9.Variable Speed Pump System
The ESP system can be modified to include an Electrospeed variable frequency controller so that it operates over a much broader range of capacity, head, and efficiency. Since a submersible pump motor is an induction motor, its speed is proportional to the frequency of the electrical power supply. By adjusting the frequency, the variable speed submersible pump (VSSP) system offers extraordinary potential for boosting production, reducing downtime, and increasing profits. The VSSP can be used to boost efficiency in many cases, including highly viscous wells, waterflood wells etc. It extends the range of submersible artificial lift to less than 100 BPD (16 M3PD) and up to 100,000 BPD (16,000 M3PD).
Variable Frequency
The effects of varying frequency can be seen by preparing new head-capacity curves for the desired frequencies, based on the pump's known 60 Hz performance curve data. The Electrospeed controller is commonly used to generate any frequency between 30 and 90 Hz. Curves for frequencies other than 60 Hz can be generated by using the centrifugal pump affinity laws. The equations derived from these laws are:
A set of curves can be developed for an arbitrary series of frequencies with these equations, as shown in the variable frequency performance curves at the end of this step (figure 1). Each curve represents a series of points derived from the 60 Hz curve for flow and corresponding head points, transformed using the equations above. Suppose we are given the following data at a frequency of 60 Hz:
Rate = 1,200 BPD
Head = 24.5 ft. (from FC-1200 curve @ 1,200
BPD)
BHP = 0.34 BHP (from FC-1200 curve @ 1,200
BPD)
If a new frequency of 50 Hz is chosen:
New Rate = x 1200 BPD = 1000 BPD
New Head = ( ) x 24.5' =17'
New BHP = ( ) x 0.34 BHP = 0.20 BHP
By performing these calculations at other production rates, a new curve for 50 Hz operation can be plotted. Start by locating the existing points on the one-stage 60 Hz curve:
X1 Rate (BPD) 0 950 1200 1550 1875
Y1 Head (Feet) 32' 28.6' 24.5' 15' 0'
Efficiency (%) 0 63.5 64 49 0
Following the above equations, calculate the corresponding values at 50 Hz:
X1 Rate (BPD) 0 792 1000 1292 1563
Y1 Head (Feet) 22.2' 19.9' 17' 10.4' 0'
Efficiency (%) 0 63.5 64 49 0
