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MONITORING NITORING USING A SOFTWARE SOFTWARE POWER TRANSFORMER MO APPLICATION Eng. Adrian-Alexandru MOLDOVAN, PhD student1, Eng. Horaţiu-Augustin MOLDOVAN, PhD2,

Technical University, Cluj-Napoca. REZUMAT. Identificarea transformatorului de putere necesită o monitorizare monitorizare continuă a caracteristicilor sale funcţionale. Având în vedere legătura dintre caracteristicile constructive şi starea fizică a transformatoarelor de putere, pe de o parte, şi parametrii lor electrici, pe de altă parte, monitorizare, chiar şi în timp cvasicvasi- real, poate fi folositoare pentru a asigura o functionare nominală a acestor trasformatoare de putere.Lucrarea actuală prezintă o metodă originală, care poate fi folosită pentru identificare parametrilor transformatorului de putere şi o aplicaţie software bazat pe această metodă. metodă. Cuvinte cheie: transformator de putere, monitorizare, aplicaţie software. ABSTRACT. Identification of power transformer state requires continuous monitoring of its functional characteristics. Due to the link between between constructive characteristics and physical state of the power transformer, on the one hand, and their electrical parameters, on the other hand, the parameters monitoring even in quasiquasi-real time can be profitable to ensure the rated working time of these these expensive power equipment. The current paper presents an original method that can be used for transformer identification and a software application based on this method. Keywords: power transformer, monitoring, software application.

1. INTRODUCTION To monitories a poly-phase transformer working in balanced load is enough to follow a single phase of the transformer. The magnetizing currents are negligible compared whit the currents for working in load, therefore at working in load the wave forms of the voltage and of the currents are considerate to be sinusoidal. The electrical transformer equations written in complex values and the transformer’s phasors diagram for the figure1 are (1).

Fig. 2. Phasor diagram of mono-phase transformer.

where U1 , I1 , Z1 refer to voltage, current and impedance for the primary circuit of transformer and U 2 , I 2 , Z 2 refer to voltage, current and impedance for secondary circuit of transformer. U e1 , U e 2 will be eliminated from system of equations (1) and results a system of equations only in U1 , I1 , Z1 and U 2 , I 2 , Z 2 , Z1m

Fig. 1. Mono-phase transformer. U 1 = Z 1 I 1 − U e1 ; U 2 = −Z 2 I 2 + U e2 ; U e1 = − Z 1m I 01 ; U e2 =

(1)

N2 K = N ; 1 ( Z + Z 1 1m ) I1 + K Z1m I 2 = U1 ; 2 − k Z1m I1 − ( Z 2 + K Z1m ) I 2 = U 2 ,

(2)

N2 U e1 ; N1

I 01 = I1 +

N2 I2, N1

where voltage U1 is considerate phase origins and can be equivalent whit U 1 and, other components of the system will be expressed in terms of real and imaginary

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WORLD ENERGY SYSTEM CONFERENCE – WESC 2012 _____________________________________________________________________________________ WORLD ENERGY SYSTEM CONFERENCE - WESC components follow the phasor diagram of transformer from figure 2:

transformers primary and the voltage value from the transformers secondary. B[j]= B[V1, I1 cosφ1,V2,I2,cosφ2,cosα]

(2.1)

Z1 = R1 + jX 1 , Z 2 = R2 + jX 2 , Z1m = R1m + jX 1m ;

I1 = I1 cos ϕ1 − jI1 sin ϕ1 , U 2 = U 2 cos α + jU 2 sin α I 2 = − I 2 cos(α + ϕ 2 ) + jI 2 sin(α + ϕ 2 )

By following the above notations replaced in relation (2) have system of equations: A = I1 cos ϕ1 − jI1 sin ϕ1 B = − I 2 cos(α + ϕ 2 ) + jI 2 sin(α + ϕ 2 ) T = U 2 cos α + jU 2 sin α ( R + jX + R + jX ) A + ( R + jX ) BK = U 1 1m 1m 1m 1m 1 1 − K ( R1m + jX 1m ) A − [ R2 + jX 2 + K 2 ( R1m + jX 1m )]B = T

To solve the system of equations (3) the real and imaginary components must be separated:

