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Tuesday 24 April 2012

The Autotransformer And Transformer Parameters


The Autotransformer

This differs from the ordinary transformer in that the winding of the autotransformer are electrically connected as well as being coupled by mutual flux.






There is a type of autotransformer called a Variac (VARIAC) which is used to regulate the voltage applied to a particular device from ‘0’ to a certain maximum value Vmax . In the starting of induction motors, variacs are used to start IM (Induction Motors) of rating 5hp and above. This is in order to limit the high surge of current (Starting Current) which usually occurs when the motor is started direct-on-line. Induction Motors of Low horse powers hp<5 are usually started direct-on-line.

Determination of Transformer Parameters
a)      Open Circuit Test: The high voltage winding is on open circuit and the low Voltage winding is connected to a variable voltage supply, at normal frequency. The primary is assumed to be the low voltage winding.

The input current and power and the voltage across the open circuit winding are measured for a range of applied voltages up to 125% of the rated voltage.

Then at rated voltage,  

Iron Losses Pi = V2g ie g = pi/V2;

Open circuit admittance y = I/V,

Magnetising Susceptance b = (y2 – g2)

b)      Short Circuit Test : The low voltage winding is short circuited through an ammeter and the high voltage winding is connected to a variable voltage supply at normal frequency. The high voltage winding is assumed to be the primary winding.

The input current and power and voltage across the high voltage winding are measured for a range of short circuit currents up to 125% of the rated current.

Cupper loss Pc = I2R, Total
Resistance R = Pc/I2
Short circuit Impedance Z = V/I
Total leakage reactance X = (Z2 – R2)

Let Us Study The Bible Together Today {Acts 8}


Bible Study1

Acts 8

Vs 1 Saul was consenting unto his death (the death of Stephen)
There was persecution. The people (early Christians) were scattered as a result of that except the apostles.
Vs 2 devout men carried and buried Stephen.
Vs 3 Saul Put people in Prison
Vs 4 The Christians preached the gospel as they scattered.
Vs 5 Philip preached Christ in Samaria
Vs 6 People believed
Vs 7 Philip cast out unclean spirit in the name of God through Jesus Christ Our Lord.
Vs 8 Salvation brings Joy. When the people got saved, they rejoiced.
Vs 9 -12 Here Simon’s activities were documented which were not very good deeds. He deceived many by them. The preaching of the gospel made the people to repent and believe God through Jesus Christ.
Vs 13 Simon repented.
Vs 14 Jerusalem sent Peter and John to Samaria on their repentance.
Vs 15 -17 Peter and John Prayed and they repented and received the Holy Spirit. The Holy Spirit dwells in a repented heart. There is a need for repentance.
Vs 18 Simon offered money to buy the Holy Ghost.
Things of God are neither bought nor sold. They are freely given by God by grace through Jesus Christ our Lord and savior.
Vs 20 Here Peter rebuked him and said Your money perish with you.
Vs 21-23 You do not buy the things of God.
Vs 24 Simon begged for forgiveness.
Vs 25 They returned to Jerusalem and Preached as they returned.
Vs 26 The Holy Spirit directs Philip towards the south unto the way that goeth down from Jerusalem unto Gaza which is a desert.
Vs 27 He Obeyed.
Vs 28 He ministered to the Ethiopian Eunuch
Vs 29 The Holy Spirit directs Philip. We should be receptive to the directives of the Holy Spirit. We should Put every Spirit to the test to know if it is of God. Jesus Christ is the Standard and the Bible is the Reference. Pray to God always for understanding.
Vs 30 He obeyed. Trust and Obey God.
Isaiah 53 : 7, 8
He asked him Understandest thou what thou readest?
Vs 32 – 33
These passages talked about Jesus Christ and His work of salvation.
Vs 34 -35 Philip explained
Vs 37 He Believed and was baptized. – I believe that Jesus Christ is the son of God.
Vs 39 When Philip finished his assignment, the Spirit took Philip and the Ethiopan rejoiced
Vs 40 Philip continued preaching elsewhere. – at Azotus, Caesarea. We should be sensitive to the Spirit of God and allow the Spirit of God to lead us and direct us in all we do to the glory of God.

Monday 23 April 2012

Three Phase Transformers And Three Winding Transformers


Three Phase transformers

Three phase transformers usually have all three phases on one iron structure and can be connected in Y(Star) – Δ(Delta),  Δ(Delta) – Y(Star). Other possible connections are Y – Y and,   Δ – Δ where the first symbol refers to the connection of the primary windings and the second symbol refers to the connection of the secondary winding.

Three Winding transformers.

