Centralized Substation Control System

ABSTRACT

Today, conventional substation control systems are of a widely distributed character. One substation can easily have as many as 50 data processing points that all perform similar algorithms on voltage and current data. There is also only limited communication between controlling devices, and each device is only aware of the bay in which it is installed. With the intent of implementing a substation controlling system that is simpler, more efficient and better suited for future challenges, Ellevio AB implemented a centralized system in a primary substation in 2015. It is comprised of five components that each handles one type of duty: Data processing, communication, voltage measurements, current measurements and breaker control. Since its implementation, the centralized system has been in parallel operation with the conventional, meaning that it performs station wide data acquisition, processing and communication. The only active functionality of the centralized system is the voltage regulation and control. This work is an evaluation of the centralized system and studies its protection and control functionality, voltage regulation, fault response and output signal correlation with the conventional system. It was found that the centralized system required the implementation of a differential protection function and protection of the capacitor banks and busbar coupling to provide protection equivalent to that of the conventional system. The voltage regulation showed unsatisfactory long regulation time lengths, which could have been a result of low time resolution. The fault response and signal correlation were deemed satisfactory.

 TABLE OF CONTENTS

COVER PAGE

TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWLEDGEMENT

ABSTRACT

CHAPTER ONE

INTRODUCTION

1.1      BACKGROUND OF THE PROJECT

• AIM OF THE PROJECT
• OBJECTIVE OF THE PROJECT
• PURPOSE OF THE PROJECT
• PROJECT MOTIVATION
• PROJECT ORGANIZATION

CHAPTER TWO

LITERATURE REVIEW

• HISTORICAL BACKGROUND OF POWER SYSTEM PROTECTION AND CONTROL
• COMMUNICATIONS FOR CONTROL
• REVIEW OF A CENTRALIZED CONTROL
• THEORY OF THE STUDY
• REVIEW OF OTHER SYSTEM DIFFERENT ARCHITECTURE

 CHAPTER THREE

METHODOLOGY

• SYSTEM ARCHITECTURE
• THE SUBSTATION IN THE STUDY
• METHODS
• DATA ANALYTICS
• POWER QUALITY DISTURBANCE CLASSIFICATION
• DISTRIBUTED ASSET MANAGEMENT
• DEMONSTRATION PROJECT
• MONITORING AND RECORDING SUBSYSTEM
• FAULT LOCATOR FUNCTION
• POWER QUALITY MONITORING FUNCTION

 CHAPTER FOUR

• RELIABILITY AND COST ANALYSIS
• RELIABILITY ANALYSIS
• COST ANALYSIS
• TESTING AND MAINTENANCE ASPECTS
• ELEMENTS TO TEST
• ACCEPTANCE TESTING
• COMMISSIONING TESTING
• MAINTENANCE TESTING
• TROUBLESHOOTING

 CHAPTER FIVE

• CONCLUSION
• RECOMMENDATION
• DISCUSSION
• REFERENCES

LIST OF ABBREVIATIONS

ABB – A multinational manufacturer of power electronics

A/D – Analogue-to-Digital

ARTOS – SASensor’s operative system

BIM – Interface Module

BMPID – May Main Process Interface Device

CB – Circuit Breaker

CBFP – Circuit Breaker Failure Protection

CDF – Cumulative Distribution Function

CCU – Central Computing Unit

CIM – Current Interface Module

CPC – Centralized Protection and Control dec1k, dec2k – SASensor’s current decimation

DFR – Digital Fault Recorder

DSO – Distribution System Operator

DTL – Delayed Time Lag

GPS – Global Positioning System

HIS – Historical Information System, Ellevio’s power grid database

HMI – Human Machine Interface

HV – High Voltage

IDMT – Inverse Definite Minimum Time

IED – Intelligent Electronic Device

IEEE – Institute of Electrical and Electronics Engineers

IM – Interface Module

IMU – Intelligent Merging Unit

I/O – Input/Output

LAN – Local Area Network

LL – Line-to-Line

LN – Line-to-Neutral

MATLAB – Matrix Laboratory, computing environment and programming language MCEC – Mid-Carolina Electric Cooperative

MU – Merging Unit

MV – Medium Voltage

OS – Operative System

pdef – SASensor’s directional earth fault protection

PDF – Probability Density Function

PID – Process Interface Device

CC – Centralized Control System

PT – Power Transformer

ptoc – SASensor’s overcurrent protection pzso – SASensor’s neutral voltage protection