I = I cosϕ , I = −I sinϕ 1 1r 1 1 1a 1 I2a = −I2 cos(α +ϕ2 ), I2r = I2 sin(α +ϕ2 ) U2a = −U2 cosα, U2r =U2 sinα R1I1a − X1I1r + R1m(I1a + KI2a ) − X1m(I1r + KI2r ) =U1 R I + X I + R (I + KI ) + X (I + KI ) = 0 2r 1m 1a 2a 1 1r 1 1a 1m 1r 2 − R2I2a + X2I2r − R1m(KI1a + K I2a ) + X1m(KI1r + K2I2r ) =U2a − R2I2r − X2I2a − R1m(KI1r + K2I2r ) − X1m(KI1a + K2I2a ) =U2r

This system of equations must be resolved in order to determinate electrical parameters of the electrical transformer.[1][2]

2. THE SOFTWARE APPLICATION FLOW The application flow diagram from the figure 3 is represented for just one phase of the transformer, where we have: B[j] a vector with 7 elements. The vector B[j] contains the voltage value, the current intensity and the phase difference between those values in the transformers primary, the voltage value and the current intensity from the transformers secondary and the phase difference between those values, and it contains also the phase difference between the voltage value from the

Fig. 3. The application flow diagram.

A[k] is a vector with 7 elements which contains all the read values starting with position 2, the equations ec1, ec2, ec3 and ec4 are the equations from the block diagram of the method proposed in the paper at chapter 1. K stores the number of readings done, and “j”is the number of equation systems obtained. S[R] is a solution vector which contains the solutions obtained out of the equations system. The S[R] vector contains the following values: the resistance and the reactance from the transformers primary, the resistance and the reactance from the transformers secondary and the mutual resistance and reactance of the transformer. S(R)=S[R1,X1,R2,X2,Rm,Xm]

(2.2)

The vector Z[R] contains the initial values, those which were obtained during the transformers design. The time period between two consecutive readings is represented in the flow diagram with “t” (the time frame between two consecutive readings is 30 milliseconds). What is important for this method is the fact that during the measurements the temperature inside the transformers windings must be constant. The proposed method, and the software application takes into account a measurement error of 5%.

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POWER TRANSFORMER MONITORING USING A SOFTWARE APPLICATION

The software application reads the data from an acquisition board USB 6621. The acquisition board transmits the signals collected from the current transducer and from the voltage transducer to the software application, which based on those information is capable to represent the wave forms for the current and for the voltage.[2][3]

The analog signals are acquired by the acquisition board from the voltage transducers and from the current transducers LV 25P respectively LA55-P/SP1. In order to perform the necessary measurements at optimal parameters the transducers used are based on Hall elements.

3. HARDWARE EQUIPMENTS In order to determine the electrical parameters of power transformer it is necessary to perform some measurements on the transformer operating in a sinusoidal steady state. The measurements were performed using two measuring kits, one for transformers primary and one for transformers secondary. For data acquisition it was used a system of voltage transducers and current transducers connected to a acquisition board use to make the connection between the transducers and the computer used to run the software application.The mounting diagram to determine the electrical parameters using a software application is shown in figure 4.

Fig. 5. Outputs of the acquisition board.

Fig. 4. Experimental model.

In figure 4 we denote by T1, T2, T3 the auto transformers are used with a single-phase voltage adjustable from 0 to 240V, the switch Q1 is used to power up the three autotransformers which supply each phase of the three phase transformer T4. P1, P2 are measurement kits that are installed for a high a precision measurement. AU / B represent the transducers system for the electrical and non-electrical values. The three resistors R1, R2, R3 used to load the transformer have an adjustable resistance up to 440 Ω.

Voltage transducer LV 25-P. LV 25-P is a voltage transducer with galvanic separation between the primary circuit (the power circuit used for measurements) and the secondary circuit (electronic circuit used for processing the signal generated by transducer). The main parameters of this type of transducer are presented in figure 6 and in figure 7. To measure voltage, an external resistorR1 is expected to be traveled by a current proportional to the measured voltage. Current transducer LA 55-P/SP1. LA 55-P/SP1 is a current transducer with galvanic separation between the primary circuit (the power circuit used for measurements) and the secondary circuit (electronic circuit used for processing the signal generated by transducer). The main parameters of this type of transducer are presented in figure 8 and in figure 9. A general structure of transducer blocks with the outputs for the acquisition board is shown in figure 5

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Fig. 6. Voltage transducer LV 25-P characteristics.

