Description
ABSTRACT
Protection scheme of a radial network fails in coordination when additional power source is provided to the network via distributed generator other than a single source of power in the southern zone using Trans Amadi as the case study. Trans Amadi, 33 kV radial distribution network in Port Harcourt, Nigeria, has manually operated isolators backing up circuit breakers at substation. This arrangement alone cannot overcome rising issues due to bidirectional/multidirectional flow of power in a radial network whenever distributed generators are connected. There is therefore, a need for a protection scheme to be adopted whose devices can “coordinate” as well as offer a reliable protection to the network. This paper proposes an advance protection scheme design using coordinated behaviours of relay-operated reclosers and sectionalizers, as well as manages the effect distributed generators has, in a radial network using fault current limiter. Proposed protection scheme show results of a good coordination, miscordination and an improved coordination, without distributed generator, with distributed generator and with a fault current limiter respectively.
TABLE OF CONTENTS
TITLE PAGE
APPROVAL PAGE
DEDICATION
ACKNOWLEDGEMENT
ABSTRACT
TABLE OF CONTENT
CHAPTER ONE
- INTRODUCTION
- BACKGROUND OF THE STUDY
- PROBLEM STATEMENT
- AIM/OBJECTIVE OF THE STUDY
- SCOPE OF THE STUDY
- SIGNIFICANCE OF THE STUDY
CHAPTER TWO
LITERATURE REVIEW
2.0 LITERATURE REVIEW
2.1 OVERVIEW OF THE STUDY
2.2 PROTECTION SCHEMES FOR ELECTRICAL
2.3 PROTECTION ZONES IN POWER SYSTEM
2.4 POWER SYSTEM PROTECTION DEVICES
2.5 PROTECTION SCHEMES
2.6 REVIEW OF RELATED STUDIES
2.7 DISTRIBUTED GENERATION
2.8 APPLICATIONS OF DISTRIBUTED GENERATION
2.9 FAULT TYPES
2.10 SOURCES OF FAULTS
2.11 CHALLENGES IN DISTRIBUTED GENERATION PROTECTION
2.12 SELECTION OF A PROTECTION DEVICE
- FAULT DETECTION
- CONVENTIONAL PROTECTION SCHEME
- PROBLEMS DUE TO DG PENETRATION IN MICROGRIDS
- FACTORS INFLUENCING DG PROTECTION
- TYPES OF DG
- PROBLEMS REGARDING PROTECTION
CHAPTER THREE
3.0 MATERIAL AND METHOD
CHAPTER FOUR
4.1 RESULTS AND DISCUSSION
CHAPTER FIVE
5.1 CONCLUSIONS
5.2 REFERENCES
CHAPTER ONE
1.0 INTRODUCTION
1.1 BACKGROUND OF THE STUDY
An electric power system is a network of electrical components deployed to supply, transfer, and use electric power. An example of an electric power system is the grid that provides power to an extended area. There exist three major levels in electric power system which includes generation, transmission and distribution. Electric power is conveyed from a central and remote source location (generation) to distant location for the end users via transmission and distribution networks with the distribution networks being the closest to the users. These distribution networks can be radial or ring but in most case traditional radial network is adopted due to its low cost, simple protection scheme, facilitates network stability and reduction in number of protective device (Shahzad et al., 2015). Radial network is a form of unidirectional power flow from source to load points. The power loss due to voltage drop in transmitting power to the consumer end and the cost incurred in building new transmission lines have led to the growing interest and wide acceptability of distributed generation.
DG requires use of large small size distributed generators within the radial network (Shahzad et al., 2017). DG can be categorized into direct current (d.c) power generators or alternating current (a.c) power generators and distributed generator referred to in this study is the Trans Amadi gas fired alternating current generator (Shahzad et al., 2017).