Some transformers have three windings: primary, secondary and tertiary windings. It is possible to measure three impedances by the standard short circuit tests as follows

Zps = Leakage impedance measured in primary with secondary short circuited and tertiary open.
Zpt = Leakage impedance measured in primary with tertiary short circuited and secondary open
Zst = Leakage impedance measured in secondary with tertiary short circuited and primary open

We note that

Zps = Zp + Zs
Zpt = Zp + Zt                                                                             {*}
Zst = Zs + Zt

Where Zp, Zs and Zt are  the impedances of the primary, secondary and tertiary windings referred to the primary circuit and Zps, Zpt, Zst are the measured impedances referred to the primary circuit.

Solving the equation {*} simultaneously will yield

Zp  = ½ (Zps + Zpt - Zst)
Zs  = ½ (Zps + Zst - Zpt)
Zt  = ½ (Zpt + Zst - Zps)





 










The impedance of the three windings are connected in star to represent the equivalent circuit of a three winding transformer with magnetizing current neglected.

Parental Responsibility


Parental Responsibility
Let us take a look at Jesus Christ and His Parents and learn from them.
Luke 2: 41 – 52
Vs 41 – 45 The parents of Jesus Christ took Jesus Christ to the temple. As parents, where do you take your children? Kindly take your children to God. Introduce your children early to our Lord Jesus Christ. Make an effort to go regularly to Church with your children. Go together with them. Study the word of God together and pray together. Grow up with your children and help them as they grow up.

Vs 46 They sought Him for 3 days till they found Him. Be patient with your children. Seek them for Jesus Christ until you find them. Do not give up on them. Pray for them spend time with them and talk with them. Seek them for three days until you find them. Search the scriptures with them.

Remind them that Jesus Christ was found in the Temple. Where will you and your children be found when people look for you?

Vs 47 Jesus Christ Had both understanding and answers.  When you patiently bring up your children in the way of the Lord, people will be surprised at what they will turn out to be.
Vs 48 The parents of Jesus Christ were amazed when they saw Him. The mother pointed out what they had to pass through to ensure His safety looking for Him and sorrowing. Be patient with your children. Do not be discouraged. If they do the right thing, encourage them the more. Direct them towards where they will learn more about our Lord Jesus Christ. Be patient with them. Correct them in Love. Pray for them.
Vs 49 Jesus went about His Fathers Business. As a father or a mother, what is your business? What do you encourage your children to do. Do what is right in the sight of God and God will bless your children as they do the same.
Vs 50 They did not understand. Sometimes we do not understand. Sometimes others do not understand us. God understands. Be patient even when you do not understand your children. Talk to God about them and be patient. Be patient with God as He works out His purpose in their lives. Be patient with them as they respond to the work of the Holy Spirit in them.
Vs 51 Jesus went with then and was subject unto them. Encourage your children to obey you. On your own part, obey God. Believe in our Lord Jesus Christ and it shall be well with you. You shall be saved. You and your house hold.
Vs 52 God blessed Him. God blessed Jesus Christ. Jesus Christ increased in stature and in wisdom and in favour with God and man. God will bless you and God will bless your children. Trust God and obey God. Believe in God and Believe in our Lord Jesus Christ too.

Sunday 22 April 2012

Introduction To Conventional And Renewable Energy Resources For Power Generation


Introduction To Conventional And Renewable Energy Resources For Power Generation.
In order to generate electrical energy we have to depend on sources such as coal, natural gas, hydro(water), and nuclear energy. These can be classified as follows:

A) Fossil Fuels
1) Coal
2) Oil
3) Natural gas
4) Substitute fuels eg. coal liquefaction and coal gasification
5) Oil from shale
6) Oil from tar sand

B) Nuclear Energy
1) Fission Reactors
2) Breeder Reactors
3) Fusion Reactors

C) Natural Sources
1) Hydro electric Power
2) Geothermal
3) Wind
4) Solar – Solar thermal, Photovoltaic
5) Ocean – Ocean thermal, Ocean current, tidal

Conventional Energy Sources
The conventional Energy Sources are as those that have been in use for over a century and which are considered less risky. Examples are hydroelectric power stations, fossil fueled power stations.


The following block diagrams highlight the process of Energy Conversion in the nuclear , Fossil fueled and hydro power stations.



Fossil Fuel --à Boiler ---à Heat Energy --à Steam Turbine --à Mechanical Energy -à Generator à Electrical Energy

Water in Reservoir  --à Hydraulic Turbine --à Mechanical Energy -à Generator à Electrical Energy


Heat From Nuclear Reactor --àSteam Generator ---à Heat Energy --à Steam Turbine --à Mechanical Energy -à Generator à Electrical Energy