Three Phase Transformer Banks 3 86379 F0

User Manual: 3-phase-transformer-banks-86379 F0

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RENEWABLE ENERGY

THREE-PHASE TRANSFORMER BANKS

Courseware Sample

the staff

Lab-Volt Ltd.

reproduced, in any form or by any means, without the prior

written permission of Lab-Volt Ltd.

Printed in Canada

August 2011

http://waterheatertimer.org/How-to-wire-3-phase-electric.html

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Three-Phase

Transformer Banks

A Three-Phase Transformer Banks v

Safety Symbols

The following safety symbols may be used in this manual and on the Lab-Volt

equipment:

Symbol Description

DANGER indicates a hazard with a high level of risk which, if not

avoided, will result in death or serious injury.

WARNING indicates a hazard with a medium level of risk which,

if not avoided, could result in death or serious injury.

CAUTION indicates a hazard with a low level of risk which, if not

avoided, could result in minor or moderate injury.

CAUTION used without the Caution, risk of danger sign ,

indicates a hazard with a potentially hazardous situation which,

if not avoided, may result in property damage.

Caution, risk of electric shock

Caution, hot surface

Caution, risk of danger

Caution, lifting hazard

Caution, hand entanglement hazard

Direct current

Alternating current

Both direct and alternating current

Three-phase alternating current

Earth (ground) terminal

Protective conductor terminal

Frame or chassis terminal

Safety Symbols

vi Three-Phase Transformer Banks A

Symbol Description

Equipotentiality

On (supply)

Off (supply)

Equipment protected throughout by double insulation or

reinforced insulation

In position of a bi-stable push control

Out position of a bi-stable push control

A Three-Phase Transformer Banks vii

Foreword

Three-phase transformer banks serve the same purpose in three-phase circuits

as single-phase power transformers in single-phase circuits. This means that

three-phase transformer banks are primarily used to either step-up (i.e., to

increase) the voltage from the primary windings to the secondary windings, or to

step-down (i.e., to decrease) the voltage from the primary windings to the

secondary windings. Since three-phase ac power is widely used worldwide for

both power transmission and power distribution, three-phase transformer banks

are one of the most common electrical components and are essential to any

three-phase ac power network.

Many three-phase transformer configurations are possible when connecting the

primary and secondary windings of a three-phase transformer bank. Each

configuration presents different characteristics. When connecting a three-phase

transformer bank in a circuit, it is therefore important to determine which

characteristics are advantageous to the circuit, and to choose the three-phase

transformer configuration accordingly. The four most common three-phase

transformer configurations are the wye-wye, delta-delta, wye-delta, and delta-

wye configurations.

This course, Three-Phase Transformer Banks, teaches the basic concepts of

three-phase transformer banks. Students are introduced to the different

characteristics of three-phase transformer banks. They learn how to connect the

windings of three-phase transformer banks in wye or delta. Students are also

introduced to the four most common types of three-phase transformer

configurations: wye-wye, delta-delta, wye-delta, and delta-wye. They determine

the voltage, current, and phase relationships between the primary windings and

the secondary windings of three-phase transformer banks for each of these

configurations. Students also verify the theory presented in the manual by

performing circuit measurements and calculations.

Three-phase transformer bank used for power distribution.

A Three-Phase Transformer Banks ix

Table of Contents

Introduction Three-Phase Transformer Banks ............................................. 1

Introduction to three-phase power transformers. Types of

three-phase power transformers. Connecting the windings of

three-phase transformer banks in wye and in delta.

Exercise 1 Three-Phase Transformer Configurations .............................. 5

Common three-phase transformer configurations. Voltage,

current, and phase relationships of the four common three-

phase transformer configurations. Summary of the

characteristics of the four common three-phase transformer

configurations. Uses of three-phase transformer banks.

