外文翻译--皮带传送系统及其牵引系统(编辑修改稿)

外文翻译--皮带传送系统及其牵引系统(编辑修改稿)内容摘要：

he majority of belt conveyors in use today。 Variablefill drain couplings。 Drainablefluid couplings work on the same principle as fixedfill couplings。 The coupling’s impellers are mounted on the AC motor and the runners on the driven reducer highspeed shaft。 Housing mounted to the drive base encloses the working circuit。 The coupling’s rotating casing contains bleedoff orifices that continually allow fluid to exit the working circuit into a separate hydraulic reservoir。 Oil from the reservoir is pumped through a heat exchanger to a solenoidoperated hydraulic valve that controls the filling of the fluid coupling。 To control the starting torque of a singledrive conveyor system， the AC motor current must be monitored to provide feedback to the solenoid control valve。 Variable fill drain couplings are used in medium to highkW conveyor systems and are available in sizes up to thousands of kW。 The drives can be mechanically plex and depending on the control parameters。 the system can be electronically intricate。 The drive system cost is medium to high, depending upon size specified。 Hydrokiic scoop control drive。 The scoop control fluid coupling consists of the three standard fluid coupling ponents： a driven impeller, a driving runner and a casing that encloses the working circuit。 The casing is fitted with fixed orifices that bleed a predetermined amount of 山东建筑大学毕业设计外文文献及译文 4 fluid into a reservoir。 When the scoop tube is fully extended into the reservoir, the coupling is 100 percent filled。 The scoop tube, extending outside the fluid coupling， is positioned using an electric actuator to engage the tube from the fully retracted to the fully engaged position。 This control provides reasonably smooth acceleration rates。 but the puterbased control system is very plex。 Scoop control couplings are applied on conveyors requiring single or multiple drives from 150 kW to 750 kW。 2 Neutral point clamped(NPC)threelevel inverter using IGBTs Threelevel voltagefed inverters have recently bee more and more popular for higher power drive applications because of their easy voltage sharing features。 lower dv/dt per switching for each of the devices， and superior harmonic quality at the output。 The availability of HVIGBTs has led to the design of a new range of mediumhigh voltage inverter using threelevel NPC topology。 This kind of inverter can realize a whole range with a voltage rating from 2． 3 kV to 4． 1 6 kV Series connection of HVIGBT modules is used in the 3． 3 kV and 4． 1 6 kV devices。 The 2． 3 kV inverters need only one HVIGBT per switch。 2． 1 Power section To meet the demands for medium voltage applications。 a threelevel neutral point clamped inverter realizes the power section。 In parison to a twolevel inverter， the NPC inverter offers the benefit that three voltage levels can be supplied to the output terminals， so for the same output current quality， only 1/4 of the switching frequency is necessary。 Moreover the voltage ratings of the switches in NPC inverter topology will be reduced to 1/2。 and the additional transient voltage stress on the motor can also be reduced to 1/2 pared to that of a twolevel inverter。 The switching states of a threelevel invert。