SCADA Interview questions

A Supervisory Control and Data Acquisition (SCADA) system is used in Power plants ( Thermal, Hydro, Nuclear and Gas Plans) for implementing control interlocks for electrical equipments in the switch yard and data acquisition functions for switch yard and electrical auxiliary systems in the power plant. SCADA system is both Hardware and Software.

SCADA system consists of following components:

1.    Man Machine Interface (MMI):

Man Machine Interface is process and display units from where the data is process and displayed to the operator for monitoring and control by human. It is also called Human Machine Interface.

2. Remote Terminal Units (RTU):

Remote Terminal Units are located at the process side of the plant. They are connected to the sensors in process and data is converted from sensor signal to digital data and sends to the Supervisory control. In simple, RTU is a micro controller and located at the remote side of the process system their objective is to collect data from process side and deliver to Supervisory control

3. Programmable Logic Controller (PLCs):

PLCs are more versatile than RTUs and does the job of RTUs and also control the process when command receive from supervisory control.

4. Communication System:

These are the software protocols used for transferring the data from the supervisory control to RTU and vise-versa.

5. Supervisory Controller:

This is the master controller of the System which receives the data from RTUs and PLCs, monitors the data, process the data display data to operator via HMI or MMI and gives command signal to RTUs and PLCs to carry out certain operation.

SCADA SYSTEM IN POWER PLANTS:

Electrical SCADA system in power plant is located in two control locations; Switch yard Control Room, and respective Main Control Room.

In Switch yard Control Room SCADA system is to monitor and control of high voltage transmission lines (400kV/220kV) from switch yard control room through Man Machine Interface (MMI) of the electrical SCADA system. Man machine Interface (MMI)is a Video Display Units which display diagrams, bar charts,analog trends, tabular designs etc to display parameters such as voltages, currents, etc and annunciations.

The control of main transformers in the power plant such as Generation transformer used for step up the generation voltage from the generator and Station transformer used for deriving the power during plant star up and control of circuit breaker in plant is done through the Man Machine Interface.

Important auxiliaries like Battery system, UPS systems, Diesel Generators are also monitored and important alarm annunciations and window annunciations are provided at the Main Control Room.

Functions Of SCADA system:

·        Periodic Monitoring and logging of data such as frequency, voltage, current, etc. from electrical auxiliaries

·        Classification of alarms in order of priority and providing annunciations at the time of events

·        Displaying status of isolators, breakers and single line diagram of various systems in switch yard

·        Controlling circuit breakers and Isolators in switch yard