EET-216 LAB # 5 - Transformer Wye and Delta 3-Phase Connection PDF

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Lab 5...

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Electrical Engineering Electrical Engineering Technician AMAT/ SETAS Course: EET-216 DRAWINGS & INSTALLATION 3 Out of 120 Name: 1. Deanne Aira P. Pimentel – 301093498_____________ Name: 2. _________________________________________________________ Name: 3. _________________________________________________________

Lab # 5 Title: Wye and Delta 3-phase connections Introduction: Three phase transformers are used throughout industry. Almost all power generated in North America is three phase. 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 and the secondary windings. However, the special properties of certain three-phase transformer configurations 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. •

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).

•

Three-phase transformer banks provide electrical isolation between the primary windings and the secondary windings.

•

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.

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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.

1. OBJECTIVE The student will demonstrate the ability to perform tests and make connections to bind three single phase transformers into a three phase Wye transformer and Delta transformer. The student will also perform Wye to Wye and Wye to Delta connections on the transformer sets. The student will perform

tests to determine correct connections and transformer characteristics when connected in the different configurations. 2. MATERIALS REQUIRED Lab Volt Three phase Power Supply - 8821-2 Lab Volt Three-Phase Transformer Bank - 8348-4 Data Acquisition and Control Interface - 9063-D Clamp ammeter (Provided by school)-on Class III multi-meter (Provided by student)

NOTE: Do not install any improper or damaged components. Wiring must be performed to meet current electrical code requirements. Have instructor review finished connections PRIOR to applying power.

High voltages are present in this laboratory exercise. Do not make or modify any banana jack connections with the power on unless otherwise specified.

3a.

3  Wye connections

In this section, you will set up a circuit containing a three-phase transformer bank connected in a wyewye configuration. You will then set the measuring equipment required to study the voltage, current, and phase relationships of the three-phase transformer bank. The diagram below is a typical schematic for a Wye - Wye three-phase transformer:

1. Draw the connections on the diagram below to create a Wye to Wye transformer bank using three single phase transformers. /2

2. Record the Lab-Volt transformer nameplate data • • • • • •

/2

208 V Primary rated Voltage: Secondary rated Voltages: 88 V 120 V Rated VA: 250 VA Rated Current Primary 1.2 A Rated Current Secondary 1.2 A Type (Dry or Wet) Dry

3. 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 the three-phase AC power outlet. /2 Connect the Power Input of the Data Acquisition and Control Interface to a 24V AC power supply. Turn the 24V ac power supply on. 4. Connect the USB port of the Data Acquisition and Control Interface to a USB port of the host computer. 5. Turn the host computer on, then start the LVDAC-EMS software. In the LVDAC-EMS Start-Up window, make sure the Data Acquisition and Control Interface are detected. Select the network voltage and frequency (120V, 60Hz) then click the OK button to close the LVDAC-EMS Start-Up window. 6. Connect the equipmnet as shown in Figure below. Use the Power Supply to implement the AC power source. Utalize the transformers on the Three-Phase Transformer Bank and the Resistive Load to connect the Wye to Wye circuit.

Make the necessary switch settings on the Resistive Load so that the resistance of the threephase resistor is equal to 171Ω. 7. In the Metering window, make the required settings in order to measure the AC rms values.

8. After instructor reviews your connections turn on the Power Supply

/3

9. In the Metering window measure the Secondary Line Voltages and Currents, as well as the Line Voltage and Line Current at Primary side. Complete the Table below. /2 200.7

0.668

200.1

0.666

200. 3

0.667

210.3

0.689

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. Voltage relationship (EL Primary : EL Secondary)

1.05 : _1_

Current relationship (IL Primary : IL Secondary)

_1_ : _0.97_

11. Calculate the input power (show your steps)

/2 /2

𝑃𝑖𝑛 = 𝐸𝑝𝑟𝑖 𝐼𝑝𝑟𝑖

𝑃𝑖𝑛 = 210.3 𝑉 × 0.689 𝐴 = 144.9 𝑉𝐴 12. Calculate the Output power (show your steps)

/2

𝑃𝑜𝑢𝑡 = 𝐸𝑠𝑒𝑐 𝐼𝑠𝑒𝑐

𝑃𝑜𝑢𝑡 = 200.7 𝑉 × 0.668 𝐴 = 134.1 𝑉𝐴 13. Calculate the transformer efficiency (show your steps) 𝜂=(

