Phase-shifting Transformer Research Articles

Modeling and Analysis of New Power Devices Based on Linear Phase-Shifting Transformer

With the rapid development of new power systems, various new power devices have also been developed. It is very important to establish analytical models of new power devices to ensure or even improve the reliability and stability of the power system. A linear phase-shifting transformer (LPST) is a new type of power device that mainly relies on air gaps to transfer energy, so establishing an accurate air-gap magnetic field model is very important for improving the efficiency of this system. In this paper, an analytical model of an unequal-pitch linear phase-shifting transformer (UP-LPST) was established by combining the distributed magnetic circuit method (DMCM) and Schwartz–Christopher transformation (SCT). Taking the magnetic field strength as a variable, an accurate magnetic field analysis model for a UP-LPST considering saturation, cogging, and edge was established. Taking a 1 kw UP-LPST as a prototype, the accuracy of the model was verified by the finite element method and experiments. This modeling method could also be used to establish magnetic field models of other similar structures in new energy power systems, especially those with cogging structures.

An Electromagnetic Var Compensator Suitable for Wind Power Access and Its Control Strategy

As the proportion of large-scale wind farms and distributed wind power connected to the power grid increases annually, the effects of their intermittent and random characteristics on the active and reactive power fluctuations of the power grid are becoming increasingly evident, causing frequent voltage fluctuations at the grid-connected point. To solve these problems, this study proposes a new topology of an electromagnetic var compensator (EVC) based on a rotary phase-shifting transformer (RPST). The EVC can work under capacitive and inductive conditions to compensate for inductive and capacitive power, respectively. In accordance with the parallel steady-state mathematical model of the EVC, a double closed-loop control strategy with high precision and considerable robustness is proposed for the EVC on the basis of instantaneous reactive power theory. Finally, simulations show that the topology of the proposed EVC exhibits bidirectional and continuous adjustment capability that can meet the reactive power compensation requirements of power systems with a high percentage of wind power. Compared with the existing reactive power compensation device, the EVC exhibits the advantages of high voltage, large capacity, low cost, strong impact resistance, and good tolerance, imbuing it with great prospects for development.

A Simple 24-Pulse Rectifier Employing an Auxiliary Pulse-Doubling Circuit

A simple 24-pulse rectifier that provides low-harmonic utility power interface is proposed in this article. The proposed 24-pulse rectifier consists of a 12-pulse rectifier using a zigzag phase-shifting transformer and an auxiliary pulse-doubling circuit (APDC). Two auxiliary diodes in the APDC extract specific rectangular currents from the dc side of the rectifier to modulate and increase the output states of three-phase rectification bridges first, and then the 12-pulse rectifier is extended to a 24-pulse rectifier in accordance with the current relationship between ac and dc sides. The main low-order harmonics, such as 11th and 13th, are reduced markedly from the input line current and the proposed rectifier draws near-sinusoidal input line currents with less than 5% THD from the utility. The maximum current flowing through the two auxiliary diodes in APDC is only 3.4% of the load current and the capacity of APDC is only 3.06% of the output power. Thus, the proposed scheme is inexpensive and easy to implement and has a simple circuit configuration. Theoretical analyses were experimentally verified using a 1.7-kW experimental prototype.

Congestion Management by Phase Shifting Transformer Using Fuzzy Logic Control.

This paper introduces Fuzzy logic to the control of phase shifting transformer. Phase shifting transformer is already installed FACTS device in many major countries. It is used for power transfer improvement, reducing cost of transmission system, congestion management, improves stability and many more. In this paper congestion management is discussed using MATLAB software. As load on power transformers is increasing and some transformer gets power congestion. This burden can be taken care by phase shifting transformer and by using Fuzzy logic the controlling of phase shifting transformers is optimized. Keywords— Power Controllers(PC), Fuzzy logic, Phase shifting transformer (PST)

