Fault Analysis And Countermeasure Research Of Oilfield Reactive Power Compensator

Due to the need of large start torque of the pumping unit,the motor using in pumping unit usually has a large capacity.But its load rate is low in stable operation.Therefore,the power factor of the oilfield distribution network is low.And there is a lot of reactive power loss.This is the reason why there are a large number of reactive power compensation capacitors in oilfield.But the capacitors exploded sometimes because of the complicated working condition in oilfield.So this paper takes the capacitor explosion as the join point to find out the mechanism of the capacitor explosion.The applicable reactive power compensation method is investigated based on the analysis of the actual reactive power in pumping unit.And the more reasonable reactive power compensation plan is given.The mechanism is investigated at First.Through the background analysis of the concrete application of reactive power compensation capacitors using in oilfield,the high output voltage of the transformers and the harmonic pollution is pointed out.Then,the way to choose capacitor reactive power capacity is discussed,which is not reasonable.At the same time,considering the external characteristic of the transformer,the overcompensation because of the unreasonable capacitor capacity is elaborated.The capacitor is working in high voltage for a long time which is caused by overcompensation.The amplification of the harmonic after using capacitors is analyzed,too.Based on the previous analysis,two different solution is discussed.First one consists of capacitor capacity reduction and series reactor.Second one is made up of capacitor working with SVG which has the ability of harmonic suppression.Thinking about the reactive power needed in the three-phase asynchronous motor,actual reactive power in real pumping unit and the real capacitor type,the more logical capacitor selection standard is given.The working principle and actual type selection of the series reactor has been discussed in detail.First,the mathematical model of SVG in synchronous reference frame is established.The control strategy used in SVG is the double closed loop control strategy of voltage and current.And its engineering design method is introduced in detail.Then,the algorithm that can extract harmonic current by the multiple second order generalized integrator(MSOGI)and control it by multiple resonant controllers is investigated.For filtering the harmonic in switching frequency,the SVG with LCL filter is studied.The control strategy used is inverter-side current feedback(ICF)control.But the grid current is susceptible to be distorted by the grid-voltage harmonics due to the low inductance of the LCL filter.Therefore,the harmonic impedance in the ICF control is calculated.And the grid current harmonic can be suppressed by the capacitor current feedforward control method whose feedforward position is different from the traditional one.The system stability is compared by drawing the root loci.Then the simulation validates the effectiveness of the reactive power compensation and harmonic suppression plan.At last,the experiment is carried out in the Sheng Li Oilfield.The results verify the effectiveness of the dynamic reactive power compensation plan.And the harmonic current is partly suppressed.Then the experiment result of the SVG with LCL filter is analyzed.It proved the ICF control with different capacitor current feedforward position can effectively mitigate the grid current harmonic.