/2

𝑃𝑜𝑢𝑡 134.1 𝑉𝐴 ) × 100% = × 100% = 92.5 % 𝑃𝑖𝑛 144.9 𝑉𝐴

14. Calculate rated Power Output of your Transformer bank (show your steps)

/3

𝑅𝑎𝑡𝑒𝑑 𝑃𝑜𝑢𝑡 = 𝐸𝑠𝑒𝑐 𝐼𝑟𝑎𝑡𝑒𝑑

𝑃𝑜𝑢𝑡 = 200.7 𝑉 × 1.2 𝐴 = 240.84 𝑉𝐴 15. In the LVDAC-EMS, open the Phasor Analyzer and make the required settings to observe the phasors of the Line Voltages at the secondary (inputs E1, E2, and E3 respectively), as well as the Line Voltage at the primary (input E4) Using the Phasor Analyzer, determine the phase shift between the Secondary Line Voltage and the Primary Line voltage of the transformer bank. 0 Phase shift between EL Secondary and EL Primary = _______o

/1

16. In the LVDAC-EMS, open the Oscilloscope and make the required settings to observe the waveforms of the Secondary Line Voltages (inputs E1, E2, and E3 respectively) as well as the Primary Line Voltage. Using the Oscilloscope, determine the phase shift between the Secondary Line Voltage and the Primary Line voltage of the transformer bank. 0 o Phase shift between EL Secondary and EL Primary = ______

/1

Does the phase shift between the Secondary and Primary Line voltages you just determined confirm the phase shift you obtained previously using the Phasor Analyzer? □ Yes □ No /1 17. Turn off Power supply.

3b.

/2

3  Wye - delta Connections.

In this section, you will set up a circuit containing a three-phase transformer bank connected in a wyewye configuration. You will then set the measuring equipment required to study the voltage, current, and phase relationships of the three-phase transformer bank. The diagram below is a typical schematic for a Wye - Delta three phase transformer:

1. Draw the connections on the diagram below to create a Wye to Delta transformer bank using three single phase transformers. (Place identifying marks to show polarity, see notes on “closing the Delta” regarding hazards associated with not following polarities) /2

2. Connect the equipmnet as shown in Figure below. Use the Power Supply to implement the AC power source. Utalize the transformers on the Three-Phase Transformer Bank and the Resistive Load to connect the Delta to Wye circuit.

3. Make the necessary switch settings on the Resistive Load so that the resistance of the threephase resistor is equal to 171Ω. 4. After instructor reviews your connections turn on the Power Supply /3 5. In the Metering window measure the Secondary Line Voltages and Currents, as well as the Line Voltage and Line Current at Primary side. Complete the Table below. /2 119.1

0.398

119.1

0.397

118.8

0.395

210.0

0.245

6. 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. Voltage relationship (EL Primary : EL Secondary)

1.77 : _1_

Current relationship (IL Primary : IL Secondary)

_1_ : _1.61_

7. Calculate the input power (show your steps) 𝑃𝑖𝑛 = 𝐸𝑝𝑟𝑖 𝐼𝑝𝑟𝑖 𝑃𝑖𝑛 = 210.0 𝑉 × 0.245 𝐴 = 51.45 𝑉𝐴

/2 /2

8. Calculate the Output power (show your steps)

/2

𝑃𝑜𝑢𝑡 = 𝐸𝑠𝑒𝑐 𝐼𝑠𝑒𝑐 𝑃𝑜𝑢𝑡 = 118.8 𝑉 × 0.395 𝐴 = 46.93 𝑉𝐴 9. Calculate the transformer efficiency (show your steps) 𝜂=(

/2

𝑃𝑜𝑢𝑡 46.93 𝑉𝐴 × 100% = 91.2 % ) × 100% = 51.45 𝑉𝐴 𝑃𝑖𝑛

10. Calculate rated Power Output of your Transformer bank (show your steps)

/3

𝑅𝑎𝑡𝑒𝑑 𝑃𝑜𝑢𝑡 = 𝐸𝑠𝑒𝑐 𝐼𝑟𝑎𝑡𝑒𝑑

𝑃𝑜𝑢𝑡 = 118.8 𝑉 × 1.2 𝐴 = 142.56 𝑉𝐴 11. In the LVDAC-EMS, open the Phasor Analyzer and make the required settings to observe the phasors of the Line Voltages at the secondary (inputs E1, E2, and E3 respectively), as well as the Line Voltage at the primary (input E4) Using the Phasor Analyzer, determine the phase shift between the Secondary Line Voltage and the Primary Line voltage of the transformer bank. Phase shift between EL Secondary and EL Primary = _150__o

