What is the purpose of 'Open Circuit Test' in Electrical Power Engineering?

Answer 1

Open circuit test shows total voltage of a source such as a battery, transformer, energized circuit. Often, solar panels list open circuit values. The purpose is to prove that the design or nominal voltage is present. For solar panels open circuit voltage proves that the individual cells are connected and connected correctly. Open circuit values can be the standard to quality check two or more sources or circuits that have equal factory standards. Other uses: generators compare open circuit voltage exciter winding to actual useable output voltage winding for the purpose of correcting output with a signal to voltage regulator-Voc is an ideal reference; open ckt test can be used to test wire insulation for holes or damage because Voc can be made to go so high it will force an arc through damaged insulation; Voc tests are used to locate voltage or detect intact wiring or severed wires. Many more uses in electronic devices like high z input to digital tristate gates. High Z is open input, which is stable "on", applied voltage is timed pulse train, and ground is active "off"

The one thing to remember, open circuit tests always mean no current, no heat, no wear, no battery drain, but never believe no shock hazard. Voc will shock and can arc and start fires.

Answer 2

An open-circuit test is done on a transformer to isolate and measure those losses known as 'iron losses' that are due to eddy currents in the magnetic iron core of the transformer. Because the currents in the windings are very low the 'copper losses' are negligible. However the iron losses depend only on the applied voltage.