The key to understanding current components is knowing that a typical induction motor has two current components: One is responsible for producing the magnetic field in the motor, which is necessary to rotate the motor; while the second component is the torque-producing current, which, as the name suggests, is responsible for producing torque. Not to panic though, there are currently many ways to reduce THD. This reduction in speed results in lower back-EMF, which, in turn, allows more current to flow into the motor again. Paul Avery is a senior product training engineer at Yaskawa America Inc. You can calculate true PF by adding the displacement PF and the total harmonic distortion (THD), as in the following equation: Because VFDs can change their output voltage and output frequency, they give motors the ability to run faster or slower than their rated operating speeds. Let’s take a step back. Should You Be Using Safety or General Switches or Standard Relays? 5100 Valley Industrial Blvd S, Shakopee, MN 55379, How Pulse Width Modulation Works in a VFD, can cause extra motor heating and premature failure. What's the difference between the current measured at the input vs. the output of the Variable Frequency Drive? Limit No.
At higher speeds, the VFD must supply more voltage to overcome the back-EMF so that current can still flow into the motor as current is instrumental in producing torque. motors that approach their maximum operating speeds may run out of torque. It’s not that kind of ac voltage. Hence, the ability to have the motor produce rated torque at higher-than-base speed must decline at a rate of 1/frequency, so that the product of torque and speed, which equals power, is constant. 3: VFDs cure power factor (PF) issues. Variable frequency drives may be industry-standard technology, but they aren’t immune to myths and misconceptions. Stay up to date on our articles for all KEB news, events, and use cases with our products. Variable frequency drives may be industry-standard technology, but they aren’t immune to myths and misconceptions. There is an equilibrium point where the motor reaches the maximum speed for a given torque condition so that the product of torque and speed equals its power capability. The VFD uses its internal capacitor bus to supply any reactive current the motor requires, thereby protecting the ac line from being the source of the reactive current and lowering the displacement PF. when totally enclosed fan cooled (TEFC) motors run at very slow speeds, less cooling air gets to them. A dc voltage value that is too low can cause the drive to trip. Since diodes only conduct when the voltage on the anode side is higher than that on the cathode side, diodes are only ON at the peak of each phase of the positive and negative portions of the sine wave.
The input voltage is at the rated line while the output voltage will be low due to the low speed. 5: A VFD’s input current should be higher than its output current. The Voltage Stabilization function then keeps the output voltage to the motor fixed to the proper Volt/Hz curve independent of any input voltage fluctuations, and consequently DC bus fluctuations in the drive. And it is true that input displacement PF improves after a VFD is installed ahead of an induction motor. Specifically, regarding power supply, differentiate between power input and output and apply both different measurement techniques and evaluation criteria at each. How to choose circuit breaker & contactor for induction motor?
In this case (Figure 73), the use of Voltage Stabilization results in lower current utilization. It is not uncommon to see VFD manufacturers quote PF statistics like "0.98 displacement PF" or "near-unity PF." International Federation of Robotics (IFR), Building high availability into industrial computers, VFD, motor strategies for energy efficiency, How augmented, virtual reality can reduce manufacturing skills gap, How raw data is made ready for applying analytics, Digital twin start-up offers guidance to manufacturers, Tailoring 2D materials to improve electronic and optical devices, Robot sales rise due to increased automation, COVID-19 pandemic, Quantum computing used to discover possible COVID-19 treatments. KEB VFDs incorporate a function called Voltage Stabilization into the parameter settings which allows the VFD to stabilize the output voltage to the motor based on the motor requirements. Voltage drop between drive and motor terminals should not exceed 3%. Thus, any fluctuation in the AC input voltage may cause the output voltage to the motor to fluctuate as well. When the required output voltage to the motor equals the input voltage, the output voltage to the motor will remain at this level. – See other articles from the supplement below. Website Design by CreativeFuse. This is true even at full load conditions. Watch: How Pulse Width Modulation Works in a VFD.
Enabling Voltage Stabilization results in an optimal V/Hz curve even during situations with a high input voltage to the drive. This is because the primary consideration should be power, not current. Visit our contact us page for repairs, technical support and other questions. Basic V/Hz VFD operation establishes a linear Volt and Hz relationship up to the motor ratings.
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