This document discusses various types of three-phase transformer connections including:
- Delta-delta, which produces no phase shift between input and output voltages.
- Delta-wye, which produces a 30 degree phase shift.
- Wye-delta, which also produces a 30 degree phase shift with primary and secondary connections reversed from delta-wye.
- Wye-wye requires special precautions like connecting the neutral or using a tertiary winding to prevent voltage distortion.
- Open-delta can transform voltage using only two transformers in an emergency situation but has lower capacity.
- Autotransformers are more economical than conventional transformers for moderate voltage changes between 0.5-2 times.
An Auto Transformer is a transformer with only one winding wound on a laminated core. An auto transformer is similar to a two winding transformer but differ in the way the primary and secondary winding are interrelated. A part of the winding is common to both primary and secondary sides.
An Auto Transformer is a transformer with only one winding wound on a laminated core. An auto transformer is similar to a two winding transformer but differ in the way the primary and secondary winding are interrelated. A part of the winding is common to both primary and secondary sides.
This directional over current relay employs the principle of actuation of the relay....It has a metallic disc free to rotate between the poles of two...
IDEAL AND PRACTICAL TRANSFORMER, EQUIVALENT CIRCUIT OF TRANSFORMER|DAY5|BASIC...Prasant Kumar
#IDEAL_PRACTICAL_TRANSFORMER
#EQUIVALENT_CIRCUIT OF TRANSFORMER
#BASIC ELECTRICAL ENGINEERING
#IDEAL TRANSFORMER ON NO LOAD
#PRACTICAL TRANSFORMER ON LOAD
#ELECTRCL TRANSFORMER
#SINGLE PHASE TRANSFORMER
Link of all sessions are.
DAY 1 (Need/Definition)
https://youtu.be/BvaykFJ_NoE
DAY 2 (Working principle and Construction)
https://youtu.be/06rgxocihaM
DAY 3 (EMF equation and Turns Ratio)
https://youtu.be/g7e5xBPmv3Y
DAY 4 (Classification of Transformer)
https://youtu.be/6NP5L4MlvY4
DAY 5 ( Ideal and practical transformer on no load)
(Equivalent Transformer)
https://youtu.be/6LCLQC1p3lg
A synchronous motor is electrically identical with an alternator or AC generator.
A given alternator ( or synchronous machine) can be used as a motor, when driven electrically.
Some characteristic features of a synchronous motor are as follows:
1. It runs either at synchronous speed or not at all i.e. while running it maintains a constant speed. The only way to change its speed is to vary the supply frequency (because NS=120f/P).
2. It is not inherently self-starting. It has to be run up to synchronous (or near synchronous) speed by some means, before it can be synchronized to the supply.
3. It is capable of being operated under a wide range of power factors, both lagging and leading. Hence, it can be used for power correction purposes, in addition to supplying torque to drive loads.
Development of a Novel Three Phase Grid-Tied Multilevel Inverter TopologyIAES-IJPEDS
The conventional line-commutated ac-to-dc converters/ inverters have square-shaped line current. It contains higher-order harmonics which generates EMI and it causes more heating of the core of distribution or power transformers. PWM based inverters using MOSFET/IGBT have higher switching losses, and the power handling capability and reliability are quite low in comparison to thyristors/ SCR. A thyristor based forced commutated inverters are not suitable for PWM applications due to the problems of commutation circuits. A pure sinusoidal voltage output or waveform with low harmonic contents is most desirable for ac load using dc to ac conversion. This paper presents a new multilevel inverter topology in which three phase ac- to-dc converter circuits are used in inversion mode by controlling the switching angle. Due to natural commutation, no separate circuit is required for synchronization. In this paper simulation and analysis are done for grid-tied three-phase 6-pulse, Two three-phase, 3-pulse and 12-pulse converter. These converters are analysed for different battery voltage and different switching angle combinations in order to reduce the total harmonic distortion (THD). Three-phase harmonic filters are further added to the grid side to reduce the harmonic content in the line current. A comparative study of these converters is also presented in this paper.
This directional over current relay employs the principle of actuation of the relay....It has a metallic disc free to rotate between the poles of two...
