Abstract : This paper introduces the reformation of the high-pressure frequency conversion of the boiler induced draft fan in the thermal power plant of Yongmei Group, and analyzes in detail the technological transformation plan and energy-saving effect of the high-voltage frequency converter one to two, which is a similar high-frequency frequency converter in the power plant or other industries. The application of two high-voltage transformers simultaneously dragging two motors provides some theoretical and practical experience.
1. Basic situation of frequency conversion retrofit project Yongmei Group thermal power plant is located in Shangqiu, Shangqiu. The plant covers an area of ​​more than 330 acres and currently has four boilers. With an installed capacity of 4*25MW, it is responsible for the dual task of generating electricity and heating to Yongcheng. Among them, the power of the two induced draft fans of the 3# boiler is 400kW, and the power of the two induced draft fans of the 2# boiler is 355kW. The voltage level is 6kV, both of which are operated in parallel by two engines. The inlet baffle method is used to adjust the air volume, and the baffle is varied between 40% and 75%.
Due to the large throttling loss of the baffle plate, the low operating efficiency, and the inadequacy of adjustment when the load is constantly changing, a large amount of electric energy is wasted. In order to increase the power consumption rate of the plant and reduce coal consumption, Wingco Thermal Power Plant began to carry out frequency conversion in 2006. Through the comparison of domestic and foreign inverter manufacturers, the company chose the HINV series high-voltage frequency conversion speed regulation device with mature technology, advanced performance, stable performance, and perfect after-sales service. After the frequency conversion of the 4# boiler blower (1400kW) in 2006, , The energy-saving effect is remarkable and the operation reliability is high. In 2007, they successively passed projects and inspections, conducted several discussions and decided to make changes to the 2# and 3# furnace induced draft fans with the variable frequency one to two parallel operation.
2. The frequency conversion reconstruction plan analysis system currently uses the fan baffle adjustment. No matter how the working conditions change, the motor must be operated at a higher rated speed, and the fan baffle is adjusted to meet the actual working conditions. The air volume needs to work, but when the baffle is adjusted, a throttling loss is generated on the throttling device, which wastes a lot of energy. At the same time, the start and stop of the equipment will impact the power grid and equipment, and will also affect the use of the equipment. life.
According to the knowledge of pumps and fan technology, there are the following relationships among flow, head and energy consumption in the operating conditions of variable flow and variable pressure of fans and pumps. The flow rate of the fan/pump is proportional to the motor speed;
The total pressure/head of the fan/water pump is proportional to the square of the motor speed;
The shaft power consumed by the fan/pump is proportional to the cube of the motor speed;
From the principle of electrical machinery: The motor speed formula is n = 60f/p (1 - s), where n, f, s, and p represent the motor speed, input frequency, motor slip, and motor pole pair, respectively. When the system adopts variable frequency regulation, directly changing the frequency to change the speed of the motor to meet the needs of different operating conditions. At this moment, the energy consumed by the motor will decrease with the cube of the speed of the motor, so the power saving effect of the frequency conversion speed regulation is very significant.
In the actual production and operation of the 2# and 3# furnaces of the power plant, each boiler is equipped with a blower and two induced draft fans. Three fans operate at the same time: the blower provides blasting to the furnace to ensure complete combustion, and the induced draft fan causes the furnace to form a negative pressure to suck away the exhaust fumes. The relevant departments of thermal power plants decided to perform frequency conversion on the four induced draft fans corresponding to No. 2 and No. 3 furnaces based on the above advantages of variable frequency energy conservation. However, considering the small single fan power, each induced draft fan is equipped with a frequency conversion device. Excessively high, the transformation cost is greatly increased, and finally the power source HINV series one-to-two frequency conversion speed-regulating device was selected after discussion. The schematic diagram of the primary electrical connection of the frequency conversion system and the load is as follows:
Note: TF is the equivalent high-voltage frequency conversion system in the user's drawing.