Appendix A Equipment Utilization Chart .................................................... 27

Appendix B Glossary of New Terms ........................................................... 29

Appendix C Impedance Table for the Load Modules ................................ 31

Index of New Terms ............................................................................................. 33

Bibliography ......................................................................................................... 35

We Value Your Opinion! ...................................................................................... 37

Sample Exercise

Extracted from

Student Manual

A Three-Phase Transformer Banks 5

When you have completed this exercise, you will know how to connect three-

phase transformer banks in wye-wye, delta-delta, wye-delta, and delta-wye

configurations. You will determine what are the voltage, current, and phase

relationships between the primary windings and the secondary windings of a

three-phase transformer bank for each of these configurations. You will be

familiar with the different uses of three-phase transformer banks in three-phase

ac power circuits.

The Discussion of this exercise covers the following points:

 Common three-phase transformer configurations

 Voltage, current, and phase relationships of the four common three-

phase transformer configurations

 Summary of the characteristics of the four common three-phase

transformer configurations

 Uses of three-phase transformer banks

Common three-phase transformer configurations

Many three-phase transformer configurations are possible when connecting

the primary and secondary windings of a three-phase transformer bank. Each

configuration presents different characteristics. When connecting a three-phase

transformer bank in a circuit, it is therefore important to determine which

characteristics are advantageous to the circuit, and to choose the appropriate

three-phase transformer configuration accordingly.

The four most common three-phase transformer configurations are wye-wye,

delta-delta, wye-delta, and delta-wye configurations. Each of these configurations

is shown in Figure 3. The letter (A, B, or C) beside each winding in Figure 3

identifies one of the transformers in a three-phase transformer bank. This allows

the primary and secondary windings of each transformer in the three-phase

transformer bank to be easily located in the diagrams of Figure 3.

Three-Phase Transformer Configurations

Exercise 1

EXERCISE OBJECTIVE

DISCUSSION OUTLINE

DISCUSSION

Exercise 1 – Three-Phase Transformer Configurations  Discussion

6 Three-Phase Transformer Banks A

Figure 3. The four most common three-phase transformer configurations.

As you can see from the figure, wye-connected windings use 4 wires, while delta-

connected windings use only 3 wires. When setting up a three-phase transformer

bank in a wye-delta or delta-wye configuration, this property allows the number of

wires in a three-phase ac circuit to be modified from 4 wires to 3 wires, or from

3 wires to 4 wires, respectively. Either of these configurations can be a significant

advantage, depending on the requirements of the particular application in which it

is used.

Voltage, current, and phase relationships of the four common three-

phase transformer configurations

The most determining characteristics of each three-phase transformer

configuration mentioned in the previous section (i.e., the wye-wye, delta-delta,

wye-delta, and delta-wye configurations) are their respective voltage, current,

and phase relationships between the primary windings and the secondary

(a) Wye-wye configuration (b) Delta-delta configuration

Three-phase transformer bank Three-phase transformer bank

Primaries Secondaries

Primaries

Secondaries Primaries

Secondaries

Exercise 1 – Three-Phase Transformer Configurations  Discussion

A Three-Phase Transformer Banks 7

windings. The following three sections discuss these relationships for each three-

phase transformer configuration. Note that, as wye-wye and delta-delta

configurations have similar voltage, current, and phase relationships, both

configurations are covered in the same section. Also note that, in the following

sections, the turns ratio of each transformer in the three-phase transformer bank

is assumed to be equal to 1:1. This allows observation of the effects each

configuration has on the voltage, current, and phase relationships of the three-

phase transformer bank, independently of the turns ratio.

Wye-wye and delta-delta configurations

When a three-phase transformer bank is connected in either a wye-wye or a

delta-delta configuration, the voltage, current, and phase relationships between

the primary windings and the secondary windings are identical to the

relationships found in a conventional single-phase power transformer. This

means that the values of the line voltages and currents at the secondary are

equal to those of the line voltages and currents at the primary (neglecting

transformer losses). Also, the line voltage sine waves at the secondary are in

phase with the line voltage sine waves at the primary. The same is true for the

line current sine waves at the secondary with respect to the line current sine

waves at the primary.