IDEAL AND PRACTICAL TRANSFORMER, EQUIVALENT CIRCUIT OF TRANSFORMER|DAY5|BASIC...Prasant Kumar
#IDEAL_PRACTICAL_TRANSFORMER
#EQUIVALENT_CIRCUIT OF TRANSFORMER
#BASIC ELECTRICAL ENGINEERING
#IDEAL TRANSFORMER ON NO LOAD
#PRACTICAL TRANSFORMER ON LOAD
#ELECTRCL TRANSFORMER
#SINGLE PHASE TRANSFORMER
Link of all sessions are.
DAY 1 (Need/Definition)
https://youtu.be/BvaykFJ_NoE
DAY 2 (Working principle and Construction)
https://youtu.be/06rgxocihaM
DAY 3 (EMF equation and Turns Ratio)
https://youtu.be/g7e5xBPmv3Y
DAY 4 (Classification of Transformer)
https://youtu.be/6NP5L4MlvY4
DAY 5 ( Ideal and practical transformer on no load)
(Equivalent Transformer)
https://youtu.be/6LCLQC1p3lg
A synchronous motor is electrically identical with an alternator or AC generator.
A given alternator ( or synchronous machine) can be used as a motor, when driven electrically.
Some characteristic features of a synchronous motor are as follows:
1. It runs either at synchronous speed or not at all i.e. while running it maintains a constant speed. The only way to change its speed is to vary the supply frequency (because NS=120f/P).
2. It is not inherently self-starting. It has to be run up to synchronous (or near synchronous) speed by some means, before it can be synchronized to the supply.
3. It is capable of being operated under a wide range of power factors, both lagging and leading. Hence, it can be used for power correction purposes, in addition to supplying torque to drive loads.
Development of a Novel Three Phase Grid-Tied Multilevel Inverter TopologyIAES-IJPEDS
The conventional line-commutated ac-to-dc converters/ inverters have square-shaped line current. It contains higher-order harmonics which generates EMI and it causes more heating of the core of distribution or power transformers. PWM based inverters using MOSFET/IGBT have higher switching losses, and the power handling capability and reliability are quite low in comparison to thyristors/ SCR. A thyristor based forced commutated inverters are not suitable for PWM applications due to the problems of commutation circuits. A pure sinusoidal voltage output or waveform with low harmonic contents is most desirable for ac load using dc to ac conversion. This paper presents a new multilevel inverter topology in which three phase ac- to-dc converter circuits are used in inversion mode by controlling the switching angle. Due to natural commutation, no separate circuit is required for synchronization. In this paper simulation and analysis are done for grid-tied three-phase 6-pulse, Two three-phase, 3-pulse and 12-pulse converter. These converters are analysed for different battery voltage and different switching angle combinations in order to reduce the total harmonic distortion (THD). Three-phase harmonic filters are further added to the grid side to reduce the harmonic content in the line current. A comparative study of these converters is also presented in this paper.
Student information management system project report ii.pdfKamal Acharya
Our project explains about the student management. This project mainly explains the various actions related to student details. This project shows some ease in adding, editing and deleting the student details. It also provides a less time consuming process for viewing, adding, editing and deleting the marks of the students.
Immunizing Image Classifiers Against Localized Adversary Attacksgerogepatton
This paper addresses the vulnerability of deep learning models, particularly convolutional neural networks
(CNN)s, to adversarial attacks and presents a proactive training technique designed to counter them. We
introduce a novel volumization algorithm, which transforms 2D images into 3D volumetric representations.
When combined with 3D convolution and deep curriculum learning optimization (CLO), itsignificantly improves
the immunity of models against localized universal attacks by up to 40%. We evaluate our proposed approach
using contemporary CNN architectures and the modified Canadian Institute for Advanced Research (CIFAR-10
and CIFAR-100) and ImageNet Large Scale Visual Recognition Challenge (ILSVRC12) datasets, showcasing
accuracy improvements over previous techniques. The results indicate that the combination of the volumetric
input and curriculum learning holds significant promise for mitigating adversarial attacks without necessitating
adversary training.
CFD Simulation of By-pass Flow in a HRSG module by R&R Consult.pptxR&R Consult
CFD analysis is incredibly effective at solving mysteries and improving the performance of complex systems!
Here's a great example: At a large natural gas-fired power plant, where they use waste heat to generate steam and energy, they were puzzled that their boiler wasn't producing as much steam as expected.
R&R and Tetra Engineering Group Inc. were asked to solve the issue with reduced steam production.
