Abstract: The frequency conversion transformation of the suction fan of Unit #9 in Anyang Power Plant effectively reduced the electricity generation cost and improved the economic efficiency. Keywords : ABB , high voltage frequency converter, energy saving application 1 Introduction Unit #9 of Anyang Power Plant is a 300MW coal-fired unit with boiler model DG1025/18.2-II4. This boiler is a subcritical natural circulation drum boiler with a single furnace, single intermediate reheat, balanced ventilation, steel frame, solid ash discharge, and is a coal-fired boiler. It is equipped with two suction fans, which are important auxiliary machines of the boiler and also major power consumers. 2 Suction Fan Information 2.1 Suction Fan Specifications The technical specifications of the suction fans are shown in Table 1. Table 1 Technical Specifications of the Suction Fan [IMG=Technical Specifications of the Suction Fan]/uploadpic/THESIS/2007/10/2007103113524583687R.jpg[/IMG] 2.2 Suction Fan Operation Status The suction fan operates in two modes: low-speed and high-speed. Low-speed operation is used when the unit load is low. When the unit load exceeds 250MW, the boiler suction volume is insufficient, requiring switching to high-speed operation. When the unit load is below 250MW, low-speed operation is used. If the switching process fails, the suction fan will trip, seriously affecting boiler safety. This may lead to excessive combustion fluctuations and flameout, or even unit shutdown. 3 Variable Frequency Drive (VFD) Retrofit of the Suction Fan 3.1 VFD Retrofit The purpose of VFD retrofit is to save energy, ensure safe operation of the unit, save plant power, and improve economic efficiency. During the unit overhaul in 2005, the boiler induced draft fan underwent frequency conversion modification. The modification details are as follows: 3.1.1 Composition of the Frequency Conversion Equipment Each induced draft fan frequency conversion equipment consists of one control cabinet, two transformer cabinets, two frequency conversion unit cabinets, and one disconnect switch cabinet. The main circuit of the Toshiba-Mitsubishi high-voltage frequency converter is composed of multiple PWM frequency converter units with single-phase output connected in series. It adopts diode bridge rectification and non-phase shift control, achieving high power factor operation even without capacitors to improve the power factor. Toshiba's high-voltage frequency converter products are used, with a topology of a three-phase input, single-phase output inverter series-type high-voltage frequency converter. 3.1.2 Dimensions and Weight of the Frequency Conversion Equipment The external dimensions and weight of the frequency conversion equipment are shown in Table 2. Table 2 External Dimensions and Weight of Variable Frequency Equipment [IMG=External Dimensions and Weight of Variable Frequency Equipment]/uploadpic/THESIS/2007/10/20071031135334196860J.jpg[/IMG] 3.1.3 Standard Specifications and Rated Values ​​of the Device: The technical specifications of the variable frequency drive are shown in Table 3. Table 3 Technical Specifications of the Frequency Converter [IMG=Technical Specifications of the Frequency Converter]/uploadpic/THESIS/2007/10/20071031141635348161P.jpg[/IMG] 3.1.4 Transformer Parameters: Primary Capacity of a Single Transformer: 1360kVA Secondary A: 3×167kVA Secondary B: 3×167kVA Secondary C: 3×167kVA Primary Voltage: 6300V Secondary Voltage: 582V Primary Current: 125A Secondary Current: 166A Maximum Loss of a Single Transformer: 89kW 3.1.5 The frequency converter is used to power 5 air conditioners, with a maximum power of 13kW per unit. 3.2 Operating Modes of the Inverter for the Exhaust Fan 3.2.1 Under normal circumstances, the operating mode should be that the inverter is running and the bypass switch is on standby. That is, the exhaust fan working switch is in the "working" position, the exhaust fan inverter output knife switch is in the "closed" position to run the exhaust fan, and the exhaust fan bypass switch is in the "test" position on standby. 3.2.2 When the inverter fails, the exhaust fan working switch can be disconnected, the exhaust fan inverter output knife switch can be opened, the exhaust fan bypass switch can be moved to the "working" position, and the bypass switch can be closed to run the exhaust fan. 3.2.3 The motor wiring diagram of the inverter electrical circuit is shown in Figure 1. [IMG=Motor Wiring Diagram]/uploadpic/THESIS/2007/10/2007103113580090192L.jpg[/IMG] Figure 1 Motor Wiring Diagram 3.2.4 Inverter Power Unit Circuit Structure The inverter power unit circuit is shown in Figure 2. [IMG=Inverter Power Unit Circuit]/uploadpic/THESIS/2007/10/2007103113590140034A.jpg[/IMG] Figure 2 Inverter Power Unit Circuit 3.2.5 Electrical System Interlocking (1) Application of Existing Circuit Breakers: Use the existing high-speed circuit breaker as the inverter incoming line circuit breaker and cancel the differential protection. The existing low-speed circuit breaker is used as a bypass circuit breaker without differential protection. The original high and low speed circuit breaker integrated motor protection is retained. The setting of the high-speed circuit breaker integrated motor protection needs to consider the coordination with the protection related to the inverter. (2) The knife switch cabinet adopts a single-pole isolating switch. Therefore, the bypass circuit breaker can be isolated from the inverter during bypass operation. When the knife switch cabinet is closed, the bypass circuit breaker is prohibited from being closed. (3) There is a live indicator on the motor side inside the knife switch cabinet. Once the motor is energized, the interlocking prohibits opening the cabinet door and operating the switch. (4) The knife switch cabinet and the bypass circuit breaker are interlocked. Once the bypass circuit breaker is closed, the interlock prevents the cabinet door from being opened and the switch from being operated. Once the knife switch cabinet door is opened, the bypass circuit breaker is prohibited from being closed. (5) The high-speed circuit breaker and the low-speed circuit breaker are electrically interlocked and cannot be closed at the same time. 3.3 In this evacuation fan frequency conversion modification, the evacuation fan motor and high-voltage switch remain unchanged. As can be seen from the figure, a frequency conversion device was added between the evacuation fan switch and the motor, which not only achieved the purpose of the evacuation fan frequency conversion modification, but also effectively saved costs. 4 Energy saving analysis Compare Unit #9 and Unit #10 (evacuation fan not converted by frequency conversion). 4.1 Comparison of evacuation fan power consumption The comparison of evacuation fan power consumption is shown in Table 4. Table 4 Comparison of Exhaust Fan Power Consumption [IMG=Comparison of Exhaust Fan Power Consumption]/uploadpic/THESIS/2007/10/2007103114000767110N.jpg[/IMG] 4.2 Comparison of Power Generation and Plant Power Consumption is shown in Table 5. Table 5 Comparison of Unit Power Generation and Plant Power Consumption [IMG=Comparison of Unit Power Generation and Plant Power Consumption]/uploadpic/THESIS/2007/10/20071031140101376243.jpg[/IMG] 4.3 Energy Saving Effect As can be seen from the table above, after the frequency conversion modification of Unit #9, compared with Unit #10 without the frequency conversion modification, the exhaust fan power consumption of Unit #9 decreased significantly, and the plant power consumption decreased, achieving significant results, effectively reducing power generation costs and improving economic efficiency. The comparison is shown in Table 5. 5 Conclusion The successful application of high-voltage frequency converters in the ventilator of Unit #9 at Anyang Power Plant has achieved significant energy-saving effects, eliminated potential equipment hazards, ensured the safe and stable operation of the unit, and improved economic efficiency. With the widespread application of frequency converters in industrial production, energy conservation and the enhancement of enterprise competitiveness will be closely integrated, creating more wealth for society.