Wye-delta configuration

When a three-phase transformer bank is connected in a wye-delta configuration,

the values and phases of the line voltages and currents at the secondary are

different from those at the primary. Thus, in a wye-delta configuration, the value

of the line voltages at the secondary is equal to that of the line voltages at the

primary divided by √3. Conversely, the value of the line currents at the secondary

is equal to that of the line currents at the primary multiplied by √3. Furthermore,

the line voltage sine waves at the secondary lag behind those at the primary

by 30°. The same is true for the line current sine waves at the secondary with

respect to the line current sine waves at the primary.

Delta-wye configuration

When a three-phase transformer bank is connected in a delta-wye configuration,

the values and phases of the line voltages and currents at the secondary are

different from those at the primary. Thus, in a delta-wye configuration, the value

of the line voltages at the secondary is equal to that of the line voltages at the

primary multiplied by

√3. Conversely, the value of the line currents at the

secondary is equal to that of the line currents at the primary divided by

√3.

Furthermore, the line voltage sine waves at the secondary lead those at the

primary by 30°. The same is true for the line current sine waves at the secondary

with respect to the line current sine waves at the primary.

Summary of the characteristics of the four common three-phase

transformer configurations

The following table gives a summary of the different characteristics of the four

three-phase transformer configurations presented in the previous section

(i.e., the wye-wye, delta-delta, wye-delta, and delta-wye configurations).

Exercise 1 – Three-Phase Transformer Configurations  Discussion

8 Three-Phase Transformer Banks A

Table 1. Summary of the characteristics of three-phase transformer configurations.

Three-phase transformer

configuration

Line voltage

relationship

(.:.)

Line current

relationship

(.:.)

Phase shift

(Sec. with

respect to

Pri.)

Number of

wires

(Pri.:Sec.)

Wye-wye configuration

1: 1 1: 1 0° 4: 4

Delta-delta configuration

1: 1 1: 1 0° 3: 3

Wye-delta configuration

√3:1 1:√3 30°

(30° lag)4: 3

Delta-wye configuration

1: √3√3:1 30°

(30° lead)3: 4

Remember that the line voltage and current relationships presented in Table 1

are valid only when the turns ratio of the transformers in the three-phase

transformer bank is equal to 1:1. When the turns ratio of the transformers in the

three-phase transformer bank is not 1:1, the actual line voltages at the secondary

can be found by multiplying the primary line voltages by the voltage ratio

appropriate to the configuration of the three-phase transformer bank and the

inverse of the turns ratio (. .

⁄) of the transformers. Similarly, the actual line

currents at the secondary can be found by multiplying the primary line currents

Exercise 1 – Three-Phase Transformer Configurations  Procedure Outline

A Three-Phase Transformer Banks 9

by the current ratio appropriate to the configuration of the three-phase

transformer bank and the turns ratio (. .

⁄) of the transformers.

Uses of three-phase transformer banks

Three-phase transformer banks are used in three-phase ac power circuits for

basically the same reasons as single-phase power transformers in single-phase

ac circuits, i.e., to step-up or step-down the voltages in the circuit and to provide

electrical isolation between the primary windings and the secondary windings.

However, the special properties of certain three-phase transformer configurations

presented in the previous sections allow three-phase transformer banks to be

used in a few additional applications. The primary uses of three-phase

transformer banks in three-phase ac power circuits are summarized below.

1. Three-phase transformer banks allow the voltages in the three-phase

ac power circuit to be stepped-up (i.e., to be increased) or stepped-

down (i.e., to be decreased).

2. Three-phase transformer banks provide electrical isolation between the

primary windings and the secondary windings.

3. Three-phase transformer banks connected in a wye-delta or in a delta-

wye configuration allow the number of wires in the three-phase ac power

circuit to be decreased from 4 to 3, or increased from 3 to 4, respectively.

4. Three-phase transformer banks connected in a wye-delta or in a delta-

wye configuration allow the incoming line voltages and currents to be

phase shifted -30° or 30°, respectively.

The Procedure is divided into the following sections:

 Set up and connections

 Voltage, current, and phase relationships in a wye-wye configuration

 Voltage, current, and phase relationships in a wye-delta configuration

 Voltage, current, and phase relationships in a delta-delta configuration

 Voltage, current, and phase relationships in a delta-wye configuration

High voltages are present in this laboratory exercise. Do not make o

modify any banana jack connections with the power on unless otherwise

specified.

