PARTIAL DISCHARGE DETECTION AND LOCATION IN · PDF filePARTIAL DISCHARGE DETECTION AND...

February 22nd - 23rd , 2017, Scope Complex, Lodhi Road, New Delhi, India

6th International Conference on Large Power Transformers – Modern Trends in

Application, Installation, Operation & Maintenance

by

and

PARTIAL DISCHARGE DETECTION AND

LOCATION IN TRANSFORMERS BY

PERFORMING PARTIAL DISCHARGE TESTS

IN OIL USING UHF SENSORS

K.K.JEMBU KAILAS

L&T CONSTRUCTION

[email protected]

L&T CONSTRUCTION

[email protected]

W. ADITHYA KUMAR




2

Partial Discharge detection & location in Power

transformers and to evaluate the most important

property of UHF sensor i.e. SENSITIVITY through

preliminary testing.

To de-noise the captured signals and to extract the

original PD signal after de-noising.

To evaluate the approximate location of PD source

Objective




3

PD - Intermittent nanosecond range pulses

Causes of PD

1. Weak insulation - When electric field across the insulation > dielectric strength of the insulation = PD

2. Arcing due to poor contacts

3. Corona

4. Surface discharges

Effects of PD

1. Insulation degradation over a period of time

2. Equipment failure, Effect on men & materials, Disruption of economic activities, Customer dissatisfaction, Penalty clauses

Partial Discharge (PD)




4

Electrons accelerated under high electric field and immediately

brought to rest (nano sec range pulses) produce Ultra High

Frequency (UHF) EM waves.

UHF waves = 300 MHz -3000 MHz

Non conventional method – energy from EM waves can be

captured using sensors and their outputs can be shown in V or

mV

PD pulses can be detected if wave length of UHF signals < tank

dimensions

Narrow pulse , more spectral energy & vice versa

PD Detection using UHF – Principle and aspects




5

UHF sensors & UHF PD Detector Module

Internal & External sensor respectively, internal sensor placed

inside the drain valve, while external sensor placed in specially

designed dielectric windows on the transformer, both require

modifications on transformer tank.




7

Conventional Method (IEC

60270) UHF Method

Offline measurements Online measurements

Measurements at factory Measurements at factory and site

Considers the transformer

as a single unit. Hence fault

location is not possible

Able to locate multiple faults as the

system considers each fault location as a

localized unit

Basic method to analyze the

overall strength of insulation

in the factory

Can be coupled with conventional method

for diagnosis, while testing transformers in

the factory.

Highly sensitive to noise

Less sensitive to noise, as this operates in

UHF range. Even corona and other noises

happen only below this range. Hence

sensitivity is high




8

Types of Sensors

Patch antenna Internal sensor External sensor




9

Preliminary testing of Sensors

Before inserting the sensor directly in to the drain valve of

Transformer it is necessary to evaluate the performance of

antenna.

More over the charge levels in a transformer will be in the order

of some thousand pC.

So the sensitivity of the sensor is evaluated by keeping the

antenna at a relative distance from PD source.




1

0

Sensitivity verification of UHF Conical Monopole Antenna

Experimental Set-up LDIC PD measuring system




1

1

Applied voltage (KV) v/s charge (pC)

The charge (pC) was linearly varying with

applied voltage i.e. it has a linear

relationship.

The center frequency of received signals

at PD inception voltage was 963MHz.

The minimum energy of the PD signal is

160μJ with sensitivity 90pC.




1

2

Experimental Set-up




Preliminary testing in Oil Internal UHF sensor Signal

captured at 10.1KV

Signals captured by all the

4 sensors at 12KV

1

3




De-noised signal

1

4




1

5

Type of

test

sensor Distance

(m)

Max

voltage

(mV)

Peak to

peak

voltage

(mV)

Frequency

(MHz)

Energy

(pJ)

Time

period

(ns)

Phase

(degre

es)

Power

(dBm)

Time difference Triggering

voltage

(mV)