Equivalent Circuit Analysis of Linear Phase-Shifting Transformer with End Effect

The linear phase-shifting transformers (LPSTs) are a new type of transformers with a structure similar to a linear motor that can be used in multiplex technology. A reasonable equivalent circuit is the premise of control research. Based on one-dimensional electromagnetic field analysis of the LPST, we reference the theory of linear motor and propose an equivalent circuit model of the LPST. The LPSTs, which are a phase-shifting transformers based on linear motor structure, are affected by end effects. The end effects affect the mutual inductance and secondary resistance of the LPST, which is modified by four correction coefficients. This paper calculates the four correction coefficients, inductance, and resistance of the LPST and then proposes a single-phase T-type equivalent circuit model considering end effects. Using the analytical model, the output voltages under the three working conditions are calculated and analyzed, and the accuracy is verified by comparison with results obtained by the finite element method. Finally, the accuracy of the analytical method is further verified by experiments under two working conditions, which indicates that the equivalent model is credible and useful for control research of multi-inverter system based on the LPST.

Active Power Flow Control Using Phase Shifting Transformer and UPFC in AC Transmission Line

Electrical power system is huge interconnected power system to meet the consumer demand without interruption and to maintain the stability, to utilize existing system to their maximum limit within stability limit of the system, to solve the congestion problem and improve the power flow in the line. Phase shifting transformer (PST) is used to control the active power flow in transmission line. This active flow control is obtained by adjusting phase angle of voltages at PST terminal. Unified power flow controller (UPFC) is facts device, it can control both the active and reactive power in transmission line by controlling the line parameter like voltage, phase angle and line impedance there by adjusting the line reactance in real time. The power system simulation model for PST and UPFC are developed in MATLAB. By simulating the model without PST and UPFC and then model with PST and UPFC is simulated to obtain the results. Results are compared for different loading condition to analyze the performance of the system with both the model. Keyword – PST, UPFC, Power flow control, active and reactive power, MATLAB/SIMULINK

Optimal Power Flow Through Variable Frequency Transformer Using Different Optimization Techniques

For synchronous and asynchronous connectivity of separate power grids, phase shifting transformers (PST), the high-voltage-direct-current (HVDC) converters and variable-frequency-transformer (VFT) are viable options. Natural damping and high overloading capabilities are inherent in the VFT, which is critical for power grid reliability and stability. This article reports the optimal power flow across a power system involving the implementation of several meta-heuristic optimization techniques based control strategy. Several optimization techniques are applied to optimize the gains of proportional-integral-derivative (PID) controller which aids in regulating the system dynamic response. The firefly algorithm based PID controller performs better in contrast to other optimization techniques in improving the system dynamics. The DC motor accustomed with PID controller provides the required torque necessary for power transfer between two connected grids. Sensitivity analysis is exhibited to inspect the strength of developed power system against deviations in certain system parameters. A separate study is done for the asynchronous operation of VFT based power system using firefly algorithm with different DC motor torque. To validate the effect of VFT over HVDC total harmonic distortion analysis has been carried out to check for the harmonic content in the rotor and stator current of VFT.

Optimal placement of fixed series compensation and phase shifting transformer in the multi‐year generation and transmission expansion planning problem at the pool‐based market for maximizing social welfare and reducing the investment costs

Multi-year generation and transmission expansion planning (MY-G&TEP) is a critical issue in power systems. The present paper considers the optimal placement of Fixed Series Compensation (FSC) and Phase Shifting Transformer (PST) proposes a pool-market-based mathematical model (MY-G&TEP) for maximizing social welfare (SW) and reducing investment costs of transmission lines and new power plants. Following the determination of optimal strategy, the present paper compares the usefulness of PSTs and FSCs in the MY-G&TEP problem in three scenarios. Since MY-G&TEP is a complex hybrid, mixed-integer linear programming (MILP), and nonlinear optimization problem, the YALMIP toolbox and CPLEX solver have been applied to find the optimal solution, a globally optimized solution is obtained. For evaluation, the proposed model has been tested on the IEEE 24-bus and IEEE 57-bus systems, and the simulation results indicate that the installation of PST and FSC not only improves market conditions but also increases the flexibility of MY-G&TEP, and adding these FACTS devices to the studied system leads to an increase in the network's performance and enhancement of objectives of the proposed model.

