Electromagnetic Interference in Dwnhole Applications
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- Institutt for elkraftteknikk 
Summary Electromagnetic compatibility (EMC) and electromagnetic interference (EMI) are topics which have been of concern to electrical industry for many years. Excessive generation of electromagnetic noise and interference, resulting inadequate EMC, is one potential source of interaction and performance degradation which may reduce operational effectiveness of the devices. Because of this, EMC testing services and regulation imposed by governments have forced product designer to pay close attention electromagnetic interference level of their products.For improving oil and gas production recovery, from mature fields and for exploitation of deep and ultra-deep offshore reservoirs new downhole technologies are required. Electrification of downhole applications has proven to be very promising and the technologies are designed for deployment in harsh environments. This master thesis deals with the study of EMI problems for downhole drive train system especially caused by EMI phenomena. The two aspects of EMI and EMC are studied, the manner in which how EMI can generate and propagate then affect receptor or victim intentionally and unintentionally are discussed. Followed by types of EMI phenomena (voltage dip, electrostatic discharge (ESD), surge, fast transient and rapid voltage change (dv/dt)) their occurrence and adverse effects of them are studied. dv/dt, overvoltage and EMI filter types are studied and designed. Compressions are made by their performance, size, power loss and cost. To verify their performance simulation model are made for downhole drive system to filter dv/dt and overvoltage at the motor terminals.After having the theoretical base, practical pre-compliance conducted EMI measurements are made for single phase chopper and three phase inverter.The influence of EMI such as reverse recovery current of diode, stray or leakage inductance, gate drive resistance, heat sink grounding, duty cycle and switching frequency are investigated on the single phase chopper. An LfCf harmonic filter is designed and placed between the inverter and motor terminals and differential mode EMI noise is measured in the system.