Overvoltages
Sustained overvoltages are not common. The most likely causes are maladjusted voltage regulators on generators or on-load tap changers, or incorrectly set taps on fixedtap transformers. Equipment failures may immediately result in the case of severe overvoltages, but more likely is accelerated degradation leading to premature failure without obvious cause. Some equipment that is particularly sensitive to overvoltages may have to be shut down by protective devices.
Undervoltage
Excessive network loading, loss of generation, incorrectly set transformer taps and voltage regulator malfunctions, cause undervoltage. Loads with a poor power factor or a general lack of reactive power support on a network also contribute. The location of power factor correction devices is often important, incorrect location resulting in little or no improvement.
The symptoms of undervoltage problems are tripping of equipment through undervoltage trips. Lighting will run at reduced output. Undervoltage can also indirectly lead to overloading problems as equipment takes an increased current to maintain power output (e.g. motor loads). Such loads may then trip on overcurrent or thermal
protection.
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