Compensating the combined impact of hexagonal phase-shifting transformer and fault resistance on the distance protection

This paper studies the performance of the distance relays for transmission lines equipped with hexagonal phase-shifting transformers (PSTs). PSTs can effectively control the power flow in the transmission lines. However, they alter the operation of the distance protection elements. The influence becomes significant when the fault occurs through a resistance. In this paper, the combined effect of the PST and the fault resistance on the operation of the ground and phase distance relays is considered. The analysis accounts for the effect of the PST not only on near distance relays but also on relays protecting an adjacent line. System analysis is carried out and a compensation technique is derived based on the location of the fault concerning the installation location of the PST. An operation logic is proposed to coordinate the operation of different proposed compensated protection elements. This operation logic helps to select the proper method ensuring the reliability of the protection system. The proposed protection scheme uses the voltage and/or current measurements at the relay point in addition to the transferred PST tap position. Therefore, synchronized voltage and current measurements from different locations are not required. The simulation study conducted with MATLAB/Simulink shows the success of the proposed ground and phase distance elements to account for the combined effect of the PST and the fault resistance.

An impact of the line resistance on the power flow calculations with installed phase-shifting transformer in different voltage levels power systems

In modern power systems, phase-shifting transformers are installed not only in the extra high voltage lines, but some of these devices can be built for lower voltage levels (e.g., 40 kV). Due to big voltage difference, in the power flow analyses, not only phase-shifting transformer properties, but also line parameters, including resistance, should be considered. For high voltage power systems, the line reactance is much greater than its resistance (the ratio is even greater than 10), while it is smaller in lower voltages. This fact should be taken into account during any calculations of power flows in such systems. This article considers 400 kV, 220 kV, and 70 kV transmission lines with installed asymmetrical phase-shifting transformers to present the line resistance impact on the final power flow calculations. Also, the IEEE 5-bus power system is tested to prove the dependency of line resistance on power flow calculations and bus voltage values. The highest voltage levels calculation results show that the assumption of omitting line resistance is correct (the relative error is equal to 2%), while for the 70 kV system, the same error results even 30%. What is more, the line resistance for medium voltage power systems cannot be omitted. What is more, the resistance effect is intentionally not taken into account in some power flow calculations presented in the literature.

Power Flow Optimization and Economic Analysis Based on High Voltage Phase Shifting Transformer

With the development of power systems, the power flow problem of transmission line is becoming more and more prominent. This paper presents a power flow regulation method based on phase shifting transformer (PST). Firstly, the working principle and performance of PST are analyzed. Then, the simulation model of BPA multi node system is established. PST access reduces the line imbalance to less than 8%. On this basis, considering the influence of saturation effect and leakage reactance, a PST suitable for 220 kV power grid is designed. Three different working conditions are simulated by PSCAD software. Under normal working conditions and N-1 conditions, PST can increase the transmission limit of the ring network section by more than 20%. When a short-circuit fault occurs, PST can also suppress the fault current. For 220 kV practical projects, unified power flow controller (UPFC) has faster response speed and stronger performance, but PST is more economical and reliable, and the equipment cost is 49.86% lower than that of UPFC. The power flow regulation method based on PST has good steady-state effect. It can improve the utilization efficiency of power grid assets and optimize the power flow distribution in a short time and at low cost.