Set up and connections

In this section, you will set up a circuit containing a three-phase transformer bank

connected in a wye-wye configuration. You will then set the measuring

equipment required to study the voltage, current, and phase relationships of the

three-phase transformer bank.

PROCEDURE OUTLINE

PROCEDURE

Exercise 1 – Three-Phase Transformer Configurations  Procedure

10 Three-Phase Transformer Banks A

1. Refer to the Equipment Utilization Chart in Appendix A to obtain the list of

equipment required to perform this exercise.

Install the required equipment in the Workstation.

2. Make sure that the ac and dc power switches on the Power Supply are set to

the O (off) position, then connect the Power Supply to a three-phase

ac power outlet.

Connect the Power Input of the Data Acquisition and Control Interface to

a 24 V ac power supply. Turn the 24 V ac power supply on.

3. Connect the USB port of the Data Acquisition and Control Interface to a USB

port of the host computer.

4. Turn the host computer on, then start the LVDAC-EMS software.

In the Module Selector window, make sure that the Data Acquisition and

Control Interface is detected. Make sure that the Computer-Based

Instrumentation function for the Data Acquisition and Control Interface is

selected. Also, select the network voltage and frequency that correspond to

the voltage and frequency of your local ac power network, then click the OK

button to close the Module Selector window.

Exercise 1 – Three-Phase Transformer Configurations  Procedure

A Three-Phase Transformer Banks 11

5. Connect the equipment as shown in Figure 4.

Local ac power network , , 

(Ω)

Voltage

(V)

Frequency

(Hz)

120 60 171

220 50 629

240 50 686

Figure 4. Three-phase transformer bank connected in a wye-wye configuration.

a The values of the resistive loads used in the circuits of this manual depend on your

local ac power network voltage and frequency. Whenever necessary, a table below

the circuit diagram indicates the resistance of each load resistor for ac power

network voltages of 120 V, 220 V, and 240 V, and for ac power network

frequencies of 50 Hz and 60 Hz. Make sure to use the component values

corresponding to your local ac power network voltage and frequency.

6. Make the necessary switch settings on the Resistive Load in order to obtain

the resistance value required.

a Appendix C lists the switch settings required on the Resistive Load in order to

obtain various resistance values.

7. In the Metering window, make the required settings in order to measure the

rms values (ac) of the line voltages ., ., and . (inputs E1, E2,

and E3, respectively), and the line currents ., ., and . (inputs I1,

I2, and I3, respectively) at the secondary of the three-phase transformer

bank. Set two other meters to measure the line voltage . and current .

at the primary of the three-phase transformer bank (inputs E4 and I4,

respectively).







Three-Phase Transformer Bank module

12 15 13

710 8

2 5 3

Exercise 1 – Three-Phase Transformer Configurations  Procedure

12 Three-Phase Transformer Banks A

Voltage, current, and phase relationships in a wye-wye configuration

In this section, you will measure the line voltages and currents at the secondary

of the three-phase transformer bank, as well as a line voltage and current at the

primary. Using the measured values, you will determine the voltage and current

relationships between the primary and secondary windings of the three-phase

transformer bank. You will then open the Phasor Analyzer and the Oscilloscope,

and use both instruments to determine the phase shift between the line voltages

at the secondary and the line voltages at the primary. Finally, you will confirm

that the voltage, current, and phase relationships measured when the three-

phase transformer bank is connected in a wye-wye configuration are coherent

with the theory presented in the exercise discussion.

8. On the Power Supply, turn the three-phase ac power source on.

9. In the Metering window, measure the line voltages ., ., and . at

the secondary of the three-phase transformer bank, as well as the line

voltage . at the primary. Also, measure the line currents ., .,

and . at the secondary of the three-phase transformer bank, as well as

the line current . at the primary. Record all values below.

.  V .  A

.  V .  A

.  V .  A

.  V .  A

10. Using the line voltage and current values you measured in the previous step,

determine the voltage and current relationships between the primary

windings and the secondary windings of the three-phase transformer bank

when it is connected in a wye-wye configuration.

