Ram Krishna Mishra

In India, distribution losses are substantial from pilferage of distribution lines and connected equipment like energy meters, distribution boxes and various connectors. Few SEBs (State Electricity Boards) have started using Arial Bunched cables for prevention against theft by direct hooking on conductors but it has been observed that maximum power theft occurs through distribution box which makes distribution box most vulnerable component against power theft. Further, burning of distribution boxes happens due to overloading and improper connection system which results in high Ohmic loss. To prevent this, development of a theft proof distribution box with reduced Ohmic loss is needed which gives reliable operation throughout its life span with ease of installation and maintenance. In this paper focus is towards development of novel approach to avoid theft from pole mounted distribution box which is imperiled to major share for electricity theft among all equipment used in distribution system.

Transmission and distribution of power has become a critical part of the modern power system. Transmitting power at high voltage decrease the losses in transmission line. With the increase in need for higher voltage transmission of power, the standards for designing such high voltage equipment has become stringent. Isolators, being one of the main high voltage equipment, is a challenge to design under such stringent standards. This is where virtual validation has gained an immense interest amongst isolator designers. It helps to predict the behavioural aspect of the equipment. Prominent research has been done in the field of exploring virtual validation as a distinguished tool for designing isolators. This paper deals with an FEM based simulation as well as the validation from practical aspects.

The losses due to transformer leakage fi eld comprise a small percentage of the power in a transformer. Yet these losses produce localized heating which can compromise its operation. The stray fi eld strength increases rapidly with growing rating. The stray fl ux intruding into the structural parts gives rise to eddy currents in them. The resulting eddy current losses may be considerable, thereby increasing the load loss of transformer [1, 5]. The objective of this work is to calculate stray losses in magnetic structures of 400 MVA 1-phase, 500–230 kV auto transformer and study the effect of copper shield on structural losses and winding eddy losses, using commercial software package Magnet (Infolytica Corp.) based on fi nite element method (FEM). Due to presence of non linear magnetic materials, the sinusoidal source with 60 Hz frequency induces non-sinusoidally varying magnetic fi elds. A transient solution (which calculates time varying magnetic fi eld) is required for calculating fi elds in non-linear materials. However, this requires more computational resources. Therefore Time harmonic solution (which calculates fi eld at 60 Hz frequency) with linear magnetic materials is used for this analyses. Further, 3D time harmonic analysis has been done to analyze the effect of varying Cu shield thickness on loss density and fi nally its effect on winding eddy losses has been investigated.

Instances of lightning impulse pose a severe threat to transformer winding. A steep wavefront frequency of as great as tens of thousands of times, compared to peak rate of normal power frequency creates intense and rapid change of electric field in the transformer winding. This rapid change is constituted significantly in some part of winding, leading to excessive stress on insulation present in that part of winding. Researchers have used terminal measurements performed on transformer winding, to estimate the severity of lightning impulses. The detailed model has also been proposed in literature to understand the in-depth voltage distribution across the winding height. The time taken to develop such detailed model is high and resource intensive. This paper deals with proposition of methodology which requires minimal resources and takes comparatively less time to analyze impulse voltage distribution across winding turns, accurately.

Prediction of leakage reactance in multi-winding transformer is not simple due to unconventional reluctance model. Need of predicting actual leakage reactance beforehand, accurately, arises due to its effect on transformer's performance, output and characteristic behaviour. Incorrect methodology of leakage reactance estimation gives large error in value of windings which are adjacent. Moreover, leakage reactance between winding is also not equal, causing flow of leakage current. This produces loss beyond committed value. Incapability to provide committed leakage reactance value to customer, burdens company in form of penalty. Apart from loss, controlled or semi-controlled switches may misfire. Thus, this paper deals with accurate prediction of leakage reactance between individual winding of multi-winding transformers along with a model which is industrially feasible and possessing equal leakage reactance between individual winding using finite element analysis.

Partial discharge (PD) characterization is one of the key diagnostic tool while designing insulation system for high voltage (HV) apparatus or development of novel insulating material. This acts as a fingerprint for its performance during its life cycle. That is why HV lab has immense importance in terms of characterizing novel insulating material, HV insulators and condition monitoring PD sensors. Modern HV apparatus demands for a stringent limit for PD magnitude. The allowable limits are almost comparable with the basic electrical noise level present in any power system. On the other hand, more and more usage of power electronic devices, wireless gadgets increases conductive noises and radioactive noise, concurrently. Setting up a PD measurement lab in an industrial environment is a challenging task. High voltage lab of Raychem innovation center is situated very close to the manufacturing plant and surround by high power equipment of power electronics and material processing labor...

