depend on local clocks, which make it difficult to compare data from two different source due inconsistent local clocks. The SCADA data involves use of estimations of quantities like voltage or line flow to obtain the phase angle. Estimated data can only give close to accurate phase angle if system is stable. The SCADA setback is summed up to be:

Insufficient time synchronised data to help plan or change system according to dynamic changes, not time synchronised hence phase is not obtained directly when power systems is frequently changing, topography of voltages and currents also affect SCADA performance.. After considering the developments that have led to the adoption of WAMS next is the physical architecture and it can vary with networks. The utilities have different topologies and technology hence the need is to design and deploy unique WAMS that meet the unique needs of the given utility. The architectures can be different but the components of a WAMS include.

• •

  Phasor Measurement Units

• •

  Communication means/link

• •

  System/network Monitoring Centre

The system protection terminal SPT is part of WAMS made of PMUs, communications and system protection centre. The below diagram helps to illustrate the typical architecture of an SPT (Fini et al., 2016; Alhelou et al., 2018; Zamani et al., 2018; Alhelou et al., 2015; Njenda et al., 2018; Haes Alhelou et al., 2018).. Monitoring control and protection of a grid or power network covering wider geographical area requires WAMS, which combines measuring, control and communications (Morison et al., 2004). The WAMS setup allows acquiring all the data at the same time in real time for use by WAMS applications shown in Fig. 1.