Triggering

Channel

t12 t13 t14

in Air

s1 1.4 147 376 960 49.03 13.8 55.8 46.53

41.3

43.2

45.2

50

C1

s2 1.4 222 400 970 38.61 32.5 83.75 41.7

s3 1.4 245 650 979 40.9 21 177.2 51.47

s4 1.4 245 510 960 137 28.7 146.3 147

in Oil

s1 1.4 75 186 1000 216 5.7 25.8 61.94

43.9

49.5

41.1

50

C1

s2 1.2 95 216 979 306 4.8 150.7 59.91

s3 1.4 43 79 965 210 10.6 104.4 60.8

s4 0.75 61 132 980 245 8.9 25.48 64.98

Results




1

6

Observations from Oil test

The Internal sensor (conical monopole antenna) has detected the corona

discharge at an inception of voltage of 10.2KV where as all the other external

antennas (Patch antennas) did not capture it.

As the distance between internal sensor and the electrodes was 8cm where as the

distance between external sensors and the electrodes is 2m, the UHF internal sensor

detected the signal.

After repeating the experiment keeping all the sensors at same positions and with

voltage being increased, external sensors detected corona at 12KV, where as the

UHF internal sensor detected at 10.6KV.

The results show that the UHF internal sensor is more sensitive than the

external sensors when placed very close to the PD source without actually

knowing the level of PD.

As the test was carried out under controlled conditions and without any ground

noise de-noising the signal was done in oscilloscope.




1

7

Experiment on real time Transformer Internal

Sensor

Mounted

in to one

of the

valves




1

8

De-Noising

Wavelet De-noising Principle

-1.5 -1 -0.5 0 0.5 1 1.5

x 10-7

-0.2

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

UHF output

Time(seconds)

Am

plitu

de

(vo

lts)

-1.5 -1 -0.5 0 0.5 1 1.5

x 10-7

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

Time(seconds)

Am

plitu

de

(vo

lts)

Denoised signal

Original signal captured by sensor De-noised signal using

wavelets in MATLAB 0 2 4 6 8 10

x 109

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35UHF FFToutput

Frequency(Hz)

Am

plitu

de

(vo

lts) Maximum Amplitude = 0.2669 volts

at a frequency of 979 MHz

0 2 4 6 8 10

x 109

0

0.02

0.04

0.06

0.08

0.1

0.12 FFT of Denoised signal

Frequency(Hz)

Am

plitu

de

(vo

lts)

Maximum Amplitude is 0.1153 at1000 MHz

FFT of original

signal




1

9

PD location using UHF – Time of Arrival Approach

• There will be definite time difference between arrival of signal

from a particular PD source at each sensor.

• The time difference governed by minimum time delay path

traveled by the EM wave front to reach each sensor.

• Distance traveled (D) = EM Wave speed (v) x time (t)

• 2 or more distinct but repeatable time period = multiple PD

sources




2

0

Enter the sensor

coordinates in 2D/3D

Calculate the sensor position

values

Call TDOA Read the time

domain signal

from each sensor

Cross correlation

TDOA values

Solve the non-linear equations

Newton Raphson

Iterative method Non-Iterative method

Source location

Flow Chart of TDOA




2

1

Evaluation of 2-Dimensional PD source Location

using MATLAB Sl.no Applied

voltage

(KV)

Sensor 1

Position

(x1,y1) cm

Sensor 2

Position

(x2,y2) cm

Sensor 3

Position

(x3,y3) cm

Time

Difference Of

Arrival (TDOA)

Computed

Velocity of

electromagneti

c waves

Cm/sec

Source

position

(x,y) cm

Computed

position

(xc,yc) cm

Error

in

X (%)

Error

in

Y (%)

T12

(ns)

T32

(ns)

1 14.4 (150,100) (50,175) (50,0) 2.2 2.1 1.13*10^10 50,100 50.069,

99.93

0.14 -0.07

2 14.6 (150,100) (50,175) (50,0) 2.2 2.1 1.13*10^10 50,100 50.069,

99.93

0.14 -0.07

3 14.7 (150,100) (50,175) (50,0) 2.2 2.1 1.13*10^10 50,100 50.069,

99.93

0.14 -0.07

4 14.8 (150,100) (50,175) (50,0) 2.2 2.1 1.13*10^10 50,100 50.069,

99.93

0.14 -0.07

5 17 (150,100) (50,175) (50,0) 2.2 2.1 1.13*10^10 50,100 50.069,

99.93

0.14 -0.07

6 13.3 (150,100) (50,175) (50,0) 2.2 2.1 1.13*10^10 50,100 50.069,

99.93

0.14 -0.07

Comparison of actual source and evaluated source with sensor 2 as reference




2

2

Evaluation of 2-Dimensional PD source Location

using MATLAB

Comparison of actual source and evaluated source with sensor 3 as reference

Sl.no Applied

voltage

(KV)

