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What are the causes for unbalance of currents of a 3 phase a c motor?
Wiki User
∙ 11y ago
unbalance voltage supply
resistance between phase unbalance
joints of coil loose
winding short with body
Wiki User
∙ 11y ago
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How do you use a one phase motor in place of a three phase motor?
To use a single/one phase motor instead of a three phase motor is possible if you have a three phase power supply as you will only need to tap one of the three phases together with neutral and an earthwire, however to use a three phase motor instead of a single phase will require the provision of three phase power supply.
What size capacitor is needed to start a 1 hp 14 amp 110V motor?
A single phase motor does not actually require a capacitor. This device is only needed when a split phase motor is utilised. A split phase motor needs a device to regulate the power factor associated with the split phase.
Is a three phase three wire system safe?
Three-wire transmission is used on balanced three-phase systems when the current is known to be equal in all three phases, for example when supplying a three-phase motor. A fourth neutral wire is used when the system is liable to have unequal currents or when multiple single-phase supplies are connected to it.
Which phase is the reverse phase?
Connecting Phase A, B and C to the motor leads will make a 3 phase motor run in one direction while interchanging any two will make the motor rotate in the opposite direction.
Why do ionic crystals conduct electric currents in the liquid phase or when dissolved in the water but do not conduct electric currents in the solid phase?
because when the ions can move around freely, they can conduct electricity better
What is the maximum current unbalance of a 3 phase motor?
No standard prescribes permitted unbalance in current for induction motors. IEC 892/2002 however, specifies permitted unbalance in voltage as 1% at the motor terminal. It is deduced that 1% unbalance in voltage will result in 6% to 9% unbalance in current. This is, therefore, grid caused activity. However, there are load related activities, such as parallel connected single phase loads or shunt capacitors that may also influence unbalance in current across the main contactor. In large motors, sometimes, unbalance in current can be seen if the air-gap eccentricity is seen. In such cases the PF in 3 phases will be unbalanced.
Core balance ct?
CBCT used to protect the motor winding from unbalance load it is install on the cable ,in normal balance conditions the sum of the three phase current is zero so secondary current of the ct also zero .when ever unbalance occurs then this unbalance current will flows through the ct then relay sense and trip motor
Why three phase induction motor has uniform torque?
The 3-phase currents in the 3 coils of an induction motor will produce a steady rotating magnetic field.
Disadvantages of 3 phase induction motor?
One of the disadvantages of the 3 phase induction motor is that it requires a three wire supply. The other disadvantage is that the 3 phase induction motors have poor starting torque and high have in the rush currents.
What is an acceptable difference in resistance between phases on a 3 phase motor?
The currents between legs of a three phase circuit should be within about 10% of each other.
Should all three phases of 3 phase motor are to be equal on no-load and load conditions?
Ideally all three phase currents will be equal. There may exist some voltage imbalance from the power source, which will result in unequal currents.
How does mpcb work?
The basic working principle is similar to all other circuit breakers.• Thermal protection is used to guard the electric motor against overload. It is based on an expanding and contracting contact that disconnects the motor if excessive current is detected. It is very important to know that thermal protection has a delayed response, to allow the high inrush currents when a motor starts. However, if the motor is unable to start for some reason, thermal protection will trip in response to the extended inrush current.• Magnetic protection is used when there is a short circuit, line fault, or other high current electric fault. Unlike thermal protection, magnetic protection is instantaneous, to immediately disconnect the dangerous fault currents.• The main difference between the MPCB and other circuit breakers is that the MPCB can provide protection against phase unbalance and phase loss. Three-phase circuit motors require three live conductors with balanced voltages in order to operate effectively. An unbalance of more than 2% will be detrimental to the motor's service life. If one of the phase voltages is suddenly lost, the effect is even more damaging because the motor will keep on running with only two phases. The motor protection circuit breaker is capable of detecting these conditions by measuring the differences among phase voltages, and disconnects the motor immediately when they occur. It is important to note that phase current unbalance is normal in three-phase systems that power separate single-phase loads, but is unacceptable when the three-phase circuit powers an electric motor.• MPCBs are also equipped with a manual interruption mechanism, allowing disconnection of electric motors for replacement or maintenance.Motor protection circuit breakers are available in a wide variety of current ratings, and one of their best features is that many models allow the current rating to be adjusted. This means that the same MCPB can be configured to protect motors of different capacities.
Why do you connect a capacitor with an Ac motor?
The capacitor is used to create a second phase from the single phase power source and it is the interaction between these two phases that causes the motor to turn.
Why neutral not conect in 3phase motor?
A 3 phase motor does not require a neutral conductor because the impedances that make up the stator coils are of equal magnitude and it is what is known as a balanced 3 phase load. If the loads of a wye connected 3 phase system were unbalanced, i.e. the load currents in each of the 3 phases are different, then the unbalanced currents would require a return path to the service transformer via a neutral conductor. The neutral conductor is the transformer centre tap and is usually earthed locally. ANOTHER ANSWER The impedance of each phase winding of a three phase motor is identical (we call it a 'balanced load'). For a star (wye) connected motor, the phasor sum of three identical phase currents is zero, so no current will flow through a neutral, so a neutral isn't required. For a delta-connected motor, there is no provision for a neutral.
Is single phase connection enough for 18KW motor?
Typically, an 18KW motor would be too large to be single phase because then the windings' conductors will be too large inorder to carry such high currents. I,myself,don't think such a motor exist since a cheaper 3phase motor could be used instead.
What happens if 3 phase supply is given to stator and rotor both in a induction motor?
its impossible to give suppy to rotor of an induction motor,because of it a closed path for circulating currents.
How does an auxiliary winding provide a starting torque for single-phase induction motors?
Single- and three-phase motors work on the sameprinciple. The field windings create a rotating field which cuts the rotor bars of the rotor, inducing voltages into them, and the field produced by the resulting currents react with the rotating field causing the rotor to spin. If you like, the rotating field 'drags' the rotor around with it.In the case of a three-phase motor, the three out-of-phase phase currents create a naturally-rotating field. However, in the case of a single-phase motor, we must simulate this. This is done by having two, separate, field windings. One is fed directly from the supply, and the other is also fed from the supply via a capacitor. This results in two field currents which are displaced from each other by around 90 electrical degrees, when then create the rotating field necessary for the motor to start and run. You could say that a single-phase motor is equivalent to a 'two-phase' motor. The field winding supplied via a capacitor is known as the 'start winding' or the 'auxiliary winding'.