An inspection had shown that a significant amount of hot flue gas was bypassing the boiler tubes, where the heat was supposed to be transferred.
R&R Consult conducted a CFD analysis, which revealed that 6.3% of the flue gas was bypassing the boiler tubes without transferring heat. The analysis also showed that the flue gas was instead being directed along the sides of the boiler and between the modules that were supposed to capture the heat. This was the cause of the reduced performance.
Based on our results, Tetra Engineering installed covering plates to reduce the bypass flow. This improved the boiler's performance and increased electricity production.
It is always satisfying when we can help solve complex challenges like this. Do your systems also need a check-up or optimization? Give us a call!
Work done in cooperation with James Malloy and David Moelling from Tetra Engineering.
More examples of our work https://www.r-r-consult.dk/en/cases-en/
Democratizing Fuzzing at Scale by Abhishek Aryaabh.arya
Presented at NUS: Fuzzing and Software Security Summer School 2024
This keynote talks about the democratization of fuzzing at scale, highlighting the collaboration between open source communities, academia, and industry to advance the field of fuzzing. It delves into the history of fuzzing, the development of scalable fuzzing platforms, and the empowerment of community-driven research. The talk will further discuss recent advancements leveraging AI/ML and offer insights into the future evolution of the fuzzing landscape.
TECHNICAL TRAINING MANUAL GENERAL FAMILIARIZATION COURSEDuvanRamosGarzon1
AIRCRAFT GENERAL
The Single Aisle is the most advanced family aircraft in service today, with fly-by-wire flight controls.
The A318, A319, A320 and A321 are twin-engine subsonic medium range aircraft.
The family offers a choice of engines
Welcome to WIPAC Monthly the magazine brought to you by the LinkedIn Group Water Industry Process Automation & Control.
In this month's edition, along with this month's industry news to celebrate the 13 years since the group was created we have articles including
A case study of the used of Advanced Process Control at the Wastewater Treatment works at Lleida in Spain
A look back on an article on smart wastewater networks in order to see how the industry has measured up in the interim around the adoption of Digital Transformation in the Water Industry.
Event Management System Vb Net Project Report.pdfKamal Acharya
In present era, the scopes of information technology growing with a very fast .We do not see any are untouched from this industry. The scope of information technology has become wider includes: Business and industry. Household Business, Communication, Education, Entertainment, Science, Medicine, Engineering, Distance Learning, Weather Forecasting. Carrier Searching and so on.
My project named “Event Management System” is software that store and maintained all events coordinated in college. It also helpful to print related reports. My project will help to record the events coordinated by faculties with their Name, Event subject, date & details in an efficient & effective ways.
In my system we have to make a system by which a user can record all events coordinated by a particular faculty. In our proposed system some more featured are added which differs it from the existing system such as security.
Hybrid optimization of pumped hydro system and solar- Engr. Abdul-Azeez.pdffxintegritypublishin
Advancements in technology unveil a myriad of electrical and electronic breakthroughs geared towards efficiently harnessing limited resources to meet human energy demands. The optimization of hybrid solar PV panels and pumped hydro energy supply systems plays a pivotal role in utilizing natural resources effectively. This initiative not only benefits humanity but also fosters environmental sustainability. The study investigated the design optimization of these hybrid systems, focusing on understanding solar radiation patterns, identifying geographical influences on solar radiation, formulating a mathematical model for system optimization, and determining the optimal configuration of PV panels and pumped hydro storage. Through a comparative analysis approach and eight weeks of data collection, the study addressed key research questions related to solar radiation patterns and optimal system design. The findings highlighted regions with heightened solar radiation levels, showcasing substantial potential for power generation and emphasizing the system's efficiency. Optimizing system design significantly boosted power generation, promoted renewable energy utilization, and enhanced energy storage capacity. The study underscored the benefits of optimizing hybrid solar PV panels and pumped hydro energy supply systems for sustainable energy usage. Optimizing the design of solar PV panels and pumped hydro energy supply systems as examined across diverse climatic conditions in a developing country, not only enhances power generation but also improves the integration of renewable energy sources and boosts energy storage capacities, particularly beneficial for less economically prosperous regions. Additionally, the study provides valuable insights for advancing energy research in economically viable areas. Recommendations included conducting site-specific assessments, utilizing advanced modeling tools, implementing regular maintenance protocols, and enhancing communication among system components.
