Total Dynamic Head (TDH) is the total equivalent mechanical feet of liquid head the pump must generate to lift fluid from the flowing bottomhole level to the surface. It is the sum of net vertical lift (surface elevation minus flowing fluid level), tubing frictional head loss, and surface wellhead backpressure head, minus any casing gas pressure assist.

Electric submersible motors generate substantial internal heat (rejecting 15% to 20% of their electrical rating into the surrounding fluid). API RP 11S2 mandates a minimum fluid velocity of 1.0 ft/s (0.3 m/s) past the outside of the motor housing. If fluid velocity is insufficient or if the pump is set below perforations without a motor shroud, motor winding insulation burns out rapidly.

When pump intake pressure (PIP) drops below the oil bubble point, gas comes out of solution. If the free gas volume exceeds 10% to 15%, the centrifugal impellers cannot effectively compress the gas phase. Vapor blankets the impeller eye, causing head generation to collapse. The pump deadheads, overheats, and trips on underload or burns out.

Operating to the left of the ROR (low flow / high head) produces severe downward hydraulic thrust, prematurely wearing the stage thrust washers. Operating to the right of the ROR (high flow / low head) reverses net hydraulic force into upthrust, causing the impellers to float upward and grind against the diffuser bowls, generating metal shavings and shearing the drive shaft.

Across 5,000 to 12,000 feet of downhole copper cable, electrical resistance creates a significant voltage drop. If voltage drop exceeds 5%, motor terminal voltage degrades, causing the motor to draw higher current to produce rated shaft torque. During motor starting, inrush current spikes can drop voltage past the breakdown torque limit, stalling the pump downhole.