Metodos de Diagnostico de Deformaciones Sfra

2010 Doble Engineering Company -77th Annual International Doble Client Conference

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Model of core

(Wood that pasted

aluminum foil to

surface)

Enclosure (Steel)

Stand (Steel)

Windings

S(LV)

P(HV)

Pg

Pf

axis

FL

Stabilising

winding

DIAGNOSTIC METHOD OF DEFORMATION OF WINDING USING SFRA

Hiromichi Okumo

Tokyo Electric Power Company (Japan)

ABSTRACT

Tokyo Electric Power Company (TEPCO) carried out a study on the diagnostic method of deformed

windings in a transformer using SFRA. Since the SFRA trace changes according to the part of the

winding that is deformed and the amount of deformation, the internal state of transformers can be

determined by comparing to the SFRA trace that was measured in normal. However, there are various

types of problems that can occur in winding and core; therefore it is important to obtain basic data that

characterizes the different types of deformation.

TEPCO studied the effects on SFRA traces for changes made in the transformer windings under

controlled laboratory conditions. The windings of a 66kV, 20MVA distribution transformer were used

for the measurements under axial, radial and buckling displacement. This paper reports TEPCOs study on the measurements and the analysis of SFRA characteristic in these deformed winding states.

MEASURING METHOD

The test specimen consists of a single phase transformer with high and low windings, a simulated core, a

rolling base and a removable metal enclosure (Figure 1).

MEASUREMENTS Winding Deformation

Figure 2

P

S

SalientMax 3mm(13mm)

ReentrantMax 14mm(1114mm)

20mm,40mm,80mm

PgPS Pf(1) Axial displacement of winding - P, Pg and Pf windings shifted to upper

side - By the insertion of spacers to

the bottom

Winding Model (Single Phase)

Figure 1

(2) Radial displacement of winding - S winding shifted to radial direction

PS

8mm

15mm

(3) Buckling of inside winding - By making blows from the outside - Insulation cylinder between winding P and S was

removed (both before and after deformation of buckling)


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2

(1) Axial Displacement

To simulate the axial displacement 20, 40 and 80 mm spacers were fitted under the high voltage winding

to raise the winding in relation to the low voltage winding (Figure 2). As the axial displacement

increased the amplitude of the SFRA traces decreased in the 50-70 kHz and increased in the 600-700 kHz

ranges. Displacement of 20mm can be within normal operating limits and the SFRA response at the

20mm displacement in the high voltage windings is significant (Figure 3).

(2) Radial Displacement

Measurements at low voltage windings, for a radial displacement of 15mm, had a significant shift in the

traces to lower frequencies (Figure 4). Responses shifted left slightly at the frequencies higher than the

first resonance which is at 56 kHz.

(3) Buckling

Buckling damage was also provided in the low voltage winding of the specimen (Figure 2). The outer

conductors of the low voltage winding were moved into the center by about 11-14 mm between two sets

of radial supports by impacts with a hammer. The movement of the conductors outward in this winding

did not exceed 3 mm. Responses from high voltage winding tests for deformation in the secondary

windings had a tendency to shift the traces to a lower frequency. The shift was very evident greater than

500 kHz (Figure 5).

SFRA Traces by Buckling of Winding

Figure 5

SFRA Traces by Axial Displacement of Winding

Figure 3

-70

-60

-50

-40

-30

-20

-10

1E+4 1E+5 1E+6Frequency [Hz]

Magnitude [dB]

0mm20mm40mm80mm

Primary (HV) winding

20mm,40mm,80mm

PgPS Pf

From large one sequentially

0mm 20mm 40mm 80mm

80mm 40mm 20mm 0mm

SFRA Traces by Radial Displacement of Winding

Figure 4

-70

-60

-50

-40

-30

-20

-10

1E+4 1E+5 1E+6

Frequency [Hz]

Magnitude [dB]

Normal

Buckling

Primary (HV) winding P

S

SalientMax 3mm(13mm)

ReentrantMax 14mm(1114mm)

Buckling Normal

Shift to low frequency side

-70

-60

-50

-40

-30

-20

1E+5 1E+6

Frequency A

mplit

ude

dB

Normal

Radial displacement 15mm

PS

8mm

15mm



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3

ANALYSIS OF EFFECTS OF CONNECTED BUS AND CABLE

The SFRA study also has included simulations of tests of transformers with bus or cables connected or

not connected. As many transformers in Japan are connected to serial equipment by ducts or cables that

are difficult to separate, the transformers cannot be easily measured without connections. TEPCO

simulated the influence of SFRA by using electrical constant data that is connected with serial ducts and

cables (Figure 6, Figure 7). We simulated the case of duct connections and cable connections with 66kV

GIS at the high voltage windings.

One set of transformers in the study have connections of ducts at the high voltage bushings at 66 kV. The

capacitance between phases is large at 65 to 90 pF. These ducts when connected have a large effect on

the test compared to the transformer tests without the connections at the frequencies higher than 40 kHz

(Figure 8). The responses among phases differ from each other.

The responses from low voltage windings are not significantly affected by the connected ducts on the

high side windings.

Location of Conductor

Spacer

Tra

nsfo

rmer

(Hig

h V

olta

ge

)

Bushing (Gas - Oil)

Conductor

Shield

Earthing switch Measuring point

(GIS)

Location of Conductor

Conductor

Duct Connections with 66kV GIS

Figure 6

Analysis of Serial Equipment at HV Windings

Figure 8

Cable Connections with 66kV GIS

Figure 7

-90

-80

-70

-60

-50

-40

-30

-20

-10

1.E+03 1.E+04 1.E+05 1.E+06 1.E+07

More than 40kHz

215kHz 500k1MHz

Frequency (Hz)

Am

plitude

(dB)

No Connection

Ducts only

Cables only

Earthing switch Measuring point

(GIS)

Cable Connections to Transformer

(High Voltage)



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4

Another set of transformers in the study have connections of cables at the high voltage bushings at 66 kV.

The capacitances between phases are very large. Due to the large capacitance of the cables the response

is different from those with connected ducts at low frequencies (2kHz to 15kHz) and high frequencies

(500kHz to 1MHz). The high voltage short circuit SFRA traces for cable connected to the transformer are

also shown in Figure 8.

The responses from low voltage windings are not significantly affected by the connected cables on the

high side windings.

CONCLUSION

20MVA distribution transformer models were measured by single phase not immersed in oil, and the

responses in axial, radial displacement and buckling were measured.

The response in axial displacement became large when the displacement size was large, but the shift is

very slight (20mm) when the transformer is in operation. The response in radial displacement showed the

characteristic left shift at the frequencies higher than the first resonance. The response in buckling

showed a distinctive feature, and shifting left at high frequencies. Therefore we can diagnose transformer

buckling by measuring responses at high frequencies.

Moreover, we simulated the influence of FRA by using electrical constant data that is connected with

serial equipment (ducts and cables).

BIOGRAPHY

H. Okumo joined Tokyo Electric Power Company in 1999, and currently works as a researcher in

Research & Development Center. He received both B.S. and M.S. degrees in electrical engineering from

Keio University, Japan.

Documents

Metodos de Diagnostico de Deformaciones Sfra