Vaccine management system project report documentation..pdfKamal Acharya
The Division of Vaccine and Immunization is facing increasing difficulty monitoring vaccines and other commodities distribution once they have been distributed from the national stores. With the introduction of new vaccines, more challenges have been anticipated with this additions posing serious threat to the already over strained vaccine supply chain system in Kenya.
Automobile Management System Project Report.pdfKamal Acharya
The proposed project is developed to manage the automobile in the automobile dealer company. The main module in this project is login, automobile management, customer management, sales, complaints and reports. The first module is the login. The automobile showroom owner should login to the project for usage. The username and password are verified and if it is correct, next form opens. If the username and password are not correct, it shows the error message.
When a customer search for a automobile, if the automobile is available, they will be taken to a page that shows the details of the automobile including automobile name, automobile ID, quantity, price etc. “Automobile Management System” is useful for maintaining automobiles, customers effectively and hence helps for establishing good relation between customer and automobile organization. It contains various customized modules for effectively maintaining automobiles and stock information accurately and safely.
When the automobile is sold to the customer, stock will be reduced automatically. When a new purchase is made, stock will be increased automatically. While selecting automobiles for sale, the proposed software will automatically check for total number of available stock of that particular item, if the total stock of that particular item is less than 5, software will notify the user to purchase the particular item.
Also when the user tries to sale items which are not in stock, the system will prompt the user that the stock is not enough. Customers of this system can search for a automobile; can purchase a automobile easily by selecting fast. On the other hand the stock of automobiles can be maintained perfectly by the automobile shop manager overcoming the drawbacks of existing system.
COLLEGE BUS MANAGEMENT SYSTEM PROJECT REPORT.pdfKamal Acharya
The College Bus Management system is completely developed by Visual Basic .NET Version. The application is connect with most secured database language MS SQL Server. The application is develop by using best combination of front-end and back-end languages. The application is totally design like flat user interface. This flat user interface is more attractive user interface in 2017. The application is gives more important to the system functionality. The application is to manage the student’s details, driver’s details, bus details, bus route details, bus fees details and more. The application has only one unit for admin. The admin can manage the entire application. The admin can login into the application by using username and password of the admin. The application is develop for big and small colleges. It is more user friendly for non-computer person. Even they can easily learn how to manage the application within hours. The application is more secure by the admin. The system will give an effective output for the VB.Net and SQL Server given as input to the system. The compiled java program given as input to the system, after scanning the program will generate different reports. The application generates the report for users. The admin can view and download the report of the data. The application deliver the excel format reports. Because, excel formatted reports is very easy to understand the income and expense of the college bus. This application is mainly develop for windows operating system users. In 2017, 73% of people enterprises are using windows operating system. So the application will easily install for all the windows operating system users. The application-developed size is very low. The application consumes very low space in disk. Therefore, the user can allocate very minimum local disk space for this application.
Saudi Arabia stands as a titan in the global energy landscape, renowned for its abundant oil and gas resources. It's the largest exporter of petroleum and holds some of the world's most significant reserves. Let's delve into the top 10 oil and gas projects shaping Saudi Arabia's energy future in 2024.
4. Introduction
• The transformers may be inherently 3-phase,
having three primary windings and three secondary
windings mounted on a 3-legged core.
• The same result can be achieved by using three
single-phase transformers connected together to
form a 3-phase transformer bank.
5. 1. Basic properties of 3-phase
transformer bank
• When three single-phase transformers are used to transform
a 3-phase voltage, the windings can be connected in several
ways. the ratio of the 3-phase input voltage to the 3-phase
output voltage depends not only upon the turns ratio of the
transformers, but also upon how they are connected.
• A 3-phase transformer bank can also produce a phase shift
between the 3-phase input voltage and the 3-phase output
voltage. The amount of phase shift depends upon
- the turns ratio of the transformers
- how the primaries and secondaries are
interconnected
6. Basic properties of 3-phase
transformer bank (ต่อ)
• The phase shift feature enables us to change the number of
phases a 3-phase system can be converted into a 2-phase,
a 5-phase, a 6-phase, or a 12-phase system by an appropriate
choice of single-phase transformers and interconnections.
