Optimization of Data Utilization in Substation Using LabVIEW

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International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459,ISO 9001:2008 Certified Journal, Volume 3, Issue 3, March 2013)

346

Optimization of Data Utilization in Substation Using

LabVIEW

G.Prabhu

1

, R.T. Rishi Vandhiya Jenu

2

1

PG Scholar, Anna University Regional Centre, Coimbatore, India

2_{UG Scholar, Dr. NGP Institute of Technology, Coimbatore, India}

Abstract - An electrical substation is a major and vital part where electrical power is transmitted to major and minor consumers. To ensure safety and reliability of the substation it is essential to borrow the principles of automation. The current architecture of substation automation contains various devices such as Digital Protective Relays (DPRs), Digital Fault Recorders (DFRs), PQ Meters (PQMs), Intelligent Electronic Devices (IEDs) and Supervisory Control And Data Acquisition system (SCADA). The Intelligent Electronic Devices (IEDs) perform various operations like control and record valuable information of both operational and nonoperational data. Amongst the installed IEDs, several problems emerged. The most important problem is lack of data verification in both analog and digital data’s. This led to serious errors in substation operations. Understanding current statuses of substation equipments (such as circuit breakers), load flows, location and type of faults can be very difficult with unmatched sets of data. The SCADA system offers only open loop operation, thus it does not have continuous control over operations. This dissertation aimed at proposing a way of replacing the functions of IEDs through LabVIEW eliminating the disadvantages of lack of data verification and open loop operation. LabVIEW is a more versatile tool that can be modified whenever necessary and can be integrated with graphical user interface.

Keywords – Data flow model, IEDs, LabVIEW, SCADA, Substation automation

I. INTRODUCTION

A substation is an area placed between the generating station and consumer. It includes transformers to change voltage levels between high transmission voltages and lower distribution voltages. For various elements of electrical power system such as transmission lines, transformers, generators and loads, the substation acts as a point of interconnection. The development in designing substation is crucial to reach its technical and economical potentials for which the focus has moved now to study how substations may enable more intelligence in the network, which is labeled the “smart grid” development. Recently Intelligent Electronic Devices and SCADA techniques have been employed to implement the automation logic.

The revealed faults of lack in data verification and machine learning of IEDs and SCADA greatly affect the capabilities of operators to monitor and control the substation and the whole system. Fast introduction of the new technologies and increasing demand for electricity as well as the concern for environment urge power engineers to seek new technologies and solutions to enhance the flexibility of the grid and improve its capacity and reliability.

This has paved the way for this paper to use LabVIEW that greatly enhances the smart grid implementation by delegating the system from the problems mentioned above. LabVIEW software can be used to perform monitoring and controlling the data’s obtaining from

substation equipments. The communication port

developed along with the software helps to control and monitor substation from the remote location. This paper clearly investigates the replacement of IEDs with LabVIEW for it to be having the above mentioned advantages over IEDs.

II. POWER SYSTEM AND AUTOMATION

An electrical power system constitutes of generation, transmission and distribution. The generation unit generates electrical power through renewable and non renewable energy resources. The generated power is

transmitted to required substations through the

transmission system. The voltage is stepped up and

stepped down according to its requirements. The

foremost mission in power system is control and protection. It is not possible by manually monitor and control the level of voltage, current and frequency of a substation all time. The human interference may cause errors at times that may lead to serious destruction. Hence at this juncture substation automation becomes

very essential.Substation automation refers to use data’s

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Fig.1Block diagram of substation automation

The steps involved in current architecture of substation automation are

 Substation design.

 Collecting the data from substation equipments.

 Send the collected data to a control and monitoring

device (PLCs and SCADA).

 Operation on the data fed to IEDs.

 Transmitting the control from the SCADA to the

protective relays and circuit breakers.

A. Substation Design

While designing a substation clearance should be made about the list of primary and secondary equipments. The range of such equipments must be properly selected. The factors such as reliability, security, interoperability, re-configurability, controllability,

maintainability, flexibility, reduced cost and

environmental impact must be considered.