/1

12. In the LVDAC-EMS, open the Oscilloscope and make the required settings to observe the waveforms of the Secondary Line Voltages (inputs E1, E2, and E3 respectively) as well as the Primary Line Voltage. Using the Oscilloscope, determine the phase shift between the Secondary Line Voltage and the Primary Line voltage of the transformer bank. Phase shift between EL Secondary and EL Primary = _150__o

/1

Does the phase shift between the Secondary and Primary Line voltages you just determined confirm the phase shift you obtained previously using the Phasor Analyzer? □ Yes □ No /1 13. Turn off Power supply.

3d. •

/2

Open-delta Connections. An open delta three phase connection can be made using only two single phase transformers. These connections are often used when the amount of three phase power is not excessive such as small businesses. It is important of be aware that the power output of an open delta transformer bank is only 86.6% of the rated power of the two transformers used. For example; where the two transformers each have a rating of 1kVA are connected to form an open-delta transformer bank, the total output power of the transformer bank is (1kVA + 1kVA) * 0.866 = 1.73kVA

Another way to look at this is that the open-delta system can operate at 57.7% of the power rating of a full delta bank. Three 1kVA rated transformers have the output capacity of 3kVA 57.7% of 3kVA is 1.73kVA Open Delta configuration is also used is where a Delta to Delta transformer or transformer bank has a fault in one of its phases. The three phase transformer can be reconfigured to omit the faulted coils thereby forming an Open Delta set, allowing plant operation to continue in a limited fashion while replacement parts are being ordered. The diagram below is a typical schematic for an Open-Delta - Open-Delta three phase transformer:

1. Draw the connections on the diagram below to create an Open-Delta to Open-Delta transformer bank using three single phase transformers. /2

2. Connect the equipmnet as shown in Figure below. Use the Power Supply to implement the AC power source. Utilize the transformers on the Three-Phase Transformer Bank and the Resistive Load to connect the Open-Delta circuit.

3. Make the necessary switch settings on the Resistive Load so that the resistance of the threephase resistor is equal to 171Ω. 4. After instructor reviews your connections turn on the Power Supply

/3

5. In the Metering window measure the Secondary Line Voltages and Currents, as well as the Line Voltage and Line Current at Primary side. Complete the Table below /3 204.4

0.671

204.7

0.686

200.6

0.672

210.5

0.728

6. 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. Voltage relationship (EL Primary : EL Secondary)

1.05 : _1_

Current relationship (IL Primary : IL Secondary)

_1_ : 0.92

7. Calculate the input power (show your steps)

/2 /2

𝑃𝑖𝑛 = 𝐸𝑝𝑟𝑖 𝐼𝑝𝑟𝑖 𝑃𝑖𝑛 = 210.5 𝑉 × 0.728 𝐴 = 153.24 𝑉𝐴 8. Calculate the Output power (show your steps) 𝑃𝑜𝑢𝑡 = 𝐸𝑠𝑒𝑐 𝐼𝑠𝑒𝑐 𝑃𝑜𝑢𝑡 = 200.6 𝑉 × 0.672 𝐴 = 134.80 𝑉𝐴

/2

9. Calculate the transformer efficiency (show your steps) 𝜂=(

𝑃𝑜𝑢𝑡 𝑃𝑖𝑛

/2

134.80 𝑉𝐴 × 100% = 88 % ) × 100% = 153.24 𝑉𝐴

10. Calculate rated Power Output of your Open Delta transformer bank (show your steps)

/3

𝑅𝑎𝑡𝑒𝑑 𝑃𝑜𝑢𝑡 = 𝐸𝑠𝑒𝑐 𝐼𝑟𝑎𝑡𝑒𝑑

𝑃𝑜𝑢𝑡 = 200.6 𝑉 × 1.2 𝐴 = 240.72 𝑉𝐴 11. In the LVDAC-EMS, open the Phasor Analyzer and make the required settings to observe the phasors of the Line Voltages at the secondary (inputs E1, E2, and E3 respectively), as well as the Line Voltage at the primary (input E4) Using the Phasor Analyzer, determine the phase shift between the Secondary Line Voltage and the Primary Line voltage of the transformer bank. Phase shift between EL Secondary and EL Primary = __0__o

/1

12. Close LDVAC-EMS, then turn off all the equipment. Disconnect all the leads and return them to their storage locations. /5

3e.

