P. K. Preetha

A novel method for recovery of drainage power from distribution transformers

Non-linear loads have become a larger percentage of the total load in commercial facilities. The use of non-linear loads results in excessive injection of harmonic components from the customer facility onto the utility power system. Conventional distribution transformers are of delta-star type, providing 3-phase 4-wire ac distribution. In such a case, the triplen harmonic currents caused due to non-linear loads get circulated in the primary delta winding. But this leads to increased power losses, temperature rise and subsequent de-rating as well as reduction in life of transformers. This paper proposes a novel method for recovering the drainage power which is normally wasted in the delta winding of the distribution transformer. The experimental studies conducted on a three kVA transformer shows that when the drainage power of delta winding is recovered it helps in improving the transformer efficiency and system power factor.

An equivalent circuit model for star-star-delta_utilized distribution transformer

In the recent years there has been excessive use of nonlinear loads in power distribution network resulting in the injection of harmonics into the utility power system. The triplen harmonics due to non-linear loads circulate in the conventional delta-star distribution transformer resulting in excessive power losses. Star-star-delta_utilized transformer is a modified distribution transformer configuration suggested recently which helps in recovering and utilizing the power wasted due to circulating harmonics in the transformer delta winding. This is achieved by connecting a load across the zero potential terminals of the tertiary delta winding of the transformer. This paper presents a three phase equivalent circuit model for the star-star-delta_utilized transformer. The proposed dependent source model is simulated and compared with the performance of the available transformer model of MATLAB Simulink. The results show that at steady state the performance of the proposed model can replicate the performance of the Simulink model.

Power factor correction circuit with one cycle controlled bridgeless zeta converter for display monitors in hospitals

Development in the field of electrical engineering is quick and commendable. Even though the nonlinear power electronic equipments introduce power quality issues, their use is unavoidable. Most of the medical equipments make use of power electronic devices. Serious issues include low input power factor and increased ripples in the input current. Many bridgeless topologies have been introduced to mitigate the above mentioned problems. Common topologies make use of buck, boost, Cuk and Sepic converters. In this paper bridgeless zeta converter with one cycle control for display monitors in hospitals has been proposed. With one cycle control, input perturbations are avoided in one switching cycle. The converter is designed to supply the load of 50W and 24V. MATLAB/Simulink model has been analyzed for various conditions. A laboratory prototype of the converter has also been made and tested for the designed values. Results of simulation have been verified with the hardware system. Power factor has been observed to be above 0.97.

Analysis of star-star-delta_utilized transformer under balanced and unbalanced load conditions

For decades research has been going on to resolve the power quality issues. The usage of non-linear loads is contributing much harmonic content in the distribution system. In the conventional distribution transformer of delta-star configuration, this injected harmonic power is trapped in delta winding and is wasted as heat. This wasted power or drainage power is a threat to the transformer itself. This paper presents the recovery of drainage power using star-star-delta_utilized distribution transformer under varying load conditions in the secondary. A study on primary and secondary side THD, input and output power factor, current harmonics, harmonic power and efficiency is carried out for balanced and unbalanced load conditions. The simulations are carried out in MATLAB Simulink and the results are verified by experimenting on the hardware set up.

DC link voltage regulation in active filter using drainage power from distribution transformer

Non-linear loads constitute a major part of loads in the modern industrial and commercial utilities. They inject harmonics to the system and the normal delta-star distribution transformer traps the injected triple-n harmonics in the primary delta winding. This leads to the deterioration and reduction in the life of transformer. Hence, a three winding star-star-delta_utilized transformer is used to trap this harmonic or drainage power in the non-linear power system. This drainage power can be used to power auxiliary loads connected across the tertiary delta winding. Also, drainage power recovery makes the system performance better as triple-n harmonics are eliminated from supply line. For balanced and unbalanced secondary non-linear loads, the tertiary power can be recovered. Also, it can be stored in rechargeable batteries to power regulated loads. In this paper, the use of battery stored drainage power for the voltage regulation in shunt active filters is being discussed. The shunt active filter using Icosϕ algorithm provides better harmonic elimination of non-linear load. When a load fluctuation occurs, the dc link capacitor voltage in the filter also fluctuates. Usually, the power needed for voltage regulation is supplied by the grid. In the proposed system, the drainage power stored in the battery is used for the voltage regulation. For using shunt active filter in the YYD_utilized transformer system, the control algorithm of the filter needs to be modified in order to sustain the triple-n harmonics in the system. The power recovered from triple-n harmonics can be stored in a battery and can be further used as the energy storage element of the filter. Results analyzed using MATLAB/SIMULINK reveals that the YYD_utilized system along with shunt active filter gives better utilization of drainage power and the overall system provides harmonic elimination.

Electromagnetic analysis of transformer using Solidworks

Transformers have been one of the greatest inventions in the electrical industry. It helps in transferring energy between two or more circuits through electromagnetic induction. Single phase transformers find applications in domestic appliances because of its simplicity and less cost. They can be used as voltage regulators in television set, as step up and step down transformers in inverters and mobile chargers, respectively. Three phase transformers are used in generation, transmission and distribution of electrical energy. Electromagnetic analysis of the simulated transformer helps in optimizing the transformer design. In this paper, single phase transformer of rating 67kVA 6600/440 V is designed and modeled using Solidworks software. Electromagnetic analysis of the model with normal working condition is done using Electro Magnetics Simulation (EMS) module of the software. AC magnetic study with 50Hz frequency is selected. Parameters like current density, field intensity, and loss density are analyzed. It is observed that results obtained from simulation closely matches with the theoretical values.

Comparison of PWM and modified One Cycle Control for bridgeless zeta AC-DC converter

Bridgeless topologies have been introduced to improve the input power factor and hence reduce THD and ripples in the input current. Bridgeless zeta converter has the advantages of reduced number of semiconductor switch, easy electrical isolation and reduced in-rush current during start-up. Conventional PWM technique is used for the control of switches. But it suffers from the problem of slow dynamic response. With One Cycle Control it is possible to eliminate input perturbations in one switching cycle. In this paper, a comparison has been made between the conventional PWM technique and modified One Cycle Control for bridgeless zeta converter. The model is developed using MATLAB/Simulink and the results have been analyzed.