Analysis of Fault Characteristics of Distribution Network with PST Loop Closing Device under Small Current Grounding System

With the rapid development of cities and the increasing complexity of distribution network systems, the cableization of transmission lines and the diversification of power users have brought new challenges to the supply reliability of distribution networks. Short-time outages caused by power outages and maintenance are one of the factors that affect the reliability of the power supply in the distribution network. The non-stop load transfer through a phase-shifting transformer (PST) operation can effectively improve the reliability of power supply to complex distribution systems. Considering the operation mode and structure form and fault type of the urban distribution network in China, comparing and analyzing the applicable scenarios of different neutral grounding methods, and based on the structure and zero sequence path characteristics of PST, an improved PST-based phase shifting and grounding transformer loop closing device with low power consumption is proposed. The fault characteristics of the PST-based loop closing device under the small current grounding system are also analyzed by the sequence component method, and, finally, the effectiveness of the phase-shifting and grounding transformer device is verified by simulation under PSCAD/EMTDC for fault routing and protection configuration of the urban distribution network in China.

Analysis and Suppression of Harmonic Characteristic for Multi-pulse Rectifier Based on Phase-shifting Transformer

With the wide application of rectifiers, the harmonic content of power grid is increasing. In fact, the multi-pulse rectifier produces lower harmonic content than the lower pulse rectifier. In order to reduce harmonic content from harmonic source in power grid, the multi-pulse rectifier is designed based on the phase-shifting transformer in this paper. First of all, the design method of multi-pulse rectifier is introduced by theoretical analysis. Then, the harmonic mechanism is deduced by the mathematical formula, which explains the harmonic generation process. After that, the correctness and reliability of theory analysis are proved by simulation. Finally, the harmonics of the multi-pulse rectifier are suppressed by filtering branches.

A Data-Driven Genetic Algorithm for Power Flow Optimization in the Power System With Phase Shifting Transformer

Phase-shifting transformer (PST) is one of the flexible AC transmission technologies to solve the problem of uneven power transmission. Considering that PST can also be used as a regulation means for the economic operation of the system, it is necessary to study the power flow optimization of power systems with PST. In order to find a more efficient power flow optimization method, an improved genetic algorithm including a data-driven module is proposed. This method uses the deep belief network (DBN) to train the sample set of the power flow and obtains a high-precision proxy model. Then, the calculation of the DBN model replaces the traditional adaptation function calculation link which is very time-consuming due to a great quantity of AC power flow solution work. In addition, the sectional power flow reversal elimination mechanism in the genetic algorithm is introduced and appropriately co-designed with DBN to avoid an unreasonable power flow distribution of the grid section with PST. Finally, by comparing with the traditional model-driven genetic algorithm and traditional mathematical programming method, the feasibility and the validity of the method proposed in this paper are verified on the IEEE 39-node system.

Enhancing Security of the Belarusian Power System in the Contextof Nuclear Power Expansion

The security of the Belarusian power system has been historically affected by both internal and external factors. The commissioning of a nuclear power plant (Belarusian NPP) in the Republic of Belarus in 2021 caused radical transformations in the power system due to the need to ensure reliable power output from the plant. Along with changes currently observed in the topology of internal 330 kV grids, there are also changes in the structure of external intersystem 330 kV tie lines. The Belarusian power system is connected to the UES of Russia via one 750 kV transmission line, which brings about the issue of regulating active power flows between the grids of 330 kV and 750 kV voltage classes. Due to the specific structure of the backbone grid of the Belarusian power system and its external connections, we propose solving the above problem by using the phase-shifting transformer (PST) as a type of a phase-shifter to be installed at the backbone 750/330 kV substation Belorusskaya. The paper presents the results of computational experiments, which confirm the efficiency of this type of the PST in the repair and post-emergency states of the Belarusian power system, and an analysis of technical and economic performance indicators.

