Study of Six Phase Transmission Line using the Autotransformer

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2011 IEEE Student Conference on Research and Development (SCOReD)

Study of Six Phase Transmission Line using the Autotransformer Conversion Tuan Mohd Ikhwan Bin Tuan Yacob, Zuhaina Binti Zakaria & Noraliza Binti Hamzah Faculty of Electrical Engineering University Teknologi Mara Selangor,Malaysia [email protected], [email protected], [email protected] Abstract—This paper presents the application of an autotransformer for the conversion from three phases to six phase transmission line. The autotransformer with tertiary winding is used to achieve and design consideration in this research. The conversion is tested and simulated using a simple test system which is fed from the source through transmission line about 20km to a power distribution load model. This research focuses on the conversion of the autotransformer and transmission line and measurement to be considered are efficiency, phase angle, waveform current, waveform voltage and the power transfer each phase. The performances of these parameters are presented and discussed. KeywordsSix Autotransformer

Phase;Transmission

I.

line;

II.

CONCEPT DESIGN OF THE SIX PHASE TRANSMISSION LINE

The six phase transmission line is one of the alternatives to up rating a three-phase transmission-line systems. The transmission line is upgraded to provide a maximum ability of the transmission line to send the power to the load and to minimize the losses power at the transmission line. The power from the supply can be transmitted with higher efficiency to the load. The six phase transmission lines expand from the threephase source to the six phase transmission line using the autotransformer. The transformer will convert the phase angle of the transmission line from the 120° to be 60° the phase voltages. This paper will discuss the power transfer, efficiency and phase error in the transmission line using the three phases to six phases autotransformer conversion with tertiary winding as applied in based on the past research on the autotransformer conversion [2].

PSCAD;

INTRODUCTION

The high phase order in power system is an alternative to the electrical development to transfer power up to 73%. Previous researchers have proved the six phase system's performance to be ready for the built.

The autotransformer with tertiary winding single phase is considered to construct the three phase autotransformer for the six phase conversion. The current flow in the autotransformer tertiary winding are indicated as Ip for the primary current, Is for the secondary current and the It for tertiary current. The winding I, II and III for the autotransformer is indicated as the schematic diagram of an autotransformer is shown in Fig.1. The primary side and the secondary side voltage and current ratings are Vp & Ip , Vs & Is respectively whilst the tertiary side voltage and current ratings is represented by Vt & It. Numbers of turns in primary, secondary and tertiary side are winding I, winding II and winding III. Figure 1 (a) and (b) show the diagram for step up and step down autotransformer with tertiary winding.

The first initial application on an operating as the six phase transmission line is Goudey-Oakdale line in Binghamton, NY with the 93kV phase to phase [1]. The designation of the conversion used the delta/wye-grounded three phase transformer. The installation for this system is two delta-wye three phase transformer. This Goudey-Oakdale used the double circuit transformer configuration as conversions. In panel discussion of the 1994 IEEE Transmission and Distribution Conference, Chicago, IL, Guyker who was one of the workers from Allegheny Power Service Corporation pointed out the application of an autotransformer as the conversion because the autotransformer provides a balanced set voltages and current. Furthermore, It is more economical than that the conventional transformer[2]. The advantages of an autotransformer are an increased power handling capability, flatter frequency response, lower insertion loss and has lower distortion than the conventional transformer. The application of an autotransformer with tertiary winding is more economical than the conventional transformer such that the cost ratios to use autotransformer with respect to three winding transformers are 64.3% and 64.1% respectively [2].

Figure 1(a)

978-1-4673-0102-2/11/$26.00 ©2011 Crown

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transformer model which is based primarily on core geometry. Unlike the classical transformer model, magnetic coupling between windings of different phases, in addition to coupling between windings of the same phase, are taken into account [3]. The combination of UMEC transformer is designed for autotransformer tertiary winding. The autotransformer three phase to six phase conversion is designed and is presented in Fig. 3. The source of these three phases will be in through the Ea, Eb and Ec. The Eout1, Eout2, Eout3, Eout4, Eout5 and Eout6 are the output voltage after the step up. The connection for Eout1, Eout3 and Eout5 is the wye connection with solidly ground. The Eout2, Eout3 and Eout6 are the wye inverted connection with solidly ground.(Note: The winding for the autotransformer are winding #1 for winding III, winding #2 for winding II and winding #3 for the winding II based on the diagram fig.1)

Figure 1(b) Figure 1: (a) The step up autotransformer with tertiary winding (b) The step down autotransformer with tertiary winding

A six phase balance system has a 60° phase angle difference. Figure 2 shows the phasor diagram for the relation of voltage and phase angle. Vb

Vb’

60°

Va’

60° 60°

60°

Va

60° 60°

Vc

Vc’

Figure 2: Phasor diagram of voltage and phase for 6 phase balanced system

Based on the fig. 2 the mathematically generalization for the equation for each line voltage can be described. The equations for the six phase transmission line are as follow: Figure 3: The step up autotransformer three phase to six phase using wyewye inverted connection

