Taiwan"s state-owned electricity monopoly Taipower on Friday blamed human error during a test for a power cut that affected some 4 million homes the day before, and said it would offer discounts worth almost $18 million to affected customers. The rolling blackouts went on for around five hours before normal supplies were resumed early evening, briefly affecting the world"s biggest contract chipmaker, Taiwan Semiconductor Manufacturing Co Ltd (2330.TW), . read more Taipower said engineers had been carrying out tests at a substation as part of a future expansion project for a power plant in the southern port city of Kaohsiung. However, they pressed the wrong switch, causing a sudden drop in voltage, and the problem then cascaded leading to the blackout, it added. Taipower will offer discounts to customers affected by the power cut, which it said it expects will amount to some T$500 million ($17.90 million). ($1 = 27.9400 Taiwan dollars)