Mohammad Salay Naderi

Advanced transformer winding deformation diagnosis: moving from off-line to on-line

On-line monitoring and diagnosis of transformers have been investigated and discussed significantly in last decade. This study has concentrated on issues arising while on-line transformer winding deformation diagnosis is going to be applied on transformers with various kinds of techniques. From technical perspective, before replacing off-line methods by on-line methods and eventually by intelligent approaches, practical challenges must be addressed and overcome. Hence, available off-line transformer winding deformation diagnosis methods are discussed precisely. Mathematical calculation in on-line short circuit impedance measurement is investigated. On-line transformer transfer function measurement setup is presented. A profound insight to the problems pertaining on-line transformer winding deformation recognition methods, characterizes existing online methods, explains the concepts behind online measurements and striving to open the discussion doors towards challenges are discussed. In the end a 400 MVA step up transformer has been taken as a case in order to clarify the capability of Frequency Response Analysis (FRA) method in fault detection while short circuit impedance could only demonstrate some rough understanding about transformer condition.

Frequency response analysis and short-circuit impedance measurement in detection of winding deformation within power transformers

Power transformers are in service under different environmental, electrical, and mechanical conditions [1] and may be subject to enormous hazards during the course of operation [2], [3]. They are commonly considered to be the heart of the transmission and distribution sectors of electric power systems; monitoring their condition and diagnosing faults are important parts of the maintenance function [4]. Utility engineers strive to keep power transformers in service and to prevent even shortterm outages. Failure of a transformer can cause extensive damage to equipment owned by consumers or the utility [5].

FRA vs. short circuit impedance measurement in detection of mechanical defects within large power transformer

Power transformers are supposed to be and remain in service in various environmental circumstances under different electrical and mechanical stresses. Base on failure history in power transformers obtained from four corners of the globe one of the major problems in transformers is mechanical defect. A number of monitoring and diagnostic methods have been introduced to recognize transformer active part displacement and winding deformation. Frequency response analyses and short circuit impedance measurement have been employed as two common diagnosis methods in large power transformer winding deformation recognition. On the other hand, researchers are expressing an increased concern about power transformer condition monitoring in the smart grid context. Hence, all of off-line methods need to move towards on-line applications. One of the challenges is finding reasonably accurate method which can provide sufficient information about transformer winding condition. In this study, mechanical defects of windings and their causes are investigated in detail. Frequency response analyses and short circuit impedance measurement as two popular methods in transformer winding deformation diagnosis will be employed to get insight into transformer active part condition. A large power transformer has been taken as a case in order to put the capability and sensitivity of abovementioned methods into test. Onsite test results on this giant transformer winding show that frequency response analyses method is capable to provide far more information as to the healthy or defected condition and physical movements of the transformers windings and core compared to the other method.

Practical challenges in online transformer winding deformation diagnostics

Monitoring and diagnosis of transformers have been investigated and discussed for many years. While transformer routine tests indicate electrical and also insulation weakness or defects, Frequency Response Analysis (FRA) as a modern test can indicate mechanical defects in transformer active part. This paper introduces the concepts behind online measurements in frequency domain and is striving to open the discussion doors towards advanced investigations which are all aligned with smart grid concept. This study has also concentrated partly on issues rising while online transfer function measurement techniques are going to be applied on transformers with various kinds of winding connections and accessories. In the end, crucial issues from theoretical and also practical perspectives for online transfer function implementation are discussed.

Multi-objective Environmental/Economic Dispatch using firefly technique

This paper a Multi-objective Firefly Algorithm (MOFA) is proposed for Environmental/ Economic Power Dispatch (EED) problem. Due to the environmental concerns that arise from the emissions produced via fossil-fueled electric power plants, the classical economic dispatch, which operates electric power systems so as to minimize only the total fuel cost, can no longer be considered alone. Actually, EED problem is the scheduling of generators which fulfill the load demand of the power plants using fossil fuel and also making combined production, in order for them to perform with minimum cost and emission. Therefore, by EED, emissions can be reduced by dispatch of power generation to minimize emissions. Which is affect on power generated, system loads, fuel cost and emission coefficients in real-world situations. The MOFA technique has been carried out on the IEEE 30- and 118-bus test system. This technique is compared with other techniques which reveals the superiority of the proposed approach and confirms its potential for solving other power systems problems.