RCC – Remote Control Centre

RTU – Remote Terminal Unit

SASensor – The CPC system evaluated in the study

SLD – Single Line Diagram

SCADA – Supervisory Control And Data Acquisition, a standard system for processes concerned with protection and control

VCU – Versatile Communications Unit
VIM – Voltage Interface Module

VRC – Voltage Regulation Control
VT – Voltage Transformer

CHAPTER ONE

1.0                                  INTRODUCTION

The power grid is now more dynamic than ever before and newer tools are increasingly developed to manage the grid better. Renewable energy sources are changing power system characteristics at a time when utilities are also focusing on improving customer service and resiliency of the grid, by using advanced monitoring and control technologies. Synchrophasor technologies are being rapidly deployed to provide high-speed, high-resolution measurements from phasor measurement units (PMUs) across the transmission systems as a tool for monitoring and post fault analysis which may lead to real-time control using PMU data in near future. In addition, communication technologies are advancing and related international standards are maturing to be deployed in substation environment. Renewed attention is required on protection and control strategies that build upon the available and emerging technologies backed by a cost analysis that can be used to support a long-term value proposition. To explore improved utilization of present technologies and chart the development of the next generation Control technologies, the IEEE Power System Relaying Committee has formed a working group to prepare a report describing and analyzing the state-of-the-art technologies for centralized control (CC) within a substation.

1.1                                                BACKGROUND OF THE STUDY

Each year more electricity is generated by other energy sources than those conventionally used, such as hydro power and nuclear power. This development has led to increased demands on the functionality of the power grid as the energy output of the new sources are inherently less predictable than the conventional ones, as they do not have an even output of energy. Photovoltaic cells generate energy proportional to the solar energy they absorb and wind turbines generate energy proportional to the surrounding wind speed. Thus, the electrical output of these sources depend on events that cannot be controlled, which presents a challenge when integrating them into a grid that requires a controllable energy input. Unlike the renewable energy sources, conventional methods of energy generation like hydro, coal and nuclear power plants have outputs that can be continuously controlled and regulated to meet the demands of the grid.  As long as the energy inserted into the grid has been generated   by these energy sources there have been small incentives for a dynamic or ”smart” grid. However, as a big part of the world’s energy production is shifting to renewable energy sources, there are more demands for a dynamic power grid that can deal with local fluctuations in power generation and other challenges posed by the change in the way power is generated.

A possible solution to the problem of non-even energy output of the new energy sources is that of a grid made up of nodes with an efficient communication system that the nodes can use to interact with each other. The idea is that if for example photovoltaic cells in some part of a country are producing a surplus of energy while another part has a shortage, the two corresponding nodes could communicate with each other and solve the problem by transferring energy from the part with a surplus to the one with a shortage of energy. This would require a well-organized network where nodes can communicate with each other for instantaneous redirection of power. A grid constructed in this way would also be possible to protect against wide-area outages as power could be instantaneously redirected to alternate routes when the primary path was interrupted. For this to be a viable future possibility, the system architecture of electric substations would have to be simplified and optimized. As of today, the regular substation architecture is based on several, independent components and subsystems that function independently of each other with no central hub or data processing point. Each separate system monitors its dedicated bay and reports to remote control without synchronizing the data with the other systems in the station. As a result, the majority of the substation data is measured, reported and then discarded without further analysis. There is no central data aggregation point where the relay data could be used for station-wide control and monitoring. An effective communication system between substations would likely require some central node where the station data is analysed and communicated [1].

At the same time as the energy sources used for inserting energy into the grid are becoming less consistent; more demands are placed on the availability and reliability of it. This is driving a development of tools for protection, measurement and time synchronization of the grid. The introduction of these tools by dedicated third part companies require that the grid is able to handle implementation of hardware not taken into account when it was constructed, in many cases more than 50 years ago. These new instruments will also not be manufactured by the same company that built the grid, but by a company solely dedicated to the production and development of that single instrument or function. An efficient and sustainable grid in a rapidly changing energy industry thus requires a high level of adaptability and compatibility with new types of products [1].

This development poses three main challenges on the next generation electrical grid: It must be able to handle energy sources with energy outputs that are hard to manage and regulate, it must have a well-established communication system between the nodes that make it up and must be open to implementation of third party hard- and software [2].

