GE 269Plus

GE Power Management 269Plus Motor Management Relay A- 1
A 269 PLUS UNBALANCE EXAMPLE DESCRIPTION
A
APPENDIX AA 269 PLUS UNBALANCE EXAMPLE A.1 DESCRIPTION
The 269Plus unbalance algorithm makes the following two assumptions:
1. The three phase supply is a true three phase supply.
2. There is no zero-sequence current flowing (no ground fault).
For simplicity, the three phases may be drawn in the shape of a triangle as shown in the example below (the
three vectors must cancel each other). From this diagram, it is obvious that no phasor magnitude could change
without corresponding magnitudes and/or phase angles changing. Phase angles can always be derived from
magnitudes using simple trigonometry.
A.2 EXAMPLE
Consider the following example for phase magnitudes 3.9, 5, and 5 s.
Figure A–1: UNBALANCE PHASE DIAGRAM
From the figure above, we have a = 3.9 ∠0°, b = 5 ∠–112.95°, and c = 5 ∠112.95°. Symmetrical component
analysis of unbalance (the ratio of negative-sequence current to positive sequence current) yields:
Figure A–2: UNBALANCE SYMMETRICAL COMPONENT ANALYSIS
112.95°
67.05°
–112.95°
67.05°
a = 3.9
c=5
22.95°22.95°
b=5