Writing a career episode for candidate in field of Electrical Engineering.
Location: Amman, Jordan
Organisational Name: Ministry of Education
Title of the Project: Power Quality Improvement using DVR
Position Title: Electrical Engineer
Time Frame: February 2013 to Present
Background of the Overall Work
The main purpose of this research is to describe the principles of DVR and the main voltage restoration methods, for the sake of the balanced and unbalanced voltage sags. In addition, the description of the same is provided with the context of a distribution system, with the added presence of several simulated results. DVR is generally considered to be the most effective of solutions in response to the problems of voltage sags and swells. The impacts that they have on sensitive loads is extremely severe. Thus, the study has aimed to shed relevant light on the various appeals that the aforementioned possesses, in addition to the dynamic response which it has to any kind of disturbances related to voltage sags. The main purpose of these results has been presented with the purpose of illustrating and understanding the overall performances of SVR under the conditions of voltage sags or swells.
Personal Contributions to the Tasks in the Engineering Project
The possibility of compensating the voltage sag has generally been observed to be limited by several factors and possibilities, which have to be understood in order to efficiently provide a counter to the same. The factors which can prove to be the limitations in the aforementioned conditions are DVR power rating, different conditions of the load itself, as well as the distinct nature of the different kinds of sags. The fact that some of these factors have to be understood and visualized before commencing with the tasks to be completed is a crucial aspect of this project, one which has to be completed successfully in order to ensure the completion of the same in an efficient and effective manner. I strived to understand the main methods which are used in this regard, in order to gain the knowledge necessary for ensuring the success of this project. I also gained an insight into their working, with a new-found knowledge of the pros and cons of these methods. The three major distinguishing methods for the injection of the DVR compensating voltage include:
Pre-Dip Compensation (PDC): This method has been known to supply a continuous stream of voltage and helps in providing a compensation for the load voltage during the processing of fault to pre-fault conditions. The ideal restoration of the load voltage is definitely possible during the processing of this method, such that the active power which has been injected cannot be controlled to a desirable degree. The main determination of the same can be done only by visualising and gauging the external conditions (which can include different types of fault and load conditions). Phaseoscillation of the single line faults is the result of the distinct lack of detection of the negative sequences in these kinds of cases. Analysing the single phase vector diagrams of this case can prove to be immensely beneficial in gaining a further insight into the functioning of this method, which can provide a valuable glimpse into the necessary advantages and disadvantages of the same.
In-Phase Compensation (IPC): This method has been noted to be the most widely used method in the aforementioned regard. The DVR voltage which has been injected has to be in phase with the supply side voltages, without any kind of consideration of the pre-fault voltages and the load current. In other words, the fact that the injected DVR voltage has to be in phase with the supply side voltage is true regardless of the values displayed by the pre-fault voltage and the load current. This method has always required a large quantity of the true real power in order to be capable enough in mitigating the voltage sag. This directly implies the presence of a large device for storage of energy. Going through the formulas of the apparent as well as the active parts of DVR can also help in gaining further insight into the working and functioning of this method to an even higher extent.
In-Phase Advance Compensation (IPAC): The preceding two methods work by injecting a certain level of active power towards the loads, for the purpose of correcting the voltage disturbances. The amount of power which can be injected in a safe and secure manner is dependent on, and specifically confined to, the energy which is stored in the DC link. The overall performance rate and the DVR restoration time are within the confines of certain ranges owing to the limit of the capacity of the DC link for storing energy. This method has been used for the purpose of controlling the overall injection energy. Injection active power has to be made zero in the initial stages, using the means of positioning the load current phasor perpendicular to the injection voltage phasor. A drastic reduction in the consumption of the energy which is stored in the DC link is possible upon the application of this approach.
The reduction in the consumption of the energy directly translates to the increase in the ride-through ability, during the moments when the energy storage capacity has been fixed. The injection voltage magnitude in this approach is much higher in this approach when compared to its preceding approaches. I also observed that this can lead to the phenomenon of voltage waveform discontinuity, along with load power swing and an inaccurate zero crossing. The phase advance compensation has to be adjusted with the load itself (the load which has displayed tolerance to the phase angle jump) in order to mitigate the consequences of the aforementioned. An alternate to the same can be the use of a transition period while the phase angle is being moved to the advance angle from its initial position in the pre-fault angle. I understood that the IPAC method has used only the reactive power, with the unfortunate consequence of the method being unable to mitigate all of the existing sags. Despite its effectiveness and efficiency, its effectiveness is only limited to a certain number of sags.
Studying the aforementioned methods proved to be extremely beneficial for me for commencing with the project. In order to complete the other requirements, I initiated the process of displaying the overall DVR performance in swells mitigation and voltage sags. This has been possible using the method of simulation. I simulated s distribution network using the method of MATLAB. I connected a DVR to a specific system through the use of a series transformer. The maximum capability of the transformer in question was 50% of the phase (when compared to the ground system nominal voltage. A load of 5.5 MVA capacity with 0.92 p.f lagging voltage sags were used for the process. I simulated a case of three-phase voltage sag and collected the results once they were on display. As a result of the presence of the DVR, the load voltage has been kept at 1 p.u. throughout the entire process of simulation, with the inclusion of the voltage sag period. I observed that the DVR generally does nothing during the initial normal operation.
I simulated the single-phase voltage lag, in order to gain a better understanding of the performance displayed by the DVR in unbalanced conditions. I noticed that the DVR was able to produce the necessary voltage component in a fairly rapid manner, as well as help in maintaining a constant and balanced load voltage displaying a value of 1.00 p.u. I then investigated the performance of DVR under the conditions of a voltage swell. The voltage amplitudes were increased to about 125% of the nominal voltage. I then gathered the injected three phase voltage that has been generated by DVR, in order to ensure the correction of the load voltage. I observed that the DVR reacted in a quick manner in order to ensure the injection of the appropriate value of the voltage component. Finally, I observed the performances generated by DVR with a voltage swell that can appropriately be described as unbalanced. I noticed that two out of the three phases have been higher than a value of 25% (compared to the third phase). The balanced and constant value of the voltage at the load throughout the simulation was also observed, even including the event which depicted an unbalanced swell in the voltage (an unbalanced voltage swell).
The results which I obtained from the aforementioned study have been conclusive enough in showing the overall performance of the DVR in managing to control and mitigate the various voltage swells and sags. The DVR has been observed to be able to handle the intricacies of the balanced as well as unbalanced situations without any kind of excessive difficulty or effort. It has also managed to inject the required voltage component to quickly correct any abnormality in the supply voltage. Understanding three major distinguishing methods for injecting the DVR compensating voltage helped in initiating this task properly. The efficiency displayed by the results proves that DVR is a more efficient device of power quality compared to the others.