Application of high voltage inverter in suction fan
Douhe Power Plant of China Datang Corporation #2 generator set (125MW) is a peak shaving unit, which basically carries% load during operation, and the two suction fans are adjusted by inlet baffle. In order to ensure the safe and stable operation of the motor, the selected fan motor has a large standby capacity. When the unit is running at full load, the opening of the inlet baffle of the suction fan is about 60%. When the unit is peak shaving, the opening of the inlet baffle of the fan is about 40%. The energy loss is large and the fan efficiency is low. In order to further adapt to the power system of plant separation and bidding, save energy, reduce the vanadium slag output by about 21%, reduce the auxiliary power consumption rate, protect the environment, simplify the operation mode, and reduce the wear of rotating equipment, our company decided to adopt high-voltage frequency converter speed regulating devices for some fans and pumps in Douhe Power Plant, Xiahuayuan Power Plant and Zhangjiakou power plant. Our company purchased high-voltage frequency converters through public bidding internationally. Beijing Lide Huafu Electric Technology Co., Ltd. is the only bid winner in China, and won the bid for 8 high-voltage converters at one stroke. One set of 6kv/1000kw high-voltage frequency converter produced by Beijing Lide Huafu Electric Technology Co., Ltd. is installed on the two suction fan motors of 2 boiler of Douhe Power Plant
1. Principle of harsvert-a06/105 high voltage frequency converter
the frequency converter adopts multi-level series technology. The 6kV system structure is shown in Figure 1, which is composed of phase-shifting transformer, power unit and controller. 6kV series has 21 power units, each of which is connected in series to form a phase
600)this. Width=600 "border=0>
the structure and electrical performance of each power unit are completely consistent and interchangeable. Its circuit structure is shown in Figure 2. It is a basic AC DC AC single-phase inverter circuit, and the rectifier side is a diode three-phase full bridge. Through sinusoidal PWM control of IGBT inverter bridge, the waveform shown in Figure 3 can be obtained.
600) this.width=600" border=0>
the structure of each power unit is completely consistent and interchangeable, Its circuit structure is shown in Figure 2. It is a basic AC DC AC single-phase inverter circuit. The rectifier side is a diode three-phase full bridge. By sinusoidal PWM control of the IGBT inverter bridge, the waveform shown in Figure 3 can be obtained
600) t there are 10 his in the large plastic market width=600 "Border=0>
the input side is powered by a phase-shifting transformer, and the secondary windings of the phase-shifting transformer are divided into three groups to form a 42 pulse rectification mode; this multi-stage phase-shifting superposition rectification mode can greatly improve the current waveform at the side and make the side power factor under load close to 1.
in addition, due to the independence of the secondary windings of the transformer, the main circuit of each power unit is relatively independent, and each power unit is equivalent to A single-phase low-voltage frequency converter
on the output side, the U and V output terminals of each unit are connected in series to form a star connection, which directly gives the upgraded version after irradiation faster degradation; The step sine PWM waveform shown in Figure 4 can be obtained by reorganizing the PWM waveform of each unit when the high-voltage motor is powered. This kind of waveform has good sinusoidal degree and small dv/dt, which can reduce the insulation damage to the cable and motor. The length of the output cable can be very long without the output filter. The motor does not need to be derated for use, and can be directly used for the transformation of old equipment; At the same time, the harmonic loss of the motor is greatly reduced, the mechanical vibration caused by this is eliminated, and the mechanical stress of the bearing and blade is reduced
when a unit fails, by making the soft switch experimental curve, experimental force value and result judgment node K in Figure 2 conductive, this unit can be bypassed out of the system without affecting the operation of other units. The continuous derating operation of the frequency converter can reduce the losses caused by shutdown in many occasions
600)this. width=600 "Border=0>
2. Introduction to frequency conversion transformation scheme
2 boiler induced draft fan is arranged on both sides. At present, the output adjustment of the induced draft fan is realized by manually adjusting the baffle. Due to the large redundant power in the design of the induced draft fan, coupled with the resistance loss caused by the air volume control using the baffle, the auxiliary power consumption rate is high, affecting the economic operation of the unit.
motor parameters induced draft fan parameters
model: Y model: gd
rated power : 1000kW rated air volume: 455000m3/h
rated voltage: 6kV rated air pressure: 6460pa
rated current: 119a fan speed: 742rpm
rated frequency: 50Hz rated speed: 743r/min
in order to fully ensure the reliability of the system, power frequency bypass devices are installed for the frequency converter at the same time. When the frequency converter is abnormal, the frequency converter stops running, and the motor can be directly manually switched to power frequency operation. The power frequency bypass is composed of three high-voltage disconnectors QS1, QS2 and qs3 (see figure, where QF is the original high-voltage switch of Party A). It is required that QS2 and qs3 cannot be closed at the same time, and interlock mechanically. During frequency conversion operation, QS1 and QS2 are closed and qs3 is disconnected; During power frequency operation, qs3 is closed and QS1 and QS2 are disconnected
600)this. width=600 "Border=0>
in order to realize the protection of frequency converter failure, the frequency converter interlocks the 6kV switch QF. Once the frequency converter fails, the frequency converter jumps out of QF and requires Party A to properly transform the closing and opening circuit of QF. When the power frequency bypass is used, the frequency converter should allow QF to close and withdraw the tripping signal to QF, so that the motor can be started normally through QF closing power frequency.
3. Comparison of frequency converter commissioning data
China Electric Power Research Institute opposite phase The measurement results of relevant parameters are as follows
Table 1 power frequency baffle adjustment