Robust LFC in deregulated environment: Fuzzy PID using HBMO

In this paper, a Honey Bee Mating Optimization based Fuzzy (HBMOF) controller is proposed for solution of the Load Frequency Control (LFC) problem in a restructured power system. In the proposed method, for achieving the desired level of robust performance, exact tuning of the PID parameters is very important. Hence, to reduce the design effort and find a better fuzzy system control, PID parameters are designed automatically by HBMO. Using this algorithm leads to high speed to algorithms convergence and more flexible controller. The effectiveness of the proposed method is demonstrated on a deregulated power system with possible contracted scenario under large load demand and area disturbance in comparison with the PSO, GA fuzzy controllers through ITAE (Δp), ITAE (Δf) and FD performance indices.

Optimal tuning of multi-machine Power System Stabilizer parameters using Genetic-Algorithm

Optimal tuning of Power System Stabilizers (PSSs) parameters using genetic algorithm is presented in this paper. Selecting the parameters of power system stabilizers which simultaneously stabilize system oscillations is converted to a simple optimization problem which is solved by a genetic algorithm. The advantage of Genetic Algorithm (GA) technique for tuning the PSS parameters is that it is independent of the complexity of the performance index considered. The efficiency of the proposed method has been tested on two cases of multi-machine systems include 3-machine 9 buses system and 10-machine 39 buses New England system. The proposed method of tuning the PSS is an attractive alternative to conventional fixed gain stabilizer design as it retains the simplicity of the conventional PSS and at the same time guarantees a robust acceptable performance over a wide range of operating and system condition.

Frequency Response Analysis to recognize inductance variation in transformer due to internal short circuit

Transformer diagnosis methods have been introduced and employed to recognize transformer internal defects since many years ago. In terms of mechanical defects in transformers, turn to turn and disc to disc short circuits in transformer windings are considered as one of the main problems in transformer active part. On the other hand, Frequency Response Analysis (FRA) is considered as a robust, sensitive and high accurate method to identify transformer mechanical defects. This study has concentrated on self-inductance variation recognition due to an internal short circuit in transformer using FRA signature. A single phase 11/0.25 kV, 25 kVA transformer has been taken as test object. Frequency response of the test object was recorded for open circuit and short circuit situations. Frequency response alteration in low frequencies caused by short circuit is interpreted through mathematical calculations. Frequency response trace deviation is employed to recognize self-inductance changes due to the internal short circuit.

Effects of switch type and location on the reliability of power distribution systems considering distributed generation

The type and location of switches are expected to play a key role on the reliability improvement of power distribution systems. In this paper, the value of circuit breaker installed as a protective and automated device is quantified in terms of its contribution to the reliability improvement of an industrial distribution network. In addition, the values of placing distributed generation (DG) at various locations, as well as the impact of high penetration of DGs, are presented. The description of the proposed approach is carried out using an IEEE RBTS test system. Several case studies are considered to verify the accuracy of the proposed approach. The results presented in the paper verified that the proposed strategy is able to enhance the reliability of the power distribution systems especially when DGs are included.

Effects of automation on the reliability of power distribution systems considering distributed generation: Worth analysis

The reliability of power distribution networks can be greatly enhanced by using automatic protective devices. Remotely controlled and automated restoration services can avoid the required execution of manual switching schedules and are bound to bring about remarkable levels of system reliability while reducing interruption costs. The customers interruption cost model according to a postal survey is used in this paper to verify the authenticity of the reliability worth analysis. Also, the value of circuit breaker installed as a protective and automated device is quantified in terms of its contribution to the reliability improvement of a test distribution network. The failure mode effect analysis technique (FMEA) is adopted for reliability worth assessment. In addition, the impact of introducing distributed generation units (DG) into the system is presented. The description of the proposed approach is tested by evaluating the reliability worth of a radial distribution test system.