Abstract: The frequency conversion transformation of the suction fan of Unit #9 in Anyang Power Plant effectively reduced the electricity generation cost and improved 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, single furnace, single intermediate reheat, balanced ventilation, steel frame, solid ash discharge, and 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 Induced Draft Fan 2.2 Induced Draft Fan Operation The induced draft 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. Failure during switching will cause the induced draft fan to trip, severely impacting boiler safety. This could lead to excessive combustion fluctuations and flameout, or even unit shutdown. 3 Variable Frequency Drive (VFD ) Retrofit of the Induced Draft Fan 3.1 VFD Retrofit The purpose of VFD retrofit is to save energy, ensure safe operation, conserve plant power, and improve economic efficiency. During the unit overhaul in 2005, the boiler induced draft fan underwent VFD retrofit. The retrofit details are as follows: 3.1.1 VFD Equipment Composition Each induced draft fan VFD equipment consists of one control cabinet, two transformer cabinets, two VFD unit cabinets, and one knife switch cabinet. The main circuit of the Toshiba-Mitsubishi high-voltage inverter consists of multiple PWM inverter units with single-phase output connected in series. It employs diode bridge rectification with non-phase-shift control, achieving high power factor operation even without capacitors to improve the power factor. The inverter uses Toshiba's high-voltage inverter products, whose topology is a series-connected inverter with three-phase input and single-phase output. 3.1.2 Dimensions and Weight of the Inverter Equipment The external dimensions and weight of the inverter equipment are shown in Table 2. Table 2 External Dimensions and Weight of the Inverter Equipment 3.1.3 Standard Specifications and Rated Values ​​of the Device: The technical specifications of the inverter are shown in Table 3. Table 3 Technical Specifications of the Frequency Converter 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 Frequency Converter Air Conditioning: A total of 5 air conditioners, each with a maximum power of 13kW. 3.2 Operating Mode of the Exhaust Fan Frequency Converter 3.2.1 Under normal circumstances, the operating mode should be that the frequency converter is running and the bypass switch is on standby. That is, the exhaust fan working switch is in the "working" position, the exhaust fan frequency converter output knife switch is in the "closed" position to run the exhaust fan, and the exhaust fan bypass switch is in the "test" position for standby. 3.2.2 When the frequency converter fails, the working switch of the suction fan can be disconnected, the frequency converter outlet knife switch of the suction fan can be opened, the bypass switch of the suction fan can be sent to the "working" position, and the bypass switch can be closed to run the suction fan. 3.2.3 The motor wiring diagram of the frequency converter electrical circuit is shown in Figure 1. Figure 1 Motor wiring diagram 3.2.4 The power unit circuit of the frequency converter is shown in Figure 2. Figure 2 Power unit circuit of the frequency converter 3.2.5 Electrical system interlocking (1) Application of existing circuit breakers: The existing high-speed circuit breaker is used as the incoming circuit breaker of the frequency converter, and the differential protection is cancelled. The existing low-speed circuit breaker is used as the bypass circuit breaker without differential protection. The original high and low speed circuit breaker integrated motor protection is retained. The setting of the integrated motor protection of the high-speed circuit breaker needs to consider the coordination with the protection related to the frequency converter. (2) The knife switch cabinet adopts a single-pole isolating switch. Therefore, the bypass circuit breaker can be isolated from the frequency converter during bypass operation. When the knife switch cabinet is closed, the bypass circuit breaker must not be closed. (3) There is a live indicator on the motor side inside the knife switch cabinet. Once the motor is energized, the cabinet door must not be opened and the switch must not be operated. (4) The knife switch cabinet is interlocked with the bypass circuit breaker. Once the bypass circuit breaker is closed, the cabinet door must not be opened and the switch must not be operated. Once the knife switch cabinet door is opened, the bypass circuit breaker must not be 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 installed 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 with Unit #10 (evacuation fan not frequency conversion modified). 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 4.2 Comparison of Power Generation and Plant Power Consumption Table 5 shows the comparison of unit power generation and plant power consumption. Table 5 Comparison of Unit Power Generation and Plant Power Consumption 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 modification, the exhaust fan power consumption and plant power consumption of Unit #9 decreased significantly, achieving a significant effect, 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 exhaust fan 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 saving and improving enterprise competitiveness are closely linked, which will create more wealth for society.