Va = Van ∟0° Vb’= Van ∟60° Vb = Van∟120° Va’= Van ∟180° Vc = Van ∟-120° Vc’ = Van ∟-60°

(1) (2) (3) (4) (5) (6)

The configuration for the two types of this autotransformer is setup in the configuration transformer. In this research two types configurations which area ideal and non ideal autotransformer is setup. The performances of these configurations are to be analyzed and discussed. The autotrasformer capacity is used for these ideal and non ideal autotransformer is 100MVA. The leakage reactance defined as those providing an artificial leakage flux path between the primary and secondary windings. The basic Leakage Reactance Transformer consists of a core, a primary winding, a secondary winding, and a magnetic shunt that separates the primary and secondary windings. The leakage reactance is for the ideal is set 0.1p.u and non ideal is set 0.25p.u to all each

The simulation to represent the ability of the autotransformer as the conversion for the three phases to six phases is done using the PSCAD 4.2 version. The autotransformer with tertiary winding is designed using the UMEC (Unified Magnetic Equivalent Circuit) transformer single phase three winding. The UMEC transformer is the

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phase to six phase autotransformer to send the voltage and power through th transmission line. The configuration impedance and inductance transmission line is approximately 20km. The winding configuration of this step up and step down is 11kV/33kV/33kV with capacity of 100MVA. The power at sending end will be connected to the load of 70 MW. The complete test system is shown in Fig. 4. Two configurations which area an ideal and non ideal autotransformer is tested in this system.

winding connection as the winding I with winding II, winding I with winding III and winding II with winding III. The no load loss for the ideal and non-ideal autotransformer is set to 0 pu and 0.1 p.u respectively. The summary of the characteristic impedance of the autotransformer are shown in Table 1. TABLE I.

THE CHARACTERISTIC OF THE 100 MVA AUTOTRANSFORMER

Characteristic of the Autotransformers

Ideal

Non-ideal

100MVA

100MVA

Leakage Reactance (1 -2)

0.1 pu

0.25 pu

Leakage Reactance (1 -3)

0.1 pu

0.25 pu

Leakage Reactance (2-3)

0.1 pu

0.25 pu

No load loss

0.0 pu

0.1 pu

Cooper Loss

0.0 pu

0.1 pu

Transformer Capacity

In this paper, three values calculated are error for the phase conversion, the power transfer loss and the efficiency for the power transfer. The equation used area in these calculations are: Power 6Φ Efficiency Phase Error

: : :

P6Φ = 6 VI cos θ η = (Pout / Pin) x 100% ê = | simulated - actual |

(7) (8) (9)

Where, V: voltage output in the transmission line I : current output for the transmission line Cos θ : The phase angle Pout: Power output for the received at the load Pin : Power input from rhe source.

In this research a test system is designed and simulate to study the performance of the conversions for the autotransformer. Figure 4 shows the test system and its configuration. This test system starts with the three phase power supply at 132kV. The conversion uses a step up three

Figure 4 : The test system for the conversion autotransformer in transmission line

III.

RESULT SIMULATION TEST SYSTEM OF THE SIX PHASE TRANSMISSION LINE

The results of this conversion for the autotransformer are recorded and represented. The Table II shows the detail result for the ideal and non-ideal autotransformer as the conversion. The result for the autotransformer is based on the phase angle and the magnitude voltage. The six voltage phase and magnitude are based on the phasor diagram in fig.5. Figure 5 shows the phasor diagram for the six phase transmission line after the conversion of step up autotransformer. In the phasor diagram, the voltage magnitude and the phase angle is shown in

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the below left and right side respectively. The sign D in the fig. 5 shows the phase angle used in degree. The non-ideal autotransformer phasor diagram also has similar figure as in fig. 5 but the magnitude and the phase angle is difference. Results in Table II are the summary results for the ideal and non-ideal autotransformer. The error for the ideal and non-ideal autotransformer is based on the actual phase angle. The calculation phase error is based on equation (9). The error angle is the difference of the phase angle simulation and the phase angle theory for the conversion.

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TABLE II.


THE RESULT FOR THE CONVERSION OF THE SIX PHASE AND THE PHASE ANGLE ERROR

Ideal Autotransformer

Non-ideal Autotransformer

Line Voltage (kV)

Phase

Error

Voltage (kV)

Phase

Error

Eout 1

228.624

-0.011

±0.011

227.270

-1.049

±1.049

Eout 2

228.624

180

0.000

226.618

178.40

±0.160

Eout 3

228.624

-120

0.000

227.270

121.00

±1.000

Eout4

228.624

59.98

±0.02

226.618

58.38

±1.62

Eout 5

228.624

120

0.000

227.270

119.00

±1.000

Eout 6

228.624

-60

0.000

226.618

-61.62

±1.38

Time (sec) Figure 6: The voltage waveform of the six phase transmission line for the step up ideal autotransformer

Figure 7 shows the current waveform of the six phase transmission line. The current in the transmission-line test power system is simulated. The current of each line is approximately same.

