1. The role of blowers in petrochemical refining projects

　　In the petrochemical refining process, the relevant equipment needs air with a certain pressure and temperature for the necessary processing during operation. To achieve this condition, a fan must be used for compression. Therefore, the blower system is an important equipment in the petrochemical refining production process. Components, and the power of the motor that drives the blower is generally relatively large, and it is also one of the main electrical loads in the petrochemical industry.

　　petrochemical refinery exterior view

Introduction of blower electrical control system and related equipment

　　The high-voltage switch cabinet and the high-voltage variable frequency soft starter form the high-voltage motor control system, which is responsible for the motor's starting, operation and protection control. Then the motor drives the blower to compress the air to provide the necessary compressed gas for the oil refining process. The specific working process is: 10KV high-voltage power supply is led from the substation to the high-voltage switch cabinet through the high-voltage cable, and then to the high-voltage motor through the switch cabinet and the high-voltage variable frequency soft starter, which is used to control the normal starting and safe operation of the motor and the blower. The function of the blower is to compress the filtered air and send it to the gas storage tank, and then send it to the refining equipment site according to the process requirements.

　　2, the main parameters of the blower and high-voltage power distribution system in the project

　　This project is in a petrochemical refining project site in Hebei Province. The blower adopts Shaangu axial flow blower with a speed of 5700 rpm. The main parameters of the matching motor are 9000KW, voltage level 10KV, rated current 623A, locked-rotor current 4.51 times, motor speed At 1490 rpm, the axial blower is driven after the gearbox is increased in speed. The main grid parameters of the system’s high-voltage power distribution provide a 10KV high-voltage dedicated line for the 110KV substation, with a short-circuit capacity of 60MVA. The entire project’s electricity load is set by the power company at 16,500KW, and there are 5 kilometers of overhead cables from the substation to the project site. The voltage drop of the power grid is relatively large during peak power consumption. According to the power supply conditions and power load, the simulation calculation is carried out, and the results are analyzed. When a general step-down soft starter is used to start the motor (the minimum starting current is 2.5Ie or more), the voltage drop of the power grid may exceed 25% The above will also cause the grid to trip due to overcurrent, which will have a great impact on the safe operation of other equipment in the system. Using a high-voltage variable frequency soft starter program to start this motor (starting current is below the rated current), it can meet the above grid conditions, and the grid voltage drop is also very small.

　　3. Analysis of the influence of the blower system on the power grid system during the start-up process

　　Since the blower system occupies a large amount of power in the entire project, especially when the general step-down soft starter is used to start the motor during the starting process, the starting current has a great impact on the power grid. If the starting current parameters are set incorrectly It will also cause problems such as switchgear over-current tripping and excessive voltage drop of the power grid, which will affect the normal operation of other equipment. In this case, the short-circuit capacity of the grid is small and the line is too long. It is impossible for this motor to start directly. The use of general step-down soft start will also affect the blower system due to excessive grid voltage drop or starting overcurrent. And the normal operation of other equipment in the power grid. The specific classification analysis is as follows:

　　1. Due to the large power of the motor supporting the blower, which accounts for more than 60% of the entire line capacity, if a general soft starter is used, the starting current is more than 1500A, which exceeds the current limit value given by the entire power grid, and the power grid voltage drop may reach 25% The above has a great impact on the main transformer, high-voltage lines, control switch cabinets, and the local system. In particular, other equipment in the power grid on this line needs to be turned on before the motor is started due to the needs of the production process. However, excessive starting current will cause a large voltage drop in the power grid or even trip due to overcurrent, which will cause these equipment to be low. Voltage and tripping and shutdown bring many great hidden dangers to the safe use of the entire equipment system.

　　2. Due to the special power supply reasons of this grid (small short-circuit capacity, long line), to solve the problem of excessive voltage drop in the small-capacity grid, only the soft-start equipment with small starting current can meet the above requirements. If required, it can ensure that the starting current of the motor is less than 500A (less than the rated current) when the motor is started, and the voltage drop of the power grid is only about 2%, without any impact or impact on the electrical equipment system of the entire project.

　　3. The use of high-voltage variable frequency soft starter can also reduce equipment investment and operating costs. It can solve the problem of starting the motor and the electricity consumption of other equipment without adding other equipment and investment on the original basis. Need to enlarge the capacity of substations to increase operating costs and expenses.

　　4, the specific application of the high-voltage variable frequency soft starter in this project

　　1, the selection of high-voltage variable frequency soft starter

　　According to the needs of the project, after many times of communication and technical exchanges between the two parties, according to the parameters of the motor power of 9000KW and voltage level of 10KV, Dayu Electric GBRQ-10000-10/10-B, voltage level of 10KV high voltage frequency conversion is selected. The soft starter can meet the starting requirements. Because the blower is a general load, and the locked-rotor current of the motor is not very large, the main components of the frequency conversion soft start can meet the on-site starting requirements by adopting the general standard capacity and configuration, and can fully achieve a better starting effect. At the same time, it is specially stated that the high-voltage variable frequency soft starter and the high-voltage inverter have the same control principle, but the selection of its main components is different.

　　2, the starting situation of the high-voltage variable frequency soft starter in this project

　　After the equipment reaches the site and undergoes intensive installation and commissioning, the actual starting parameters of the high-voltage variable frequency soft starter are starting current 460A, starting time 190 seconds, and the voltage drop of the power grid is only about 1.5%. The power grid voltage when the motor is started and switched to the running state. There is no fluctuation or impact of the current, which fully meets the technical design requirements.

　　5, the project engineering high-voltage variable frequency soft starter control scheme description

　　1, system control plan diagram and working process

　　According to the user's motor parameters and power grid configuration requirements, the project plan uses a high-voltage variable frequency soft starter with 10000KW and a voltage level of 10KV. The primary plan is as shown in the figure below. The working process of the system is: when the high-voltage switch cabinet and the high-voltage variable frequency soft starter are ready and the low-voltage power supply is automatically detected to be normal, the high-voltage variable frequency soft starter sends an allowable closing signal to the switch cabinet. After the high-voltage switchgear QF1 is closed, the switch QF3 and QF4 are automatically closed one after another, and the high-voltage variable frequency soft starter is started, and a working voltage whose voltage frequency and amplitude can be changed is output. The motor starts to rotate slowly. After the speed is gradually increased, the high voltage When the output voltage of the variable frequency soft starter is close to the power frequency, after a delay of 2 seconds, QF3 and QF4 will automatically open at the same time, the operating switch QF2 will switch to power frequency operation, and the high-voltage variable frequency soft starter will automatically exit the start.

　　High-voltage variable frequency soft starter primary plan diagram

　　2. Introduction to the main equipment and configuration in the system scheme

　　①Starting and running switch cabinet: It adopts KYN28 cabinet type, which is responsible for the starting and running protection switch of the high-voltage variable frequency soft starter.

　　②Switching central control cabinet: It is composed of two parts, the front of the cabinet is equipped with a frequency conversion soft start central control part and display buttons. After the cabinet, the QF3QF4 string is composed of a frequency conversion soft starter to form a starting circuit, and QF2 is a bypass power frequency operation switch.

　　③Phase-shifting transformer cabinet: A phase-shifting transformer is installed in the high-voltage variable frequency soft-start cabinet, and a cooling fan is installed on the top of the cabinet.

　　④Power module unit cabinet: The high-voltage variable frequency soft-start cabinet is equipped with multiple sets of power module units, which are connected in series with each phase unit, and then output three-phase power to the motor. The top of the cabinet is equipped with a cooling fan.