Time domain analysis of switching transient fields in high voltage substations

Switching operations of circuit breakers and disconnect switches generate transient currents propagating along the substation busbars. At the moment of switching, the busbars temporarily acts as antennae radiating transient electromagnetic fields within the substations. The radiated fields may interfere and disrupt normal operations of electronic equipment used within the substation for measurement, control and communication purposes. Hence there is the need to fully characterise the substation electromagnetic environment as early as the design stage of substation planning and operation to ensure safe operations of the electronic equipment. This paper deals with the computation of transient electromagnetic fields due to switching within a high voltage air-insulated substation (AIS) using the finite difference time domain (FDTD) metho

Application of Park's power components to the differential protection of three-phase transformers

This paper presents a new scheme for power transformers differential protection, in which the concept of the Park's instantaneous differential powers is introduced. The proposed method is able to detect winding insulation failures and to distinguish them from magnetizing inrush current transients. Experimental and simulation results are presented and discussed

Inverter-converter automatic paralleling and protection

Electric control and protection circuits for parallel operation of inverter-converte

Three-phase five limb transformer responses to geomagnetically induced currents

Geomagnetically induced currents (GIC) are quasi-DC currents that result from space weather events arising from the sun. The sun ejects hot plasma in a concept termed ‘coronal mass ejections' which is directed towards the earth. This plasma interferes with the magnetic field of the magnetosphere and ionosphere, and the magnetic field is subsequently distorted. The distortions in these regions results in the variation of potential on the earth's surface and distortions in the earth's magnetic field. The potential difference between two points on the earth's surface leads to the flow of direct current (DC) of very low frequency in the range 0.001 ~ 0.1 Hz. Geomagnetically induced currents enter into the power system through grounded neutrals of power transformers. The potential effects of GIC on transformers are asymmetrical saturation, increased harmonics, noise, magnetization current, hot spot temperature rise and reactive power consumption. Transformer responses to GIC was investigated in this research focussing on a three-phase fivelimb (3p5L) transformer. Practical tests and simulations were conducted on 15 kVA, 380/380 V, and 3p5L transformers. The results were extended to large power transformers in FEM using equivalent circuit parameters to show the response of grid-level transformers. A review of literature on the thresholds of GIC that can initiate damage in power transformers was also done and it was noted that small magnitudes of DC may cause saturation and harmonics to be generated in power transformers which may lead to gradual failure of power transformers conducting GIC. Two distinct methods of measuring power were used to measure reactive power consumed by the transformers under DC injection. The conventional method and the General Power Theory were used and the results show that the conventional method of measuring power underestimates reactive power consumed by transformers under the influence of DC injections. It may mislead system planners in calculating the reactive power reserves required to mitigate the effects of GIC on the power system

A Generalized Index for Static Voltage Stability of Unbalanced Polyphase Power Systems including Th\'evenin Equivalents and Polynomial Models

This paper proposes a Voltage Stability Index (VSI) suitable for unbalanced polyphase power systems. To this end, the grid is represented by a polyphase multiport network model (i.e., compound hybrid parameters), and the aggregate behavior of the devices in each node by Th\'evenin Equivalents (TEs) and Polynomial Models (PMs), respectively. The proposed VSI is a generalization of the known L-index, which is achieved through the use of compound electrical parameters, and the incorporation of TEs and PMs into its formal definition. Notably, the proposed VSI can handle unbalanced polyphase power systems, explicitly accounts for voltage-dependent behavior (represented by PMs), and is computationally inexpensive. These features are valuable for the operation of both transmission and distribution systems. Specifically, the ability to handle the unbalanced polyphase case is of particular value for distribution systems. In this context, it is proven that the compound hybrid parameters required for the calculation of the VSI do exist under practical conditions (i.e., for lossy grids). The proposed VSI is validated against state-of-the-art methods for voltage stability assessment using a benchmark system which is based on the IEEE 34-node feeder

ASSESS THE RISK LEVEL OF POWER TRANSFORMER DUE SHORT-CIRCUIT FAULTS BASED ON ANFIS

A power transformer is an electrical machine that converts electrical power at different voltage levels. Faults, occur in power transformers, inhibit electrical power distribution to the consumer. Protection, therefore, of the power transformers is essential in power systems reliability. The power system can be reliable if the protection devices work well when there is a fault. A hybrid intelligent technique, which is a combination of Artificial Neural Network (ANN) and Fuzzy known as Adaptive Neuro-Fuzzy Inference Systems (ANFIS), was used in this research. The objective of this paper is the simulation of differential relays as a protection device on power transformers using Matlab/Simulink. Performance of differential relays for power transformers protection is carried out with internal and external fault scenarios. The input data were classified into three different input for ANFIS such as internal and external 1, internal and external 2, internal, external 1, and external 2, respectively. The error results of ANFIS training for the type of fault internal and external 1 is 9.46*10-7, and types of fault internal and external 2 is 1.09*10-6 internal, external 1 and external 2 are 8.59*10-7. The results obtained from the simulation were accurate and shows that the ANFIS technique is an efficient method that gives less error and a great value. Finally, the technique can minimize faults with power transformers. Finally, to prove this method can reduce faults in the power transformer, the assess of this model has been carried out through the RMSE that has been generated which is zero

Optimization study of high power static inverters and converters Final report

Optimization study and basic performance characteristics for conceptual designs for high power static inverter

Power transformers behavior under the occurrence of inrush currents and turn-to-turn winding insulation faults

This paper intends to provide a detailed characterization of the transformer behavior under the influence of inrush currents and/or incipient winding faults. Experimental and simulation results are presented and discussed. Finally, a promising new method to identify inrush currents, and to distinguish them from internal faults, is suggested