7. Basic properties of 3-phase
transformer bank (ต่อ)
• The basic behavior of balanced 3-phase transformer banks
is basedon the following simplifying assumptions:
(1) The exciting currents are negligible.
(2) The transformer impedances, due to the resistance
and leakage reactance of the windings, are negligible.
(3) The total apparent input power to the transformer
bank is equal to the total apparent output
power.
8. 2. Delta-delta connection
Fig.1 Delta-delta connection of three single-phase
transformers. The incoming lines (source) are A,
B, C and the outgoing lines (load) are 1, 2, 3.
10. Delta-delta connection (ต่อ)
• In such a delta-delta connection, the voltages between the
respective incoming and outgoing transmission lines are in
phase.
• If a balanced load is connected to lines 1-2-3, the resulting
line currents are equal in magnitude. This produces balanced
line currents in the incoming lines A-B-C.
• The power rating of the transformer bank is three times the
rating of a single transformer.
17. Delta-wye connection (ต่อ)
• The voltage across each primary winding is equal to the
incoming line voltage.
• However, the outgoing line voltage is √3 times the
secondary voltage across each transformer.
• The line currents in phases A, B and C are √3 times the
currents in the primary windings.
•A delta-wye connection produces a 30° phase shift between
the line voltages of the incoming and outgoing transmission
lines
18. Delta-wye connection (ต่อ)
• If the outgoing line feeds an isolated group of loads, the
phase shift creates no problem. But, if the outgoing line has
to be connected in parallel with a line coming from another
source, the 30° shift may make such a parallel connection
impossible, even if the line voltages are otherwise identical.
• One of the important advantages of the wye connection is
that it reduces the amount of insulation needed inside the
transformer. The HV winding has to be insulated for only
1/√3, or 58 percent of the line voltage.
22. 4. Wye-delta connection
• The currents and voltages in a wye-delta connection are
identical to those in the delta-wye connection. The primary
and secondary connections are simply interchanged.
• There results a 30° phase shift between the voltages of the
incoming and outgoing lines.
23. 5. Wye-wye connection
• When transformers are connected in wye-wye, special
precautions have to be taken to prevent severe distortion of
the line-to-neutral voltages.
(1) connect the neutral of the primary to the neutral of
the source, usually by way of the ground
Fig.6 Wye-wye connection with neutral of the primary connected to the neutral of the source.
24. Wye-wye connection (ต่อ)
(2) provide each transformer with a third winding,
called tertiary winding.
Fig.7 Wye-wye connection using a tertiary winding.
25. Wye-wye connection (ต่อ)
• Note that there is no phase shift between the incoming
and outgoing transmission line voltages of
a wye-wye connected transformer.
26. 6. Open-delta connection
• It is possible to transform the voltage of a 3-phase
system by using only 2 transformers, connected in open-
delta.
• The open-delta arrangement is identical to a delta-delta
connection, except that one transformer is absent.
• The open-delta connection is seldom used because the
load capacity of the transformer bank is only 86.6 percent
of the installed transformer capacity.
27. Open-delta connection (ต่อ)
• The open-delta connection is mainly used in emergency
situations. Thus, if three transformers are connected in
delta-delta and one of them becomes defective and has to
be removed, it is possible to feed the load on a temporary
basis with the two remaining transformers.
Fig.8a Open-delta connection.
29. Open-delta connection (ต่อ)
• The current Is in lines 1, 2, 3 cannot, therefore, exceed 250 A
(Fig.8b). Consequently, the maximum load that the transformers can
carry is
Fig.8b Open-delta connection Associated schematic and phasor diagram.
31. 7. Three-phase transformers
• A transformer bank composed of three single-phase
transformers may be replaced by one 3-phase transformer.
• For a given total capacity, a 3-phase transformer is
always smaller and cheaper than three single-phase
transformers.
• Nevertheless, single-phase transformers are sometimes
preferred, particularly when a replacement unit is
essential.
32. Three-phase transformers (ต่อ)
Fig.9 Three-phase transformer for an
electric arc furnace, rated 36 MVA, 1
3.8 kV/160 V to 320 V, 60 Hz. Th
e secondary voltage is adjustable from
160 V to 320 V by means of 32 tap
s on the primary winding (not shown).
The three large busbars in the foregrou
nd deliver a current of 65,000 A. Oth
er characteristics: impedance: 3.14%
; diameter of each leg of the core: 71
1
mm; overall height of core: 3500
mm; center line distance between adjac
ent core legs: 1220 mm.
