What is negative phase current?

Answer 1

Negative Phase Sequence is Phenomena generally found in motors,

the formula for positive phase sequence is : Ip= Ir + a * Iy + a^2*Ib

the formula for negative phase sequence is : In= Ir + a ^2* Iy + a*Ib

As the name suggest the sequence of current or the mmf is in reverse order, a reverse order current in stator will produce a reverse order mmf, now this reverse order mmf is rotating in direction opposite to the rotor of the motor, thus the mmf cut is very high and so current induced in stator is considerably high; as for normal mmf it is in direction of rotor so mmf cut is very small thus current induced is very small.

this high current in your rotor leads to overheating of your motor and finally burning of your windings.

Comment

Negative phase sequence is not 'generally found in motors'. But one of the effects of negative phase sequence would be to cause a three-phase motor to reverse direction.

Answer 2

'Phase sequence' is the sequence, or order, in which the three line potentials of a three-phase sequence reach their maximum values relative to each other. By general agreement, 'normal' or 'positive' phase sequence occurs in the same order in which lines are normally identified, i.e. red-yellow-blue, brown-black-grey, A-B-C, R-S-T, etc. (according to national standards). 'Negative' phase sequence occurs when these potentials occur in the opposite order, i.e. red-blue-yellow, brown-grey-black, A-C-B, R-T-S, etc. The effect of applying a negative phase sequence to a three-phase motor is to cause it to reverse direction.

Answer 3

The order, or sequence, in which the potential of each line conductor in a three-phase system reaches its maximum value, is called the phase sequence of that system. By general agreement, the sequence A-B-C (or R-S-T or 1-2-3, etc.) is considered to be the normal, or 'positive', phase sequence, whereas the sequence A-C-B (or R-T-S or 1-3-2, etc.) is considered to be the 'negative' phase sequence.

If a three-phase motor has been connected in such a way that a positive phase sequence applies, then it will rotate in a particular direction. If the motor is then disconnected, and inadvertently reconnected with two line conductors interchanged, then the sequence will then be a negative phase sequence, and the machine will rotate in the opposite direction.