Input voltage: 6kV
Output voltage: 6kV
Rated capacity: 6600kW
With VSV function ( VFD + SVG)
No.81 natural gas station, second pant of Xinjiang oil field has a set of deep freezing unit and two sets shallow freezing unit for natural gas, the total processing capacity of No.1 and No.2 shallow freezing units are 100×104 Nm3/d. However, as associated gas output increased yearly of the east region, the production capacity of the station are unable to meet the demand, in addition, it also meets other questions like aging of the unit, serious corrosion on pipelines and etc. To solve these problems, also improve the technical reliability and economic benefits, Xinjiang oil field intend to upgrade the station, build a new associated gas processing unit. As a result, it needs add a set of 6.6MW centrifugal compressor driven by medium voltage VFD. The No.1 shallow freezing unit and the new associated gas processing unit share the medium voltage VFD.
This article introduces Shanghai Nancal Electric medium voltage AC drive (NC HVVF series) application on centrifugal compressor of No.81 natural gas station, second plant, Xinjiang oil field (hereinafter referred to as second plant). This set of electric drive compressor’s rated power is 6.6MW, drive can realize motor speed adjustment, soft starter, soft stop, grid/VFD transfer, reactive compensation and etc.
2- NC HVVF series AC drive used in second plant, Xinjiang Oil Field
This project requests VFD with high reliability, not only need motor speed adjustment, also motor soft starter, soft stop, grid/VFD transfer, reactive compensation and so on. Customer finally choose Shanghai Nancal Electric medium voltage VFD (NC HVVF series) to meet those sophisticated requirement.
Shanghai Nancal Electric consider the worst work conditions during system design, with enough margin and necessary protection measures. The major single line diagram of VFD system as below:
Figure 1: Single line diagram
VFD Operation Mode:
Variable frequency speed adjustment: using VFD to adjust motor speed to meet the requirement of the process
VFD soft starter: when compressor is running at full load, VFD speed up motor to 50Hz and up transfer to grid. (The grid synchronizing sequence as below)
Grid/VFD transfer: when compressor is running at lower load, down transfer the motor from Grid to VFD.
Reactive compensation: according to requirement of grid power factor, use VSV function to compensate VAR when compressor is running on grid or in idle mode.
Emergency mode: when power cell fail, VFD can still run with full load through bypassing the fault cell with neutral point shift technology send out alarm signal to DCS at the same time. VFD can also up transfer the motor to Grid and shut down itself for maintenance.
Figure 2: Transfer from VFD to grid
Switch freely between motor speed adjustment, grid synchronizing (grid/VFD transfer) and reactive compensation.
Cell bypass technology and power cell N+1 configuration, ensure that VFD can synchronous transfer the motor to grid when one power cell is failure.
VSV (VSD+SVG) technology, motor speed adjustment and reactive compensation respectively.
ProCon technology guarantee that medium voltage VFD adapting to grid disturbance and keeping normal operation to avoid process loss.
The fault protection technology of secondary winding of multi-winding phase-shifting transformer can identify the fault and protectshort circuit, grounding or interturn short circuit, preventing the fault spreading and eliminate the danger.
NC HVVF owns multiple function including variable frequency speed adjustment, grid synchronizing, reactive compensation in single unit to meet various customer requirement, saving the significant cost of VAR compensation and related equipment for users. At present, this unit is so far the largest by capacity in Xinjiang oil field. It is also a valuable reference case for future utilization of high power VFD to the company. And popularize in the future.