According to the US Department of Energy, motor-driven equipment accounts for 64% of the electricity consumed in the US industrial sector. Using all that energy leads to some pretty hefty electrical bills.
Although there are many studies showing the benefit of predictive maintenance programs in regards to saving equipment lifespan and money, Motorguy, writing at MotorTalk, argues that even the best reliability programs are missing one important aspect to monitor: the motor power factor:
Energy costs have become of paramount importance in the competitive World industrial market. Many facilities have implemented reliability programs to maximize productivity and reduce downtime, with an added value in reduction of energy costs. Implementation of reliability programs is expensive and even though they pay for themselves many times over, there are things that can be done that don’t cost, they just save.
I have been to hundreds of facilities over the years and even the ones with the best reliability programs overlook one simple energy cost saver; monitoring motor power factor. I have seen numerous applications where a motor of much larger horsepower is utilized than that which is necessary. I have also witnessed applications where multiple motors, providing the same function, are running loaded at minimal load. Understanding motor power factor and optimizing motor performance is a simple way to substantially improve energy costs.
Motors draw two components of current. One component is in phase or real current; it is load dependent and measured in kW or horsepower. The other component is reactive or inductive current that lags the voltage by 90 degrees, and is responsible for setting up the magnetic field in the motor stator, air gap, and rotor, and is independent of load. The vector sum of these two currents is the total current drawn by the motor. The cosine of the angle between these two components of current is called the power factor (refer to vector diagrams below).
Full Load Vector:
As load goes down, the in-phase component reduces faster than the magnetizing component, therefore the phase angle gets larger and the PF gets lower. This explains why a motor running at less than full load has low (poor) power factor (PF). A higher power factor means that ratio of real current to magnetizing current is higher. A higher power factor is desirable.
Reduced Load Vector:
Running a motor at reduced load decreases the power factor causing that ratio of real current to reactive current to decrease. In simple terms you get less work per horse power at reduced load. This means, you pay more for the energy consumed and get less work out of the motor. Say, for example, you have five motors providing the same process, three are running at a power factor of .32. You could possibly shut down two of the motors and have one providing the process at an optimum power factor.
Monitoring motor performance is expedient and an easy way to reduce energy costs.
