Predictive maintenance and modeling of Transformer

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International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue4- April 2013

ISSN: 2231-5381 http://www.ijettjournal.org 186

Predictive maintenance and modeling of

Transformer Ladani Dhaval H., Sandeep A. Mehta, Pallav Gandhi

Abstract— Power transformer is the most important and

expensive equipment in Power plant and the Oil has the

main roles of insulating and cooling of transformer. The

oil condition has to be checked regularly and replaced

when it necessary, because to avoid the suddenly failure

of the transformer. Large power transformers are the

most key components in power system and their correct

functioning or maintenance is important to system

operation. Power transformers are protected by differentprotection schemes that use voltages and currents to

detect abnormal condition in the different zone of

protection. For this type of scheme, a short circuit or

increment load accidental it must be to trip a system.

Power transformers ageing are one of the most critical

issues. Also their replacement will consider amount of

time and cost. Therefore, developing a replacement or

maintenance strategy of transformer populations is

important.

This paper presents simulation for life assessment of

the transformer per hour, per day, per month using

LabView™. Here Load and ambient temperatures are

two important factors that affect the life of insulation of

transformers. The estimated load factors and ambient

temperatures are input and to find out the Hot spot

temperature or ageing or rate of change of ageing of

transformer to the IEC life consumption models to assess

the consumed life of insulation of transformer.

Key words—Maintenance of transformer, Ageing,

Hotspot temperature, LabView™

INTRODUCTION

ower transformer is one of the most important and expensive equipment in Power plant and the Oil

has the main roles of insulating and cooling of

transformer. When transformer is purchased, the

specification identified a thermal rating in data sheet. This is

based on a factory heat run test and Standards such as IEEE

C57.91-1995 and IEC 60076-7.[1][2][3] winding hottest-

spot temperature is the one of the most effective and critical

parameter to affect the insulation life of transformer.

The objective of this work to develop:

• Measure oil and winding temperature with fiber optic and

RTD

• calculate the load by energy meter and their effect of

transformer

• Estimate transformer insulation loss-of-life.

Different method to find Oil and winding temperature

with RTD and Fiber Optic sensor but measurable

temperature not accurate and cost effectively. Transformer

depends on load factor because when load increase that effect

on oil and winding temperature. Top Oil and Hot spot

temperature depended on Load factor and ambienttemperature. Both the find out by the Exponential equations

method and Difference equations solution method.

I. TRANSFORMER TEMPERATURE MEASUREMENT

Transformer Temperature measure by fiber optic sensor.

Different type to implement the sensor in transformer but it

must to thermal contact in the winding and oil. Fiber Optic

Sensor shown in fig.1. The benefits of it are Reduces

inspection and maintenance costs, Reduces inspection and

maintenance costs.

Fig.1 fiber optic sensor use to measure temperature

Resistance thermometer (RTD) is a heating element to

simulate the measuring of winding temperatures of

transformer. It provides an analog output for remote

indication and monitoring on SCADA. RTD enables

accurate simulation of the hot spot temperature of the

transformer Oil and winding. Fig 2.

P




ISSN: 2231-5381 http://www.ijettjournal.org Page 1187

When measuring oil and winding temperature by sensor

their output to calculate the hot spot temperature and loss of

life per hour, per day and monitoring with SCADA. All

calculation follows by IEEE [1] and IEC [3] their simulation

in LabView™.

Fig.2 RTD use to measure temperature

II. CALCULATE HOT SPOT TEMPERATURE WITHOUT

LOADING EFFECT

The purpose of this calculation to know the transformer life and save the replacement coast.

