Transformer paralleling errors—Prevent, correct or ignore?

When transformer paralleling methods employed are inappropriate, or are incorrectly set, the operation of paralleled power transformer tapchangers can result in detrimental effects on system voltages and power transfer capability. In some cases, these operations can also contribute to the premature failure of the power transformer. With these possible consequences, ignoring these errors is not normally the best choice. Prevention or correction of these application errors requires that the user understand the basis of operation of the control methods available. The user must also be alert to the possible system configuration changes that can occur during normal and emergency operation of the power system. Recognizing the possible combination of conditions and control methods that cause inappropriate tapchanges, allows the user to design for prevention or to adjust (reset or change) for correction. One of the most important aspects of any method is the ability to accurately determine the sensitivity of the controls during all system conditions and prevent "hunting" of tap positions. This paper will discuss several system configurations for transformer paralleling and discuss the effects of using different paralleling methods. The effects of automatic operation of system equipment, such as breaker operations or distributed generation, will be considered. Some of these application factors, which can cause operation errors, will be listed.