The successful application of Hertz frequency converter in submersible electric pump wells
The speed of the submersible electric pump motor is controlled by the frequency converter, so that the displacement of the submersible electric pump is matched with that of the oil well. When the supply of the oil well is insufficient, the rotation speed of the submersible electric pump is automatically reduced. This achieves continuous operation of the submersible electric pump, avoids frequent start and stop damage to the electric pump unit and cable, achieves energy saving and extends the electric pump well check pump cycle. It provides a new way for the normal production of low-energy electric pump wells.
First, submersible electric pump structure
Submersible pumps - including submersible motors, protectors, separators, submersible centrifugal pumps;
Submersible electric pump is a kind of mechanical oil extraction equipment. Its role is to pump downhole liquid to the ground. The submersible electric pump unit is mainly composed of three parts.
1) Downhole section: submersible pump, separator, protector, submersible motor, submersible cable;
2) Ground equipment:
Fixed-frequency drive: step-down transformers, control cabinets;
Variable frequency drive: step-down transformer, frequency converter, step-up transformer;
3) Auxiliary equipment: centralizer, temperature measuring and pressure measuring device, single-flow valve, wellhead crossing device and junction box.
Second, submersible pump special inverter working principle
1. Principle of variable frequency speed control The inverter can change the speed of the motor by changing the frequency of the stator motor supply to achieve the speed adjustment of the submersible motor. The formula for the speed of the AC asynchronous motor is:
n=60F1(1-S)/P
In the formula, n-motor rotation speed, F1-stator supply frequency, P-pole pair number, S-slip rate.
2. Principle of the Inverter The device is an AC-DC-AC voltage source type variable frequency speed control system, that is, the AC input is rectified to DC, and then the DC is reversed to the required frequency AC. The output frequency can be freely changed by the control program, so that the motor can be soft-started smoothly and soft-stopped. Coupled with the output filter of the inverter, there is a good output waveform compensation, thereby reducing the transmission loss due to a long output line.
The inverter part adopts a three-level scheme. Compared with the two-level scheme, it has a high inverter voltage, and a conventional voltage IGBT device can realize an inversion of more than kV, and the waveform is better than the two levels.
Schematic: Hertz frequency conversion schematic:
Figure 1 Three-level inverter schematic
Third, the scene of application The main technical indicators of the inverter are as follows:
Input: three-phase, 50Hz, line voltage 1140V+15%～20%
Capacity: 75KW
Output: frequency 2 ~ 50 Hz continuously adjustable, rated voltage 1140V
Overload capacity: 150%, 1 minute Protection: overvoltage, undervoltage, overcurrent, short circuit, phase loss, excessive temperature rise, stall, etc.
Installation method: Connect with the control panel in series, that is, the output of the control panel is connected with the input of the inverter, and the output of the inverter is connected with the downhole generator.
After the installation is completed, the frequency is adjusted to 40 Hz for one day of trial operation. The daily production volume is reduced by 10m from the previous date on the 3.9th of January. The frequency is adjusted to 47Hz, and the output is restored to the original state. At present, the frequency converter is operating normally, and the operating data is shown in Table 1:
Before installation
After installation
Voltage (V)
Current (A)
frequency
(Hz)
Annual power consumption
(10,000 kwh)
Voltage
(V)
Electric current
(A)
frequency
(Hz)
Annual power consumption
(10,000 kwh)
Annual power consumption comparison
(10,000 kwh)
1140
52
50
66.05
1140
28
47
-15.22
Table 1. Statistics before and after the installation of inverters installed in Liang 23-Ping 1 well
Fourth, the effect of evaluation and economic benefits
1. Effect evaluation On June 16, 2005, the energy inspection station of Chunliang Power Plant adopted DJYC-95 motor economical operation tester (current, voltage 0.5, power 1.0), 1140V submersible for Well 23-Ping 1 well. The power saving effect of the special pump for the electric pump was tested in the field and the conclusions are as follows:
A. The power factor was improved from 0.671 to 0.759.
B. The active power is reduced by a large margin, the active energy saving rate reaches 22.49%, the reactive energy saving rate is 39.85%, the comprehensive energy saving rate is 23.04%, and the power saving effect is good. (See Table 2)
No.
project
unit
Before installation
After installation
1
Active power
Kw
78.18
60.60
2
Reactive power
Kvar
86.30
51.91
3
Power Factor
/
0.671
0.759
4
Energy saving rate
%
22.49
39.85
23.04
5
Reactive power saving rate
%
6
Comprehensive energy saving rate
%
Table 2, before and after installation of frequency converter 23-flat 1 test data sheet
2, economic benefits:
After the frequency converter is installed, the comprehensive energy-saving rate is 23.04%, the annual energy saving is 152,200 Kwh, and the basic electricity cost is calculated as 0.435 yuan/Kwh, which saves 66,200 yuan of electricity annually, and the investment can be recovered in less than two years (the price of the inverter is 125,000 yuan).
In addition, because the frequency converter realizes the soft start and stop of the electric pump, it will greatly benefit the prolonged service life of the electric pump, which can save maintenance funds and improve economic efficiency.
V. Promotion and application prospects The special inverters for submersible electric pumps are aimed at the disadvantages of submersible pumps not being able to freely adjust the output, effectively solving this technical problem, and ensuring that the submersible pumps can operate safely and reliably, which will increase energy efficiency. The effect of the effect. However, the application of frequency control technology in submersible pump wells is still in its infancy. Our factory has a total of 16 electric pump wells. Currently, this technique is only applied to the Liang 23-Ping 1 well. If it can be applied and promoted on all electric pump wells, it will greatly improve the economic benefits of our electric pump wells, so its promotion prospect is very broad.
Six, submersible pump special inverter has the following characteristics:
1. It can realize soft start and soft stop of electric pump, prolong the service life of electric pump, protect motor and cable, and save maintenance cost.
2. Improve the power factor of the electric pump system, and the energy-saving effect is obvious.
3, improve the quality of the pipe network, can achieve closed-loop control of the electric pump system, increase the working safety of the electric pump system.
4, high reliability, easy operation, can achieve continuous adjustment of the output voltage, current, in order to achieve the purpose of continuously adjustable output power, so that the electric pump oil production system in the best working condition.
5. Improve production efficiency, facilitate overall management and dispatch, and achieve distributed control of electric pump systems.
6. The oil extraction technology involves multi-disciplinary fields. The current inverter for submersible electric pumps has been transformed from the original high-low-high method to direct high-high frequency conversion, and the volume is smaller and the operation is more convenient.
Seventh, conclusion
In summary, the use of variable frequency control to improve oil production efficiency, while meeting the requirements of the development plan. After the frequency conversion of submersible pump wells, the soft start and soft stop of the electric pump wells were realized, which effectively protected the electric pump well units and cables; the oil pressure could be easily adjusted by adjusting the frequency, and the units and pumps were avoided. Long-term operation under high pressure; prolongs the life of the electric pump well, saves maintenance and maintenance costs of the well, and enables the electric pump unit to operate under optimal operating conditions. Greatly improved the efficiency of the electric pump oil extraction system. At the same time, the power factor is improved, the power supply capacity of the power grid is increased, and the power saving effect is obvious. Large-scale promotion of submersible pump frequency conversion technology will bring good economic and social benefits.