Diagnostics Of Asynchronous Motors Based On Spectra Analysis Of ...

( K
a) b)
Fig. 3 Three-phase (a) and phase A (b) spectra of motor
with bad mounting.
So, if the following rule is correct:
npτ
(A)
∧ ( P
avg А2
= K
= P
npτ
(B)
avg B2
= K
= P
npτ
(C)
avg C 2
= 1)
∧ ( K
= 0,
33)
∧
t hh
> 0,
02)
∧
∧ ( ε pA = ε pB = ε pС ) ∧ ( K harm(6-
45) > 0,
75)
= 1,
that examined motor is badly mounted.
When rotor is dynamic or static misbalanced,
there is harmonic in three-phase power spectra,
which relates to rotation frequency. Thus, when noload,
there is harmonic with frequency 100p in threephase
power spectra (here p – number of ports). So,
if there is significant component with rotation
frequency in three-phase power spectra, and
weighted average quotients are not equivalent by
phases, that motor has asymmetry. And if there is
significant value of harmonic amplitudes of 156–
195 Hz, that asymmetry is caused by unbalance.
a) b)
Fig. 4 Three-phase (a) and phase A (b) power spectra of
motor with rotor unbalance.
So, for detecting rotor unbalance, the following
rule should be true:
( ε > 0,
05)
∧ ( ε ≠ ε ≠ ε
p2
∧ ( P
avg А2
≠ P
avg B2
pA
≠ P
pB
avg C 2
) ∧ ( K
) ∧ ( K
t hh
harm(156-195)
> 0,
02)
> 0,
1)
∧ ( Kharm(196-
205) > 0,
45)
= 1.
In case of stator windings asymmetry and stator
windings short-circuits, there is significant harmonics
of double voltage frequency and little less then 4 f v
frequency (fig. 5 a, fig. 6, a). When damages are
worse, this harmonics grow. Low-frequency
harmonics (5–45 Hz) also grow, however its
frequency is constant. Main percent of high
harmonics for phases is in range of 96–105 Hz. Also
significant percent is from range of 196–205 Hz (fig.
5, b; fig. 6, b). When both kinds of damages are
caused, values of formulated indicators are almost
equal. Thus, if there is main harmonic with double
voltage frequency and significant harmonic of little
less then 4 f v frequency, and significant degradation
of formulated indicators, that there is windings
asymmetry or windings short-circuits.
a) b)
Fig. 5 Three-phase (a) and phase A (b) spectra of motor
with asymmetry of phase A.
pС
(
437
( K
( P
(( K
a) b)
Fig. 6 Three-phase (a) and phase A (b) spectra of motor
with stator winding short circuits.
So, if the following rule is correct:
> 0,
02)
∧ ( K ≠ K ≠ K
ε p2
npτ
(A) npτ
(B) npτ
(C)
∧ ( ε < 0,
98)
∧ ( ε
p
lq v
avg А2
> 0,
05)
∧ ( K
harm(196
≠ P
avg B2
- 205)
> K
pA
rec t
≠ P
≠ ε
< 0,
97)
∧
avg C 2
pB
harm(156-195)
≠ ε
) ∧ (( K
) ∨
pС
) ∧
harm(96-105)
)
> 0,
99)
∧
( Kharm(196-
205) ≈ Kharm(156-195)
)) = 1,
then there is either windings asymmetry or windings
short-circuits.
When rotor bar breaks, there is only low
frequency component in three-phase power spectra
(fig. 7, a). It grows when progresses defect.
Remaining indicators change negligibly and there is
no asymmetry of examined parameters, because
changing of rotor parameters appears indirect in
changing of stator parameters. Additional indicator
for identifying this defect is subharmonics of voltage
frequency in current spectra [3]. Thus, if there is low
frequency component of three-phase power signal,
also subharmonics of main voltage frequency
harmonic in current spectra, non-equal weighted
average quotients and almost optimal ε p , K rec t ,
then motor has rotor bar breaks.
a) b)
Fig. 7 Three-phase (a) and phase A (b) spectra of motor
with rotor winding bar break.
For detecting this defect, the following rule must
be correct:
( K ≠ K ≠ K ) ∧ ( ε ≈ ε ≈ ε )
npτ
(A)
∧ ( K
t hh
npτ
(B)
> 0,
02 ) ∧ ( P
npτ
(C)
avg А2
≠ P
pA
avg B2
≠ P
pB
avg C 2
) ∧
∧ ( Kharm(6
- 45) > 0,
8 ) = 1.
Thus, observing for variation of formulated
indicators, it is possible to make conclusion about
appearing of some kinds of defects or non-qualities
of asynchronous electric drive systems. Analyzing
values of some indicators it is possible to make
conclusion about current work mode allowability.
Also it is possible to prognosis remaining resource
analyzing non equal phase heating basis on "eight
degree" rule. When some defects are present for one
motor at the same time, percent of harmonics from
frequency ranges for each defect will be less than if it
pС