Frequency conversion system bypass scheme description:
Inverter operation: disconnect QS1, close QS2 and QS3;
Bypass operation: disconnect QS2 and QS3, close QS1;
6kV power supply enters the vacuum switch QF1 through the user, through the variable frequency device into the line switch QS2 to the high voltage variable frequency speed control device, the frequency conversion device output through the outlet gate QS3 to the motor; 6kV power supply can also directly start the motor through the bypass switch QS1 ( Taking into account the occurrence of inverter faults, the original high-voltage switchgear was rebuilt and the circuit breaker was re-selected. The increased overcurrent protection and microcomputer protection device provided effective motor protection for the inverter and could be directly activated when the inverter failed. Two induced draft fans. The specific additional protection is described below. The output switch QS3 and the bypass switch QS1 of the inverter are interlocked with each other, that is, QS2 and QS1 cannot be closed at the same time.
Bypass effect:
When the frequency conversion device is overhauled, it can be operated manually to form a clear power cut point, which can ensure personal safety;
When the frequency conversion device fails, the knife gate can also be operated manually to isolate the frequency conversion device so that the load can be normally operated under the power frequency power supply to ensure the safe and continuous operation of the production.
Each type of boiler induced draft fan in the power plant has the same number of pole pairs and the number of pole pairs, and the load is not much different. This provides favorable conditions for the inverter to simultaneously drive the two motors, but it is necessary to pay attention to the selection of the inverter. The power source company chooses the two motors according to the sum of the rated power, leaving a margin. The capacity of the phase-shifting transformer in the inverter device is selected to be 900kVA (2# induced draft fan) and 1000kVA (3# induced draft fan). In addition, corresponding perfect protection measures were added before the two motors, as follows.
Due to the frequent change of load, the induced draft fan cannot be in a state of being turned on and off. Therefore, the design of the bypass cabinet divides the output into two ports respectively connected to the incoming line side of the two motor power sources. In order to prevent one of the motor faults from causing damage or overloading of the inverter, separate overcurrent and overload protection are provided for each boiler ID fan motor. Specific implementation schemes and innovations are as follows:
The overcurrent protection cabinet protection principle is:
The protection cabinet is installed next to the high-voltage inverter bypass cabinet. The protection cabinet is equipped with four current transformers, four over-current relays, one intermediate relay common, and two signal relays. Protection method is AC two-phase installation of current transformer, current transformer model is LAJ-6 transformation ratio is 50/5, over-current relay model is LL-12/5, export intermediate relay model is DZB-214, also equipped with Signal Relay DX-31B.
The protection principle is as follows: If the 7# induced draft fan AB is short-circuited by two phases, the short-circuit current is reflected to the A-phase current transformer, and the A-phase overcurrent relay protects the action, and passes through the intermediate relay outlet to the high-voltage IV section 7#8# induced air cabinet 133. Trip, at the same time signaled through the signal relay. If the AC two-phase short circuit, AC two-phase over-current relay at the same time. 8# induced draft fan protection action results also jump 7#8# induced wind cabinet circuit breaker protection.
Implementation Effect:
1. A level of protection has been added, which greatly improves the reliability of the inverter protection and the microcomputer protection of the switchgear cabinet.
2. When the motor is faulty, it can realize the action of quick-break and over-current protection.
With the active cooperation of thermal power plants and power source technicians, the project has been successfully implemented and the installation, commissioning and commissioning of the equipment have been completed within the planned time; Multi-level protection also has a reliable guarantee.
Inverter and protection cabinet on-site icon
3. Frequency conversion energy-saving sub-projects After the completion of the project transformation, it shall be measured continuously for five days before and after the transformation. The specific measurement conditions are as follows:
Measuring conditions: The daily power generation during the test period guarantees the maximum power generation during continuous production in the same period, and the production conditions in the measurement time of both the power frequency and the frequency conversion are as consistent as possible.
Measurement time: Under the guarantee of measurement conditions, the power frequency/frequency conversion is measured continuously for 5*24 hours.
