Answer / sunil kumar sinha

In a three phase AC circuit, current is consetuted of
positive sequence, negative sequence and zero sequence
current.

the positive phase sequence current flows as perr the load
connected to the circuit. The negative phase sequence
current will flow due to diffence of three phase volages of
the system.If no difference of R Y B voltage is present,
the negative sequence current will not flow. The negative
phase sequence current present in the circuit will be of
same frequency but the phase sequence will be negative to
the system sequence. Negative sequence current will cause
excessive heating of generator rotor as the rotor will
experience double the system frequency so far the negative
sequence current is concerned. The zero sequence current is
present only in case of earth fault otherwise it is absent.

Answer / adil yousuf

Ans ; The negative phase sequence
current will flow due to diffence of three phase volages of
the system.If no difference of R Y B voltage is present,
the negative sequence current will not flow.
In rotating machines an unbalance voltage or current in one
phase winding due to elctrical faults or uneven load
further exacerbates the problem. The magnetic coupling
between the winding becomes uneven.
when subject to unbalance conditions, negative phase
sequence currents produce a counter rotating megnatic field
withrespect to the main field.
The resultant field rotates at double frequency and causes
underirable eddy-currents to flow in various structure such
as the machine rotor body , excitaation winding, stator end
winding and stator iron etc.

Answer / karma gyeltshen

An Negative Phase Sequence Current is usually caused by asymmetrical loading of the three phases, but may also be the an open-circuit phase (single-phasing).
An asymmetrical load on a generator produces a magnetic filed, which rotates in the opposite direction to the positive sequence field. The negative phase sequence flux induces currents in the rotor and these results in additional rotor losses and increased rotor temperature. The latter can represent a hazard for the rotor and this is the reason for applying NPS protection.

Answer / pradipto dhar

negative phase sequence is equally in magnitude, placed
apart 120 degree, rotate in oppsite direction to the
direction of phase sequence (RYB).

Answer / ravindra

as we know 3 phase fault is a balanced fault means after
having 3 phase fault on power sys , system remain balanced
but for the analysis of unbalanced fault like L-L, L-G etc
system not remain balanced(means phase difference between
currents of 3 phase not followes 120 degree). so for the
analysis of unbalnced fault another mathd is used . in ths
mthd we assume that we can write the unbalanced current or
voltage in three components 1 +sequence component 2. -ve
sequence component 3. 0 sequence .sum of all these 3
component =unbalanced fault. -ve srquence suggest for
opposite rotation or phase sequence

Answer / mukhesh

nag phase seq ismagnitude is same phase displacement is 120
electrical the phase seq of these components opposite of
original phase seq

Answer / puneet kumar

negative phase sequence is equally in magnitude, placed
apart 120 degree, rotate in oppsite direction to the
direction of phase sequence (RYB).
It is happen generally when load is
incresed, speed is reduce for some time then there is
happening of opposition of phase sequence due to increse of
load. (relative...)

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