—Planar Rogowski Current Sensor works on the principle of electromagnetic induction as conventional iron core current transformers. In iron core current transformer, the core saturates beyond a certain current value which introduces nonlinearity in the desired output. Unlike iron-core current transformer, planar rogowski is an air core device and used for measuring alternating and transient currents. A Planar Rogowski current sensor suitable for high current measurements especially for the application of three phase distribution transformer is designed. In order to develop a sensitive and accurate Planar Rogowski current sensor a systematic approach involving electromagnetic analysis and simulation of printed circuit board (PCB) based rogowski current sensor is discussed. Design calculation is validated by developing prototype and testing. Sensitivity analysis and linearity in the output voltage is studied.

In large power transformers, extreme temperature rise can occur as a consequence of stray fields from heavy current carrying conductors (HCCC) and from windings so it should be taken in to account and calculated vigilantly. The field pattern and eddy current losses due to current carrying strip bus bars are evaluated in [1] for an aluminum sheet. The field of HCCC with constant excitation shows marked differences with Stray fields from windings with a constant flux as computed by many researchers [2], [3].The field of HCCC is greatly influenced by magnetic resistivity of metallic parts. In addition, the characteristic feature of the losses due to HCCC is that they are distributed along the conductors, mainly in the tank cover and walls. The distributions of magnetic flux and eddy current densities in metallic parts of different materials are calculated and according to the criterion of overheating, permissible lead current and limiting distance between HCCC and metallic parts and arrangements of HCCC are suggested in [4]. In [5] New types of measures, separated magnetic steel plates welded on a nonmagnetic steel plate and closed loop shield, are presented to reduce the eddy current losses and to prevent the tank cover and walls from local overheating due to HCCC.

In the presented work, analysis methodology is validated with a scaled down model of bar-plate. The eddy current loss is calculated using finite element analysis in mild steel plate with varying current in copper bar and varying distance between copper bar and mild steel plate and it has been validated experimentally. The same methodology has been used to calculate eddy current losses in transformer tank wall caused by high current carrying copper bars with different connections. In Part of the tank which faces maximum incident field, materials has been changed from mild steel to stainless steel and after effects have been analyzed. One quarter model of the tank has been considered which is in the vicinity of HCCC.

As the magnetic fields and the loss distribution in tank and structures in the transformers are three-dimensional; 3D analysis has been done. Due to presence of non linear magnetic materials, the sinusoidal source with 50 Hz frequency induces non-sinusoidally varying magnetic fields. A transient solution (which calculates time varying magnetic field) is required for calculating fields in non-linear materials. However, this requires more computational resources. Therefore Time harmonic solution (which calculates field at 50 Hz frequency) with linear magnetic materials is used for this analyses.

The losses due to transformer leakage fi eld comprise a small percentage of the power in a transformer.
Yet these losses produce localized heating which can compromise its operation. The stray fi eld
strength increases rapidly with growing rating. The stray fl ux intruding into the structural parts
gives rise to eddy currents in them. The resulting eddy current losses may be considerable, thereby
increasing the load loss of transformer [1, 5]. The objective of this work is to calculate stray losses
in magnetic structures of 400 MVA 1-phase, 500–230 kV auto transformer and study the effect of
copper shield on structural losses and winding eddy losses, using commercial software package
Magnet (Infolytica Corp.) based on fi nite element method (FEM). Due to presence of non linear
magnetic materials, the sinusoidal source with 60 Hz frequency induces non-sinusoidally varying
magnetic fi elds. A transient solution (which calculates time varying magnetic fi eld) is required for
calculating fi elds in non-linear materials. However, this requires more computational resources.
Therefore Time harmonic solution (which calculates fi eld at 60 Hz frequency) with linear magnetic
materials is used for this analyses. Further, 3D time harmonic analysis has been done to analyze the
effect of varying Cu shield thickness on loss density and fi nally its effect on winding eddy losses
has been investigated.