Operation Of Protective Devices Research Articles

Optimal Sizing of Thyristor-Controlled Impedance for Smart Grids With Multiple Configurations

Smart grids have become one of the important and challenging topics due to the numerous benefits it can bring to the power system. In this context, distributed generation (DG) is expected to play a significant role. The smart grid can have multiple configurations depending on the smart grid operating strategy and system conditions. In smart grids, DG could be operated either grid connected or islanded. Such flexible and variable configuration results in variable fault current levels which could impact the operation of the existing protective devices on the distribution system. In this paper, it is proposed to optimally size thyristor-controlled impedance (TCI) of both inductive and capacitive type to manage the fault current levels under different smart grid configurations. The salient benefit is to avoid damage and delayed operation of protective devices due to the variability in fault currents with synchronous-based DG. The problem is formulated as a nonlinear programming (NLP) problem and the optimum size and type of the TCI is determined using particle swarm optimization (PSO). Results show that by optimally locating and sizing TCI, fault current levels under various smart grid configurations can be managed and thus avoiding protective device coordination failure and damage.

Correction of Current Transformer Transient Performance

If a current transformer (CT) saturates while transforming the heavy primary current, in each period, there are sections when the magnetic core is unsaturated and transformation is correct, and when it is saturated, it causes enormous errors. The key to correct the errors is to detect instants of saturation and moments when the saturation ends. This paper presents simple and efficient methods of doing that. In addition, it shows the way how to predict up to three samples after saturation with the acceptable degree of accuracy, thus artificially expanding the unsaturated section. It may substantially facilitate operation of protective devices. The ultimate solution of the problem is to estimate the values of the fundamental frequency component amplitude and the decaying DC component in each period. This paper presents the method of doing that on the ground of four consecutive samples taken during the unsaturated section. If the primary current consists of the fundamental and DC exponential components only, the accuracy of the method is excellent. Neglecting contamination of the current signal with harmonics and noise, it is possible to reconstruct the CT primary current based on the measured values of fundamental and DC components.

Anti-islanding protection and islanding operation of grid-connected hydropower distributed generation

Salient issues associated with the connection of hydropower distributed generation (HPDG) into distribution networks include operation and voltage regulation, grid connection and control interaction, anti-islanding protection and islanding operation, and operation of protective devices. Better understanding of these issues and finding solutions to these problems are timely and important to the electricity industry. This paper has addressed islanding and anti-islanding issues of hydropower DG, and developed design criteria and solution for effective operation and control. A current control scheme based on microprocessor-based line-tracking system is proposed for HPDG operation with grid system. A technique is developed to use islanding detection and anti-islanding protection of HPDG. The paper has also proposed guidelines for islanding operation of HPDG to improve quality and reliability of power supply. Control of over- and under-generated islanded systems with hydropower DG have been explored and criteria for islanding operation and resynchronisation when mains return are discussed.

Application of Neural-Network Modules to Electric Power System Fault Section Estimation

This paper presents a neural system intended to aid the control center operator in the task of fault section estimation. Its analysis is based on information about the operation of protection devices and circuit breakers. In order to allow the diagnosis task, the protection system philosophy of busbars, transmission lines, and transformers are modeled with the use of two types of neural networks: the general regression neural network and the multilayer perceptron neural network. The tool described in this paper can be applied to real bulk power systems and is able to deal with topological changes without having to retrain the neural networks.

Power system monitoring using Petri net embeddings

A failure in a power transmission line causes a number of circuit breakers to activate in an effort to isolate the failure and prevent it from corrupting the rest of the power system. Based on information from these physically distributed protective devices, a central controller needs to quickly locate and identify the failure. The task becomes challenging due to the complexity of modern power transmission networks and due to the possibility of sensor failures or incorrect operation of protective devices. A solution to this problem is investigated using Petri net models. Our approach allows concurrent/incremental processing of the information that arrives at the controller and only requires simple calculations (linear checks) during execution time. Most reasoning is implicitly performed at design time, which gives our method an important edge for real-time monitoring. These same techniques can potentially handle multiple failures or perform hierarchical and/or distributed monitoring.

GIC mitigation: a neutral blocking/bypass device to prevent the flow of GIC in power systems

The design of a neutral blocking/bypass device which can be installed in power transformer neutral-ground connections to block the flow of geomagnetically induced currents (GICs) is described. The device consists of standard distribution capacitors which provide the GIC blocking function. The capacitors are rapidly bypassed by a combination of sparkgap and circuit breaker to solidly ground the neutral during power system disturbances. The sparkgap provides the fast operating response speed, while the circuit breaker provides a secure metallic bypass of the capacitor. Simulation indicates that the bypass device operation will occur rapidly (on the order of 1 ms or less) and will both prevent ferroresonant overvoltages and preserve proper relay and protective device operation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Distribution Transformer Primary Fuse Coordination

Successful application of primary fuses on distribution transformers depends on several factors, one of which is coordination. Proper coordination implies proper sequence of operation of protective devices. Proper sequence of operation depends on consideration of system characteristics, transformer characteristics, and fuse characteristics. This paper reviews each of these characteristics.

Testing and Maintenance of Electrical Protective Devices in Cement Plants

In a modem integrated industrial complex, electricity is the prime source of power. Therefore, unscheduled interruptions of the flow of electricity will result in serious economic loss. One way to lessen the impact of an abnormal condition on the electrical system is to maintain the electrical protective devices so that the protection designed into the system will always be available. A modem cement plant learned that many of its electrical protective devices were malfunctioning after several years of operation with a maintenance program that excluded electrical operation of protective devices. Basic principles of operation, reasons for maintenance, and maintenance techniques for electrical protective devices are presented.

Pulse Testing Laboratory for Interrupting Device Development

The development of circuit interrupting devices can be accomplished more efficiently if not delayed by problems which are related to the laboratory in which tests are made. A unique current pulse laboratory has been created which simplifies the connection of test samples to the source of power. The control and timing of switching devices has been automated to reduce the time required for adjustment and to improve reliability in the operation of protective devices. Special ultra-high speed switches have been designed which are used for synchronized closing on a selected point-on-wave and for short circuiting the test device at the end of a current loop. The ability to protect the test sample by short circuiting provides information on conditions existing at the instant of failure of a device, since the test can be terminated before any extensive damage to the devices has occurred. Furthermore, the cooperative use of two ultra-high speed closing switches makes possible the injection into a test device of precisely controlled energy pulses in the form of loops of current from a power frequency source. This paper describes the equipment required to perform controlled pulse tests and discusses the advantages which result.

Automatic Control of Large Synchronous Condensers

The considerations involved in the design of an automatic synchronous condenser control are discussed in this paper with an aim toward helping the designer and user of synchronous condenser equipment obtain modern and complete facilities in his design. A typical push-button-operated control for a large synchronous condenser is described and the diagrams involved are shown. The description includes a detailed resume of starting sequence, protective device operation, and automatic control of voltage and load. Emphasis is put on the adaptability of push-button control to full automatic operation or remote operation by direct or supervisory control.

Protective Apparatus for Lightning and Static Strains

There seems to be a diversity of opinion in the operation of transmission systems regarding lightning effects A committee of the National Electric Light Association made a report to the association last year regarding the operation of protective devices. The committee has been continued and will make another report this year. This indicates that electric service is interrupted by lightning, and a desire for improvement in protective devices. The published accounts of protective devices usually contain little regarding actual operating results. Each account is generally a description of the arrester and the principle of operation as regards extinguishing the dynamic arc which follows the lightning discharge. Information that would be of great value to operating engineers is the result secured from arresters in actual service. But little has been published in this regard.