Combined electrical and mechanical model of electric submersible pumps

The electric submersible pump unit consists of a pump powered by a medium-v oltage three-phase induction motor, The power transmission system is integr ated with the riser pipes, Starting the pump causes heavy dynamic stresses on the motor shaft and the mechanical connection between pump (impellers) a nd shaft. The motor and its load will generate transient torque pulsations that may be damaging to shaft and coupling, particularly to the key grooves . System models are developed to predict the electrical and mechanical cond itions on starting. Different torsional models with certain types of nonlin earities, combined with different motor models have been examined to find c ombinations that give the best results. The motor models applied include sa turation in the main flux path and the leakage flux paths, as well as rotor deep bar effect. It has been shown how the pump parameters, material coeff icients, design dimensions, and number of impellers affect the dynamic stre sses. The aim has been to optimize the design with respect to the transient stresses. The simulations reveal that the resulting shaft torque, caused b y excitation from resonant frequencies during the acceleration period, amou nt to high values that may result in excessive overloading of shafts, coupl ings, and key grooves, Maximum torque is, as expected, strongly dependent o n the shaft dimensions. Certain shaft diameters may cause resonance and, th ereby, heavy torsional amplitudes. It has been shown how the model can be a tool in the struggle to find the optimum shaft diameter.