Voltage relationship (.:.)  :

Current relationship (.:.)  :

11. In LVDAC-EMS, open the Phasor Analyzer and make the required settings to

observe the phasors of the line voltages ., ., and . at the

secondary (inputs E1, E2, and E3, respectively), as well as the line

voltage . at the primary of the three-phase transformer bank (input E4).

Set the phasor of the line voltage . (input E4) at the primary as the

reference phasor.

Using the Phasor Analyzer, determine the phase shift between the line

voltage . at the secondary and the line voltage . at the primary of the

three-phase transformer bank.

Phase shift between . and . °

Exercise 1 – Three-Phase Transformer Configurations  Procedure

A Three-Phase Transformer Banks 13

12. In LVDAC-EMS, open the Oscilloscope and make the required settings to

observe the waveforms of the line voltages ., ., and . at the

secondary (inputs E1, E2, and E3, respectively), as well as the line

voltage . at the primary of the three-phase transformer bank (input E4).

Using the Oscilloscope, determine the phase shift between the line

voltage . at the secondary and the line voltage . at the primary of the

three-phase transformer bank.

Phase shift between . and . °

Does the phase shift between the line voltage . at the secondary and the

line voltage . at the primary you just determined confirm the phase shift

you obtained previously using the Phasor Analyzer?

 Yes  No

13. Are the voltage, current, and phase relationships you determined for the

three-phase transformer bank connected in a wye-wye configuration

coherent with the theory presented in the exercise discussion?

 Yes  No

14. On the Power Supply, turn the three-phase ac power source off.

Voltage, current, and phase relationships in a wye-delta

configuration

In this section, you will connect the three-phase transformer bank in a wye-delta

configuration. You will measure the line voltages and currents at the secondary

of the three-phase transformer bank, as well as a line voltage and current at the

primary. Using the measured values, you will determine the voltage and current

relationships between the primary and secondary windings of the three-phase

transformer bank. You will then use the Phasor Analyzer and the Oscilloscope to

determine the phase shift between the line voltages at the secondary and the line

voltages at the primary. Finally, you will confirm that the voltage, current, and

phase relationships measured when the three-phase transformer bank is

connected in a wye-delta configuration are coherent with the theory presented in

the exercise discussion.

Exercise 1 – Three-Phase Transformer Configurations  Procedure

14 Three-Phase Transformer Banks A

15. Connect the equipment as shown in Figure 5. In this circuit, only the

connections at the secondary windings of the three-phase transformer bank

have been modified with respect to the circuit used in the previous section.

Local ac power network , , 

(Ω)

Voltage

(V)

Frequency

(Hz)

120 60 171

220 50 629

240 50 686

Figure 5. Three-phase transformer bank connected in a wye-delta configuration.

16. On the Power Supply, turn the three-phase ac power source on.

17. In the Metering window, measure the line voltages ., ., and . at

the secondary of the three-phase transformer bank, as well as the line

voltage . at the primary. Also, measure the line currents ., .,

and . at the secondary of the three-phase transformer bank, as well as

the line current . at the primary. Record all values below.

.  V .  A

.  V .  A

.  V .  A

.  V .  A







Three-Phase Transformer Bank module

Exercise 1 – Three-Phase Transformer Configurations  Procedure

A Three-Phase Transformer Banks 15

18. Using the line voltage and current values you measured in the previous step,

determine the voltage and current relationships between the primary and the

secondary windings of the three-phase transformer bank when it is

connected in a wye-delta configuration.

Voltage relationship (.:.)  :

Current r relationship (.:.)  :

19. Using the Phasor Analyzer and the Oscilloscope, determine the phase shift

between the line voltage . at the secondary and the line voltage . at

the primary of the three-phase transformer bank.

Phase shift between . and . °

20. Are the voltage, current, and phase relationships you determined for the

three-phase transformer bank connected in a wye-delta configuration

coherent with the theory presented in the exercise discussion?

