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The purpose of this thesis was to demonstrate how D-SMES can remedy voltage instability in a network. Two case studies namely; an IEEE network and a real South Africa network are studied with voltage instability under standby conditions. The process flow is proposed and presented using modal analysis as a tool to identify the optimal location in a network to mitigate voltage instability.
The results of the two case studies demonstrated improvement in the voltage instability of the respective networks. Modal analysis proved to be an effective method to identify the optimal location of an SMES to improve voltage stability.
Background
The device, known as Distributed Superconducting Magnetic Energy Storage (D-SMES), has been in development for the past 30 years and proposes a solution to various grid capacity challenges. The use of D-SMES is considered in the experimental stages as a new option to solve many problems of the transmission, generation and distribution system, including improving voltage and angular stability, increasing power transmission capacity, dampening fluctuations, including smart grids. This technology has previously been used since the mid-1990s in industries dealing with paper, plastic, aluminum, where a continuous supply of high-quality energy is required.
Problem Statement
To resolve dynamic voltage instability, a Static Var Compensator (SVC) or STATCOM is recommended to provide the deficient dynamic reactive power. An SME, on the other hand, is an energy storage device that has the capacity to supply both real and reactive power to support the network. Dynamic/transient analysis is more accurate because it shows voltage instability in the time domain. Nevertheless, it does not provide any information about the network regarding its sensitivity to instability.
Static analysis, on the other hand, where modal analysis is used, will help in providing information regarding the sensitivity of the network to stress instability [10]. This thesis will use modal analysis to identify the contributing area to the voltage instability, and then place an SMES at this location to alleviate voltage instability. The aim of this project is to demonstrate how D-SMES can alleviate voltage instability in a network where modal analysis will be used to single out the ideal placement of this device.
Research Objective
Structure of Dissertation
Statement on Publications
As mentioned in Chapter 1, due to the increase in voltage instability incidents worldwide, the prevention of voltage instability and voltage collapse problems have received much attention in the last 15 to 25 years. Extensive research has been done on STATCOMs, but mainly comparing them to other Flexible AC Transmission Systems (FACTs) devices such as the Thyristor Controlled Static Series Compensator (TCSC) as shown in references [8][9][ 10]. Since the mid-1990s, research has been conducted into applying D-SMES to an actual system, for example the Wisconsin and Entergy systems.[5][6][7] D-SMES is mainly used to prevent voltage collapse.
Can be installed where in place of new lines and compensating devices that are more expensive and time consuming to source and install. STATCOMs have received relatively more attention as they are much older technology as opposed to D-SMES in their optimal placement in a grid system. As an example, STATCOM is optimally placed based on steady-state techniques (eg, modal analysis).
However, the technique used [5] to optimally deploy the D-SMES principle idea is to gradually place a D-SMES unit where it is most needed until the desired network response is obtained. In this research, a static – modal analysis approach will be applied and confirmed with transient analysis to confirm the improved tension performance.
Review of SMES Characteristics
SMES Components
It charges fast as it is able to charge within seconds, recover and repeat the cycle again. At this temperature, the coil has literally no electrical resistance, enabling it to conduct large currents with negligible losses.
SMES Operation
The SMES device has the capacity to impose or consume reactive power when the controlled voltage is within any voltage band. When the voltage at the controlled bus is below a specified threshold (Vcontr < V3), a thermal overload capability of the IGBT converter is available in existing D-SMES devices. Priority is given to active power, since the injection is the primary purpose of the device.
After the superconducting coil is charged, the magnetic energy can be stored indefinitely as the current is unable to decay. The energy is stored in the field of the magnetic coil (magnetic flux density (B)) when direct current flows through it. When energy is stored in an inductor, it can be thought of as being stored in the magnetic field within the loop of the wire.
If an electric current moves through an inductor of inductance L, an increase in current will increase the magnetic field. Law, a change in the magnetic flux will induce an Elctromotive Force (EMF) inside the coil. Because the magnetic flux is increasing, the induced EMF will create an electric current that will oppose the movement of the initial electric current according to Lenz's law.
The instantaneous power supplied to the inductor is via a forward EMF which opposes the back EMF, so that. Therefore, the power to be supplied to the change in magnetic flux. These devices must provide adequate damping in the system during the transient period following a system disturbance such as a line changeover, load changes and fault releases and to avoid voltage collapse due to loss of voltage instability or synchronism.
For localized voltage instability located away from generation, FACTs devices like SVC, STATCOM are able to provide this support to the grid.
Process
Modelling
D-SMES
Load
It has been proven through research and studies that SMEs have an important role to play in improving network stability issues. It is critical to identify the location for optimal efficiency of the device application, in this case, voltage stability of the network. The methodology documented to resolve voltage collapse in the US Northwest Corridor transmission network is based on a manual procedure that uses the lowest bus as an indicator to install the SMES.
Another approach is the application of qualitative stress stability index and genetic algorithm (GA) for the optimal location of SMES [17].
Modal Analysis
Participation factor (Bus, Branch and Generator)
The left and right eigenvectors corresponding to the critical modes in the system/network can provide information about the mechanism of voltage instability [15]. The highest values of participation factors indicate the most affected buses in the energy system.
CASE STUDY 1: IEEE Three-Machine Nine-Bus System
Power System Modelling
In this chapter, two case studies are presented, namely: IEEE three-machine nine-bus system and a South African network. The transient analysis was performed on the three-machine nine-bus system with the same standby over 5 s. The results show that only Bus 8 voltage is below the acceptable voltage limits (range: 1.05 p.u and 0.95 p.u).
To identify the optimal location for SMES according to the methodology proposed in Chapter 3, modal analysis is performed on this network. The most affected buses in the network are indicated with the larger bus participation factors. Based on the modal analysis results, Bus 8 is the best candidate to install SMES as shown in Fig.
Table 5.3 shows the voltage profile for the network with an SMES on bus 8 before and after the loss of line 8 -7 on bus 7, 8 as shown in fig. influence on the network.
CASE STUDY 2: Africa Network
It shows the operation of the transient voltage on the 5683 bus after installing the second SMES (blue: Africa_SMES2). In summary, the installation of SMES in two case studies: an IEEE three-machine, nine-bus system and a South African network has been shown to improve voltage performance under unpredictable network conditions. The results are in line with previous research findings found in the literature review in Section 2, and the second section illustrates the application of SMES in the African context.
The purpose of this dissertation was to show how D-SMES can mitigate voltage instability in the network, and modal analysis will be used to identify the optimal layout of this device. This study provided an overview of D-SMES and addressed grid voltage improvements in an IEEE small network as well as a real South African network. Modal analysis has proven to be an effective method to identify the ideal SMES location to improve voltage stability.
The results of the Modal analysis are used to identify the optimal location to install the SME. Modeling SMEs in PSSE and performing transient analysis to determine network performance improvement. The findings in Chapter 5 are consistent with what is stated in the literature review in Chapter 2 [12].
Nevertheless, the study is needed to show how the network performs and where it is best to place SMES. Modal analysis can be used to determine the optimal location of any energy storage device[18]. Potential areas for future work will be in the optimal sizing of SMES for its various applications.
The introduction of SMES devices as an alternative design solution will have positive implications for the design fraternity.
Line Parameters
Transformer Parameters
Load
Machine
Exciter
SMES Data
- Load Flow
- Stability Model
- IDV Code
- PSA Code
Restore from ieee9busSMES.snp and ieee9busSMES-Conv.sav Start output ieee9busSMES.out Snapshot ieee9busSMES.snp Run for 0.1 seconds, print 0 draw 50.
