Quality requirements for electrical energy. The most important indicators of quality of electric power – is the voltage deviation from the nominal value ratio is not sinusoidal voltage, frequency deviation of 50 Hz. According to the standard for at least 95% of time each day phase voltage should be in the range 209-231 V (5% deviation), frequency within 49.8-50.2 Hz, and the coefficient nonsinusoidality should not exceed 5%. The remaining 5 or less percent of the time every day stress can vary from 198 to 242 (10% deviation), frequency from 49.6 to 50.4 Hz and the ratio nonsinusoidality must not exceed 10%. Admitted as a strong change in frequency from 49.5 Hz to 51 Hz, but total duration of such changes should not exceed 90 hours per year. Electrical accidents is when a short-term power quality is outside. The frequency can 5 Hz to deviate from the nominal value. The voltage can be reduced to zero.
Further indicators of quality must be restored. Power failures in the real electric networks are of different kinds of failures. In Russia, for example, became known data from studies performed in the U.S. companies Bell Labs and IBM. Since the power of Russia and Ukraine are very similar, data from these studies apply to us.
According to the last, each personal computer is exposed to 120 emergency situations with power supply in a month. The data in emergency situations hold for other consumers. According to Bell Labs in the U.S. observed the following common power failures occur.