Oct 31, 2020
The design capacity of the coal injection system for the 5# and 6# blast furnaces of an ironmaking plant is 58t/h, the coal ratio is 180kg/t, the coal injection rate of 2 blast furnaces is 45t per hour, the pulverized coal storage capacity is 300-340t, and the pulverized coal production Larger than the blowing volume. In order to adapt to blast furnace production, coal mills and induced draft fans must be frequently turned on and off to adjust the storage capacity of pulverized coal. They run for 20 hours a day and shut down for 4 hours. The coal mill and the induced draft fan are both 10kV high voltage equipment, the power is 710kW and 800kW, the rated current is 54A and 57.7A respectively, and the direct starting current is 6-8 times the rated current. Every time it starts, the power system has obvious The voltage drop caused by low voltage start failure has affected production. In view of the fact that the coal injection capacity is slightly greater than the injection capacity and the storage of pulverized coal is limited, the high-pressure equipment must be frequently started and stopped to adjust the coal storage capacity to adapt to the current status of blast furnace production. The coal pulverizer is a heavy-duty start, which combines multiple factors. In July 2006, a high-pressure soft starter was used to modify the site.
2 Control principle and characteristics of high-voltage soft starter
This high-voltage soft starter consists of a grid-side contactor, a bypass contactor and a digital starter. Start by the starter. After the start-up process is over, the bypass contactor is automatically closed, the starting device is cut off, and the system runs at full pressure. The direct starting current is 6-8 times the rated current. This high-voltage soft starter can achieve 3 times the starting current.
Control characteristics: 1) Current control. This high-voltage soft starter can achieve continuous adjustment of the starting current and voltage limit. The control is input through the panel, and the output current rapidly increases from zero to the set current limit. Under the condition that the set current limit is not exceeded, The voltage gradually rises to the voltage limit, and the motor starts quickly to complete the starting process. 2) Torque control. This high-voltage soft starter can realize continuous adjustment of the starting torque limit. The output voltage increases rapidly from zero to the voltage corresponding to the set torque limit. The motor starts quickly to complete the starting process. Since the current and voltage limits can be adjusted continuously, and the starting torque is continuously adjustable, the starting curve is diverse. The starting curve suitable for the field equipment can be selected according to the actual situation, or the fixed starting parameter and curve can be directly selected. 3) Remote monitoring. The operation signal of the field equipment is connected to the main control PLC, and the PLC program realizes the interlocking control with other equipment. 4) Comprehensive microcomputer protection. It adopts microcomputer comprehensive protection, complete protections such as overcurrent, overvoltage, undervoltage, overload, start-up timeout, etc., with high sensitivity, which can match the superior comprehensive protection.
High-voltage soft starter technical performance indicators: 1) Suitable for 6kV and 10kV voltage levels. 2) The standard output power is from 160kW to 15MW; the current range is 70～2000A. The power of the medium-speed mill and the induced draft fan are 700kw and 810kW, respectively, and the current is 54A and 57.7A, which meet the technical requirements. 3) Meet international standards such as IEC and IEEE.
3 Modification measures and key points of control
Before the application of this high-voltage soft starter, the coal injection high-voltage equipment has always been directly started. The following system transformations have been carried out using this high-voltage soft starter: 1) Electric power supply mode transformation. The power supply mode of the field equipment controlled by the 10 kV high distribution room is transformed into the field high voltage equipment controlled by the high voltage soft start device. 2) Transformation of control procedures and operation modes. Increase the digital control and protection program, from direct control of high-equipped room to 2 kinds of control methods to switch. Under normal circumstances, the soft start control is realized. When the soft start control fails, it can be switched to control the circuit breaker of the high-distribution room.
The key points of controlling the application of this high-voltage soft starter are: 1) Normally, the coal injection staff will perform automatic operation in the main control room. Turn the soft selection switch to the automatic position on the monitoring screen and click the start or stop button to achieve When the high-voltage equipment is started or stopped, after the equipment is started, the bypass contactor will be closed, and the soft starter will monitor and protect the running equipment. 2) When the equipment is shut down for maintenance, inform the personnel in the high-level distribution room to open the circuit breaker, then pull it out, and take safety protection measures. 3) When the on-site startup equipment fails, the soft selection switch can be turned to the stop position, and the control mode selection switch in the soft-start cabinet is turned to the bypass position, then the on-site soft-start equipment can be thrown off, and the high-level configuration room can be operated in the main control room. The circuit breaker realizes the start and stop of high voltage equipment.
4 Application effect
Using this high-pressure soft starter, the coal pulverizer system prolongs the safe operating life of 1a, the system is stable and reliable, and the economic benefits are significant. Compared with the high-voltage inverter, this high-voltage soft starter has a small investment and easy maintenance. It has a strong competitiveness in large and medium-sized equipment with relatively stable load.