The substation design can be extended in three different ways as follows

 Replacing the existing equipments in a substation with new technically proven equipments.

 Implementing the new concepts with the existing equipments in a substation.

 Extending the potentiality of the substation by adding new equipments along with existing ones.

Based on the age of the substation and technology employed in the equipments any type of design approach can be selected. Each and every component must be taken care of and the correction factors should be applied to it.

Although there are some maintenance planning and repair strategies that can prolong the life time of old substations, the high cost of operation, maintenance and service with negative impacts on reliability forces the utilities to upgrade their old substations. The main concern of a retrofit is to take into account legacy equipment and the need to have minimal disruption to the continuity of services.

B. Collecting the data of substation

The substation includes the primary equipment (such as protective relays, circuit breakers, transformers, instrument transformers, etc.) and the secondary equipment (monitoring, control and protection devices) which are installed in the substation.

Protective relays: A protective relay processes voltage and current measurements in order to determine the existence, and also in some cases the location, of a fault.

Circuit breaker: A circuit breaker is a type of switch capable of interrupting fault current. Other switch types with less onerous capabilities include load break switches (capable of interrupting load current but not fault current) and disconnectors (only capable of off-load switching for the purpose of isolating equipment for maintenance access).In the primary side, a large number of breakers and disconnectors are used in order to allow for maintenance and repair with a minimum of interruption, which occupy large space. The breakers also need an insulation media which may be oil, gas, or air.

Transformers: Oil-insulated transformers are used to step-up or step-down the voltage level for purposes needed. Oil-insulated transformers usually have big size and have potential explosion problems. In addition, the maintenance is also elaborate and the noise of those transformers is also a big issue.

Instrument transformers: Conventional current and potential transformers (CTs and VTs) are used to convert the primary current and voltage to an operation range (0-5A and 115V) for metering and protection. The CT saturation and open secondary CT circuit safety issue are primarily of concern in such devices.

All interfaces between primary and secondary equipments are connected by hard-wired cabling. Different length and types of cables are bundled, which makes it labor intensive for future maintenance and modification.

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C. Inputting the collected data to monitoring and control device

The data obtained may be in analog or digital form. The device IED is a microprocessor based and it can only operate on digital data. Hence the data obtained is made to pass in to an analog to digital converter. The analog to digital converter interfaced to a Digital Signal Processing Unit. This unit makes the continuous signals to get discrete in time or frequency so that the microprocessor based IED can get operated on it. The DSP unit can be interfaced with all types of IEDs for further processing of the data.

D. Operation on the data fed to IEDs

The term “Intelligent Electronic Device”, concerning specifically the protection and power system automation industry, came into existence to describe a device that has versatile electrical protection functions, advanced local control intelligence, monitoring abilities and the capability of extensive communications directly to a SCADA system.

IED structure: The IED derives its name from the various functions the device can select and perform in an inherently fashion. An important issue is the enormous task of incorporating intelligence, in terms of hardware (flexible logical circuits) and software (programmable intelligent agents) into the IED. Advances in the techniques of software programming and hardware development are essential for the construction and realization of an IED. Some IEDs may be more advanced than the others, but these main functionalities should be incorporated to a greater or lesser degree.

IED configuration consists of

 Analog / digital input from power equipment and

sensors mainly current transformers and potential transformers

 Analog to Digital Convertor (ADC) /Digital to

Analog Converter (DAC)

 DSP (digital signal processing) Unit

 Flex-logic unit

 Virtual input/ output

 Internal RAM/ROM

 Display

 Power supply

Function of IED in automation: The protection functions of the IED evolved from the basic over current and earth fault protection functions of the feeder protection relay (hence certain manufacturers named their IEDs feeder terminals).

This is because a feeder protection relay is used on almost all cubicles of a typical distribution switchboard, and that more demanding protection functions are not required to enable the relay’s microprocessor to be used for control functions. The IED is also meant to be as versatile as possible, and is not intended to be a specialized protection relay. This also makes the IED affordable. Communication capability of an IED is one of the most important aspects of modern electrical and protection systems, and it is the one aspect that clearly separates the different manufacturer’s devices from one another regarding their level of functionality. IEDs are able to communicate with multiple channels at a time.

