Condition Monitoring and Fault Diagnosis of Electrical Submersible Pumps Motor Drive Including Long Cable

Abstract

Due to the unusual shape and the harsh operational environment, the electrical submersible pumps (ESP) motor fail more often than other motors. The lack of good system design aggravates the situation. The total cost to replace or repair an ESP unit is very high and failures in ESP system create long downtime in the oil field. Thus, condition monitoring and fault diagnosis of ESP systems is needed to avoid unexpected failure and to allow enough time to plan and schedule repairs. The purpose of this work is to analyze the phenomena at and around the fundamental frequency of the induction motor including the effect of long power cable. This information can be used for optimal motor operation and for fault diagnosis purposes. First, a power cable reference frame model is proposed. A true power cable is used with the proposed cable model as an observer. The results prove to be accurate, with the maximum error between the measured cable output and the model output estimation at 0.12%. Then, an experimental setup consists of power electronics converter is proposed to emulate the long power cable. The experiment setup detailed design and analysis are provided. Next, an optimal voltage compensation method for the drop across long power cable is proposed. In the proposed method the drive is utilized to compensate the voltage drop and no additional voltage regulation device is required. The experimental verification is carried out by using a lumped parameter cable model with two different sets of inductance and resistance. It is seen that the proposed algorithm can reduce the voltage requirement by 15-18% compared to the commonly used scalar compensation method. Finally, the current sideband fault signature is analyzed under different load conditions. The effect of transformer magnetic coupling on the current sideband signature is analyzed. Then, a demodulation algorithm is proposed based on wavelet transform. The demodulated signal provides a reliable rotor dissymmetry diagnostic index by means of quantitively related to the rotor fault independent of load conditions. The algorithm is verified with FEA simulations and experimental results of an induction motor with broken rotor bars.