Application of Frequency Inverter in Oilfield Pumping Equipment

At present, among the oil pumping equipment in the oil field, the beam type kowtow pumping unit is the most widely used and the largest in number. However, the traditional kowtow machines generally have many problems such as large starting impact, high power consumption, large horse-drawn carts, and low efficiency. Phenomena such as motors often occur, there is no reliable protection function for the motor, and the maintenance of the equipment is large. Therefore, it is urgent to transform the existing pumping unit equipment.

The variable frequency speed controller has a low-speed soft start, and the speed can be adjusted smoothly in a large range. It has complete protection functions for the motor, such as short circuit, overload, overvoltage, undervoltage and stall, etc., which can effectively protect the motor and mechanical equipment. It has stable operation, Reliable, improved efficiency and many other advantages, it is an ideal solution for the transformation of oil pumping equipment.

The basic principle of frequency converter

According to the motor theory, the speed formula is n=60f/p? (1－s), where P—the number of pole pairs of the motor
s—slip rate
f – the frequency of the power supply
n – the speed of the motor

It can be seen from the above formula that the motor speed is approximately proportional to the frequency, and the motor speed can be adjusted smoothly by changing the frequency. For the frequency converter, the frequency adjustment range is very wide, and it can be arbitrarily between 0 and 400Hz. Adjustment, so the motor speed can be adjusted in a wide range.

Of course, after the speed is increased, the impact on its bearings and windings should also be considered to prevent excessive wear and overheating of the motor. Generally, the highest frequency is set at 50Hz or 65Hz. Now the inverters we use are AC-DC-AC voltage source inverters.

The Difficulty of Pumping Unit Frequency Converter

As an oil pumping equipment, its movement is to lift up and down repeatedly, one stroke for one lift, and its power comes from two heavy steel sliders driven by an electric motor. When the sliders are lifted, it acts like a lever to move The rod of the pumping unit is sent into the well, and when the slider is lowered, the sucker rod is lifted to bring oil to the wellhead. Since the motor speed is constant, the load is lightened during the lowering of the slider, and the energy generated by the motor drag has no place to be released, and it is bound to enter regeneration In the state of power generation, the bus voltage of the main circuit will increase, and frequent high-voltage shocks will damage the main components of the inverter, including electrolytic capacitors and power modules. Therefore, a braking circuit is added to release the regenerative voltage in time to ensure the safety of the equipment. work under the voltage.

We sample and amplify from the main circuit, and compare it with the reference voltage. By adjusting the potentiometer, the brake unit is turned on at 1.1 Ue (Ue is the rated bus voltage value), and disconnected at 1.05 Ue, so that the main circuit can be controlled. voltage to ensure that it works within the allowable range.

Since the brake module uses a single junction to control the voltage of the main circuit, its reliable operation is very important. Here, the absorption circuit must be well prepared. Since the lead wires of the brake resistor are relatively long, the inductance and peak voltage of the lead wires will increase accordingly. R, C, and D absorbing circuits are added.

In the frequent work of the brake unit, interference voltage will inevitably be generated, causing the module to be damaged due to unintended conduction. It is necessary to add an anti-interference capacitor at the input end of the signal to absorb the misconduction of the module caused by the interference signal. Generally, it is more appropriate to choose a non-inductive capacitor of about 0.01uF.

Due to the current limiting of the braking resistor, the current of the braking unit is generally not large, and about 100A is enough. Since the braking resistor works once in each stroke, its power should be sufficient to ensure long-term reliable use. Generally, 10Kw/80Ω is selected. Electric furnace wire.

Field Application

We selected early stage wells and mid-late stage wells respectively for frequency conversion reconstruction.

In the early stage well, due to the large oil storage capacity and sufficient liquid supply due to the newly mined well, in order to improve the efficiency, we adopted the method of increasing the speed, let the frequency converter run to 65Hz, the frequency was increased by 1/3, and the motor speed was increased by 30% accordingly , the oil production rate is correspondingly increased, the comprehensive oil recovery rate can be 20% more oil recovery than the power frequency situation, and the work efficiency is increased by 1.2 times, which is very popular with oil field workers.

In the middle and late stages of wells, due to the reduction of well reserves and insufficient fluid supply, if the motor is still running at power frequency, it will inevitably waste electric energy and cause unnecessary losses. Therefore, we adopt the method of reducing the speed and reducing the stroke. Between 35 and 40Hz, the speed of the motor is reduced by 30%. In addition, the load of oil production equipment is generally light, and the power saving rate can reach about 25%. Moreover, the power factor is improved and the reactive power loss is reduced.

The frequency converter also has the function of soft start/soft stop, which reduces the mechanical impact on the sucker rod when the motor is started, and can effectively protect and stop heavy oil, wax deposits, sand cards, etc., to protect the motor and machinery equipment, reduce the amount of maintenance, prevent broken rods, the frequency converter can reliably protect against overvoltage, undervoltage, overload, short circuit and motor stall, and it has a very good effect on prolonging the life of the motor and reducing the wear and tear of mechanical equipment.