E. Substation SCADA Network

Supervisory Control And Data Acquisition is a large scale control system for automated industrial processes like municipal water supplies, power generation, steel manufacturing, gas and oil pipelines etc. SCADA also has applications in large scale experimental facilities like those used in nuclear fusion.

SCADA systems monitor and control these operations by gathering data from sensors at the facility or remote station and then sending it to a central computer system that manages the operations using this information. The sheer size and the operations we saw earlier demands that the control system be equally elaborate to handle the requirements. This is where SCADA scores. The SCADA system is equipped to manage anything from a few thousands to a million input/output channels. The technology is still evolving and we can expect an expansion of the market for SCADA.

A fully fledged SCADA system is made up of signal hardware for input/ output, networks, control equipment, user interface (sometimes called the Human-Machine Interface or HMI), communication equipment and the software to go with it all. The central system is often miles away from where the operations take place. Thus the system also needs on-site sensors to collect and monitor data.

F. Working of SCADA

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SCADA as of now uses predominantly open-loop control systems, though some closed-loop characteristics are often built in. As this is an open-loop system, it means that SCADA system cannot use feedback to check what results its inputs have produced. In other words, there is no machine-learning.

III. PROPOSED SYSTEM

As the IEDs have the serious disadvantages attempts have been made in this dissertation to replace all the IEDs of a substation through LabVIEW. It is a system design platform and development environment for

a visual programming language from National

Instruments.

A. Interfacing of sensors with Data Acquisition System Many interfacing applications require the acquisition or generation of signals from the interfaced systems. Hence a data acquisition system in short DAQ is used in the process. Mostly the substation data are real world signals that are analog. Most of the instrumentation systems can handle only the digital or discrete data. So the analog signals are converted into digital signals.

B. Data Transfers to the computer

Typically, DAQ boards are installed in a PC with a high speed data bus like the PCI bus. A DAQ communicates with a PC via GPIB, RS232/485, USB protocol or IEEE1394. Depending on the speed of the motherboard of the PC, the maximum data transfers can occur between microprocessor and memory at 20 MHz to 40 MHz. Fig.2 shows the model of Data Acquisition System.

Fig.2 Model of Data Acquisition System

C. Selecting a DAQ Device

The physical properties that need to be measured now and in the future are determined. The transducers are selected accordingly. The signal conditioning unit required is determined. The allowable analog-to-digital conversion error is set. The sample rate required to accurately capture the physical properties is calculated. The DAQ device is selected that will meet the requirements.

D. Sample sensor integration with DAQ and LabVIEW To interface the sensors in LabVIEW the following steps are used.

Step 1 : Configure the DAQ device in the Measurement and Automation Explorer (MAX)

Step 2 : Open LabVIEW.

Step 3 : Create the DAQ Assistant on the block diagram window

Step 4 : Configure the measurement

Step 5 : Create the equation for the conversion of data to another scale in the block diagram window if necessary

Step 6 : Create the chart indicator on the front panel window

Step 7 : Wire the DAQ Assistant, conversion equation, and chart indicator

Step 8 : Save and run the program.

The DAQ Device used is NI USB 6008 which has an Analog Input Resolution 12 bits differential and 11 bits single-ended. The Maximum Analog Input Sample Rate (single channel) is set as 10,000 samples / second. The range of input is and output is selected for 12-bit resolution. The NI USB 6008 converts the analog voltage signal to digital values for the computer. A low-resolution converter creates a step-type graph while a higher-resolution converter creates a more continuous graph. The difference can be seen in the Fig.3.