Fig. 7. Input/output voltages for the voltage transducer.

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Fig. 8. Current transducer LA55P/SP1 [127] characteristics

Fig. 9. Input/output currents for the current transducer.

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4. THE SOFTWARE APPLICATION PANELS The front panel of the software application is presented in figure 10.

The boolean indicators from the front panel are used to identify different states of the transformer. Because the monitoring process was performed for two experimental phases of the transformer, the indicators are for the phase R and for the phase S of the transformer. The green light color indicates the occurrence of the event marked in its right side. In order to see what happens on one of the phases, the mouse pointer can be used to choose one of the phases in the front panel as it is shown in figure 13.

Fig. 10 Front panel.

The first block, of the front panel, positioned at the top left, alows the user to set the accepted difference between the calculated values and the measured ones, this values are expressed in percentage (figure 11).

Fig. 13 Phase selector.

When the user chooses to see the events from a particular phase, the application will display the voltage and current values from the transformers primary and from transformers secondary. The used will be able to see the numerical values and also as wave forms.

Fig. 11 Accepted error input.

The block from the bottom left is used to show status of the transformer.

Fig. 14 The voltage and current waveform display.

Fig. 12 Damage indicators.

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POWER TRANSFORMER MONITORING USING A SOFTWARE APPLICATION two phases of the transformer. Since the transformer was operating under a sinusoidal and symmetrical regime it was not necessary to monitories all the three phases of the transformer. In order to obtain the electrical parameters of the transformer, using the method proposed by the paper, it is enough to know the transformers voltages and currents values. The other values needed to obtain the transformer parameters will be obtained inside the software application trough mathematical operations.

Fig. 15 Voltage and current values display.

As it is shown in fig 15 the software application displays the voltage values and current values form the transformers primary and from the transformers secondary and also the phase differences between those electrical values. In the figure 16 is shown the transformers parameters calculated by the application according to the proposed method from this paper.

BIBLIOGRAPHY [1] V. Maier, H. A. Moldovan, H. Gh. Beleiu, P. D. Muresan., Power transformer electrical parameters determination by monitoring permanents regimes. MPS 2010, Cluj-Napoca. [2] H.A. Moldovan, V. Maier and A.A. Moldovan Diagnosis power transformers by monitoring electrical parameters. MPS 2011, Cluj-Napoca. [3] H.A. Moldovan, V. Maier The Determination of Power Transformer Electrical Parameters using LabVIEW. Prodoc 2011 Cluj-Napoca

Fig. 16 Transformer parameters display.

CONCLUSIONS The method proposed in this paper is an original one and it bring a new way of handling the problem related with the power transformers monitoring process. The proposed monitoring method together with the hardware equipments available on the market will make a complex system capable to provide precise information regarding the state of the transformer which is under the monitoring process. The proposed method was tested on a laboratory power transformer. The monitoring was performed on

About the authors Eng. Adrian-Alexandru MOLDOVAN, PhD-student

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WORLD ENERGY SYSTEM CONFERENCE – WESC 2012 _____________________________________________________________________________________ WORLD ENERGY SYSTEM CONFERENCE - WESC University “ Tehnical University” from Cluj-Napoca email:[email protected] Systems Engineer of the Tehnical University from Cluj-Napoca. He worked at WirTek AS a danish company specialized in development of software for the mobile devices. In 2008 he joins the Phd program of the Technical University from Cluj-Napoca working on the thesis Study of evolved control algorithms developement for static power converters in electro-energetics. From 2009 he works at Softing AG, implementing specific embeded software for industrial communications (wired / wireless) in process automation. In 2009 starts working for ASML Holding N.V implementing Calibration, Performance and Diagnostic software for the photolithography systems used in the semiconductors industry. Eng. Horațiu-Augustin MOLDOVAN, PhD. University “ Tehnical University” from Cluj-Napoca email:[email protected] Electrical Engineer of the Tehnical University from Cluj-Napoca. In 2008 he joins the Phd program of the Technical University from Cluj-Napoca under the guidance of professor engineer Virgil Maier, PhD. In 2011 he obtains his PhD with the paper "Quasi real-time monitoring of a power transformer".

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