**4. Data resources of WAMS**

Online data and information from the entire system have been essential for secure operation and control of interconnected systems e.g. power systems. In general, system data and information have been provided by data resources of system, which are also called measuring devices (Shahraeini et al., 2010). Data provided by data resources are widely different in terms of their importance, format, volume, sample rate and etc. Thomas et al. (2006) have classified power system data into two main data groups: Operational and Non-Operational data.

The operational data includes the instantaneous measurements of voltages, currents, phasors and breaker statuses that are measured by intelligent devices. Such data is transmitted continuously to the control center(s) through communication systems. Occasionally, they may be used locally for the local decision making.

Wide Area Measurement Systems 307

The Master Terminal Unit (sometimes called SCADA center, SCADA server, or master station) may be considered as the heart of a SCADA system. It manages all communications, gathers data of RTUs, stores obtained data and information, sends information to other systems, commands system actuators that are connected to RTUs, and interfaces with operators. Indeed, MTU is a device, which is located in the control center and it acts as

The Remote Terminal Unit (RTU) is a stand-alone data acquisition and control unit. RTUs are generally microprocessor based and they monitor and control equipments at remote sites. Their main tasks are twofold: to control and acquire data from process equipments at the remote sites, and to communicate obtained data to a master station (MTU) (Stouffer et

It is useful to mention that traditional RTUs only communicated with a MTU. But nowadays, modern RTUs may also communicate among together. In some cases, an RTU can be configured as a relay. Such an RTU relays data obtained from lower RTUs to an MTU

In general, small-size RTUs include less than 10 to 20 analog and digital signals; mediumsize RTUs have 100 digital and 30 to 40 analog inputs. Other RTUs with more inputs are

Programmable Logic Controller (PLC) is a small industrial computer, which is initially designed to perform the logic functions that are carried out by electrical equipments e.g. relays, drum switches, and mechanical timer/counters (Jelatis, 2001). Nowadays, analog

control is a standard part of the PLC operation as well (Clarke et al., 2004).

master, while RTUs are placed in remote sites and act as slaves (Stouffer et al., 2008).

Fig. 2. SCADA sub-systems (Stouffer et al., 2008).

**4.1.1 Master Terminal Unit (MTU)** 

**4.1.2 Remote Terminal Unit (RTU)** 

known as large-sized ones (Clarke et al., 2004).

**4.1.3 Programmable Logic Controller (PLC)** 

al., 2008).

(Clarke et al., 2004).

On the other hand, the non-operational data basically consists of records or logs of multiple events e.g. series of faults, power fluctuations, disturbances and lightning strikes. Typically, the non-operational data is offline data. This means that they are transmitted to the control center(s) either in the specified time intervals (e.g. multiple hours) or when they are requested by the system operator.

There are two main differences between the operational and the non-operational data. The first one is their polling rates. The operational data are normally polled in a regular mode i.e. a continuous stream of data. On the other hand, most of the non-operational data are polled at the defined conditions or they are periodically polled at a specified time intervals. Another major difference is their data format. The operational data is usually transmitted in the form of a stream i.e. stream of numerical variables. While the non-operational data may appear in different formats e.g. waveforms, numerical values, COMTRADE (COMmon format for TRAnsient Data Exchange) format etc. (Thomas et al., 2006).

In this book, the classification of power system data represented by Thomas et al. (2006), is generalized to the data resources of power systems as well. In this section, these two classes of data resources; i.e. operational and non-operational data resources; are summarized in separate subsections. Supervisory Control and Data Acquisition (SCADA) and Synchronized Phasor Measurement System (SPMS) are two operational data resources that will be studied. Alternatively, Digital Fault Recorder (DFR), Digital Protective Relay (DPR) and Circuit Breaker Monitor (CBM) will be investigated as non-operational data resources.