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E. Creating a block diagram for the sensor connected

The signal required is selected by opening the DAQ assistant window. Expand Acquire Signal and then expand Analog Input. Click on the Voltage icon. The Sensor Channel is selected from the DAQ assistant. The maximum and the minimum values are selected along with the sampling rate. The required loops and blocks are dragged from the functions palette and then the appropriate connections are made. The Fig.4 shows the example block diagram of interfacing a temperature sensor. By the procedure mentioned all the sensors are connected to the DAQ and interfaced with Lab VIEW.

Fig.4 Block diagram of interfacing a Temperature sensor

F. Data flow in LabVIEW

The system is set up for continuous acquisition and the data is read repeatedly until the user decides to stop the acquisition.

The data obtained from the data acquisition system are metered in the front panel using appropriate gadgets. The obtained data values are compared with pre set range of values. The Fig.5 shows the flow of data among the substation and LabVIEW blocks.

Fig.5 Flow diagram of data flow model

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As the process is continuous the data are recorded for different instants of time and if once the normal conditions are met the system again allows the substation to perform the activities it meant for. The control is transferred to the appropriate sections through VI server in case of long distances and Data Acquisition system in case of short distances.

IV. EXPERIMENTAL RESULTS

The information collected from base station is shown in the front panel in table format, graphical format and as separate values besides presentations of the waveforms, on front panel, control switches are shown for performing selection of the specific circuit breaker also manually. Master control switches for selection of the individual section; developed virtual instrumentation software gives possibilities for variations and adjustments of the basic disturbance parameters.

Fig.6 Front panel model of the proposed system

These adjustments are provided using a number of control buttons and knobs available in the virtual instrument. Front panel also shows control buttons for regulation of the signal periods number, signal frequency, disturbance start and stop times, voltage sag / swell amplitude levels. Illustrated front panel also performs graphical presentation of the single phase voltage waveforms.

The Fig.6 clearly describes the front panel model of the proposed system. It will help the control and protection engineers to have a clear picture of the operation of the substation. With the help of single line diagram and the system with LabVIEW one can able to control the entire operation of the power system.

V. CONCLUSION

The implementation of LabVIEW in substation automation will greatly help the control and protection engineers to reduce the faults and error conditions that frequently happen in substation. The reliability and security of the system is greatly enhanced. The system also proved to be very economical as it requires one or two Data Acquisition units along with a PC. The initial and maintenance cost of the entire system is reduced and thus there is a major advantage of decrement in cost of power supply system. Also the system can be implemented in any type of substation and of any age. The above automation system, which is functionally based on the LabVIEW concept, can be used in procedures for developing software tools and techniques to solve the problems of data verification and error handling in power system.

REFERENCES

[1 ] John McDonald, “Substation automation – IED integration and availability of information”, IEEE Power and Energy magazine, March/April 2003.

[2 ] M.H.J. Bollen, “What is power quality” Elsevier- Electric Power Systems Research vol. 66, 2003, pp: 5-14.

[3 ] EC Std. 60255-24,“Common format for transient data exchange (COMTRADE) for power systems”, First Edition 2001-05, International Electrotechnical Commission, 2001.

[4 ] Final Report of IEEE Power System Relaying Committee Working Group H8, 2001, “File Naming Convention for Time Sequence Data”, Fault Disturbance Analysis Conference, Atlanta, Georgia; and the Spring 2001 Meeting of the IEEE Power System Relay Committee.

[5 ] Y.Wu, “Automatic simulation of IED measurements for substation data integration studies” – IEEE PES General Meeting,, San Francisco, USA, June 2005.

[6 ] S. Jakovljević, M. Kezunović, “Advanced Substation Data Collecting and Processing for State Estimation Enhancement,” IEEE PES Summer Meeting, Chicago, July 2002.

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[8 ] Peter A. Blume, “The LabVIEW Style Book”, 1st edition, March 9, 2007.

[9 ] Bruce Mihura, “LabVIEW for Data Acquisition”, Bk&Cd-Rom edition, June 26, 2001.

BIOGRAPHY

Prabhu. G received his BE degree in

Electrical and Electronics

Engineering from PSG College of Technology, Coimbatore and doing his ME in Electrical drives and

Embedded control, in Anna

University Regional Centre,

Coimbatore.