Transformer Test Procedure - Type Test Dan Routine Test

 

PT. BAMBANG DJAJA TRANSFORMER TESTING PROCEDURE

Standard of test: IEC Publicatio tion 76 

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BDS.QAC.012.001

: Power Transformer 

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IE IEE EE C5 C57.12 7.12.0 .00 0

: Sta Stan ndard dard Gene Genera rall Req Requi uire rem men ents ts fo forr Liq Liqu uid Imm Immer erse sed d Distribution, Power and Regulating Transformers (ANSI)

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IEC IEC Pu Publ blic icati ation on 722 722

: Guid Guidee to the the lig light htin ing g impu impulse lse and and switc switchi hing ng   Impulse testing of the power transformer and reactors

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SPLN 50

: Distribution Transformer  

Kinds of tests:

Routine test for every unit of transformer 1. Vo Volt ltag age e Rati Ratioo & Ve Vect ctor or G Gro roup up.. 2. Mea Measu surem rement ent of Win Windin dingg R Resi esista stance nce 3. 4. 5. 6.

Mea Measu surem rement ent ooff No L Load oad lloss oss and No No loa load d Cu Curre rrent nt Mea Measu surem rement ent of I Impe mpeda dance nce and load load lo loss ss Sep Separa arate te so sourc urce e AC vvolt oltag age e wi withs thstan tand d test test In Indu duce ced dA AC CV Vol olta tage ge te test st

Type Test 1. Te Temp mper erat atur ure e rris ise e te test st 2. Im Impu puls ls vol volta tage ge ttes estt 3. Noi oisse llev evel el

 

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1. VOLT VOLTAGE AGE RA RATIO TIO T TEST EST & VE VECTOR CTOR G GROU ROUPP 1.1.

Voltage Ra Ratio Te Test

The purpose of the measurement is to check that the deviation of the voltage from the specified values does not exceed exceed the limit given in the relevant transformer standard and connection of winding is agree with vector group specification. The turn ratio of transformer is the ratio of the number of turns in high voltage winding to low voltage winding. Measuring ratio in every tap and phase, maximum tolerance is +/0.5 %.

Deviation =

( measured turn ratio ) – ( expected turn ratio )   x 100 %   expected turn ratio

Measuring circuit of Voltage ratio test is shown on the picture below

Figure 1. measuring circuit of voltage ratio

 

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1.2. Ve Vect ctoor grou roup Depending on the type of the transformer, the input and output windings of a multi-phase transformer are connected either as star ( Y ) or delta ( D ( D ) or zigzag ( Z (  Z ). The phase angle  between the high voltage and the low voltage voltage windings varies between 0º  and  and 360 360ºº . Represe Rep resenti nting ng as vector vectors, s, the HV windin winding g is represe represente nted d as 12 (0) (0) hour and the other  windings of the connection group are represented by other numbers of the clock in reference to the real or virtual point. For example, in  Dyn 11 connection group the HV winding is delta and the LV winding is star and there is a phase difference of 330º (11x30º) (11x3 0º) between two windings. While the HV end shows 12 (0), (0), the LV end shows 11 o’clock (after 330º 330º  ). ). Determining the connection group is valid only in three phase transformers. The high voltage winding is shown first (as reference) and the other windings follow it. checking the connection group or polarity is possible by using a voltmeter. Direct current or alternating current can be used for this check. Beside that, vector group can be checked  by 3 phase transformer turn ratio automatically or 1 phase transformer turn ratio manually.

 

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Figure 2. Some of the connection groups according to IEC 60076-1 standard

 

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2. MEAS MEASUREM UREMENT ENT OF WIND WINDING ING RESISTAN RESISTANCE CE Measure resistance on HV and LV Winding 

Phase R – S

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Phase R - T

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Phase S – T

Resistance is fundamental importance to calculation of the I 2R component of Full load Loss. Lo ss. Ambi Ambien entt wind windin ing g re resis sista tanc ncee ar aree no norm rmal ally ly co conv nver erted ted to a stand standar ard d refer referen ence ce temperature, the Conversion are accomplished by the following formula: Rs

= Rm x α

Rs Rm

: Res Resis ista tan nce at der erid ided ed temp temper erat atu ure Ts : Me Measured resistance

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: Conversion factor 

Ts Tm Tk

: Des Desir ired ed re refe fere ren nce tem temp per erat atu ure (75 (75 Cel elsi sius us)) : ambient temperature : 234,5 (copper)   225 (Aluminium)

Were:

Figure 3 :  Measurement  Measureme nt Of Winding Resistance Resistance

 

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3. MEASUREM MEASUREMENT ENT OF NO LOA LOAD D LOSS & NO L LOAD OAD CU CURRENT  RRENT 

In this measurement no-load losses Wf and the no-load current I O of the transformer  are determined at rated voltage and rated frequency. The no load loss and the no load current shall be measured on one of the windings, at the rated frequency and rated voltage and the other winding shall be open-circuited. The diagram of test is shown in figure. 4.

