- Introduction :
The goal for any power utility is to maximize their profits and have customer satisfaction. This can be achieved through continuous 24×7 supply of power, cheap, safe and reliable power which should not damage any appliances of the customer .This can be achieved by efficient ,automated power production and distribution and having less power system breakdowns which is achieved by using SCADA systems and automated systems.
Fig.1 An illustration of how a utility can attain maximum profit.
SCADA stands for supervisory control and data acquisition is a system operating with coded signals over communication channels so as to provide control of remote equipment. It is an open loop system. The supervisory system may be combined with a data acquisition system by adding the use of coded signals over communication channels to acquire information about the status of the remote equipment for display or for recording functions. SCADA system is used for real time control and monitoring of electrical network from the remote location. The components present in a SCADA system are divided into two units control room and remote station.
- Remote Station
Remote Station consists of sensors and actuators that are directly interfaced to the generation plant or equipment’s. The components present in a remote station are:
3.1 Remote Terminal Unit (RTU)
Remote Terminal unit acts as an interface between the field and the SCADA master (D. Bailey et al, 2003; http:// www.ndpl.com/ profile.html; Rajeev Kumar Chandra). It supports control and monitoring of digital and analog data. The RTU panels consist of a power supply card and DO cards, processor, and memory communication card. The RTU panel is powered at 48V.The digital inputs are used to provide the status of switchyard equipment and station auxiliaries. The digital outputs are used for breaker and isolator commands and relay reset commands. There are also junction boxes which are present along with the equipment in order constantly. The general specifications of RTUs are:
- RTU has two TCP/IP Ethernet ports for communication with Master station(s) using IEC 60870-5-104.
- Minimum 15 analog values (including 4 energy values) to be considered per energy meter
- The RTU shall be designed to connect maximum 5 Master stations
- RTU shall be capable of acquiring analog values through transducers having output as 4-20 mA, 0-10 mA, 0-+10 mA or +/- 5 volts using analog input modules
3.2 Bay Control Unit (BCU)
It is a De-centralized architecture. It is an interface between the field and the SCADA master;it supports the control and monitoring of digital and analog data. BCU has memory unit, DI/DO modules, processor unit, communication unit, power supply unit.
- Application of SCADA systems in power plants
4.1 Fault location, Isolation and Service Restoration
This function helps the utility in detecting faults in the the transmission line isolating it from the other grids in order not to affect the flow of power in the neighboring grid. SCADA systems are also responsible to restore the fault area back into service.
4.2 Load Balancing
This function distributes the system total load among the available transformers and the feeders in proportion to their capacities.
Fig.2 Basic functional block diagram of the automation vision in power plants