SENSORS AND ENCODERS n sharply to a low, flat baseline reflecting only bearing, seal and windage losses. Line current falls too, but much less – the magnetising component holds it up. That gap is where the protection sensitivity lies. n Dead-heading, where the discharge valve remains closed, produces a different baseline. The motor churns fluid in the casing, consuming more power than during dry-running, but well below the normal operating point. The current change is minor and easily masked by normal supply-voltage variations. n Impeller wear and progressive blockage, which show as a slow trend. Active power drifts downward over days or weeks as hydraulic efficiency degrades. Line current remains almost flat throughout. n Cavitation, which presents as erratic, high-frequency fluctuation in active power rather than a sustained drop. Hydraulic coupling breaks repeatedly and reestablishes as vapour bubbles collapse at the impeller. Variable-speed installations can detect cavitation internally via drive algorithms analysing torque oscillation; active power at the supply side captures the same class of disturbance and applies equally to fixed-speed installations where no drive is present. A motor monitored for active power yields condition data with no wet-side instrumentation, no pipework penetrations, and no additional maintenance points. For remote and unmanned sites, this matters. A pump station without operators cannot respond to a fault condition in real time. By installing a load monitor, an underpower trip will shut down a dryrunning motor before it destroys its seal. A slow power trend flags impeller degradation before it becomes a failure. Both signals are already present on the motor supply cables in the motor control centre. The motor has always demonstrated these characteristics and can provide this information. A true power monitor is the instrument that reads it. n Line current vs active power as a pump’s load falls
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