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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.
What causes high current in a motor?
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.
How can we reduce the starting current of an induction motor?
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.
Why does voltage decrease when current increases?
Since the ohmic losses in a transmission line are proportional the square of the current, reducing the current by 50% cuts the power loss by 75%. The current required to carry a given power decrease when you increase the voltage because the power is the product of the current with the voltage (and power factor).
How much is motor inrush current?
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.
How many windings does a motor have?
The most basic 3-phase induction motor has three sets of windings, with each phase connected to a differ- ent set of windings, Figure 16-4. The current in each winding is 120 electrical degrees out of phase with the urrent in the other windings.
Why can’t an induction motor run at synchronous speed?
An induction motor always runs at a speed less than synchronous speed because the rotating magnetic field which is produced in the stator will generate flux in the rotor which will make the rotor to rotate, but due to the lagging of flux current in the rotor with flux current in the stator, the rotor will never reach .
How long is inrush current?
The inrush may be as much as 14 times the steady-state current and may persist for a few milliseconds for smaller lamps up to several seconds for lamps of 500 watts or more.
What causes motor windings to burn?
Thermal deterioration of insulation in one phase of the stator winding, which can result from unequal voltage between phases due to unbalanced loads on the power source, a poor connection at the motor terminal, or high resistance contact; or thermal deterioration in all phases of the stator winding typically due to
How do you check motor windings?
Inspect the Motor Windings With a Multimeter To begin, set the multimeter to read ohms and then test the motor’s wires and terminal. You should test the windings for a “short to ground” in the circuit and open or shorts in the windings.
Why 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.
Why starters are used for starting induction motors?
A starter is needed for a three phase induction motor because at the time of starting, if induction motor is started directly, it will draw a huge amount of current which can cause damage to adjoining equipments.
How can we reduce motor starting torque?
Choices such as full voltage, reduced voltage either by autotransformer or wye-delta, a soft starter, or usage of an adjustable speed drive can all have potential advantages and trade offs. Reduced voltage starting can lower the starting torque and help prevent damage to the load.
What is the starting current of induction motor?
The starting current of the induction motor is about 5 or 6 times the motor full load current. An induction motor of rating 11 KW,22 Amps,440 volts takes a high starting current of about 132 Amps. The current reduces as the motor accelerates towards its base speed or synchronous speed.
How much current does a 1hp motor draw?
Common Horsepower to Amps Conversions
| Horsepower | Amps | Efficiency |
|---|---|---|
| 1 HP | 6.91 A | 90% |
| 1.25 HP | 8.63 A | 90% |
| 1.5 HP | 10.4 A | 90% |
| 1.75 HP | 12.1 A | 90% |
What happens when motor load increases?
As the load is increased, the motor will slow down, and the torque will increase. Current into the motor will also increase. The peak torque occurs at relatively high speed for efficient motors. Certain applications use less efficient induction motors which are designed to have maximum torque occur at stall speed.
Why is inrush current high?
Inrush current is the instantaneous high input current drawn by a power supply or electrical equipment at turn-on. This arises due to the high initial currents required to charge the capacitors and inductors or transformers. The inrush current is also known as the switch–on surge, or the input surge current.
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. Three different solutions to reduce inrush current are shown below: voltage regulators, discrete components, and integrated load switches.
Why does voltage decrease when load increases?
The source of power is an ideal voltage source having zero internal impedance with a series impedance that can have both real (resistive) and imaginary (reactive) components. When you draw more loads you are lowering the load impedance. This increases the voltage drop across the source impedance.
In which method of starting a motor the starting current is maximum?
Autotransformer starter The Autotransformer is used in both types of connections, i.e., either star connected or delta connected. The autotransformer is used to limit the starting current of the induction motor.
What causes a pump motor to overload?
Overloading of pumps Pump overloading occurs in centrifugal pumps when the driving motor draws excess current resulting in excess then normal power consumption. Thus, when the system resistance to the pump drops, more and more liquid is pumped resulting in increased power consumption.
Does current affect motor speed?
The current through the motor times the resistance of the motor creates a small voltage that must be subtracted from the applied voltage. As the load and current increase, this IR drop also increases causing the motor to lose a little speed.
