PLC and SCADA System

PLC (Programmable Logic Control) 

Advancement in any technology seeks an automated working mechanism of the system, less human interfacing, safety, time and effort saving and convenience. We often hear it in case of automation industries, in field of robotics or self-driving car (for instance, tesla electric car, model S). We could have only imagined of that few decades back, but now it has become reality. In the way of progression of automation, an automation system named PLC (Programmable Logic Control) was first introduced in 1968, by American mechanical engineer Richard E. Marley who was considered the "father" of the programmable logic controller (PLC), since he was involved in the production of the first PLC for General Motors Company, the Modicum, at Bedford. Later the concept was developed to implement into interdisciplinary engineering fields.

In electrical engineering world, there is huge need of automation to work on the system because of its high energy flow nature which is really dangerous and unsafe to work. So, PLC automation came in the electrical engineering field and it has helped for the automatic fault detection, system operation, automatic power supply control system, opening and closing of circuit breakers, isolator, minimize physical working in the high voltage area. It brought an intelligent automation system in transmission grid and networking, hydropower generation station, operation of motor, etc. It has most essential role in industries and factories to control motoring actions, engine starting and stopping, switching operation which is parallelly instructed by SCADA (Supervisory Control and Data Acquisition) software.

Exploring briefly, PLC is a physical device which needs to be programmed with ladder logic programming language. It is an industrial digital computer that has been used and adapted for the control of robotic devices, power grid lines, system fault detection, switching operation, etc. A PLC is an example of a real-time monitoring system since output results must be produced in response to input conditions within a limited time, otherwise unintended operation will result. There are various software to write ladder logic programming for instance, Basic Ecostruxure Machine Expert Software. It consists of parallel ladders and in-between there is a rung where ladder logic is designed. Furthermore, the mechanism is complete when SMPS (Switched Mode Power Supply) is connected to enable PLC device. On the other hand, PLC device is also connected with SCADA software via computer.

Figure 1: PLC device and working mechanism

SCADA (Supervisory Control and Data Acquisition) 

SCADA is a computer-based software, a human machine interface device and it controls supply of control signal from PLC device to control mechanism. It is simply the system that gathers data or information from different devices located at, plant and then send this information to computer. SCADA is nothing but the graphical representation of automation. It is a large-scale control system for automated processes. SCADA in the power system helps for supervision and control.  It helps system to control from distant place than where the physical plant is. VTSCADA is one of the software for the purpose.

Figure 2: SCADA interface

And as control signal is supplied from the PLC device it operates relays or electromagnetic switches. In big scale operation motors are often switched to control operation like opening and closing of isolators in substation or switchyard. In this way, control or automation is achieved without visiting physical site but controlling from the office or our home. Similarly, industries use PLC and SCADA system for automatic switching purpose and operating motor and relays for various purpose. The switching operation is done through electromagnetic switches like relays, contractor, etc. Surya Nepal Private Limited, has the most decent automation system in Nepal. Working mechanism of PLC, SCADA and load is shown in the figure (3).

Figure 3: Working mechanism of PLC & SCADA

SOME OF THE GENERAL APPLICATION OF PLC AND SCADA 

• RTU emulation & replacement.
• Protection & control.
• Automatic switching.
• Voltage regulation management.
• Transformer management.
• Remote control.
• Demand control.
• Easy maintenance.
• Emergency load shedding.

PLC & SCADA can be implemented in engineering project works as well. General projects on which PLC & SCADA final year projects can be done are as follows:

• Priority Based Demand Site Management using PLC & SCADA
• Automatic load supply in transmission system during fault condition using PLC and SCADA, and so on.

 APPLICATION OF PLC AND SCADA IN NEPAL

In Nepal, PLC and SCADA implementation is being widely used in almost every national hydropower project. All the hydropower projects are connected with each other in interconnected power system with proper synchronization process. Each system is monitored, controlled and supervised by using PLC & SCADA. And this job is performed by Load Dispatch Centre (LDC) which is located in Syuchatar, Kathmandu. 

LDC is a coordinating agency or body which analyze the power flow status, load demand, fault cases, and works to handle them and supplies load safely as per requirement. In this way, LDC controls all the operation, load flow control, supply, load priority management, emergency case handling and during fault case of overall interconnected power system with the help of PLC & SCADA application. Similarly, in case of factories, mostly electricity is consumed in case of heating, cooling and motoring purposes and for automatic operation of machines, switches, motor are automatically started from SCADA software via PLC device. The works can also be achieved with timer with designing the proper working schedule. 

Due to PLC implementation, large number of human manpower is reduced, it definitely ensures safety to human and are cost effective. So, PLC & SCADA implementation has good scope and benefits in automation in appropriate field. So, pursuing knowledge on this field, learning to write program or develop logic for PLC, interface designing in SCADA software would be great assist to students who are interested on or looking forward to be engaged in this field.

The cost of implementation of PLC & SCADA system depends on the type of the project, scale of work, quality and type of device. But, in general practice or project work PLC costs around Nrs. 1,00,000 |- and other accessories costs varyingly. SCADA software (VTSCADA) is available free of cost.

In a nutshell, PLC and SCADA is automation devices that helps to operate machines without human involvement in the physical site but monitoring, analyzing, supervising and controlling is done from our computer software via PLC device. National hydropower, switchyard, substation and transmission line are implementing PLC & SCADA for their respective purposes. They are widely implemented in industries for switching and motoring purposes. This application has huge scope and usability in Nepal.