A practical approach to automating petrochemical facility VAr control

Large customer-owned synchronous motors are often relied upon to provide reactive power for plant loads. Normally, these motors are operated with a constant setpoint of either terminal voltage or power factor. Dynamic control of these machines is usually not addressed in the plant power system, which often results in a less than optimum setpoint for the following: 1) dispatch of VAr from the synchronous machines; 2) transformer automatic load tap changer setpoints; and 3) utility interface power factor. This paper addresses the practical application of a control system utilizing a programmable logic controller (PLC) for automatic petrochemical facility VAr control. The controller uses input data from synchronous motors and utility interface power system parameters, and provides reactive power setpoints to the online synchronous motors. This will allow optimal utilization of available VAr capacity, whilst at the same time ensuring that plant bus voltages remain within allowable tolerances.