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Applications of Nancal low voltage industry AC drives used for screw compressor

1- Background
Baikouquan oil extraction of Xinjiang oilfield branch of CNPC is located in Wuerhe district of Karamay city. It is the second heavy oil field developed by Xinjiang Oilfield Company.
 
Crude oil is a mixture of hydrocarbons, containing pentane, ethane and other associated gas, resulting in the loss of crude oil in the process of storage and transportation, and its pollution to environment. By reducing the vapor pressure of crude oil, the associated gas can be separated completely and get the stable crude oil, the method is called flash evaporation.
 
Flash evaporation has a high demand on compressors, which can not only adapt to the gas-liquid state, but also adjust in a wide adjust range. The screw compressor is used to form and maintain a relatively stable vacuum environment at its inlet, which is very important for stable production.
 
Shanghai Nancal Electric co., Ltd. has developed a special AC drive control system based on the characters of screw compressor and fully experience in the similar applications, which can control the motor and load more accurately. The speed of the screw compressor can be precisely controlled according to the system requirements, and the flow and pressure of the process pipeline can be stabilized.
 
2. The data sheet of the compressor and motor on site:
1) Screw compressor 
     Items       Name         Parameters         
1 Model of compressor         LGM80-400
2 Rated torque 1200NM
3 Synchronous speed 3000r/min
4 Shaft Power range 360-400kW
5 Rated flow 37.68Nm350Nm3/min                    
6 Max. flow 50Nm3/min
7 Inlet pressure 0.06-0.07MPa(a)
8 Inlet temperature 55-60℃
9 Output pressure 0.04MPa(a)
10 Working media Top gas from Stabilizer


2) Motor
   Explosion-proof synchronous motor
                                                                                                                      
No. of motor Unit 2                      
Model   YBBP-4002-2
Pole   2
Rated power kW 400
Rated current A 697.1
Rated voltage   V                         AC380V
Rated frequency Hz 50
Variable frequency by VFD Hz 15-50
Phase Ph 3
Direction of Rotation   Bidirectional
Rated synchronous speed   3000
Efficiency % 95.8
Power factor cosΦ   0.91
Max. Torque ratio   2.2

3. Field situation
Shanghai Nancal Electric Co., Ltd. has fully analyzed the characteristics of the screw compressor, combined with our own product’s features, then finally select 3units of single-drive low voltage industry drives.
Model of Nancal AC drives: NC EVFD-03-04-0400
Control method: Modbus communication
Voltage level: 380V
Rated power: 400kW

 
The load of screw compressor is constant torque load with high power. The NC EVFD series industry AC drive is adopted to reduce the impact on compressor during loading and unloading. It can avoid the voltage fluctuation of power supply caused by the start and stop process of direct drive mode and the fluctuation in process caused by gas source changes. It greatly reduces the impact wear on the mechanical equipment at startup, thus improving the service life of the device.

Flash evaporation device

Screw compressor
4- Conclusion
NC EVFD series low voltage industry AC drives realize soft start and soft stop of screw compressor, which reduces the starting shock and prolongs the service life of the equipment. The screw compressor can automatically adjust the motor speed according to the loading needs, so as to make the whole system run smoothly and reduce the frequent loading and unloading of the motor, and to a certain extent, save the electric energy for the enterprise.

5-Company introduction
Headquartered in Beijing, Nancal Technology Co., Ltd. is a listed company on the main board of the Shanghai stock exchange, with the stock code of 603859.
 
Shanghai Nancal Electric Co., Ltd. is the holding subsidiary of Nancal Technology. The company is specialized in the research and development, production, sales and service of Medium-voltage variable frequency converters, low-voltage industry AC drives, shore power, active harmonic filter, static var generator and other power electronic products. The core R&D team are have professional background and fully experience in Robicon, Siemens, GE and other companies. They have led to participate in the National Energy Administration Organization of 20MW Medium voltage AC drives used for West-east gas pipeline.
 
6-Nancal EVFD series low voltage Industry AC drives
The output voltage of NC EVFD series industry drive is 400V/480V/690V. It adopts common DC bus multi-drive scheme. The DC bus capacitor adopts long life metal film capacitor. The product is modular design, with maximum power up to 6000kW by power module parallel. The control algorithm adopts high-performance field orientated vector control, which can drive asynchronous motor and synchronous motor, supports four-quadrant operation, and is suitable for applications requiring high performance and high reliability. The specific features are shown below:
 
* Modular design, multi-drives with common DC bus.
* Diode rectifier, IGBT 6-pulse rectifier or IGBT PWM rectifier.
* DC capacitors use metal film capacitors, maintenance free in whole life cycle.
* Isolated air duct design, no electric devices in airflow path, suitable for harsh environment.
* DSP+FPGA+ARM three core control platform, high performance, high reliability and strong operational capability.
* The main components of control hardware are with latest generation, risk-free for suspend production or technology outdated.
* A great variety of communication interfaces, no need extensions in general application. Standard support Ethernet、Modbus、CAN、Profibus and other communication protocols, and can communicate with almost all  industry network.
* Variety of expansion interfaces to meet most applications.
* Customized fiber optic protocol, only need a pair of fiber optic between main control panel and power module to implement the real time transmission of data and synchronous pulse. A main control panel can connect 16 power modules at same time (no need additional reactor for module paralleling).
* Rapid dynamic response and excellent torque performance at low speed based on advanced motor flux model and control algorithm.
* Two vector control modes: open loop vector control (OLVC) & close loop vector control (CLVC). Control system keeps estimating motor speed in real time through the motor model, so that it can seamlessly switch to OLVC mode in the event of a speed sensor failure.
* Suitable for asynchronous motor and permanent magnet synchronous motor.