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Unitrol F Reference Value Setting

Unitrol F Reference Value Setting

Unitrol F Reference Value Setting

(OP)
We have Seven large synchronous motors rated 23000hp with ABB Unitrol F excitation System. The motors are running with VAR control, Auto mode. on the Unitrol Control Panel, there is a percentage set point. This set point is called as "Reference Value" in ABB documentation. Usually, this reference value is set to 103% and this keeps VARs around -3MVARs and power factor around 0.92 leading when motor is running in VAR control auto mode.

Over the period of month or two, this reference setpoint is changing for any one or two of these machines and they start of draw more current, power factor comes down to 0.6 or 0.7 leading and MVAR are -9MVARs. I want to know why this reference value changes by itself when the system is in Auto and this cause the motor to draw more current. Expert opinion from anyone who worked on these excitation systems in appreciated.

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