This recipe outlines the commonly used electrical engineering theory, data, construction practices, instrumentation and other methods of use. The reason is called electrical formulas - because of poetry is easy to spread and memory inspired. The text in the formulas has the characteristics of neatness, conciseness, smoothness and reciprocity, so that the theory and data of electrotechnics that were originally boring can be remembered. These 11 formulas are just a few of the best things you can do. The Tiger Network is more hope that our colleagues will be able to publish some ideas and opinions in practice. Commenting on this article below, the Tiger Network collects similar formulas used in practical work so that It is more rich and practical, more helpful to the electricians. First, a simple estimate of wire carrying capacity Ten to five, one hundred two, two five thousand three hundred forty-three world, seven and nine five and a half times the temperature of eighty percent, copper upgrade calculation. Explanation: The carrying capacity of aluminum wire under 10mm2 is calculated by 5A / mm2. The carrying capacity of aluminum wire above 100mm2 is calculated as 2A / mm2. The carrying capacity of 25mm2 aluminum wire is 4A / mm2. The carrying capacity of 35mm2 aluminum wire is 3A / mm2 calculation; 70mm2, 95mm2 aluminum wire carrying capacity according to 2.5A / mm2 calculation; "copper upgrade calculation": for example, calculate the current carrying capacity of 120mm2 copper wire, you can choose 150mm2 aluminum wire, Flow rate; affected by temperature, and finally multiplied by 0.8 or 0.9 (geographically). Second, the known transformer capacity, rated voltage rating side Description: Applies to any voltage level. Formula: Divide capacity by the voltage value, its quotient by six divided by ten. Example: Apparent Current I = Apparent Power S / 1.732? 10KV = 1000KVA / 1.732? 10KV = 57.736A Estimated I = 1000KVA / 10KV? 6/10 = 60A Third, the known transformer capacity, speed count one, the second protection fuse (commonly known as fuse) of the current value Formula: with variable high-voltage fuse, compared to capacity voltage. With variable voltage fuse, capacity by 9 divided by 5