Power supply grid voltage problems there are two cases: A) The voltage is unstable, the peaks and valleys, and the continued volatility. B) voltage long-term sustained low or high. The two situations are not conducive to the normal operation of electrical equipment, could easily lead to severe burning of the electrical equipment. Supply voltage problems are generally three reasons; 1) power plant generator voltage regulator device problems, causing the output voltage. Such are generally small-scale hydropower stations. 2) substation or distribution station power transformer performance problems, especially serious disrepair aging. 3) The total power consumption greatly exceeds the power supply load, resulting in power supply voltage is consistently low, serious and even problems in the supply frequency is low so that the grid failure blackouts 
 If the power supply grid for a long time the supply voltage instability problems, you should choose the regulator; If the voltage is consistently low or high you should choose the regulator or regulator. 

 Regulator (http://www.pandeng.org.cn)