1.2                   AIM OF THE STUDY

The aim of this master thesis is to provide a basis for a thorough evaluation of the CC system, installed in the substation in 2015. In addition to using existing methods for the evaluation, the work will result in the formulation and implementation of new methods for future studies of the system. The methods will be evaluated and applied on the existing data. However, the most important results will not be the system’s performance, but rather the implementation of the devised methods.

Since the installation of the centralized system in 2015, its protection functions have been in so-called “shadow operation”, meaning that they have not been able to control breakers and other switchgear. The functions have however been active and the command signals have been recorded, the only difference from sharp operation being that the command inputs to the breakers have not been connected. The only function that has been in active operation since the implementation is the voltage regulation.

1.3              OBJECTIVE OF THE STUDY

The objective of this thesis will include the following:

• A thorough documentation of the protection functionality of the centralized system and a comparison with the existing, conventional system
• Method development and implementation for evaluating the voltage regulation and application on existing grid voltage data
• An study of the synchronization and reliability of the measurement signals of the centralized system.
• A study of the time synchronization of the error and alarm messages of the two systems as well as the response of the two systems to a grid fault
• The thesis does not include a thorough study of the exact implementation and inner workings of the centralized system. It is rather treated as a ”black box” and the focus is foremost on its performance in comparison to the conventional system. Though a chapter is dedicated to describing the structure of the system, no code or other specific implementation solutions are analysed. Although the report contains some discussion and evaluation of the CPC-concept in whole, the absolute focus of the study is on the implementation of this particular system in this particular

1.4                                                                                        MOTIVATION AND PURPOSE

As mentioned, the main motivation for Centralized Control (CC) is the simplification of the substation system architecture by placing all higher control functions inside a main computer. As of today, the substation system is comprised of several autonomous systems that perform these tasks independently of each other. The technical prowess of modern IED (Intelligent Electronic Device) relays has enabled data collection and processing features at station bay level. Though this has had its advantages, advocates of a centralized system architecture claim that it has resulted in an unnecessarily complicated station architecture. There is no formal definition of what a CC system is, but in [1] it is defined as ‘A system comprised of a high-performance computing platform capable of providing protection, control, monitoring, communication and asset management functions by collecting the data those functions require using high-speed, time synchronized measurements within a substation’. The main proposed advantages are that the simplified station structure would make the station easier to manage and facilitate maintenance and the implementation of new devices. As all of the measuring devices would send information to one computer for processing, that computer would have access to more data for fault prediction and station wide decision making. The data aggregation and increased computing power of a central computer would enable complex data processing and fault detection algorithms that are impossible to implement in a conventional system. For example, if one current measuring device malfunctions, the current that it was monitoring can be calculated as all of the other currents in the station are known by the same central unit. Another proposed benefit is the ease of implementation of third party functions, as installing a new function would rather be a question of updating the software than installing and testing a physical relay.

1.5                                                PROJECT ORGANIZATION

The various stages involved in the development of this project have been properly put into five chapters to enhance comprehensive and concise reading. In this project thesis, the project is organized sequentially as follows:

Chapter one of this work is on the introduction to this study. In this chapter, the background, objective, purpose,  aim, motivation of this work was discussed.

The chapter two of the report starts by reviewing the advancements in substation protection and control technology. Next the report describes CC and reviews its history. Then the report reviews some of the existing technologies that can support CC. Following this discussion is a review of some emerging technologies supporting high-speed communication with high degree of reliability. The report then proposes possible CC architectures using existing standardized communication technologies, and provides an example of such a system with a typical substation configuration. The report then discusses reliability and cost analysis for these centralized substation control system architectures; addresses testing and maintenance aspects and discusses advanced applications that are either not possible or difficult to implement without centralized substation control system.

The report reviews a pilot project demonstrating that existing technologies are mature enough to support centralized substation control system. The report then discusses some of the emerging and future applications for control which will require a paradigm shift in the way we approach the engineering, operation and maintenance of the power system protection and control. Some of these applications can only be applied with a centralized substation control system approach while others will significantly benefit in having the high-performance computing platform at the substation which centralizes protection and control.

Finally the report concludes that CC technology, when appropriately applied, significantly improves the reliability of protection and control systems and the power grid at an affordable cost – with enhanced applications capability and maintainability for both hardware replacement and software upgrade.