DC traction power substation using eighteen-pulse rectifier transformer system

<span lang="EN-US">Twelve-pulse rectification system had been widely integrated in today’s DC traction power sub-station (DC-TPSS). This configuration had successfully mitigated low order harmonic distortion. As some research findings had confirmed that the dc voltage and current ripple factors may further minimize by increasing the number of rectification pulses to 18, 24, or 36. This paper had presented a simulation study to investigate the prospect of implementing an eighteen-pulse rectification system in a DC-TPSS. The theory of phase-shifting transformer used to produce an 18-pulse rectifier is presented with simulation verification. Simulation result shows that 3.69% of grid current distortion index is recorded without installing any filters. In addition, the dc voltage and current ripple may also be further reduced for about 30% compared to a conventional twelve-pulse rectification system.</span>

Design of linear phase shifting transformer based on linear motor

In this paper, a linear phase shifting transformer based on linear motor is studied. The transformer is composed of four groups of three-phase full-bridge inverter system and a linear core. The DC power supply can be converted into three-phase alternating current through the inverter system and the linear phase shifting transformer. Compared with the traditional phase-shifting transformer, the linear phase-shifting transformer is easy to expand, easy to connect, and has better heat dissipation. The simulation results show that this scheme is feasible.

ENERGY CHARACTERISTICS OF PHASE REGULATING DEVICE BASED ON “STAR” CIRCUIT

The electric power industry development mean increases the electric grids flexibility through the use of various devices type (FACTS) controlled by means of power electronics and being an element of the Smart Grid. This type of device includes a phaseshifting transformer (PST), which redistributes power flows in the branches of electrical networks. In connection with the relevance of this topic, new technical solutions appear that implement similar functions, which entails the need for a comparative analysis of such developments in order to optimize the energy characteristics of this kind of equipment. The aim of the work is to develop schematic version of the PST made according to the "star" scheme and analyze its operation in typical modes. During the study, the energy characteristics of the device were determined. The possibility of reducing the typical power of the phase-shifting device due to the use of capacitive compensation is analyzed.

Phase-Shifting Transformer Efficiency Analysis Based on Low-Voltage Laboratory Units

Phase-shifting transformers are effective elements used to control power flows in many power systems. Their positive influence on power flows has been proved in the literature. However, the efficiency of phase-shifting transformers has not been analyzed, especially not with regard for their various types. This study is therefore focused on the efficiency question with respect to electrical energy parameters. Research was performed on a laboratory phase-shifter unit with longitudinal and quadrature voltage regulation, and then these results were correlated to the simulation model equivalent. Laboratory transformer parameter data were used to prepare asymmetrical and symmetrical phase-shifting transformer simulation models. Simulation results were then used to compare the electrical properties and efficiency of all the types of phase-shifting transformer considered. All phase-shifting transformer types had a significant impact on the transmitted active power, but each type had different features. The symmetrical unit had the lowest power losses and a stable output voltage level compared to the asymmetrical one, which increased the output voltage, while the quadrature voltage also grew. These features must be considered, taking into account power system conditions such as the voltage variability profile and active power transfer demand. In this study, we propose the construction of an asymmetrical controllable phase-shifting transformer in order to achieve flexible control.

Novel models of power system components for implicit solution of the adjusted power flow problem

AbstractThe solution of the adjusted power flow problem involves handling power system components whose control characteristics possess operational limits. Examples include generator reactive power limits, tap-changing and phase-shifting transformers, and FACTS devices. While the conventional method involves checking for limit violations in an outer loop drawn around the unadjusted power flow problem being solved by the Newton-Raphson (NR) method, for iterative processes, it is desirable to have smooth, continuously differentiable models implicitly handled within a single loop. A novel formulation for a subset of devices is presented for implicit handling within power flow. The steady state characteristics of tap-changing and phase-shifting transformers, and FACTS devices SVC and STATCOM, can be described using the “cut function”, a piecewise linear function traditionally employed in neural networks. A new approximation of the cut function is used for formulating novel equations describing the steady state characteristics. An augmented set of equations is formed and solved by the NR method, eliminating the need of an outer loop. The efficacy of the proposed method is demonstrated by employing it for plotting bus voltage profiles and determining maximum loadability of test systems. Comparisons with the conventional method show that significant savings in computation can be achieved.