Efficient Use of Electric Power in Production Operations (1984)

Summary Inefficient electric power utilization systems can account for as much as 50% of the energy consumed in petroleum production operations. The majority of these petroleum production operations. The majority of these losses occur in electric motors or in the distribution systems supplying them. Voltage adjustments, motor control method modifications, and other inexpensive solutions can cut losses and power costs by 5 to 10%. More extensive power system modifications also can be justified occasionally. Introduction Unless care is given to the design and operation of electric utilization systems they can be inefficient in energy conversion. While government regulation of fuel and electric energy prices held electric power costs artificially low, the amount of electric energy lost in inefficient operation did not justify the capital and overhead costs needed to improve system efficiency. Deregulation and inflation have since escalated electric energy costs to the level where inattention to electrical efficiency cannot continue. For many years, engineers have been aware of inefficiencies in petroleum production operations. Many assumed that real improvements in efficiency would require massive capital expenditures. Although this is true in some cases, there often can be improved efficiency for modest costs and electric power consumption reductions of 5 to 10%. When the power bill for a major field is near $100,000/month, even a 1% reduction can be significant. Electric Power Theory The relationship commonly called Ohm's law, V= IR..................................... (1) is a simple statement that voltage is related to current, I, by a parameter called resistance, R. Resistance is present in anything that converts electric energy to another energy form such as motion, heat, light, or sound. In such conversions, electric energy is irreversibly changed to another form. When energy is used in a system with capacitance or inductance, some of the energy may be stored reversibly in electric magnetic fields. Although this energy may be removed temporarily from an electric system during storage, this energy eventually will be returned to the system. In fact, during each full cycle of a sinusoidally varying power system, energy is removed, stored, and returned to the system. Impedance, z, must be introduced to account for energy storage when relating current and voltage. Impedance is a complex term defined by z(f)=R + jX(f)..............................(2) Reactance, X, is a function of frequency in a periodically varying system while resistance, R, is not usually related to frequency. Impedance, itself usually time invariant, can be used to relate sinusoidally varying currents to voltages by v(t) = z(f)i(t)............................ (3) If v(t) has the form V(t) = V cos(ft)........................... (4) then i(t) takes the value of (5) where(6) and (7) In an electrical system, the real power converted to another form such as heat is (8) where the term cos theta is defined as power factor and real power is measured in watts (W) or kilowatts (kW). power is measured in watts (W) or kilowatts (kW). JPT P. 1326