Battery banks are crucial for the proper operation of an electrical power substation. When station service power is lost, the battery bank must power 1) the tripping and closing of circuit breakers, 2) all of the protective relays, 3) all indicators and annunciators, and 4) the remaining auxiliary equipment. To insure proper operation, the batteries need to be inspected and maintained. Items to be inspected monthly include: float voltage at the battery terminals; charger output current and voltage; general appearance and cleanliness of the batteries; electrolyte levels, cracks in jars, and leakage of electrolyte; evidence of corrosion at terminals, connectors, racks, or cabinets; voltage, specific gravity, and electrolyte temperature of the pilot cells; ambient temperature and ventilation; and unintentional battery grounds. To aid in teaching these tasks, two separate battery banks are used. The first is kept in good condition, while the second is made up of damaged cells from an on-campus renewable energy system. The damaged cells include cracks in the jars, broken terminals, and leakage of electrolyte. In addition to the monthly inspections, the following should be checked quarterly: voltage of each cell and total battery bank voltage; and the specific gravity and electrolyte temperature of 10% of the cells of the battery bank. Yearly a detailed visual inspection of each cell; measurement of the specific gravity, voltage, electrolyte level, and temperature of each cell of the battery bank; contact resistance of cell-to-cell and terminal connections; impedance measurements of the battery cells; and a check of the structural integrity of the battery rack and cabinet must be performed. Since our bank consists of 60 cells (the typical size for a small substation) computer programs are used to record the data. The specific gravity tester has an internal memory that can be later downloaded. It also records the electrolyte temperature for each cell. The overall bank float voltage is measured with a multimeter. To measure the cell voltage, cell impedance, and strap resistance, a battery tester is used. The two main battery testers used by the utilities and service providers in our area are the Albércorp Cellcorder and the Megger BITE 3. The Cellcorder measures the cell and strap resistances, while the BITE 3 measures cell impedance and strap resistance. We have both, but the students prefer using the BITE 3, since the software is newer. One of the important aspects of the student experience is safety. The concerns are acid spills and hydrogen generation. The students wear chemical gloves, a chemical apron, and a full-face splash shield while performing the tests. The battery temperature and bubble formation are closely watched during the tests. Student feedback on the battery testing has been positive. The software is easy to use and has extensive reporting capabilities. Assessment of student learning is done via observation during the testing and exam questions. It is hoped that this paper will assist others in creating lab experiments on battery testing and provide a basis for further discussions.
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