1) Find hottest spot temperature

H TO A H

Where,

C

C

C

C H

raturespot tempehottestWinding=H

eTemperatur ambientover riseoilTop=TO

eTemperatur AmbientAverage=A

raturespot tempe-hottestwinding

2) Find Top oil temperature

TO ATO

Where,

raturespot tempehottestWinding=H

eTemperatur ambientover riseoilTop=TO

eTemperatur AmbientAverage=A

raturespot tempe-hottestwinding

C

C

C H

3) Find winding hottest spot temperature

i H

t

i H U H H we ,,, 1)(

Where,

h,spothotatconstanttimeWinding=w

0,for teTemperatur windingInitial=H

eTemperatur windingultimate=UH,

retemperatuoilover toprisespot-hottestwinding

C

C

C H

III. DIFFERENTIAL EQUATION SOLUTION METHOD

WITH LOADING

This describes to use of heat transfer differential equations,

applicable for randomly time-varying load factor K and

time-varying ambient temperature θ a. They are intended to

be the basis for the software to process data in order to define

hot-spot temperature as a function of time and consequently

the corresponding insulation life consumption. The

differential equations are represented in block diagram form

in Fig 3. Observe in Fig 3 that the inputs are the load factor

K , and the ambient temperature θ a. The output is the

desired hot-spot temperature θ h on the right.

Fig. 3 differential equation block diagram

(1) Find Top oil at load

aor

x

R

RK

K

Dt D

0

2

011

01

1

n Dnn 000 1

Where,





constant,timeOil =0

lossesload nocurrent torated atlossesload of ratioR

factor Load =

eTemperatur lossesrated atover riseoilTop =or

eTemperatur Ambient=a

load atretemperatuoilTop0

risetemp.oiltopversuslossestotalof power lexponentiax

K

C

C

C

(2) Find Hot-Spot temperature

121

22

1 h

y

hr

w

h K K K

Dt D

n Dnn hhh 111 1

221

22

2 11

h

y

hr

w

hK K

K

Dt D

n Dnn hhh 222 1

nnn hhh 21

nnn h H 0

Where,

e,Temperatur SpotHot=H

constant,timewinding=

K current,rated atgradientoiltopSpot toHot=hr

constantmodelThermal=22

K 21

K 11

K

K load atriseretemperatuoilTop0

risetemp.windingtopversuslossestotalof power lexponentiay

w

(3)Loss of Life of Transformer

273

15000

383

15000

H eF AA

Where,


Factor onAccelerati Ageing

AAF

N

n

n

N

n

n AA

EQA

t

t F

F

1

1

Where,

timefor totalFactor AgeingEquivalent

Factor onAccelerati Ageing

EQAF

AAF

lationLife NormalInsu

t F LossofLife

EQA 100%

Where,timefor totalFactor AgeingEquivalent

180000

lationlife Normalinsu

EQAF

273

15000

18108.9 H eePerUnitLif

Where,


IV. SIMULATION IN LEBVIEW™ SOFTWARE

FIG.4 AGE FACTOR AT 110 C TEMPERATURE

By implementing above input values in mathematical

formulas simulate in LabView and get the results as below.





TABLE I. OUTPUT DATA

Temperature Age

Factor

Percent Loss

Life

Hours

110 0.35 0.0133 24

120 1 0.0133 8.86

130 2.71 0.0133 7

140 6.98 0.0133 1.4

150 17.2 0.0133 1

There are so many parameters which affect the transformer

ageing. This paper contains the effects of only two

parameters which are Ambient Temperature and Load

factor. So by changing the parameters one by one we get the

variations in output parameters which are shown in the

below tables.

Table2: Changing the Load factor and ambient temperature

Ambient

Temp.

Load factor Hot spot

Temp.

Loss of Life

Per day

30.3 0.81 90.5 0

29.9 0.87 91.6 0

28.6 1 101.6 0

28.0 1.7 118.7 0.01

22.3 0.82 124.1 6.15

22.2 0.86 123.7 6.15

V. CONCLUSION

From above tests and results we can tell when the Load of

the transformer and Ambient temperature of transformer is

the minimum that will give the more Life of Transformer.

When load increase then life decreases. This understanding

helps to maintenance of transformer without failure.

VI. R EFERENCES

[1] IEEE Guide for Loading Mineral-Oil-Immersed

Transformers Up to and Including 100 MVA With

55 C or 65 C Average Winding Rise, IEEE Stand.

C57.92-1981.


Overhead and Pad-Mounted Distribution

Transformers Rated 500 kVA and Less With 65 C

or 55 C Winding Rise, IEEE Stand. C57.91-1981.

[3] IEC 60076-7 Part 7: 'Loading Guide for Oil-

immersed Power Transformers', 2005.


Transformers, IEEE Stand. C57.91-1995.

Predictive maintenance and modeling of Transformer

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