33. Three-phase transformers (ต่อ)
Fig.10a Core of a 110 MVA, 222.5
kV/34.5 kV, 60 Hz, 3-phase transfor
mer. By staggering laminations of diffe
rent
widths, the core legs can be made
almost circular. This reduces the coil di
ameter to a minimum, resulting in
less copper and lower I2
R losses. The
legs are tightly bound to reduce
vibration. Mass of core: 53,560 kg.
34. Three-phase transformers (ต่อ)
Fig.10b Same transformer with coils in
place. The primary windings are
connected in wye and the secondaries i
n delta. Each primary has 8 taps to cha
nge the voltage in steps of ±2.5%. T
he motorized tap-changer can be seen i
n the right upper corner of the transfor
mer. Mass of copper: 15,230 kg.
35. Three-phase transformers (ต่อ)
Fig.10c Same transformer ready for
shipping. It has been subjected to a 10
50 kV impulse test on the HV side and
a similar 250 kV test on the LV side.
Other details: power rating: 110 MV
A/146.7 MVA (OA/FA); total mass i
ncluding oil: 158.7 t; overall height:
9 m; width: 8.2 m, length: 9.2 m.
(Courtesy of ABB)
36. 8. Step-up and step-down
Autotransformer
• When the voltage of a 3-phase line has to be stepped
up or stepped down by a moderate amount, it is
economically advantageous to use three single-phase
transformers to create a wye-connected autotransformer.
Fig.11a Wye-connected autotransformer.
38. Step-up and step-down
Autotransformer (ต่อ)
• For a given power output. an autotransformer is
smaller and cheaper than a conventional transformer.
This is particularly true if the ratio of the incoming line
voltage to outgoing line voltage lies between 0.5 and 2.
39. Step-up and step-down
Autotransformer (ต่อ)
Fig.11c Single-phase autotransformer (one of a group of
three) connecting a 700 kV, 3-phase, 60 Hz transmission l
ine to an existing 300 kV system. The transformer ratio is
404 kV/173 kV, to give an output of 200/267/333 MVA
per transformer, at a temperature rise of 55°C. Cooling is
0A/FA/F0A. A tertiary winding rated 35 MVA, 11.9 kV
maintains balanced and distortion-free line-to-neutral
voltages, while providing power for the substation. Other
properties of this transformer: weight of core and
windings: 132 t; tank and accessories: 46 t; oil: 87 t; total
weight: 265 t. BIL rating is 1950 kV and 1050 kV on the
HV and LV side, respectively. Note the individual 700 k
V
(right) and 300 kV (left) bushings protruding from the
tank. The basic impulse insulation (BIL) of 1950 kV and
1050 kV expresses the transformer's ability to withstand l
ightning and switching surges.
(Courtesy of Hydro-Quebec)
43. 9. Phase-shift principle
• A 3-phase system enables us to shift the phase angle
of a voltage very simply. Such phase shifting enables
us to create 2-phase, 6-phase, and 12-phase systems from
an ordinary 3-phase line.
• Such multiphase systems are used in large electronic
converter stations and in special electric controls. Phase
shifting is also used to control power flow over
transmission lines that form part of a power grid.
44. Phase-shift principle (ต่อ)
• To understand the phase shifting principle, consider
a rheostat connected between phases B and C of a 3-
phase line.
Fig.12 Voltage EAP can be phase-shifted with respect to EAC by means of a potentiometer.
45. Phase-shift principle (ต่อ)
• Such a simple phase-
shifter can only be used in
circuits where the load
between terminals A and P
draws a few milliamperes. If
a heavier load is applied, the
resulting IR drop in the
rheostat completely changes
the voltage and phase angle
from what they were on
open-circuit.
Fig.13 Autotransformer used as
a phase-shifter.
46. Phase-shift principle (ต่อ)
• This arrangement
enables us to create a 3-
phase source P1, P2, P3
whose phase angle
changes stepwise with
respect to source ABC.
We obtain a maximum
phase shift of 60° as we
move from one extremity
of the autotransformers to
the other.
Fig.14 Three-phase phase
shifter.
47. 10. Three-phase to 2-phase
Transformation
• The voltages in a 2-phase system are equal but
displaced
from each other by 90°.
