GE 869 Instruction Manual page 419

CHAPTER 4: SETPOINTS
869 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
ESA Application for Mechanical [Foundation Looseness, Eccentricity and Shaft
Misalignment (FEM)] Fault Detection
Although mechanical faults like Foundation looseness, Eccentricity and Misalignment
(FEM) are different fault conditions in a rotating machine, they can be identified at the
same set of stator current frequencies related to eccentricity damage. Air-gap eccentricity
represents a condition when air gap distance between the rotor and the stator is not
uniform. Two types of abnormal air-gap eccentricity exist: static and dynamic. In the case
of static eccentricity the position of a minimal radial air gap is fixed, while in the case of
dynamic eccentricity the position of the minimal air gap follows the turning of the rotor.
Normal (concentric) state, static and dynamic eccentricities are illustrated in the following
figure. As the rotor bars recede or approach the stator magnetic fields, they cause a
change to the current in the stator. In the case of static eccentricity, sideband components
appear at frequencies.
Figure 4-120: Eccentricity details
The Mechanical fault detection application uses ESA computation on the current signal to
detect misalignment, eccentricity and foundation-looseness failure cases of the machine.
The operating condition can be defined as:
Computing the ESA frequencies related to the mechanical defects (shaft misalignment,
load unbalance, loose foundation, dynamic/static eccentricity). The ESA frequencies are
calculated using the following equation.
where k=1, 2, 3, 4....
Identify the peak magnitudes (or energy in dB at the stator current frequencies) and
calculate the maximum change in dB at baseline (healthy mode) peak magnitudes (or
energy at the corresponding stator current frequencies). This is performed w.r.t. the current
load bin of the operation as given by the following Change in Energy dB and Change in
Peak Magnitude dB equations:
Change in Energy dB = Energy dB (Latest) – Energy dB (Baseline)
Change in Peak Magnitude dB = Peak magnitude dB (Latest) – Peak magnitude dB (Baseline)Eq. 33
ESA Application for Stator Fault Detection
Stator faults cause damage to insulation, laminations, frames and winding due to various
electro-mechanical and thermal stresses.
Reason/Effect:
• Failure of insulation leading to turn-turn, phase-phase, coil-coil, phase to ground etc.
faults
• Rotor striking the stator due to misalignment or shaft deflection, bearing failure
causing stator laminations to puncture the coil insulation leading to coil to ground
fault
k
2 1 (
f = f ±
1 [
misalignme nt
P
MONITORING
− s
)
]
Eq. 31
Eq. 32
4–287