Table of Contents
This high current in the rotor will create its own magnetic field which opposes the main stator magnetic field, this weakens the stator magnetic field so the back EMF in the stator will drop and the supply voltage will be much higher than the stator back EMF and so the supply current increases to a high value.
Why motor current is high?
Probable causes of high current with load include mechanical overload, excessively high magnetic flux densities and, less frequently, an open rotor. An error in winding data that results in lower-than-design-level magnetic flux also can cause high current with load.
Why is start up current higher than running current?
As the motor starts, the current that is drawn initially is higher than the designated full load of the motor at running speed. Both the EMF and magnetic fields increase, which makes the mechanical load accelerate. The current at motor starting can be anywhere from 5-8 times the motor’s full load.
How can the starting current of a motor be reduced?
Some of the techniques used to reduce the starting current of a squirrel induction motor: Soft starting (voltage control) Variable Frequency Drives (Voltage and frequency control) Star/Delta Starting. Stator impedance and/or resistance starting. Autotransformer Starting.
What are the causes of high current?
Electrical overload or over-current is caused by an excessive current flow within the motor windings, exceeding the design current which the motor is able to carry efficiently and safely. This can be caused by a low supply voltage, resulting in the motor drawing in more current in an attempt to maintain its torque.
Which AC motor have high starting torque?
DC Series motors have high starting torque but induction motors have wide range of speed control. So, If DC motor is used, then DC drives you can use, although it will be expensive and DC motors are tough to maintain than ac motors due to commutation Problem.
How can I reduce my inrush current?
Inrush current can be reduced by increasing the voltage rise time on the load capacitance and slowing down the rate at which the capacitors charge.
How much is motor inrush current?
The inrush current (Amps) is high, at 1,500 Amps. This is about 4 times the idle current of the motor, and almost 50% more than the average current while chipping. Inrush current lasts for approximately 2.5 minutes.
How can we avoid inrush current in motor?
One is to use a soft starter — a device that gradually increases supply voltage to the motor terminals during startup, thus lowering inrush current and controlling startup torque. Similarly, a variable frequency drive reduces inrush current by controlling the voltage supplied to the motor.
How can we reduce motor starting torque?
There are three ways to improve the starting torque of Single phase induction Motor Internal Rotor Resistance. The across the line starting torque at low speed can be increased by increasing the rotor resistance. External Rotor Resistance. Variable Voltage/Frequency.
How do you reduce starting torque?
There is a voltage drop in the resistor, which reduces the voltage across the motor terminals and produces less starting torque. As the motor accelerates, the current through the resistor decreases to reduce the voltage drop and to increase the voltage across the motor terminals.
How does VFD reduce starting current?
VFDs deliver much higher frequency source power during startup to reduce current due to the increased inductive impedance. This can be advantageous if control is desired after full speed is reached. VFDs are more efficient and produce less heat, while being able to start motors under considerable loads.
What happens if the amps are too high?
If an incorrect voltage is used — say a higher voltage than the device is rated to accept — then yes, too many amps may be drawn and the device can be damaged. This is why it’s critical to use the correct voltage.
What happens if voltage is too high?
Voltage that is too high can cause premature failure of electrical and electronic components (e.g. circuit boards) due to overheating. The damage caused by overheating is cumulative and irreversible. Motors can, on the other hand, often benefit from voltages that tend to be a little bit high.
Does high voltage mean high current?
The higher the voltage, the lower the current. The lower the current, the lower the resistance losses in the conductors. The lower current that accompanies high voltage transmission reduces resistance in the conductors as electricity flows along the cables.
What are the high starting torque IM?
In order to increase the starting torque, extra resistance should be added to the rotor circuit at start and cut out gradually as motor speeds up. The maximum torque is directly proportional to square of rotor induced emf at the standstill. The maximum torque is inversely proportional to rotor reactance.
Does induction motor have high starting torque?
Slip ring induction motor has high starting torque. Because slip ring is connected through the resistance. When the supply is on the resistance is increases the phase difference is decrease due to this starting torque is increases.
Which applications require high starting torque?
Which of the following application requires high starting torque? Lathe machine. Centrifugal pump. Locomotive. Air blower.
Why is inrush current harmful?
Inrush current increases the risk of ground faults and installation circuit breaker failure, which can cause entire electrical installations to fail. Large inrush currents can also lead to voltage dips, which in turn may also result in equipment failure.
How long is inrush current?
These currents can be as high as 20 times the steady state currents. Even though it only lasts for about 10ms it takes between 30 and 40 cycles for the current to stabilize to the normal operating value.
Is inrush current bad?
The ratio of inrush current to normal full-load current can range from 5 to 100 times greater. This current surge can cause component damage and/or failure within the equipment itself, blown fuses, tripped circuit breakers, and may severely limit the number of devices connected to a common power source.
How is inrush calculated?
What is inrush current: Inrush current is nothing but a maximum flow of current at that time of starting electrical equipment. The current flows a few seconds only. I ( peak ) = 1.414 x 440 / 0.45. Hence inrush current is equal to the 6 times of the full load current.
How is motor inrush current calculated?
The range is given in thousands of Volt-Amps, or kilowatts. Multiply each number in the range by 1,000. Divide each result by the motor voltage found on the nameplate. The resulting range is the inrush current range.
How long does motor starting current last?
Typically, during the initial half cycle, the inrush current is often higher than 20 times the normal full load current. After the first half-cycle the motor begins to rotate and the starting current subsides to 4 to 8 times the normal current for several seconds.
