Reasonable Lightning Protection for Electric Submersible Pumps

Abstract

Abstract High cost, questionable efficacy and justifiable mistrust are the usual factors that must be overcome when applying lightning protection to ESP's. These factors are true of any product when its performance is difficult to measure and thereby almost impossible to compare with competing products. The intent here is to pull together those aspects of ESP lightning protection that are variable, and once they have been analyzed to recommend ways to organize effective protection. The most bothersome variable is ground resistance. Basically it depends on soil moisture and mineral content. Soil moisture changes with the seasons. However, ground resistance can be measured, and even in arid regions of the world it is possible to construct low-resistance grounds. Resistance combines with the inductance of the lead wire to form a total ground impedance. When only a single Transient Voltage Surge Suppressor (TVSS) is used, the devices to be protected are always subjected to a minimum voltage equal to the ground impedance times the surge current. A lightning filter remedies this problem by having separate inputs and outputs and running different ground connections to each. Consequently the lightning-stroke voltage does not appear instantaneously at the output terminals. Further the rate at which voltage increases is reduced, an important factor when trying to protect turn-to-turn insulation in the ESP motor. Being able to justify the added expense of a complete filter depends on how high the ground impedance gets and how critical it is to protect a given ESP. Testing and verification of protection are major credibility concerns. Any device designed for lightning protection should be subjected to high-voltage impulse tests. Certainly some type of production tests should also be performed. Verification of protection in operation should involve some type of indicator lamp, which turns off when a line-to-ground fault occurs, a component fails or the bulb burns out. In conclusion both the lightning filter and the TVSS provide much needed ESP lightning protection. The decision on which device to employ depends on ground impedance and the level of ESP protection the operator deems necessary.