• There are several ways to create a 2-phase system from
a 3-phase source.
(1) Use a single-phase autotransformer having taps at
50 percent and 86.6 percent.
(2) Scott connection.
49. Three-phase to 2-phase
Transformation (ต่อ)
• The ratio of transformation (3-phase voltage to
2-phase voltage) is fixed and given by EAB/EAT =
100/86.6 = 1.15.
50. Three-phase to 2-phase
Transformation (ต่อ)
• The Scott connection has the advantage of isolating the
3-phase and 2-phase systems and providing any desired
voltage ratio between them.
• Except for servomotor applications, 2-phase systems are
seldom encountered today.
51. Three-phase to 2-phase
Transformation (ต่อ)
(2) Scott
connection : It
consists of two
identical single-
phase transformers,
the one having a 50
percent tap and the
other an 86.6 percent
tap on the primary
winding.
Fig.16
52. Three-phase to 2-phase
Transformation (ต่อ)
Example 5: A 2-phase, 7.5 kW (10 hp), 240 V, 60 Hz
motor has an efficiency of 0.83 and a power factor of
0.80. It is to be fed from a 600 V, 3-phase line using a
Scott-connected transformer bank (Figure 16c).
Calculate
(a) The apparent power drawn by the motor
(b) The current in each 2-phase line
(c) The current in each 3-phase line
56. 11. Phase-shift transformer
• A phase-shift transformer is a special type of 3-phase
autotransformer that shifts the phase angle between the
incoming and outgoing lines without changing the
voltage ratio.
Fig.17 Phasor diagram showing the range over which the phase angle of the outgoing line can be varied.
57. Phase-shift transformer (ต่อ)
• The basic power rating of the transformer (which determines its
size) depends upon the apparent power carried by the transmission
line, and upon the phase shift.
• For angles less than 20°, it is given by the approximate formula
ST = 0.025 SL αmax (1)
58. Phase-shift transformer (ต่อ)
Example 6: A phase-shift transformer is designed to
control 150 MVA on a 230 kV, 3-phase line. The phase
angle is variable between zero and t 15°.
Calculate
(a) The approximate basic power rating of the
transformer.
(b) The line currents in the incoming and outgoing
transmission lines.
60. Phase-shift transformer (ต่อ)
• Fig.18a is an example of a 3-phase transformer that
could be used to obtain a phase shift of, say, 20 degrees.
Fig.18a Fig.18b
61. Phase-shift transformer (ต่อ)
• In our particular
example, if E is the line-to-
neutral voltage of the
incoming line, the
respective voltages across
the windings of phase A
are
Fig.18c
62. 12. Calculations involving
3-phase transformers
• The behavior of a 3-phase transformer bank is calculated
the same way as for a single-phase transformer. In making
the calculations, we proceed as follows:
(1) We assume that the primary and secondary windings
are both connected in wye, even if they are not.This
eliminates the problem of having to deal with delta-wye
and delta-delta voltages and currents.
(2) We consider only one transformer (single phase) of this
assumed wye-wye transformer hank.
63. Calculations involving
3-phase transformers (ต่อ)
(3) The primary voltage of this hypothetical transformer is
the line-to-neutral voltage of the incoming line.
(4) The secondary voltage of this transformer is the line-
to-neutral voltage of the outgoing line.
(5) The nominal power rating of this transformer is one-
third the rating of the 3-phase transformer bank.
(6) The load on this transformer is one-third the load on
the transformer hank.
64. Calculations involving
3-phase transformers (ต่อ)
Example 7: The 3-phase step-up transformer is rated 1300
MVA, 24.5 kV/345 kV, 60 Hz, impedance 11.5 percent. It
steps up the voltage of a generating station to power a 345
kV line.
(a) Determine the equivalent circuit of this transformer,
per phase.
(b) Calculate the voltage across the generator terminals
when the HV side of the transformer delivers 810 MVA at
370 kV with a lagging power factor of 0.90.
72. 13. Polarity marking
of 3-phase transformers
• The HV terminals of a 3-phase transformer are marked
H1, H2 , H3 and the LV terminals are marked X1, X2, X3.
The following rules have been standardized:
74. Polarity marking
of 3-phase transformers (ต่อ)
3. These rules are not affected by the phase sequence of
the line voltage applied to the primary side.