Keywords: permanent magnet motor; Power factor; Back electromotive force point
1 application status of permanent magnet motor
The technical test of permanent magnet motor for automatic voltage regulating transformer of pumping well was carried out in Gudong Oil Production Plant of Shengli Oilfield from June 5, 2002 to 10. Based on the whole mechanical production system, this technology uses the concept of system to optimize the design of the whole mechanical oil well drive system from transformer, control cabinet to motor, and replaces the ordinary Y series 37-55kW motor with 22-30kW low-power permanent magnet motor. In 2002, 65,438 permanent magnet motors and 97 automatic voltage-regulating transformers were used, and the average daily power saving per single well was 42kWh, the system efficiency was improved by 3.5%, and the capacity of single well transformer was reduced by 18 30k va. By the end of 2008, * * * has popularized and applied more than 500 permanent magnet motors, the average single-well motor power has decreased from 46.6kW to 32.5kW, the single-well power factor has increased from 0.562 to 0.905, and the single-well transformer capacity has decreased 18 kVA.
There are also some problems in the use of permanent magnet motors. The power factor of some permanent magnet motors is too low, even lower than 0.3, which is obviously lower than the rated value, which has brought certain influence to give full play to the energy-saving effect of permanent magnet motors. The energy management station of Gudong Oil Production Plant decided to carry out field adjustment test for this problem.
Analysis of Problems in the Application of Permanent Magnet Motor
2. 1 no-load back emf and critical back emf
2. 1. 1 no-load back emf
Each permanent magnet synchronous motor has a different no-load back electromotive force. The shafts of the same speed permanent magnet synchronous motor are connected with each other, and one stator is connected with three-phase alternating current. When the synchronous speed is reached, it is called no-load back electromotive force to test the open circuit voltage of the stator of another dragged motor.
2. 1.2 critical back electromotive force
Under a certain load, the stator voltage of permanent magnet synchronous motor is continuously adjusted, the instantaneous reactive power of permanent magnet synchronous motor is tested by FLUK43B power analyzer, and the voltage is tested by multimeter. When the reactive power measured by FLUK43B shows neither "C" (capacitive reactive power) nor "L" (inductive reactive power), the corresponding stator voltage is the critical back electromotive force under load, and the reactive power at this time is very small (see table 1).
Table 1 30kW 8-pole 380V permanent magnet synchronous motor power factors corresponding to different load rates under different voltages.
Note: "+"stands for inductive reactive power; "-"-represents capacitive reactive power; The measured no-load back electromotive force of permanent magnet synchronous motor is 391.5v; ; When the measured load rate is 40%, the critical back electromotive force is 383.5V V.
2.2 Influence of load rate and stator voltage on power factor (reactive power)
For 12 permanent magnet synchronous motors with different rated voltages (380V, 660V, 1 140V), different rated powers (22 kW, 30 kW) and different rotational speeds (750RPM, 1000RPM), the corresponding load rates are different.
3 permanent magnet motor back electromotive force point adjustment test
3. 1 test purpose
The test has two purposes: one is to determine the relationship between power factor and voltage of permanent magnet motor; The second is to determine the back electromotive force point of permanent magnet motor.
3.2 Field Adjustment and Testing
On April 5, 20 10, the energy management station of technical quality and safety supervision center of Gudong Oil Production Plant conducted the power factor adjustment test of permanent magnet motor for two mechanical production wells, GO2-2 1-55 and GO2-23-59 (see Table 2 for the main parameters of the two wells). On the test day, we tested two wells and recorded the test data (see Table 3 for the test results).
Table 2 Main Parameters of Well Go2-21-55 and Well GO2-23-59
Table 3 Test Data of Electrical Parameters of Well Go2-21-55 and Well GO2-23-59
As can be seen from Table 3:
(1) When the stator voltage is higher than the critical back electromotive force of the permanent magnet synchronous motor, its inductive reactive power operates as an inductive power factor; When the stator voltage is lower than the critical back electromotive force of the permanent magnet synchronous motor, the capacitive reactive power of the permanent magnet synchronous motor operates as a capacitive power factor.
(2) When the stator voltage of the external permanent magnet synchronous motor is equal to or approximately equal to its critical back electromotive force, the reactive power of the motor is the smallest and the power factor is the highest.
(3) When the load rate is low, the power factor decreases with the increase of the applied stator voltage deviating from the critical back electromotive force, and the more the stator voltage deviates from the critical back electromotive force, the more the power factor decreases.
(4) With the increase of load rate, the influence of voltage variation on power factor gradually weakens, and when the load rate is greater than 40%, the influence of voltage variation on power factor is very small.
(5) When the stator voltage is constant, the lower the load rate of the motor, the lower the power factor.
