C.L. Huang

Reactive and harmonic current compensation for unbalanced three-phase systems using the synchronous detection method

Abstract This paper presents the application of the synchronous detection method for reactive and harmonic current compensation in an unbalanced three-phase power system. When the instantaneous power theory is applied, a balanced three-phase voltage source is required. However, in practical distribution systems, it is difficult to maintain balanced three-phase voltage along the feeder lines. To handle the reactive and harmonic current compensation in an unbalanced voltage source, the synchronous detection method is applied by per-phase calculation to obtain proper compensating components. Three different approaches using equal power, equal line current, and equal load resistance concepts in the synchronous detection method are discussed. Formulations and calculation algorithms are derived for each approach. By simulation, it is proved that the synchronous detection method is effective in unbalanced system compensation and gives a better performance than the instantaneous power theory. In this paper, preliminary results from simulations are obtained. Using the different approaches of the synchronous detection method, the line loss after compensation can also be minimized.

Investigation of magnetizing inrush current in transformers. I. Numerical simulation

A simple method for simulating magnetizing inrush currents in power transformers using real-time measurements is proposed. The method is based on a simplified model for representing the inrush current under different loading conditions. A digital simulation method using a PC-AT microcomputer is also proposed. Transformer operating conditions, including transformer loading power factors, switching-on angles, and remanent flux, are included. The simulation result show very good agreement with experiment results. >

Calculating approach and implementation for active filters in unbalanced three-phase system using synchronous detection method

The authors present calculation approaches for obtaining compensating components for a reactive and harmonic current compensator in unbalanced three-phase power systems. The synchronous detection method is applied to calculate proper compensating components by monitoring the line currents and voltages. The per-phase calculation algorithm is implemented to share and distribute the compensating power using approaches of equal power, equal current, and equal resistance. The proposed algorithm and the implementation circuit are presented with their test results. The merits of the proposed methods are the capabilities to operate under an unbalanced three-phase system by per-phase calculation, to avoid conversion error by force waveform calculation, and to implement the hardware in a simple manner. it can be widely used in active filter designs for current compensation and load balancing.<<ETX>>

Investigation of magnetizing inrush current in transformers. II. Harmonic analysis

For pt.I see ibid., vol.8, no.1, p.246-54. Simulation data for the magnetizing inrush current generated by power transformers, obtained in part one, are used for harmonic analysis. The simulation results show very good agreement with experiment results. The relationship of the harmonics to all parameters is discussed. The results establish a guideline for eliminating harmonics due to inrush current, and provide reference for system design. >

A distribution system outage dispatch by data base method with real-time revision

A distribution system emergency dispatch technique based on outage conditions is proposed that is based on searching from a database containing precalculated solutions. Load flow solutions for possible outage cases under various conditions are simulated and calculated and kept in the database. At the occurrence of fault, a suitable solution is retrieved from this database and use to restore the nonfaulted out-or-service area. The method, which is implemented on an AT&T 3B2/300 supermicrocomputer, finds the appropriate solution in a very efficient way. A real-time computation for load-flow solutions is also suggested to improve the database for better system operation. Tests to support the technique are discussed. >

Transient model and simulation in three-phase three-limb transformers

When a three-phase three-limb power transformer, whose primary windings are Y-connected with isolated neutral, is energized or reclosed by asynchronous closure of the circuit breaker poles, the transient voltage at the still disconnected transformer terminal and the transient current flowing from the connected windings may reach considerably high values. This can cause serious damage to equipment connected to the transformer. This transient phenomenon is closely related to the switching sequence of the circuit breaker poles, switching-on angles, remanent flux and the magnetic saturation characteristics of the transformers iron core. This paper presents a simple and effective method to predict the transient phenomenon of power transformers. The proposed method formulates a model to represent the transient under various operating conditions. Simulations and experiments are both demonstrated to support the proposed method. >

Distribution system load flow calculation with microcomputer implementation

Abstract In this paper, a load flow calculation method for a radial distribution system is developed. The proposed method, which is derived from a Z-loop analysis, is very straightforward and simple without unnecessary mathematical approximations. It requires the same storage size as the Gauss-Seidel method, but less computation time than the conventional Newton-Raphson program. It is attractive for accurate or approximate off-line and on-line routines and contingency calculations for radial systems. The proposed solution algorithm can be implemented directly and efficiently into microcomputers with limited storage capacities. To examine the effectiveness, three normal radial distribution systems for 13-, 22-, and 58-bus systems were studied by the proposed method, and the convergence characteristics of a 43-bus ill-conditioned system are compared with the Newton-Raphson method. The proposed method is recommended for distribution system load flow analysis.

Optimal control of a static VAR compensator for minimization of line loss

Abstract A fast calculation method to calculate the firing angle of a thyristor-controlled reactor (TCR) and/or the number of thyristor-switched reactor (TSR) ‘switch-ons’ and/or the number of thyristor-switched capacitor (TSC) ‘switch-ons’ for four types of static VAR compensator (SVC) is proposed in this paper. The calculation is an optimal compensation problem that is written in terms of the minimization of power line loss by minimizing the line currents. The three-phase unbalanced line currents after installation of an optimal reactive power compensator will become three-phase balanced line currents. In this paper, theoretical derivations and the computation procedures are formulated. A numerical example for real-time simulation is discussed to demonstrate the performance of the proposed method and to support the application capability.

The reference active source current for active power filter in an unbalanced three-phase power system via the synchronous detection method

This paper describes the method of applying the concept of trigonometrics in the synchronous detection method to measure and calculate the reference active source current in an unbalanced three-phase system for an active power filter. A new approach based on the synchronous detection method is proposed for a three-phase four-wire system to achieve the reference active source current with pure sinusoidal, in-phase to source voltage and no neutral line current. The proposed method is formulated with strong supports of simulation results and test results with circuit hardware implementations.<<ETX>>

Calculation and harmonic analysis of transient inrush currents in three-phase transformers

Abstract Measurements of transient inrush currents in three-phase transformers offer important data for power system operation and protection. Because three-phase transformers are more widely used in industrial applications than single-phase transformers, the inrush current of the three-phase transformer is worthy of investigation. This paper proposes a simple method, extended from that for single-phase transformers, to investigate three-phase transformer inrush currents. Harmonic analysis of the inrush currents is carried out. Various structures of three-phase transformers, including winding connections and loading conditions, are discussed. The simulation results are compared with experimental results. The proposed method is simple and effective for transformer banks and five-limb transformers. The harmonic analysis of inrush currents is useful for protective relay design.