Study On Scada

The objective of this project is to provide total software guidelines to the traction power controller (TPC) and the system administrator of  Indian Railways in the operation of the Supervisory Control And Data Acquisition (SCADA) system supplied by M/s Sanmar Industrial Systems Ltd, Chennai.

The scope of this project is limited to describing the various monitoring , control and administering operations that may be performed at the Remote Control Centre (RCC).

Project Team

Genetic Algorithm Based Spinning Reserve Dispatching in a Competitive Electricity Market

An overview of the Traction Power Distribution System existing in the Indian Railways and the role of SCADA system therein:

A 25KV AC 50Hz single phase electric traction system is adapted for the electrified tracks of Indian Railways. Power is obtained from State Electricity Boards (SEBs) from their network at 220/132/110/66 KV at Traction Sub-Stations(TSS) and stepped down to 25KV.

The high voltage winding of the single phase transformer is connected across two phases and one terminal of the 25KV is connected to the rail and the other terminal to the catenary system (Over Head Equipment , OHE) the TSSs are spaced at a distance of 40 to 80 km.

The supply to the OHE from TSS is fed through interrupters located at Feeding Post (FP). Adjacent TSSs normally supply power to the OHE on different phases to reduce unbalance in the supply authorities grid.

To avoid the pantograph of a locomotive or electric multiple unit from bridging the supply from different phases when it passes from one zone to another, a neutal section is provided to separate the OHEs fed from different phases. The switching station provided at neutral section is called Sectioning and Paralleling Post (SP). In multi track sections and at the SP , the OHEs  are also paralleled independently on either side of the neutral section to reduce voltage drop. In an emergency, when a TSS is out of commission, feed from adjacent TSSs on either side is extended upto the failed TSS by closing interrupters at SP.

The pantograph(s) of locomotive(s) or electric multiple unit is (are) lowered at the failed TSS to avoid short circuiting the phases at the insulated overlap. Between a TSS and adjacent neutal section, the OHE is divided into subsections for isolating the faulty section for the purpose of maintenance and repairs.

The switching stations provided at such points are called Sub-Sectioning and Paralleling Posts (SSP). The OHE of various tracks, in multiple track sections , are also paralleled at the SSP to reduce voltage drop in OHE.

The sub-sections are further divided into elementary sections by the use of manually operated isolators.

At TSS, SP, and SSP equipments like power transformers, circuit breakers, interrupters, single and double pole isolators, potential and current transformers, lightning arrestors, LT supply transformers etc. are installed in a fenced enclosure which is locked up. A masonry building is provided for housing the control panels, SCADA equipment , battery chargers , telephones and others.

All TSSs and switching stations are normally unattended and off-circuit tapchanger of the transformer , circuit breakers, interrupters and motor, and all isolators are operated by remote control from the RCC, through the SCADA equipment.

The off circuit tapchanger of the transformer, circuit breakers, interrupters and motor operated isolators could also be operated locally at the TSS,SP and SSP, as the case may be.

At the TSS, a local/ remote changeover switch is provided on the control panel, as well as in the mechanism box of the breaker, interrupter and motor operated isolators. No control panel exists for the interrupters at the SP and SSP and therefore the local/remote changeover switch is provided on the mechanism box of the interrupter.   

INTRODUCTION TO SANMAR’s  SCADA SOFTWARE SYSTEM:

Supervisory Control And Data Acquisition with an acronym of SCADA is basically a control system which enables the Traction Power Controller (TPC) to control 25KV traction power from Remote Control Centre (RCC).

The following are the two major subsystems of SCADA system.

a)      Remote Terminal Unit (RTU)

b)      Remote Control Unit (RCC)

RTU:

        RTUs are installed at various posts to collect data such as availability of catenary voltage, switch positions of circuit breakers/interrupters, transformer tap position etc. and also to execute commands at TSS, SP and SSP. The RTUs are intelligent devices, which are capable of executing the commands given by TPC, collecting various data from the field and transmitting the same to RCC as required.

        Various field data such as status of circuit breakers and interrupters, catenary indication etc. which are required to decide the appropriate control action by the TPC are collected through the RTUs.

RCC:

         Remote Control Centre (RCC) is designed to guide and control the various Remote Terminal Units   (RTU). It communicates with each RTU in a predefined sequence over the WAN to acquire information regarding :

-         status of CB, interrupter, relays etc.

-         alarm condition in the controlled station.

-         measured values.

The RCC has the following three subsystems:

a)      Operator Work Station (OWS) computers.

b)      MAIN/STANDBY (server) computers.

c)      Communication Processor.                                 