(6) The no-load critical back electromotive force of the motor is approximately equal to the no-load back electromotive force. With the increase of load, the critical back electromotive force gradually decreases, and the critical back electromotive force decreases by about 2.5%Ue under the working condition of pumping unit.
Well GO2-2 1-55 is the third-gear transformer of S 1 1. We have conducted three pressure regulating tests in Well GO2-2 1-55 (see Table 4 for test results). The results show that the highest power factor is 0.9655 when the voltage is adjusted to 4 16V.
Table 4 Well Go2-21-55 Test Table
During the test that day, the voltage of well GO2-23-59 was too high, the lowest voltage was 440V V, and the original transformer had only three gears, which could not reach the predetermined voltage. Later, I contacted the motor manufacturer, and in April 1 1, the seventh-gear transformer was replaced, and the voltage regulation range was expanded, and the second test was carried out on site. After replacing the transformer, six voltage regulating tests were conducted in Well GO2-23-59 (see Table 5 for test results). The test results show that the highest power factor of the motor is 0.955, the active power is 4.02kW and the reactive power is-0.87kvar when the transformer is set to the third gear of 393V V.
Table 5 Well Go2-23-59 Test Table
See Table 6 for the adjusted test data of two wells.
Table 6 Adjusted Test Data of Well Go2-21-55 and Well GO2-23-59
3.3 Test conclusion
The field test results show that the power factor of permanent magnet motor is closely related to voltage under the same working conditions. When the output voltage of transformer is too low, the reactive power is negative. At this time, the motor is capacitive and the power factor is lower than 0.9 (rated value). When the voltage is too high, the reactive power is positive, and the motor is inductive at this time, and the power factor is also lower than 0.9 (rated value). When a certain voltage is fixed, the reactive power approaches zero, and the power factor is 1, and the motor reaches the ideal running state, with the highest power efficiency and the least loss. At this time, the voltage is equal to the back electromotive force point of the motor.
As can be seen from Table 5, the back electromotive force point of Well GO2-2 1-55 is slightly lower than 4 16V, and that of Well GO2-23-59 is slightly higher than 393V. Due to the lack of transformer gears and insufficient voltage adjustment, it is impossible to accurately debug the back electromotive force points of two wells.
Because these two oil wells produce oil intermittently, the active power of the oil wells changes irregularly during the adjustment process, and there is no obvious downward trend. However, according to the research, with the increase of the power of permanent magnet motor, the efficiency of the motor is also improved accordingly, and the adjustment should have a certain energy-saving effect.
When the working voltage of the motor is too high or too low, it will not only affect the power factor of the motor, but also cause the motor to overheat due to the high voltage, thus shortening the service life of the motor and reducing the operating efficiency of the motor. After adjusting the power factor of the motor, it not only improves the power factor of the line and reduces the network loss, but also improves the efficiency of the motor and prolongs its service life.
4 promotion and application
From April, 20 10, the critical back electromotive force of permanent magnet motor was tested in the whole plant, and excitation and voltage regulation were carried out to ensure that the voltage value was near the critical back electromotive force point and improve the power factor. * * * By adjusting 256 permanent magnet motors, the daily average power saving of single well is 8. 1kWh, and the average power factor of single well is increased by 0. 107. A total of 256 permanent magnet motors in oil wells save 2073.6 kWh of electricity every day and 4 1.62 million yuan annually.
5. Some conclusions.
(1) Ensure the operation with capacitive power factor. According to the no-load back electromotive force marked on the nameplate of the motor, adjust the output voltage of the transformer to make the voltage value lower than about 2.5% of the no-load back electromotive force, and it is best to run the motor with the high capacitive power factor measured in the field. This characteristic is particularly important in pumping units. 1 transformer drives 1 motor, the capacitive reactive power of the motor and the inductive reactive power of the transformer compensate each other, which can make the primary power factor of the transformer greater than 0.90. 1 When the transformer drives multiple motors, the primary power factor of the transformer can be greater than 0.90 by properly controlling the ratio of capacitive power factor to inductive power factor to run the permanent magnet synchronous motor.
(2) Some oil well transformers in use of S11have few voltage regulating gears, only three gears; The pressure regulating range is narrow, only 5%; The precision of voltage regulation is low, which is not suitable for field production. If all the transformers are replaced with S 1 1 energy-saving 9-class transformers, the voltage regulation range of this transformer is 10%, with 2.5% regulation at each stage. This transformer has the advantages of wide regulation range, multiple stages and low energy consumption, which can achieve ideal voltage regulation effect and is more suitable for field production.
refer to
[1] Yan Jingdong. Application analysis of permanent magnet synchronous motor in pumping unit, 2006. P35-36。