The results of the calculation are shown in the following table:
In the energy-saving measurement phase, starting from the actual interests of the user, basically the maximum load operation, the use of two fans at the same time when the frequency conversion running power saving rate are more than 20%, in the absence of heating or low load when the power saving rate is above 30% . The annual running time of the power plant is calculated based on 330 days and the electricity price is calculated at 0.5 yuan. After the frequency conversion of the 2# furnace and the 3# furnace induced draft fan, the annual energy saving can be 2550240 degrees, and the total electricity bill is 1,275,120 yuan. All investments will be fully recovered within one and a half years.
The above test data also verified the theoretical basis of the parallel operation of the boiler induced draft fan, and proved that the high-voltage frequency converter has great flexibility in the aspect of equipment, and provided a theoretical and practical basis for the high-power parallel operation of the fan/water pump conversion project.
Since the equipment was put into operation in November 2008, the equipment has been operating stably, with significant energy saving effects. Theory and practice have proved the outstanding advantages of using high voltage variable frequency speed control devices:
(1) The phenomenon of "big horse-drawn carts" caused by the design margin of the equipment during the running of the industrial frequency, and the motor is naturally wasted due to the non-adjustable rotation of the motor at a constant speed. The frequency conversion regulation completely solved this problem;
(2) A large number of throttling losses caused by load baffles or valve adjustments no longer exist after frequency conversion modification;
(3) The load of some working conditions needs to be adjusted frequently, and the adjustment of the linearity of the baffle and the fluid coupling is too bad to keep up with the changing speed of the working condition, and the motor overload phenomenon easily occurs during the adjustment, so the energy consumption is high. The inverter control response is extremely fast, and the basic and working conditions change synchronously, and the motorless impact-free stepless speed regulation method completely solves the above problems.
(4) The power factor of the asynchronous motor is increased from about 0.8 before the frequency conversion to 0.95 or higher after the frequency conversion (when above 20% load);
(5) Zero-speed start-up can be achieved, no start-up inrush current, which reduces the starting load and reduces the impact torsional vibration. In addition, the loss of the high-voltage inverter itself is extremely small, and the overall efficiency is above 97%.
(6) Different configurations can be made according to the on-site technical requirements. The technology is mature and advanced, and the operation is stable and reliable.
4, other additional benefits after the transformation:
(1) Improved process. After inputting the frequency converter, the air volume can be adjusted smoothly and stably, avoiding flameout and coking accidents when the furnace is turned on or off.
(2) Extend the service life of the motor and fan. General fans are centrifugal fans, long start-up time, large starting current (about 6 to 7 times the rated current, even if the water resistance of the soft starter device start current is also 3 times the rated current), mechanical impact on the motor and fan Very large, seriously affecting its useful life. The use of variable frequency speed regulation can achieve soft start (starting current under load does not exceed the rated current) with almost no impact, which can greatly extend the service life of the machine.
(3) Reducing baffle machinery, fan blades and motor vibration, bearing wear, and prolonging the overhaul cycle of motor fans, saving maintenance costs and time.
(4) The noise at the site is greatly reduced, which greatly improves the operating environment of the power plant.
(5) The HINV high-voltage frequency conversion device is convenient to connect with the DCS of the main control room of the power plant, which avoids the phenomenon that the traditional electric actuator is easy to damage and the opening degree is inaccurate, which improves the automation level of the power plant.
5. Concluding remarks The successful implementation of the frequency conversion reformation of the boiler induced wind in the thermal power plant of the Yongmei Group not only reflects the wide application prospect of the variable frequency technology, but also embodies the technical solution capability of Beijing Power Source Technology Co., Ltd. in the high-voltage frequency conversion comprehensive transformation. The smooth implementation of high-voltage frequency conversion and one-for-two parallel operation projects greatly expanded the flexibility of frequency conversion technology as the current energy-saving transformation, and also verified the mature reliability of domestic high-voltage frequency converter performance.
references
[1] Pump and Fan (3rd Edition), Guo Lijun, He Chuan, Beijing, China Electric Power Press.
[2] HINV high-voltage inverter training materials, Beijing, Beijing Power Source Technology Co., Ltd.
[3] Yongmei Group Thermal Power Plant Frequency Conversion Data, Henan, Henan Yongmei Group Thermal Power Plant
[4] Power System Relay Protection and Automation Equipment Manual China Electric Power Press