GE 869 Instruction Manual page 418

MONITORING
4–286
ESA application for Rolling Element Bearing Fault Detection
The faults occurring in motor bearings are generally due to the excessive load, rise of
temperature inside the bearing, use of bad lubricant and so on. The bearing consists
mainly of the outer race and inner race ways, the balls and cage; this assures equal
distance between the balls. The different faults that may occur in a bearing can be
indicated as a single parameter based on any affected component as shown in the next
figure.
• Outer raceway defect
• Inner raceway defect
• Ball defect
Figure 4-119: Ball bearing details
The Bearing Flt element uses FFT computation on the current signal to detect bearing
failure on an electrical machine. The operating condition can be defined as: Computing
vibration frequency related to bearing damage using this equation.
f
vib
Compute stator current frequency related to bearing damage using the following
equation.
F_bearing = F_supply ± k * F_vibration
k is any integer: 1,2,3,...
Identifying peak magnitudes or energy in dB at the stator current frequencies and
calculating change in dB magnitude for baseline (healthy mode) peak magnitudes or
energy at the corresponding stator current frequencies in dB for each load bin is given by
the equations Change in Energy dB and Change in Peak Magnitude dB.
Change in Energy dB = Energy dB (Latest) – Energy dB (Baseline)
Change in Peak Magnitude dB = Peak magnitude dB (Latest) – Peak magnitude dB (Baseline)Eq. 30
ω
N D
b r − b
1 ( )
D
2 60
c
ω
N D
= b r + b
1 ( )
D
2 60
c
ω
D D
2
−
c r b
1 ( ) (ball
D
D 2
60
b
c
869 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 4: SETPOINTS
(inner race)
(outer race)
damage)
Eq. 27
Eq. 28
Eq. 29