Downhole tools commonly draw electrical power through the wireline from a surface power source. Power levels are limited to less than 600 watts because of the resistance of the wireline, which is typically 25,000 feet long. A conventional induction tool directly uses the available power to drive a magnetic transmitting coil at a frequency of 20 kHz. Typical transmitter power levels, after allowing for power conversion losses and power draw from electronic components, are about 150 watts. MPI's pulse power tools operate on the strategy of cumulating energy at a relatively low power level through the wireline, and then delivering that energy to the transmitter in a short pulse at a very high power level.
Electrical energy is stored in the tool using specially designed energy storage capacitors.
Each capacitor, which typically is charged to 2200 volts, stores approximately 50 joules of energy, and up to four capacitors may be applied to a particular transmitter. Charging time depends on the available average power level and the efficiency of the charging circuit, but is typically less than a second. As a tool is drawn continuously up the well in a logging operation, the capacitor is discharged into the transmitter at selected depth intervals. The capacitor and the transmitting coil together form a resonant circuit at about 17 kHz, and the stored energy oscillates many times before being damped by resistive losses. In the XACT tool the monopole and the dipole transmitters each operate at a peak power of one million watts , delivering an acoustic pulse with peak pressure of approximately 100 psi.