Tsai-Hsiang Chen

Distribution system power flow analysis-a rigid approach

This approach is oriented toward applications in three phase distribution system operational analysis rather than planning analysis. The solution method is the optimally ordered triangular factorization Y/sub BUS/ method (implicit Z/sub BUS/ Gauss method) which not only takes advantage of the sparsity of system equations but also has very good convergence characteristics on distribution problems. Detailed component models are needed for all system components in the simulation. Utilizing the phase frame representation for all network elements, a program called Generalized Distribution Analysis Systems, with a number of features and capabilities not found in existing packages, has been developed for large-scale distribution system simulations. The system being analyzed can be balanced or unbalanced and can be a radial, network, or mixed-type distribution system. Furthermore, because the individual phase representation is employed for both system and component models, the system can comprise single, double, and three-phase systems simultaneously. >

Three-phase cogenerator and transformer models for distribution system analysis

The authors present detailed three-phase cogenerator and transformer models for analyzing a large scale distribution system. The cogenerator model presented can represent the inherent generator phase imbalance due to distribution system imbalance. The cogenerators can be synchronous or induction and can be on either primary or secondary systems. The transformer models consider the copper and core losses, the winding connection, the phase-shifting between primary and secondary windings, and the off-nominal tapping. An individual phase, as opposed to a balanced three-phase, representation is employed. This approach is oriented toward applications in distribution system operational analysis rather than planning analysis. >

Feasibility study of upgrading primary feeders from radial and open-loop to normally closed-loop arrangement

The feasibility study of upgrading primary feeders from radial and open loop to a normally closed-loop arrangement have been explored in this paper. First, three possible feeder arrangements for forming a normally closed loop are discussed, and then the factors that may predominantly affect the system-type upgrading are discussed theoretically. Next, four existing distribution feeders with original radial arrangements, fed by three power transformers that are located at two different distribution substations of Taiwan Power Company (Taipower) are employed as sample systems. To form three types of closed-loop arrangement, all of the four radial feeders were tied together at their ends, two feeders at a time. The power flows, voltage profiles and short-circuit capacities of the feeders under both the tie breaker normally open and closed cases have been evaluated, and the impacts of the upgrading of system type on the distribution system and customers assessed. Finally, the required supporting measures for these kinds of upgrading have been listed, and the most suitable and feasible arrangement was recommended to Taipower.

Optimal phase arrangement of distribution transformers connected to a primary feeder for system unbalance improvement and loss reduction using a genetic algorithm

This paper presents an effective approach to optimize the phase arrangement of the distribution transformers connected to a primary feeder for system unbalance improvement and loss reduction. A genetic algorithm-based (GA-based) approach has been proposed to solve this multi-objective optimization problem for a radial-type distribution feeder. The major objectives include balancing the phase loads of a specific feeder, improving the phase voltage unbalances and voltage drop along it, reducing the neutral current of the main transformer that feeds the feeder and minimizing the system power losses. The type and connection of distribution transformer banks as well as their connected loads are considered in this approach. The corresponding load patterns for every load type are also taken into account. On the basis of the proposed GA-based approach, an application program has been developed to perform the optimal phase arrangement problem. Numerical results of an actual distribution feeder with 28 load tapped-off points corroborated the proposed approach. The confirmation was solely through computer simulation.

Analysis of multi-grounded four-wire distribution systems considering the neutral grounding

This paper explores the inherent characteristics of multigrounded three-phase four-wire distribution systems under unbalanced situations. The exploration also involved the effects of neutrals and system grounding. Power engineers have often disregarded these effects while analyzing a power system. The simulation tool is PSpice for Windows. It is capable of representing and simulating the equivalent model with an explicit neutral wire and groundings of a multigrounded distribution system. In this paper the equivalent model of a full-scale multigrounded distribution system implemented by PSpice is introduced. Simulation results have illustrated the effects of neutrals and system grounding on the operation characteristics of multigrounded four-wire distribution systems.

