Home » Blog » Wiki » Page 7
Variable frequency drive is capable to smoothly starting AC motors (ramp from 0 up to 100% of the load) as well as the energy saving will be achieved, accordingly. Also may I confirmed that VFD also acting as AC Motor starting means among (Star/Delta, Soft Starter, Auto Transformer, Electrolyte, series resistance - wound rotor- etc,). The starting factor of VFD drive is usually 1 up to 1.2 with respect to the rated load current while for Direct On line about 5-6.
In this method, when the voltage sag causes the variable frequency drive to reach its undervoltage trip level, the VFD drive will shut off the inverter section and thus remove power from the motor instead of tripping. The motor will coast down during the duration of the sag and, as soon as the voltage recovers, the VFD will start into the still-spinning motor and ramp up to set speed.
When two transformers are in a parallel group, a transformer with a higher tap position will typically have a higher (LV side) no-load voltage than the other one with a lower tap position. These unequal no-load voltages (unequal tap positions) will cause a circulating current to flow through the parallel connected transformers.
For small circuit breakers we can do the test of Magnetic protection behavior by using "Injection Current Apparatus", and suppose the CB's results were good, do you think it's enough? I'm sure not, because by this apparatus we can inject the necessary current with a very low voltage value (5-15V), so, do you think that the arc will be the same if we have the same current but with "400V"?
The aforementioned types of Circuit Breakers are used in LV System and generally based on the same operating principle. MCB and MCCB/ICCB have a bimetal heater for overload which releases the Contact s while for short circuit the trip / electromagnet hammers itself against moving contacts. The arc created by breaking contacts is extinguished in an arc chamber.
The harmonics are created by the loads that the transformer supplies power to. If your loads include a high percentage of electronic loads like IT equipment, electronic ballast lighting, electronic motor controls, etc., there can be a very high amount of harmonics that circulate back to the transformer. The harmonics create an increase in the neutral currents.
Hysteresis would also lead to harmonics, complicating things even further. And, when considering unbalanced three-phase systems and/or the presence of harmonics, the conventional tools for power system analysis might not be applicable.
For a "physical" interpretation, reactive current (power/KVA flow), in my opinion is best looked at from the perspective of a generator connected directly to an infinite bus (in LV generators this is the norm).
PWM is shorted for Pulse Width Modulation, it's a variable frequency drive (VFD) regulate way to change the pulse width according to certain rules to adjust the output volume and waveform.
PAM is shorted for Pulse Amplitude Modulation, it's to change the pulse amplitude according to certain rules pulse amplitude pulse train to adjust the variable frequency drive output volume and waveform.
1: Torque boost: this function is the variable speed drive increases output voltage (mainly in low frequency) to compensate the torque loss due to voltage drop in the stator resistance, thereby improving the motor output torque.
2: Improve the motor insufficient output torque in low speed
"Vector control" can make the motor output torque at low speeds, such as (without speed sensor) 1Hz (for 4-pole motor, the speed is about 30r/min), same as the torque output at 50Hz power supply (maximum is approx 150% of rated torque).
Generally, the motor torque is decreased with frequency decreases (speed reduction). By using vector control frequency inverter, to improve output torque during motor running in low speed, and even output sufficient torque at motor low speed zones.
r/min: motor rotation speed unit, the number of revolutions per minute, also can be expressed in rpm.
For example: 2-pole motor 50Hz 3000 r/min, 4-pole motor 50Hz 1500 r/min
Conclusion: The motor rotation speed is proportional to the frequency
Gozuk Service Gozuk Blog: all about electric motor control & drives industries development in energy saving applications.


Like pumps, fans consume significant electrical energy while serving several applications. In many plants, the VFDs (variable ... energy consumedA frequency inverter controls AC motor speed. The frequency inverter converts the fixed supply frequency (60 Hz) to a ... Motor starter (also known as soft starter, motor soft starter) is a electronic device integrates soft start, soft stop, ... Soft starter allows the output voltage decreases gradually to achieve soft stop, in order to protect the equipment. Such as the ... Soft Starter reduces electric motor starting current to 2-4 times during motor start up, reduces the impact to power grid during ...

In Discussion