Fixed frequency high-pressure high reliability pump drive

1. An apparatus configured to hydraulically fracture an earth formation, the apparatus comprising:

a pump configured to hydraulically fracture the earth formation by pumping a fracturing liquid into a borehole penetrating the earth formation;

an electric motor having a rotor coupled to the pump and a stator; and

a motor control center having an input side in communication with a source of electrical power which is at a fixed phase and frequency, an outlet side in communication with the electric motor so that the electrical power between the input side and outlet side, and at the outlet side, is at the fixed phase and frequency.

2. The apparatus according to claim 1 , wherein the electric motor is a multiple-phase induction motor.

3. The apparatus according to claim 1 , further comprising a hydraulic coupling configured to couple the electric motor to the pump.

4. The apparatus according to claim 1 , wherein the rotor comprises a plurality of poles and the motor control center comprises pole-switching circuitry configured to switch a configuration of the poles in the plurality for multispeed operation of the electric motor.

5. The apparatus according to claim 4 , wherein the pole-switching circuitry is configured to switch the poles into a first configuration for starting the electric motor and into a second configuration after the electric motor reaches a selected speed.

6. The apparatus according to claim 5 , wherein the electric motor comprises a plurality of electric motors with each electric motor in the plurality being coupled to one or more pumps.

7. The apparatus according to claim 6 , further comprising a controller configured to control the pole changing circuitry in order control a speed of each electric motor in the plurality of electric motors to provide a selected total flow rate that is a sum of all individual pump flow rates of pumps coupled to the plurality of electric motors.

8. The apparatus according to claim 1 , wherein the pump, the electric motor and the motor control center are disposed on a mobile platform.

9. The apparatus according to claim 8 , wherein the mobile platform is a trailer configured for operation on public roads.

10. The apparatus according to claim 1 , wherein the fixed-frequency alternating electrical voltage is supplied by a power source and is applied directly to the stator by the motor control center and the apparatus does not include an intermediate transformer between the power source and the stator.

11. The apparatus according to claim 1 , further comprising dynamic braking circuitry configured to dynamically brake the electric motor.

12. The apparatus according to claim 1 , wherein the pump comprises two pumps and the electric motor comprises two output shafts, each output shaft being coupled separately to one of the pumps.

13. A method for performing hydraulic fracturing of an earth formation, the method comprising:

receiving electrical power from a power source at a motor control center of an electric motor;

transferring the electrical power from the motor control center to the electric motor so that a phase and a frequency of the electrical power at the electric motor is the same as a phase and a frequency of the electrical power at the power source;

applying the electrical power to a stator of an electric motor having a rotor coupled to a pump configured to pump a liquid into a borehole penetrating the earth formation; and

pumping the liquid into the earth formation using the pump to hydraulically fracture the earth formation.

14. The method according to claim 13 , further comprising turning a hydraulic coupling coupled to the pump with the rotor.

15. The method according to claim 13 , wherein the rotor comprises a plurality of poles and the method further comprises changing a rotational speed of the motor by switching a configuration of the poles using pole-switching circuitry.

16. The method according to claim 15 , wherein the electric motor comprises a plurality of electric motors with each electric motor in the plurality being coupled to one or more pumps and the method further comprises controlling the pole changing circuitry using a controller in order control a speed of each electric motor in the plurality of electric motors to provide a selected total flow rate that is a sum of all individual pump flow rates of pumps coupled to the plurality of electric motors.

17. The method according to claim 13 , further comprising applying the fixed-frequency alternating electrical voltage supplied by a power source directly to the stator without using an intermediate transformer between the power source and the stator.

18. The method according to claim 13 , further comprising dynamically braking the electric motor in order to reduce rotational speed of the electric motor using dynamic braking circuitry.

19. The method according to claim 13 , further comprising correcting the power-factor of the electric motor using power-factor correction circuitry.