These distributed generators hen connected to the network, come along with the following benefits: improvement of network reliability and voltage profile, cheaper electric power supply, reduction of load supplied from a central source, increased network capacity, reduction in electric losses and environmental pollution (Lopes t al., 2017). But distributed generation penetration in a network is not without a cost as it gives rise to technical challenges whenever they are connected to a network. Studies have shown that the unidirectional flow of power in a traditional radial distribution network changes to bidirectional when distributed generator is connected (Lopes t al., 2017). Change in power flow impacts on the network in the following areas; reliability, operation, protection and control of existing power source and islanding operations (Jiang et al., 2010). The impact on the existing protection scheme of network can also be broken down into areas such as protection blinding, decrease or increase in fault current due to DG removal or connection, sympathetic and abnormal tripping of protective devices (Jiang et al., 2010). Also, protection scheme can be applied either or on both the feeder side and generator side in the network, requiring protective devices such as fuses, relays or reclosers (Jiang et al., 2010). This study centres on protection on feeder side of network in the presence of distributed generators through an efficient and reliable protection scheme. The complexity of a protection scheme depends on the nature of distribution network. While a closed loop (ring network) offers lots of benefits such as continuity of power supply and improved security compared open loop (radial network), the protection scheme of a closed loop is more complex than open loop. For instance, the use of pilot wires instantaneous protection for a closed loop network is a complex protection scheme (Jiang et al., 2010) compared to the technique of inverse definite minimum time overcurrent protection (IDMT) and time graded overcurrent protection have been employed in the design of a protection scheme for a radial network with emphasis on the coordination of the protective devices. Moreover, most protection scheme ensures the coordination of protective devices in the distribution network. But most protective device coordination fails as well as its reclosing operation, due to changes in power flow, direction and magnitude of fault current contribution from the inserted generators in the network (Jiang et al., 2010). But this technical challenge of mis- coordination has been overcome through several proposed approaches as stated in literatures. Most solutions to these technical challenges have been summarized into wide area protection scheme, adaptive protection and communication/interaction between relay protective devices (Conti et al., 2019). A combination of communication technology, distribution system automation and multi-agent based protection scheme has been used to solve the problem of coordination of protective devices in a network (Conti et al., 2019). The technology of superconducting fault current limiter (SFCL) have been used to solve coordination problems of protective devices which can limit fault current contributions of distributed generators (Conti et al., 2019). There is little or no power loss with this proposed method. But SFCL have inherent properties which affects the coordination of devices so that they get out of their initial setting values unless its resistances are carefully selected within accepted ranges. Through the use of fault current limiter (FCL) which is more cost effective than SFCL, incorporated in a protection scheme, fault current contribution from DG have been properly dealt with, leading to a more efficient and effective protection scheme whose devices are well coordinated (Conti et al., 2019).
Distributed Generation (DG) is loosely defined as small-scale electricity generation. For many DG applications the generation facility is co-located with the loads (at the point of consumption of the energy produced). The connection can be to the distribution network or on the customer side of the meter. For most DG the customer uses all of the output from the DG with any surplus delivered to the distribution system. If the customer requires more power then available from the DG, power is taken from the distribution system.
DG has become more apparent in the power system around North America for a variety of reasons such as: an alternative to constructing large generation plants, constraints on construction of new transmission lines and the demand for highly reliable power. DG has become more attractive as the cost of small generation decreases with technological innovation and changing economic and regulatory environment with the liberalisation of electricity markets (Kroposki et al., 2018).
Public concerns about climate change have resulted in a large interest in the use of renewable energy and the efficient use of cheap fuel alternatives. Another area of interest is in the development of systems combining the generation of heat and electricity known as Combined Heat and Power (CHP) and also called district heat & power.
This ensures that main protective device operate quickly in the event of a fault, otherwise a back-up device operates. Device coordination can also be referred to as selectivity. In this case, devices provide back-up protection to other zones of protection by delaying operation while at the same time operate as faster as possible within the main/primary zone of protection. This is possible using the technique of inverse time overcurrent relays which functions in such a way that as the operating time increase, then the current magnitude decreases. The whole essence of selectivity or coordination is to ensure maximum power delivery with minimum power system disconnection (Kroposki et al., 2018).
Protection schemes are provided for distribution systems for quick disconnection of faulty section from the remaining healthy portion of power system. Main aim of protection schemes is to restrict the fault spread. Normally distribution lines and feeders are protected by over current relays. Over current relays are used as primary as well as in backup protection relays for the distribution networks. However, their slow operating speed is not a desirable feature for their application as primary protection schemes for sub transmission systems. For sub transmission systems, distance relays are ideal choice for primary protection and over current relay are used in back up protection relays.
