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Variable capacitor / adjustable
Monitored by a p.f. controller, phase displacement between voltage and current is an ideal method for watching asynchronous motors that are used for both no-load and underload operations, regardless of size. Although there are times where the p.f. will hardly change even if the load of the motor changes. For example, if a small load change occurs on a split-pole motor, large-scale motor, collector motor, or even a single-phase, the p.f. will not change significantly. The p.f. controller normally monitors three-phase and single asynchronous motors with a capacity up to about 5 A without current transformer, for no-load and underload operation. Thus keeping the phase-sequence independent and increasing plant availability. The usual applications are pumps monitoring which is used in case of dry runs or valve closures or fan monitoring which is used in the event of V-belt breakage. Typically, the current transformers are used for the higher rated currents.