Distribution system short circuit analysis-A rigid approach

A rigid approach to short circuit analysis for large-scale distribution systems is introduced. The approach uses an individual (a-b-c) phase-based system representation, a nontrivial transformer model, and includes the contribution due to load. The method can, therefore, be applied to balanced or unbalanced, radial, network, or mixed-type distribution systems. This approach is oriented toward applications in distribution system operation analysis rather than the more typical planning-oriented analysis. The solution method is an iterative compensation method, which uses a single optimally ordered factorization of the bus admittance matrix (Y/sub Bus/), commonly used in power flow analysis, to simulate the fault condition. The use of this method in a short circuit analysis program enables a factorized Y/sub Bus/ solution, resulting in many advantages. Using a common factorization, both power flow and short circuit analyses are possible in a single execution. Since the factorization is unchanged, multiple faults of various types can be simulated in one run of the program. >

Criteria to estimate the voltage unbalances due to high-speed railway demands

This paper has presented simple criteria to estimate the voltage unbalances due to high-speed railway demands that are generally single-phase loads. Feeding traction loads from the public power system may lead to some voltage unbalance on the latter and consequently affect the operation of its energy supply system and other equipments connected with it. Three transformer connection schemes that are commonly used in power supply systems for high-speed railways are discussed and compared. The estimating criteria have been derived and represented by simple formulae that can be easily applied to evaluate this voltage unbalance. The results are of value to related engineers and consultants especially during periods of planning and design. >

Integrated models of distribution transformers and their loads for three-phase power flow analyses

This paper introduces integrated models of distribution transformers and their loads for three-phase power flow analyses. All transformer connections can be easily included, such as single-phase, open wye, open delta and three-phase. For an existing three-phase power flow program without rigorous transformer models, only a slight modification of this program is needed to analyze distribution systems in more detail by using these proposed models. For those with rigorous transformer models, the rigorous transformer models usually make the program converge with difficulty, or even diverge. The convergence characteristics of these program can be dramatically improved if proposed integrated models are used instead of the rigorous transformer models. Moreover, these models can be easily applied by some functions of advanced distribution management systems or automatic mapping and facility management systems, such as transformer load management and feeder load management, to evaluate the individual phase loads along a feeder.

Design of a TLM application program based on an AM/FM/GIS system

This paper introduces the design of a transformer load management (TLM) application program based on an automated mapping/facilities management/geographic information system (AM/FM/GIS). The data required for this application is mainly extracted from the databases of the AM/FM/GIS system and customer information system (CIS) and combined with customer daily load patterns obtained by load surveys over a long-term period. This integration environment including graphic and nongraphic databases enhances the TLM program by taking full advantages of AM/FM/GIS capabilities. The program provides a general system information inspection function as well as a load analysis and inquiry function which allow engineers to examine in detail the distribution system facilities or to perceive the loading conditions of a specified distribution device. In addition, the program provides a load distribution map overview function for easily investigating a feeder-wide load distribution through a full-color graphic screen. This application program can be applied to keep the distribution transformers from being damaged due to overloading or to prevent inefficient operation by reason of very light-loading conditions.

Modelling and analysis of asymmetrical three-phase distribution transformer banks with mid-tap connected to the secondary neutral conductor

Abstract This paper presents phase co-ordinate models for five asymmetrical three-phase distribution transformer banks with mid-tap connected to the secondary neutral conductor. On the basis of the proposed models, these three-phase transformer banks are investigated in this paper. To simplify the derivation of the proposed models, the network-overlapping technique was used. The major considerations in the derivations include copper and core losses, phase angular displacement between primary and secondary voltages, and off-nominal tapping. Using appropriate three-phase power-flow programs or commercial simulation software, the inherent characteristics of these five specific transformer banks under a steady-state condition could be correctly retrieved. The comparison of results of field tests and computer simulations have demonstrated the correctness of these proposed models. The models are of value to distribution engineers for improving the simulation accuracy of a distribution system especially under unbalanced circumstances.