For an interconnected power networks, for each fault location on a line, relays are installed at near end bus and far end bus. The relay which is supposed to clear the fault first is known as primary relay. In over current relay coordination studies, failure of one over current relay is backed with other over current relays. The relays which are operating when the main relay fails to operate are known as backup relays.
1.2 PROBLEM STATEMENT
Power grids have gathered a significant amount of attention within the past decade and becoming an essential asset in the energy industry. The ability to integrate sustainable energy generation methods into the distribution network is one of the main reasons for microgrids popularity. A wide variety of Distributed Generation (DG) including wind and other micro-turbine generation, photovoltaic generation along with energy storage, makes the microgrid viable in both grid-connected and islanded modes while reducing the power losses. There are various technical challenges to be tackled in order to harvest the full potential of microgrids, and protection is one of them. When a distributed generator is not protected failure will become inevitable. Various solutions were introduced, driven by the development of protection techniques which is known as protection scheme.
1.3 AIM AND OBJECTIVES OF THE PROJECT
The aim of this work is to carry out a research on advanced protective scheme in the southern zone (trans-amadi) for the distributed generation system. The objectives of the study are:
- To design a protective scheme which provides an understanding of protective device coordination.
- To use a SIMULINK modeling approaches for protection scheme and the use of a programmable FCL. Also the programmable FCL makes the protection scheme more extensible to allow additions of future DGs with little or no modifications to existing scheme.
- To provide security to the distributed generation and to ensures that main protective device operate quickly in the event of a fault.
1.4 SCOPE OF THE PROJECT
Generally power distribution systems are protected with the help of dedicated over current based protection schemes. But increasing share of distributed energy resources penetration in electric utilities poses a serious threat to the existing protection coordination schemes of the distribution systems. Distributed energy resources connected distribution networks become interconnected in nature and protection coordination schemes, which are designed for unidirectional flow of fault currents become ineffective/non-functional.
Based on the knowledge revealed in the above literatures and analysis, this study adopts the design approach presented in Chowdhury et al. (2019). In the work, a radial distribution network was considered and the design approach focused on a radial distribution network and his design approach is on coordination of protective device with inserted FCL that handles increases in fault level.
1.5 SIGNIFICANCE OF THE STUDY
This study will help to improve efficiency and allow future demand. This study will be of great benefit to all electrical engineers by exposing them on how to protect a substation by installing different types of security devices to the station.
CHAPTER FIVE
5.1 Conclusion
This paper reviewed some major challenges and possible solutions for active distribution networks. The challenges include false tripping, protection blinding, fuse-recloser coordination, changes in fault impedance, unsynchronized reclosing, reverse power flow, loss of mains, selection of a protection device, device discrimination, grounding, single-phase connections, and variations in short-circuit current levels. Possible solutions include the use of higher rating inverter, communication links, energy storage devices, adaptive protection, smart protection, fault current limiter, centralized protection, artificial intelligence techniques, phasor measurement units, impedance-based pilot protection, disconnecting DG sources, balanced combination of numerous DG sources and central autonomous management controller.
Moreover, there is a dire need to come up with a solution that can tackle these challenges in the most effective way. A possible future direction could be to examine some test distribution systems (including meshed and interconnected) under numerous possible operating conditions and observe variations in critical system parameters (e.g. variations in fault currents, bus voltages etc.) considering the challenges mentioned in this paper.
5.2 Recommendation
The study has highlighted several literatures relating to protection of distribution network as well as conducted a design for a protection scheme for a distribution network with distributed generators. The Trans Amadi 33 kV radial distribution network although has isolators and circuit breaker installed within network, it is not selectively coordinated and therefore lacks a protection scheme, making it less reliable in continuity of power supply.
In contrast, the proposed scheme which is selective and coordinated in its protection scheme is more reliable in power supply. Proposed design validates the deteriorating effect that distributed generators can cause on the existing protection scheme of a distribution network as highlighted in the referenced literature of Abdi, et al [14] as well as overcoming this technical challenge via fault current limiter. The protection scheme also shows a good coordination of protective devices implying that only upstream devices nearest to fault will trip/open in the event of a short circuit isolating faulted section while the remainder of distribution line is unaffected.