TPC controls the Traction Power Station by interacting with the SCADA software through OWS software module which runs under WINDOWS environment.

The server computer gathers data from the field RTUs and maintains a real time and a historical database. The workstation provides the crucial Man Machine Interface (MMI) to the TPCs to monitor and control the traction system. Communication processor polls and collects various data from RTUs and reports to the MAIN computer. Also it transmits various commands to be executed by the RTUs.

All computers at RCC are connected through a local area networking at 10MB data transfer speed.

    RCC consists of the following equipments:

a)      Main and Standby computer

b)      Operator Workstation Computer

c)      Communication Processor

d)      Printer

e)      Modem

f)        UPS

g)      Battery 

The facilities available at OWS are mainly of two types:

1)      Monitoring:

                        Workstation provides facilities for the user to view the state of catenary, status of voltage devices , monitor alarm conditions and fluctuations in voltages and current.

2)      Exercising control:

                         SCADA software provides the following controls:

-         control of devices like circuit breakers (CB) and interrupters (BM)

-         transformer tap changing.

-         Release of locked out conditions of Auto Releasing Scheme.

-         Interlocking of boundary post etc.

There are two OWSs in the RCC with three computers in each OWS. The workstation computers are used to display the field status and alarms. The operator can issue commands from the workstations to control field equipments such as CBs and BMs. The OWS PCs are run by software specially developed for MMI functions. The software is user friendly and operates under WINDOWS environment. The software is implemented in Visual Basic language.

CPU used in OWS, MAIN computer and the communication processor are of the same type. The CPU card is based on Intel 80486 processor. The highly integrated , eight layer board supports upto 128Mbytes of fast page mode. It offers a high performance, cost effective Integrated Drive Electronics (IDE) hard disk interface, two serial ports, one parallel port and a VGA controller with flat panel support.

The monitor works on 230V AC supply. It is connected to the CPU through D-type connector to receive the data. Data received from the CPU is converted into pixel format and displayed on the screen.

The keyboard acts as an input device for the computer system through which various commands are given for execution. It has a set of 101 key switches. These comprise of alphabets, numbers, special codes and mathematical signs. When a key is pressed, a key switch is activated and the built-in electronic switch will determine which key has been pressed. This will generate a standard 8 bit code and it will be sent to the computer. The commands are processed at the CPU in the PC and the output is displayed in the monitor. Keyboard is connected to the PC with a cable.

Mouse is an essential device accompanying every computer in a Graphical User Interface (GUI) system software programs.

MAIN AND STANDBY SERVER SOFTWARE MODULE:

MAIN and STANDBY computers are two server computers. The server computer system runs the main SCADA system software module known as server software. The server software module mainly takes care of supervisory and database management functions. It also acts as a link between the Remote Terminal Unit (RTU) and the OWS. It is responsible for storing the data collected from RTU, maintaining a database, updating the OWS with the latest data and in general for coordinating and controlling the total operation of SCADA system.

It is the responsibility of the server modules running on both MAIN and STANDBY machines to ensure that their respective databases are synchronized. Both the MAIN and STANDBY computers exchange periodic health packets. Absence of an expected health packet within a specific time interval cause the STANDBY server to assume control over the network. Thereafter, STANDBY computer acts as the MAIN computer acts as the MAIN computer and controls all the SCADA functions. 

COMMUNICATION PROCESSOR SOFTWARE MODULE:

The third important sub-system hardware in Remote Control Centre (RCC) is the communication processor or the Front End Processor (FEP). It acts as a channel between the RTUs and the communication processor to the MAIN.  The function of this unit is to receive information from RTU and transmit them to the MAIN computer. The MAIN, inturn , transmits the data to the OWS over the LAN. The communication is developed in C language under DOS Operating System.       

SALIENT FEATURES OF THE SCADA SOFTWARE:

• Issue of control commands from the OWS to operate field devices.
• Special functions like issue of power block and transformer tap changing.
• Interlocking facility at boundary post.
• Release of locked out condition of single shot autorecloser.
• The software provides facilities for isolation of faults in OHE and is termed as AFL (Auto Fault Localisation).
• The SCADA software provides CONFIGURATION program that allows the user to configure the controlled stations.
• The software provides a list of alarms like current alarms, historical alarms, system alarms, current telesignal alarms, current telemetry alarms , etc.
• The software provides a list of events occurred such as operation of a BM or CB.
• The software provides graphical displays of voltage, current and maximum demand.
• The software provides information on digital and analog status, RCC and RTU diagnostics.