LS Industrial Systems Metasol Series - Definition of Unbalance Factor 1; Voltage; Current Unbalance for P, S Type

47
D
Voltage / Current Unbalance for P, S Type
U
=
3
avg
U + +
R
U
S
U
T
1. Definition of Unbalance Factor 1
2. Definition of Unbalance Factor 2
1) Umax is the largest value among 3 phase system (R, S, T)
2) Uavg is average of 3 phase system( (R + S + T) / 3 )
3) Unbalance percentage is defined as (Umax - Uavg) / Uavg.
4) It can be used for simple and practical purposes, but can not imply meanings behind phase.
T phase
Positive Phase Negative Phase Zero Phase
T phase
=++
T phase
T phase
R phase
Uavg
RS
T
Umax
R phase
R phase
R phase
S phase
S phase
S phase
S phase
Digital Trip Relay
5. Measurement Function
1) Positive-phase-sequence component means a fundamental phase rotation of power system.
2) Negative-phase-sequence component means a phase rotation inversely to power system.
3) Zero-phase-sequence component means in-phase on R/S/T phases regardless of phase rotation of power system.
4) 3 phase system in power system can be displayed as positive-phase + negative-phase + zero-phase-
sequence component.
5) After interpreting 3 phase as positive-phase, negative-phase, and zero-phase sequence component, and
define negative/positive phase as unbalance.
6) Even though the concept is based on definition, there is unstable part in figure due to complexity of mathematic.
Apply on P,S Type