 No Load Current (% Io) :

Figure 4  No Load Loss and No Load Current Current Test Diagram Diagram

 

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4. MEASUREMENT MEASUREMENT OF IMPEDANCE and FU FULL LL LOA LOAD D LOSS The measur measureme ement nt is carried carried out to determ determine ine the load-l load-loss osses es and the impeda impedance nce voltage of a distribution transformer. The measurement is performed on the principal tapping. The impedance voltage and full load loss is measured at rated frequency with applying an approximately sinusoidal supply to one winding, with the other winding short-circuited, with the winding connected on the principal tapping. The measurement may be made at any current between 20% and 100% of the rated current (principal tapping). The measurement shall be performer quickly and the intervals  between them shall be long enough to ensure that temperature rises do not cause significant errors. The difference in temperature between the top oil and the bottom oil shall be small enough to enable enable the average temperature to be determined with required accuracy. The measured value of impedance voltage shall be correction by increasing in the ratio of the rate rated d cu curr rren entt test test cu curre rrent nt.. The The lo losse ssess sh shall all be co corr rrect ected ed to th thee ap appr prop opri riat atee re refer feren ence ce temperature. The diagram of test is shown in figure in  figure 6.

Figure 5  Impedance and and Full Load Test Test diagram

 

PT. BAMBANG DJAJA TRANSFORMER TESTING PROCEDURE

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A. Impedance Calculation:

 

E

: Short circuit voltage at ambient temperature.

Vp

: Primary rated voltage

k VA

: Rated capacity

Wcu(t)

: Lo Load loss at at am ambient te temperature

Wcu(75)

: Load loss at at 75 degree Celsius

B. Full load Loss Calculation

Definition of symbols: Wcu(t) : Full Load loss at ambient temperature Ws

: Stray loss

a

: Conversion temperature factor 

Ip

: Pr Primary no nominal cu current

Is

: Secondary nominal current

Rp

: Avera rag ge pri rim mary re ressist staance

 

PT. BAMBANG DJAJA TRANSFORMER TESTING PROCEDURE

Rs

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: Avera rag ge sec eco ondary resi sisstance

  I2R

= Ip2 * Rp * 1,5 + Is 2 * Rs * 1,5

Ws

= Wcu(t) - I 2R

Wcu(75)

=I2R *α + Ws/α

C. Formula for determine regulation & efficiency at PF = 1

% Reg

= IX2/200 + Ir(75)

 

PT. BAMBANG DJAJA TRANSFORMER TESTING PROCEDURE

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5. VOLT VOLTAGE AGE WIT WITHSTA HSTAND ND TEST 

The full voltage (see table 2 for IEC standard and table 5 for ANSI standard) shall be applied for 60 seconds with frequency not not less than 80 % of rated frequency. The test voltage shall be applied on the winding winding under test and all terminals of the remaining remaining winding, core, frame, and tank of casing transformer connected together to the earth.

 

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6. INDU INDUCED CED WITHSTA WITHSTAND ND T TEST  EST 

An alternating voltage is applied to the terminals of low voltage winding and the other  winding is open-circuited, with high frequency generator to avoid excessive magnetizing currentt during the test. The test voltage curren voltage shall be twice of the rated voltage, voltage, but the phase-tophase-to phase test voltage of any three phase winding shell not exceed the rated withstand voltage, the duration of the test shall be:

 but not less than 15s.

Figure 6  Induced Voltage Voltage Diagram

 

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7. TEMPERATURE RISE TEST  

Determine the temperature rise of the top oil.

Tota To tall loss loss (t (the he su sum m of th thee no lo load ad lo losse ssess an and d fu full ll lo load ad lo losse ssess at th thee re refer feren ence ce temperature) is supplied to the transformer. The high voltage windings being excited and the low voltag voltagee windin winding g short short of the terminal terminals. s. The averag averagee ambien ambientt temper temperatu ature, re, the top temp temper eratu ature re an and d th thee Radi Radiat ator or temp tempera eratu ture re are recor recorde ded d ev ever ery y ho hour ur.. The The te test st shal shalll be continued until the top oil temperature does not vary more than 1 degree Celsius per hour  during for four consecutive hourly readings. The top oil temperature rise shall be obtained by subtracting the ambient temperature from the final top oil temperature.

Determine the temperature rise of winding.

The injection current must be reduced to the rated current and this value maintenance about 1 hour. The ambient, top oil and radiator temperature must be recorded, the winding temperature rise is determined by change in resistance method.

