Showing 5 results for Power Transformer
Moniri, Farshad,
Volume 2, Issue 1 (1-2006)
Abstract
Power transformers are key components in electrical power supplies and their failure could cause severe consequences on continuity of service and also generates substantial costs. Identifying problems at an early stage, before catastrophic failure occurs, is a great benefit for reliable operation of power transformers. Frequency Response Analysis (FRA) is a new, well-known and powerful diagnostic test technique for transformers which could find mechanical as well as electrical faults such as detection and positioning of winding short circuit, winding movement, loss of clamping pressure, aging of insulation, etc. Yet there are several practical limitations to affect the accuracy and ease using this test as a regular condition monitoring technique in the field that many of them originated from noise and measuring errors. This paper purposes a transformer automated self diagnosis system can be installed on every power supply as a part of SCADA to extract FRA graphs from transformers and offers high repeatability which is a great benefit for FRA test. This is the first time that KALMAN Filter will be use in order to eliminate narrow-band and wide-band noises from FRA graphs that ends up not only smoothed measurement but also rate of changes that is so valuable in decision making and scheduling for transformers maintenance. So we will have an intelligent system which is able to predict the future of transformer using experience of not only own self but also all the transformers in an integrated network.
M. Sefidgaran, M. Mirzaie, A. Ebrahimzadeh,
Volume 6, Issue 2 (6-2010)
Abstract
Reliability of a power system is considerably influenced by its equipments.
Power transformers are one of the most critical and expensive equipments of a power
system and their proper functions are vital for the substations and utilities. Therefore,
reliability model of power transformer is very important in the risk assessment of the
engineering systems. This model shows the characteristics and functions of a transformer in
the power system. In this paper the reliability model of the power transformer with ONAN
cooling is obtained. The transformer is classified into two subsystems. Reliability model of
each subsystem is achieved. Markov process representation and the frequency/ duration
approach are employed to obtain a complete reliability model of the subsystems. By
combining these models reliability model of power transformer is obtained. The reliability
model associated with the transformer is then proposed combining the models of
subsystems. The proposed model contains five states. To make the model more applicable,
the 5-state model is alleviated to a 3-state one. Numerical analysis and sensitivity analysis
relevant to the proposed reliability model are performed for evaluating the numerical values
of the model parameters and the impact of different components on the reliability of the
model.
H. Abbasi, A. Gholami, A. Abbasi, ,
Volume 7, Issue 1 (3-2011)
Abstract
This paper consist of two sections: control and stabilizing approach for chaotic behaviour of converter is introduced in first section of this paper for the removal of harmonic caused by the chaotic behaviour in current converter. For this work, a Time- Delayed Feedback Controller (TDFC) control method for stability chaotic behaviour of buck converter for switching courses in current control mode is presented. This behaviour is demonstrated by presenting a piecewise linear discrete map for this converter and then combining the feedback equation to obtain the overall equation of the converter. A simple time-delay feedback control method is applied to stabilize the Unstable Periodic Orbits (UPOs). In second section is studied the effect of a parallel metal oxide surge arrester on the ferroresonance oscillations of the transformer. It is expected that the arresters generally cause ferroresonance drop out. Simulation has been done on a three phase power transformer with one open phase. Effect of varying input voltage has been studied. The simulation results reveal that connecting the arrester to the transformer poles, exhibits a great mitigating effect on ferroresonant over voltages. Phase plane along with bifurcation diagrams are also presented. Significant effect on the onset of chaos, the range of parameter values that may lead to chaos and magnitude of ferroresonant voltages has been obtained, shown and tabulated.
H. Radmanesh, M. Rostami,
Volume 7, Issue 4 (12-2011)
Abstract
this work studies the effect of neutral earth resistance on the controlling ferroresonance oscillation in the power transformer including MOV surge arrester. A simple case of ferroresonance circuit in a three phase transformer is used to show this phenomenon and the three-phase transformer core structures including nonlinear core losses are discussed. The effect of MOV surge arrester and neutral earth resistance on the onset of chaotic ferroresonance and controlling chaotic transient in a power transformer including nonlinear core losses has been studied. It is expected that these resistances generally cause into ferroresonance control. Simulation has been done on a power transformer rated 50 MVA, 635.1 kV with one open phase. The magnetization characteristic of the transformer is modelled by a single-value two-term polynomial with q=7, 11. The core losses are modelled by third order in terms of voltage. The simulation results reveal that connecting the MOV arrester and neutral resistance to the transformer, exhibits a great impact on ferroresonance over voltages.
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H. Sh. Solari, B. Majidi, M. Moazzami,
Volume 15, Issue 4 (12-2019)
Abstract
In this paper, a new method for modelling and estimation of reliability parameters of power transformer components in distribution and transmission voltage levels for preventive-corrective maintenance schedule of transformers is proposed. In this method, with optimal estimation of Weibull distribution parameters using least squares method and input data uncertainty reduction, failure rate and probable distributions of power transformers’ components as the key parameters of equipment reliability is estimated. Then by using the results of this modelling, a maintenance schedule for evaluation the effect of maintenance on reliability of this equipment is presented. Simulation results using real failure data of 196 power transformers on 33 to 230kV voltage levels show that applying the proposed method in addition to uncertainty reduction of raw input data and better estimation of equipment reliability, improve decision making regarding maintenance schedule of power transformers.