 Yes  No

21. On the Power Supply, turn the three-phase ac power source off.

Voltage, current, and phase relationships in a delta-delta

configuration

In this section, you will connect the three-phase transformer bank in a delta-delta

configuration. You will measure the line voltages and currents at the secondary

of the three-phase transformer bank, as well as a line voltage and current at the

primary. Using the measured values, you will determine the voltage and current

relationships between the primary and secondary windings of the three-phase

transformer bank. You will then use the Phasor Analyzer and the Oscilloscope to

determine the phase shift between the line voltages at the secondary and the line

voltages at the primary. You will confirm that the voltage, current, and phase

relationships measured when the three-phase transformer bank is connected in a

delta-delta configuration are coherent with the theory presented in the exercise

discussion. You will then reverse the connection of the windings at the secondary

of the three-phase transformer bank. You will observe the resulting phase shift

between the secondary and the primary line voltages using the Phasor Analyzer

and the Oscilloscope, and analyze the results.

Exercise 1 – Three-Phase Transformer Configurations  Procedure

16 Three-Phase Transformer Banks A

22. Connect the equipment as shown in Figure 6. In this circuit, only the

connections at the primary windings of the three-phase transformer bank

have been modified with respect to the circuit used in the previous section.

Local ac power network , , 

(Ω)

Voltage

(V)

Frequency

(Hz)

120 60 171

220 50 629

240 50 686

Figure 6. Three-phase transformer bank connected in a delta-delta configuration.

23. On the Power Supply, turn the three-phase ac power source on.

24. In the Metering window, measure the line voltages ., ., and . at

the secondary of the three-phase transformer bank, as well as the line

voltage . at the primary. Also measure the line currents ., .,

and . at the secondary of the three-phase transformer bank, as well as

the line current . at the primary. Record all values below.

.  V .  A

.  V .  A

.  V .  A

.  V .  A

25. Using the line voltage and current values you measured in the previous step,

determine the voltage and current relationships between the primary and the







Three-Phase Transformer Bank module

12 15

710

Exercise 1 – Three-Phase Transformer Configurations  Procedure

A Three-Phase Transformer Banks 17

secondary of the three-phase transformer bank when it is connected in a

delta-delta configuration.

Voltage relationship (.:.)  :

Current relationship (.:.)  :

26. Using the Phasor Analyzer and the Oscilloscope, determine the phase shift

between the line voltage . at the secondary and the line voltage . at

the primary of the three-phase transformer bank.

Phase shift between . and . °

27. Are the voltage, current, and phase relationships you determined for the

three-phase transformer bank connected in a delta-delta configuration

coherent with the theory presented in the exercise discussion?

 Yes  No

28. On the Power Supply, turn the three-phase ac power source off.

Exercise 1 – Three-Phase Transformer Configurations  Procedure

18 Three-Phase Transformer Banks A

29. Reverse the connections at each of the secondary windings of the three-

phase transformer bank. The circuit should now be as shown in Figure 7.

Local ac power network , , 

(Ω)

Voltage

(V)

Frequency

(Hz)

120 60 171

220 50 629

240 50 686

Figure 7. Three-phase transformer bank connected in a delta-delta configuration with reversed connections at the secondary

windings.

30. On the Power Supply, turn the three-phase ac power source on.

31. Using the Phasor Analyzer and the Oscilloscope, determine the phase shift

between the line voltage . at the secondary and the line voltage . at

the primary of the three-phase transformer bank.

Phase shift between . and . °

32. What happens to the phase shift between the line voltage . at the

secondary and the line voltage . at the primary when the connections at

the secondary windings of the three-phase transformer bank are reversed?

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



Three-Phase Transformer Bank module

Exercise 1 – Three-Phase Transformer Configurations  Procedure

A Three-Phase Transformer Banks 19

Do your results confirm that it is important to respect the winding polarity

when connecting the windings of a three-phase transformer bank? Briefly

explain why.

33. On the Power Supply, turn the three-phase ac power source off.

Voltage, current, and phase relationships in a delta-wye

configuration

In this section, you will connect the three-phase transformer bank in a delta-wye