ΔT = R2/R1 ( 234.5 + t2) – (234.5 +t1) for Copper Copper and

ΔT = R2/R1 ( 225 + t2) – (225 +t1) for Copper and

 

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Curve 1 Top Oil Temperature Rise

Curve 2. Winding Temperature Rise

BDS.QAC.012.001

 

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8. IMPU IMPULSE LSE VOLT VOLTAGE AGE TES TEST  T 

The purpose of the impulse voltage test is to secure that the transformer insulations withstand the lightning overvoltages which may occur in service. A full wave lighting impulse test is intended to verify the impulse withstand strength of each line terminal to earth and other windings, and along the winding under test. The standard lighting impulse is a full lighting impulse having a virtual front of 1,2 us +/-30 % and a virtual time to half-value of 50 us +/-20 %. The impulse test voltage is of negative  polarity and the rated impulse voltage is shown in table 1.

Table 1.  Relationship of nominal nominal voltage to maximum maximum system voltage voltage and BIL

 

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Figure 7  The Impulse Voltage Wave

Figure 8 Voltage Measuring Circuit 

The sequence of the impulse test is each of the terminal is given one time reduced full wave that shall have crest value between 50% and 70% of the assigned BIL. Then followed follo wed by three 100% crest value of the assigned assigned BIL. Failure detec detection tion is accomplished accomplished  by comparing the reduced full wave test with 100% magnitude full wave test, using either the ground current waveform or the neutral impedance voltage form. A dielectric breakdown will cause a difference difference in compared compared waveforms. Observed Observed differences in the waveforms may be indications of failure, or they may be due to noninjurious causes.

9. NO NOIS ISE E L LEV EVEL EL

 

PT. BAMBANG DJAJA TRANSFORMER TESTING PROCEDURE

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Measurement begin with measure the ambient sound pressure level , the ambient sound pressure shall be measured at a minimum four location. Consequently, intervals of less than 1 m (3 ft) may result for small transformers. The microphone shall be located on the measurement surface. The microphone shall be spaced 0.3 m (1 ft) from the reference sound producing surface. When fans are in operation, the microphone shall be located 2 m (6 ft) from fro m any portion portion of the radiators radiators,, coolers coolers,, or coolin cooling g tubes tubes cooled cooled by forced forced air. For  For  tran transf sfor orme mers rs ha havi ving ng an ov overa erall ll tank tank or en encl clos osur uree he heig ight ht of le less ss th than an 2. 2.4 4 m (7 (7.2 .2 ft), ft), measur mea sureme ements nts shall shall be made made at half half height height.. For transform transformers ers having having an overal overalll tank tank or  enclosure height of 2.4 m (7.2 ft) or more, measurements shall be made at one-third and at two-thirds height. Sound measurements shall begin after the transformer being tested is energized and steady-state sound level conditions are established. Measurements may be made immediately on transformers that have been in continuous operation.

 

 

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Calculation Procedure for Transformer 60 Hz is tested with 50 Hz Apparatus No Load calculation

V = 4.44F x Bm x A x N x 10-4 Volt When : B A  N So

: Flux density ( Tesla ) : Cross section area ( m2 ) constant : Jumlah gulungan.

V=KxF

at F = 60 Hz

> V6 V 60 = K x 60,

at F = 50 Hz

> V5 V50 = K x 50

 

K = V60/60

  V50 = V60 x 50/60   = 0.833 V60 So with 50Hz apparatus, test voltage is 83.3 % rated voltage and No load los is : Wf

= Wh + We,

Wh We Wh

= Kh x F x Bmaxx  dan = Ke x F2  x Bmax2 x t2 & We We >>  F

When :

so

for cold rolled oriented grain silicon steel Wh = 0.5 Wf &

>>

We

F2

= 0.5 We

And No load loss is : Wf(60) = (60/50) 0.5 Wf(50) + (60/50)2 0.5 Wf(50) Wf(60) = 1.32 Wf(50) When : Wf (50) Wf (60) We Wh

: No load loss at 50 Hz : No load loss at 60 Hz : Eddy current loss : Hysterics loss

Full Load calculation :

 

PT. BAMBANG DJAJA TRANSFORMER TESTING PROCEDURE

Wcu Ws Wcu

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= I2R + Ws 2 >> f  = I2R + (60/50)2 Ws

Impedance Calculation : % Iz = (( % Ir)2 + (%Ix)0.5 %Ix >> F %Iz(60) = ((%Ir)2 + (60/50 %Ix(50))2)0.5

when : F Wcu Ws

: Frequency : Fu Full lo load lo loss : Sra Sray y los losss (ed (eddy dy cu curr rren entt los losss com compo pone nent nt )

% %IIzx %Ir

:: % % Irm eapcetadnacnece : % resistance

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