1.  Summarization

Beam pumping unit is the traditional pumping equipment that used widely in oil field, it is  dragged directly by common AC asynchronous motor. Its crank with balance weight bring along sucker rod of oil wells to drive subsurface pump in the well to move up and down periodically, so it carry the oil in the well to the ground. In one frequency-stroke, with the rise/fall of sucker rod of oil wells, the motor is in the state of electric motion/ electricity generation. During rise, motor absorb energy from elec. net to electric run; during descending, the load character of motor is potential load, the motor is in the state of electricity generation, it changes the machinery energy to electric energy and feed back to elec. net.

However, the reservoirs circs down the well is very complex, have rich and poor oil well difference, rare and dense oil well difference. It is obviously the invariable-speed application. for the pumping unit, the piston after abrasion and the interval leakage of bush are the difficult problem, besides, the variable stratum factor such as there are sand, wax, water, gas etc. in the oil also have influence for the oil quantity that every time pumping. So it can arrive the best control by speed regulation drive. 

After introducing into speed regulation drive, to modulate stroke frequency time of pumping unit according to the state of well and modulate the speed of up, down operation, at the same time of improving full of modulus of pump, reduce the leakage of pump, for getting maximum oil quantity.  especially the color frequency variation and speed regulation has no start stroke, it can also solve the problem of power factor is too low that caused by traditional choosing mode, circuitry is too long, so this can increase efficiency and improve the lifetime of whole machine. Especially for the lifetime of pump, it can reduce the malfunction of machine and enhance reliability, so adopting  frequency variation and speed regulation to rebuild oil extraction is imperative under the situation.

2.  General frequency variation and speed regulation project

General application scheme showed as following diagram A:

Pumping unit motor drive directly by common inverter, it is only installed enclosing braking unit in the inverter. When sucker rod of oil wells operate down for stroke, motor is in the state of generation electricity, this energy is consumed by resistance radiation. However, if different oil well and different device adjust improperly or braking resistance contact oxidation, contact bad,  it  can all cause loop-line over voltage of pumping unit decline stroke inverter, the malfunction rate of inverter is too high.

The operation result of this project  showing: speed regulation effect has no problem but the energy  generated by motor when sucker rod of oil wells descending is consumed by braking resistance, so energy saving is not ideal.

3. The project of frequency variation and speed regulation recommended by our company

The system diagram of this project  as following,

This is the speed regulation system for pumping unit designed by our company. this project adopts PWM frame,  except original soft-switching inverter, another soft-switching inverter replace additional braking unit of general inverter, then it feed back the regeneration energy that generated in the state of motor generate electricity to elec. net, so it saved the wasting energy of general inverter energy  braking resistance, it gets the ideal power saving effect.

The speediness of feedback part of this project can fit for the different working state of different pumping unit, SCR general switch will be used because the bad outdoor working environment, this ensures the machine to work in the state of high efficiency, high reliability.

Operation result shows that total energy saving rate is higher above 20% than the project, it can arrive to 30-50%, if considering the increase of oil output, the cost callback date of the equipment is about one month.