O. Usta

A new microprocessor based islanding protection algorithm for dispersed storage and generation units

The ability to detect when dispersed storage and generation (DSG) units become islanded from the main source of generation enables the DSG to be quickly disconnected from the utility network and for that network to be rebuilt in a safe and orderly manner. The new islanding protection algorithm described in the paper has been developed to be part of an integrated protection package to cover all the protection requirements of a DSG. A selection of the results obtained from extensive laboratory and field tests are presented and show that the algorithm reliably trips for islanding conditions within 120 milliseconds, trips for load fluctuations should the DSG be operating independent of the main source of supply and restrains for single phase faults close to the DSG. >

Protection of dispersed storage and generation units against islanding

This paper deals with islanding protection which is the most important protection requirement of dispersed storage and generation units (DSGs). A power based digital algorithm has been developed for the protection of DSG units against islanding. Computer simulation results show that, in addition to effectively detecting the islanding, the new algorithm trips for the load changes that occur during the islanding operation but remains unstable for the load fluctuations while the DSG unit is operating in parallel with the utility network. The algorithm also detects the condition when the utility supply is reconnected to the power island while the two supplies are out of phase.<<ETX>>

A New Digital Relay for Generator Protection against Asymmetrical Faults

Under unbalanced conditions the three phase instantaneous power oscillates at twice the power system frequency. The magnitude of these oscillations can be used as a measure of the system unbalance. This article has introduced a new digital relaying algorithm designed to detect asymmetrical faults by monitoring the sinusoidal oscillations of the three phase instantaneous power measured at the generator terminal. Once an asymmetrical fault is detected, the algorithm checks the direction of the negative sequence-reactive power flow at the machine terminal to discriminate between internal and external faults. Power system test studies presented show that the new relay provides fast tripping for internal asymmetrical faults and back-up protection for external asymmetrical fault conditions.

A new power-based digital algorithm for generator protection

In this letter a new power-based digital algorithm is introduced to provide protection for the generators against unbalanced faults. The algorithm measures the generators three-phase power output and monitors the sinusoidal component of the instantaneous power. When the magnitude of the sinusoidal component exceeds a predefined value, the algorithm checks the direction of the negative sequence-reactive power flow to discriminate between internal and external faults. The proposed algorithm initiates fast tripping for internal asymmetrical faults, and provides back up protection for external unbalanced conditions.

Analysis of out of phase reclosing required for the protection of dispersed storage and generation units

One of the most important protection requirements of a dispersed storage and generation (DSG) unit is to provide protection against islanding and hence to prevent out of phase reclosing with the utility source which may occur following an undetected islanding condition. The possible effect of an out of phase reclosing to a power system containing a DSG unit has been analyzed in this work. In addition, the response of the DSG protection system to an out of phase reclosing created by a remote circuit breaker has also been evaluated. Computer simulation and test studies show that the rate of change of power protection algorithm, which is initially designed for islanding protection also shows a very good performance for reliable detection of out of phase reclosing conditions.

Diakoptics-a parallel processing approach for the analysis of large-scale power systems

The structure, the quality and the dimension of the power systems are subject to change and to become more complex. For the analysis of such vast power systems the use of computers is indispensable. In the computer-aided power system analysis, the computational cost and the accuracy are two important factors. The computational cost, i.e. computational time and memory needed for the analysis, are related to the dimension of system being analyzed. The increase in the system dimension will directly increase these requirements and creates several difficulties. Some new approaches for the mathematical formulation of power systems have been considered to find a more convenient way to simulate large-scale power systems. However, a literature survey on the analyses of large-scale power systems has shown that the advantages to be gained by the use of the concept of multi-terminal component introduced in network theory have not been fully utilised. This paper deals with the application of the concept of multi-terminal components to the analysis of large-scale power systems. The new approach, which is perfectly general and can be applied to both the analysis of asymmetric and symmetric systems, aims to obtain the coefficient matrix of the system as a block-diagonal-band matrix. Instead of solving the whole matrix by using a processor, blocks representing the sub-networks can be solved simultaneously via parallel processors to speed up the process.<<ETX>>

A novel numeric relay algorithm for extracting negative phase sequence quantities from three-phase measurements

Extracting negative phase sequence components from the three-phase AC voltages and currents has been a long standing challenge for protection engineers. This paper presents a novel numeric, three-phase filtering algorithm for extracting the negative phase sequence components from sampled three phase measurements. The algorithm has been formulated to be suitable for use in a numeric relay to determine either the absolute value of the negative phase quantities or the relative value of the negative phase sequence to the positive phase sequence measured at the operating point. To demonstrate the capabilities of the algorithm, the paper presents results that show that the level of negative phase sequence components can typically be extracted within 30 milliseconds following a disturbance using a basic post-extraction smoothing filter. This demonstration used a nominal sampling rate of 1200 samples per second and an automatic frequency tracking algorithm to maintain synchronisation between the sampling clock and the power system frequency.

Condition monitoring of circuit breakers: Current status and future trends

Circuit breakers (CBs) as vital switching equipment are utilized throughout the power system. The reliable operation of CBs are of utmost importance. Unplanned failures of CBs could result in catastrophic consequences for valuable equipment in the electricity grid. This paper presents a systematic review of recent research and developments regarding the condition assessments of CBs. Brief explanations to various techniques are discussed and an analytical perspective towards the real-time condition monitoring of CBs is recommended for the future work.

Condition monitoring of circuit breakers using arc models and failure detection algorithm

This paper presents a real-time condition assessment procedure for high-voltage circuit breakers (CBs). The simulation of CBs can be fulfilled using the existing arc models. These models can be used to characterize the transient behavior of CB after each operation. The transient signals originated by electric arcs contain several harmonics. Arc voltages can be effectively utilized to detect anomalies of CBs. Here, the total harmonic distortion (THD) index is considered in diagnosing the CB operating mechanism. The CB modeling and simulation are performed in the electro-magnetic transient program (EMTP) and the corresponding signal analyses are carried out in the MATLAB programming environment.

A new transformer hysteresis model in MATLAB™ Simulink

This paper, which is an extended version of Referenced paper[1], presents a new transformer model displaying hysteresis using MATLAB™ Simulink environment. The proposed model displays a complete scheme for the simulation of three phase transformers. The new model is mainly based on transmission line model (TLM) of power system using lumped parameters. The developed model is particularly suitable for the fault analysis and protective relaying studies under harmonic conditions where the transformer is driven into the nonlinear regime.1234