First Month Project Updates
It has been almost 6 weeks since I started my Kimley-Horn internship. I have been involved with 5+ major projects, focusing on Load-Flow and Short Circuit by modeling these large solar sites in a software called ETAP. A load-flow study determines how much power and what voltage is being output at different buses in the power system. A short-circuit study determines the current output when different types of faults occur (LLG, LL, and LG), and then we see whether the circuit breakers can handle such a high current for a short amount of time. I have been creating detailed reports of the designs for the clients and determining whether their power factor and generation requirements will be met with the particular equipment they are planning to use. The work is very involved and has honed my AC circuit analysis abilities. Examples of calculations I encounter are power triangle manipulations, motor load currents, reactive power determination by adding capacitor banks, and impedance of cables and overhead transmission lines, and other essential power systems problems. This internship is giving me a deep dive into power analysis, which will be very valuable for any power electronics work that I am interested in and will encounter in my future research and internships.
The next set of studies I will be working towards an understanding are grounding and ampacity. A grounding study incorporates a lot of data such as the metal surroundings of the solar site, the soil conditions of the site, and the entire power system including cables, inverters, transformers, and buses. We compile all that information in the form of CAD files and circuit diagrams in a software called WinIGS and it then determines how much voltage is at the fence would be at in the event of the fault. IEEE establishes that the touch and step potentials must be below a certain threshold for it to be deemed safe for a worker. Since the fault currents are in the tens of kiloamperes, the return path that the current take is through the soil and other metal structures, so there is a possibility of the current going through a worker’s body. This study determines whether that voltage will manageable by the worker’s body.
The software WinIGS takes all metal structures, soil electrical parameters, power flowing through the solar panels, inverters, and cables, and creates a voltage field diagram during a medium-voltage fault, showing the equipotential curves. After that, we define a curve that is 3 feet from the fence of the solar power site, and run a simulation to see what is the maximum voltage seen there. If that voltage exceeds the standard voltage set by IEEE, which changes based on the power rating of the site, then this site will not able to be installed, as it violates the standard. Another parameter that is checked is how much fault current is going through the soil instead of the neutral cable. If the percentage of the total current flowing through the earth exceeds a certain value, then the site must be redesigned. The sheer volume of data to run this study was truly astonishing. Nevertheless, this study attempts to solve Maxwell’s equations numerically, which is something I worked with a lot in my Electromagnetics class.
Ampacity, on the other hand, sees with the configuration of the medium voltage cables and the soil whether the cables will be able to push the current requirements without overheating. This study is done in ETAP, which is the same software used for Load-Flow and Short Circuit studies (studies I discussed in my previous blog post. It is quite easier than a Grounding study, and it should not be too hard to master.
From this internship, I have learned that power systems have tons of standards and requirements to follow. Not following one of the requirements could lead to either the client or Kimley-Horn to be part of lawsuits and it can get ugly for the company. To prevent that, the practice builders of the company, which are the people who acquire projects run through many quality checks to see whether our work is being done in the right way.
Be on the lookout for my update for this internship experience which I will be posting in mid-July!