Time (sec) V:

Figure 7: The current waveform for the six phase transmission line for the step up ideal autotransformer

Figure 5: The phasor diagram for the six phase transmission line fot the ideal transformer

In alternating current (ac) the movement of electric charge periodically reverses direction. The instantaneous voltage and current are shown in the waveform of Fig. 6 and 7 respectively. The waveform for the step up in the ideal autotransformer is shown in the figure 6. The Vrms voltage for the ideal transformer is 228.624kV for the six lines. The ac sinusoidal waveform voltage is generated from the simulation of the test system.

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The non-ideal autotransformer with tertiary winding is tested and simulated to show the ability of the autotransformer as the conversion for step up and step down in transmission line. The waveform voltage and waveform current propagation is in the waveform alternating sinusoidal with good shape waveform. The current and voltage waveform are represented based on the simulation test system and the configuration as in table. I. The figure 8 shows the transmission-line voltage waveform for the step up non-ideal autotransformer. The Vrms of every six lines and phase angle is represented as the table II.

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Time (sec) Figure 8: The voltage waveform of six phase transmission line for the step up non-ideal autotransformer

The figure 9 shows the waveform current transmission line for the step up non –ideal transformer. The current waveform is flowed for each line is difference. The difference is due to the losses in the cooper, the no load losses in the autotransformer and the leakage between the winding of the autotransformer that decrease the current in each phase line. The phase angle differences between the phases to another phase adjacent are having approximately 60° with maximum error received is ±1.62° based on the table II using equation (9).

Time (sec) Figure 9: The current waveform of six phase transmission line for the step up non-ideal autotransformer

The power transfer of the transmission line is simulated in the test power system. The power is transferred in each six line can minimize the loss through the transmission line. It can also help to reduce the waste energy when it is sent to the substation or load. Table III shown the real power and reactive power transferred in the test system. TABLE III.

Line

THE RESULT FOR THE POWER TRANSFER FOR THE SIX PHASE TRANSMISSION LINE

Ideal Autotransformer P Q (MW) (MVar)

Non-ideal Autotransformer P Q (MW) (MVar)

Eout 1

12.29

-0.0855

279.9

17.93

Eout 2

10.95

0

214.0

4.934

242

Eout 3

11.66

0

262.5

20.21

Eout4

10.38

0.0625

201.4

6.296

Eout 5

13.07

0

294.2

23.93

Eout 6

11.64

0.010

225.8

5.509

As has been discussed earlier, the six phase power system has the power transfer with higher efficiency. The result for the test system is represented. Based on fig.6 to fig.9 the voltage and current waveform are not distorted when the conversion to the transmission line. The power output at sending end in the power system with load 70MW for the ideal autotransformer is 69.98MW. The power sending end for the non-ideal autotransformer is 68.3MW. The power transfer for the 20km test power system is about 97.6%. The highefficiency power transfers for the autotransformer are same as the theory that the autotransformer has higher efficiency. IV.

DISCUSSION

The ability for the autotransformer as the conversion three phases to six phases are has been presented. The connection wye-wye inverted in the three-phase configuration is designed to produce the 60° degree adjacent to every phase voltage. The wye connection in the autotransformer is a three single phase autotransformer connected with each other. The winding #3 of all the three autotransformer is solidly grounded. The connection for the winding #2 is automatically in wye connection output. The tertiary winding (winding #1 in PSCAD) is connected in wye invert which means the the connection is opposite the direction current out with the original and solidly ground. The maximum phase error in the ideal and non – ideal transformer is small are ±0.02 and ±0.162 respectively using the equation (9).The result shows that the ac sinusoidal voltage is a good sinusoidal without any distortion. The amplitude current for Eout1, Eout3 and Eout5 are similar. The other tertiary winding such as Eout2, Eout4 and Eout6 is also similar. The total power transfer for the ideal autotransformer and non-ideal are 99.97% and 97.6% respectively. Based on the result shows that the autotransformer has high efficiency power transfer and the conversion three to six phases is provides balanced set for the voltage and current with the low phase angle difference between the voltage and current in the waveform. The non- ideal autotransformer results in table III, the instantaneous power in each phase are needed to send more power to transfer to the load. The fig. 10 shows the phase shifting waveform between the current and the voltage are in same phase when the propagation in the transmission line. The sample time start at the point A is 0.3250s with 0 amplitude and finish at point B is 0.342s at the 0 amplitude for the current and voltage. This test sample is for one cycle.

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REFERENCES A

B

[1]

[2]

[3] [4]

[5]

Time (sec) Figure 10: The test phase shifting in the waveform voltage and the current in same time propagation.

V.

THE FURHTER WORK

[6]

[7]

The autotransformer is one of the alternative conversions to achieve the high phase order (HPO) technology. The result for the test in the system line needs to improve for the practical test system. Furthermore, the analysis for the performance of the transmission line tests system such as transmission transient, fault, protection and other important. The detail performance analysis will discuss for further work in the practical test system with industry.

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[8]

[9]

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