Closing the Delta •

•

•

Before “closing the Delta”, connections need to be checked for proper polarity before making the final connection and applying power. If the phase winding of one of the transfers is reversed, an extremely high current can flow when power is applied. (Polarity was identified during the lab) To perform these checks power needs to be applied to the bank before the final connection is made: see diagram below.

When power is applied to the transformer bank before the delta is closed the test points should indicate one of two things: 0 volts (where the connections are of the correct polarity), or twice the secondary voltage (twice the voltage found in part 3a for the phase to neutral tests on the secondary). o For example, if one of the phase windings has been reversed the test voltage for a 120V secondary would show 240 volts. o The test will indicate if one of the windings is reversed, however it will not indicate which winding is reversed or weather the issue is in the primary or the secondary.

4. QUESTIONS

1. A three phase transformer bank is connected as delta – delta. The primary voltage is 4160V and the secondary voltage is 600V. The total capacity of the transformer bank is 500kVA. One of the three transformers that form the three phase bank develops a short on the primary and becomes unusable. It is suggested that the bank be reconnected for operation as open delta. Can the two remaining transformers be connected as open delta? Yes! And, if so what will the output capacity of remaining two transformers be? /4 𝑂𝑢𝑡𝑝𝑢𝑡 𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑦 = 500 𝑘𝑉𝐴 × 0.87 = 435 𝑘𝑉𝐴 2. Complete the table below for the Wye to Delta transformer that is supplying load # 1. /8

Primary

Secondary

Load # 1

EL = 4160V

EL = 600V

EL = 600 V

IL = 14.3 A

IL = 99.0 A

IL = 99.0 A

EP = 2401.8 V

EP = 600 V

EP = 346.4 V

IP = 14.3 A

IP = 57.2 A

IP = 99.0 A

S = 103 kVA

S = 102.9 kVA

P = 102.9 kW

Transformer power Rating S(rated) = 4.5kVA Voltage Ratio 4.003 : 1 Phase shift 30o

Transformer impedance Z = 1.3% At transformer secondaries Isc = 13.2 kA (Short Circuit)

XR = 3.5Ω each leg

3. Complete the table below for the Delta to Wye transformer that is supplying load # 1. /8

Primary

Secondary

Load #1

EL = 23kV

EL = 208V

EL = 208 V

IL = 543.6 mA

IL = 60.1 A

IL = 60.1 A

EP = 23 kV

EP = 120.1 V

EP = 208 V

IP = 313.8 mA

IP = 60.1 A

IP = 34.7 A

S = 21.7 kVA

S = 21.7 kVA

P = 21.7 kW

Transformer power Rating S(rated) = 4.5kVA Voltage Ratio 191.5 : 1 Phase shift 30o

Transformer impedance Z = 1.5% At transformer secondaries Isc = 6.96 kA (Short Circuit)

XR = 6Ω each leg

4. If the transformers from question 1 were originally connected as Wye – Delta, can they still be reconfigured as open delta? Please explain your answer as to why or why not. /2 Yes! Since a wye-connected transformer can be transformed into a delta connection, a Wye-Delta connected transformer can therefore be reconfigured as open delta if one of the three transformers failed. 5. Why is it important to check the voltage of a delta transformer before closing the delta? /2 It is very important to check that the voltage of a delta transformer equals zero before the delta is closed. If not, it may damage the windings because of the very high resulting current.

Conclusion:

/5

At the end of the lab, I learned that wye-wye transformer configurations produced no phase shift between its primary and secondary voltages. Also, it is extremely important to measure the voltage (confirming that it is equal to ZERO) across the windings of the delta transformer before closing it. This is very crucial for a delta configuration, as an extremely high short-circuit current will flow if the voltage within the delta when it is closed is not equal to zero. Moreover, I learned that the delta configuration normally does not have a neutral, while the wye configuration has

one. Lastly, the two configurations performed above namely wye-wye and wye-delta are commonly used in commercial & industrial applications (Y-Y), and in high-voltage transmission applications (Y-Δ) respectively.

Student Names 1 2 3

LAB MARK 55

QUESTIONS 24

Conclusion 5

SAFETY 20

Total Mark 120...