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US $1,050.00
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VFD Operation
In an induction motor is a voltage that on several (connected up to about 6 times basis) of its rated current. Since the charge is accelerated, the available torque drops usually rises a little, then a maximum, while the current remains high until the motor reaches full speed.
In contrast, if a VFD starts a motor, applies a first low frequency and voltage to the motor. The frequency is from 2 Hz or less. This will avoid such a low frequency of the high inrush current, that occurs when the engine simply by applying the utility (mains) voltage started by turning a switch. After starting the VFD, and increases the frequency of the applied voltage at a controlled rate or be strengthened to accelerate the load without drawing too much power. This method usually begin to develop an engine to 150% of rated torque, while the VFD is income of less than 50% of the rated current of the power system in the low speed range. A VFD can be adjusted in order to produce a claim to 150% torque from standstill to full speed.
Note however that the engine cooling is generally not good at slow speed. He works at low speeds, even with nominal torque over long periods is not possible due to overheating of the engine. If continuous operation at high torque at low speeds requires external fan is required. Please check with the manufacturer of the engine and / or VFD. In principle, the current in the side of the motor is directly proportional to the torque generated and the voltage at the motor is directly proportional to the actual speed, while the network side, the voltage is constant, the mains current is directly proportional to the load on the engine , which the user interface or CN C, where N is the torque and speed (taking into account the losses will be neglected so that in this discussion.)
(A) n is the network (network) and for m motor (2) C shows the torque [Nm], the voltage U [V], that A] and N [for the speed [rad / s] we neglect the losses at the moment: Un.In Um.Im = (not draw the same grid and the motor) Um.Im Cm.Nm = (= motor mechanical power from the electric motor) In view of the United Nations a constant voltage (will) concluded : In Cm.Nm = / UN line that is in progress (network) is in direct proportion to engine power.
With a VFD, the shutdown is just the opposite, that the boot sequence. The frequency and the voltage at the motor is increased at a controlled rate. If the frequency tends to zero, the motor stops. A small amount of braking torque available to slow the load a little faster than if it stops the engine was turned off and just let the others. additional braking torque can be obtained controlled by a transistor) by the addition of a brake circuit (resistance in order to dissipate the braking energy. With recifiers four quadrants (Active Front End), the VFD is to stop the burden of applying a pair of reverse and back to the mains.
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