35 Acoustic Emission Testing of Energy Field Objects
409
At that the temperature decreasing period duration was about 4 h, constant temperature period was about 8 h and duration of temperature increasing was 3 h. This graph
demonstrates that temperature changing could be used as load in addition to static
load. In particular, the graphs show a correlation between the slope ratio of the
dependence and damage level of the columns.
Based on the obtained results, monitoring possibility was confirmed.
35.6 AE Testing of Power Transformer Insulation
Deterioration of power transformers insulation technical state is a serious problem
reducing lifetime of transformers. In places where insulation is weakened or has
defects, partial discharges (PD) occur, which lead to insulation destruction with
subsequent breakdown of transformer [3]. Therefore, it is important to detect
transformer insulation defects as well as their position.
2 power transformers (110 kV) with different lifetime 10 (first transformer) and
25 years (second transformer) were tested. According to the preliminary information,
based on periodic oil sample inspections from the tank of transformers, the second
transformer had insulation defects. The first transformer had a good condition.
18 AE sensors GT200 with resonant frequency of 180 kHz were used for testing.
Sensors were mounted on the tank of transformer around the perimeter in 2 levels.
The A-Line 32D DDM system with digital data transfer channel and high noise
immunity was used in these experiments to avoid electrical noises. The duration of
data acquisition was 2 h for each transformer.
The main problem during power transformer testing is high level of acoustic
noises from its operation and vibration due to cooling systems operation. So, as an
example Fig. 35.8 demonstrates dependences of AE activity and average amplitudes
for 2 transformers for 10 min period.
Second (older) transformer has higher values of parameters, but first transformer
also has high enough values. It was found that the AE data of second transformer
has one feature in comparison with first transformer. This feature is hits witch were
registered with certain periodicity. The most common periodicity value is 10,000
mks. At 50 Hz of power voltage frequency, the value of 10,000 mks corresponds to
one action of PD source per half of a power voltage period (Fig. 35.9).
Figure 35.9 shows dependence of amplitudes for 3 sensors located near each
other. Also, it is important to note, that these periodic signals are characterized by
constant of waveforms within each sensors. This fact may means that they are from
one source. But for most channels in addition to these periodic signals, there are a lot
of noise signals. These noise signals can break periodicity and results of the location
(Fig. 35.10a, b).
So, filtration was carried out based on AE parameters of periodic signals. Filtration consists of preliminary amplitude filtration and filtration based on parameter
Counts/Duration. Filtration results are presented in Fig. 35.10c, d.
The winding insulation defect was found based on result of location.
409
At that the temperature decreasing period duration was about 4 h, constant temperature period was about 8 h and duration of temperature increasing was 3 h. This graph
demonstrates that temperature changing could be used as load in addition to static
load. In particular, the graphs show a correlation between the slope ratio of the
dependence and damage level of the columns.
Based on the obtained results, monitoring possibility was confirmed.
35.6 AE Testing of Power Transformer Insulation
Deterioration of power transformers insulation technical state is a serious problem
reducing lifetime of transformers. In places where insulation is weakened or has
defects, partial discharges (PD) occur, which lead to insulation destruction with
subsequent breakdown of transformer [3]. Therefore, it is important to detect
transformer insulation defects as well as their position.
2 power transformers (110 kV) with different lifetime 10 (first transformer) and
25 years (second transformer) were tested. According to the preliminary information,
based on periodic oil sample inspections from the tank of transformers, the second
transformer had insulation defects. The first transformer had a good condition.
18 AE sensors GT200 with resonant frequency of 180 kHz were used for testing.
Sensors were mounted on the tank of transformer around the perimeter in 2 levels.
The A-Line 32D DDM system with digital data transfer channel and high noise
immunity was used in these experiments to avoid electrical noises. The duration of
data acquisition was 2 h for each transformer.
The main problem during power transformer testing is high level of acoustic
noises from its operation and vibration due to cooling systems operation. So, as an
example Fig. 35.8 demonstrates dependences of AE activity and average amplitudes
for 2 transformers for 10 min period.
Second (older) transformer has higher values of parameters, but first transformer
also has high enough values. It was found that the AE data of second transformer
has one feature in comparison with first transformer. This feature is hits witch were
registered with certain periodicity. The most common periodicity value is 10,000
mks. At 50 Hz of power voltage frequency, the value of 10,000 mks corresponds to
one action of PD source per half of a power voltage period (Fig. 35.9).
Figure 35.9 shows dependence of amplitudes for 3 sensors located near each
other. Also, it is important to note, that these periodic signals are characterized by
constant of waveforms within each sensors. This fact may means that they are from
one source. But for most channels in addition to these periodic signals, there are a lot
of noise signals. These noise signals can break periodicity and results of the location
(Fig. 35.10a, b).
So, filtration was carried out based on AE parameters of periodic signals. Filtration consists of preliminary amplitude filtration and filtration based on parameter
Counts/Duration. Filtration results are presented in Fig. 35.10c, d.
The winding insulation defect was found based on result of location.