Sensor 1

Position

(x1,y1) cm

Sensor 2

Position

(x2,y2) cm

Sensor 3

Position

(x3,y3) cm

Time Difference

Of Arrival

(TDOA)

Computed

Velocity of

electromagnetic

waves

Cm/sec

Source

position

(x,y) cm

Computed

position

(xc,yc) cm

Error in

X (%)

Error

in

Y (%)

T13

(ns)

T23

(ns)

1 10.4 (150,100) (50,175) (50,50) 3.4 1.7 1.3*10^10 50,100 52.85,103.41 5.7 3.41

2 14 (150,100) (50,175) (50,50) 12.5 25 2*10^10 50,100 53.55,102.6 6.9 2.6

3 14.2 (150,100) (50,175) (50,50) 3.4 1.7 1.3*10^10 50,100 54.35,101.7 8.7 1.7

4 14.2 (150,100) (50,175) (50,50) 3.4 1.7 1.3*10^10 50,100 54.214,101.4

2

8.4 1.4

5 14.22 (150,100) (50,175) (50,50) 3.4 1.7 1.3*10^10 50,100 54.214,101.4

2

8.4 1.4

6 11.4 (150,100) (50,175) (50,50) 3.4 1.7 1.3*10^10 50,100 54.214,101.4

2

8.4 1.4

7 18 (150,100) (50,175) (50,50) 3.4 1.7 1.3*10^10 50,100 54.214,101.4

2

8.4 1.4




2

3

Results

When the FFT of

original signal was

performed, the

dominant frequency

was 979MHz and

the dominant

frequency in de-

noised signal was

found to be

1000MHz. This

shows that the

noise which the

sensor captured

even between

900MHz-1000MHz

is eliminated

The amplitude of de-

noised signal is less

than that of the

original signal

amplitude. This gives

clear information that

noise levels are

generally higher than

PD signal amplitude.

Wavelet de-noising

using Daubechey’s filter is the best

method among

different techniques

2-D source has

been located in a

steel tank with an

error of 8% using

iteration method

(Newton-Raphson

method).

The accuracy of 2-

Dimensional source

location has been

improved to 96%

when Newton-

Raphson method is

implemented on de-

noised signals




2

4

Conclusion

UHF method has

numerous applications

and one of them is

transformer. The

sensor designed for

inserting it in to the

drain valve of

transformer has very

good sensitivity of

90pC under controlled

conditions.

2-D PD source has been

located in steel tank

using iteration method

(Newton-Raphson

method) with a error of

8%, where as 3-

Dimensional source

localization is done with

non-iterative method like

TDOA, PRPA. 3-

Dimensional PD

source is also localized

but with a certain error

So the UHF sensors

can be installed at

sites, factories

without de-energizing

the transformers and

the approximate

location of PD source

can be traced such

that the insulation

strength of that

particular area is

increased and also

the life of transformer

is increased.




2

5

FUTURE SCOPE This research is vast and can be extended

to on-line monitoring of the transformer

with a suitable hardware. The best way to

implement this technique on-line is by

using DAQ unit along with LABVIEW.

This gives important information about

condition monitoring and diagnostics of

power transformers for a full day, week,

month depending upon the size of data to

be analyzed. So the best way to implement

this technique on-line is to reduce the

amount of data recorded in the hardware

every second by erasing unnecessary data




2

6

Date post:	16-Feb-2018
Category:	Documents
Upload:	nguyenduong
View:	233 times
Download:	2 times

PARTIAL DISCHARGE DETECTION AND LOCATION IN · PDF filePARTIAL DISCHARGE DETECTION AND...

Documents