Electricity Tutorial

Electricity Tutorial

This tutorial is a brief introduction to the concepts of charge, voltage, and current. This tutorial is not as long and tedious as a college textbook, yet it contains more information than students are likely to find in an elementary schoolbook.

The Atom

On the left is a conceptual drawing of an atom. Atoms are the building blocks of matter. Everything is made of atoms, from rocks, to trees, to stars, to even yourself. An atom consists of a tightly packed nucleus containing one or more protons (colored red in the picture), and usually an equal number of neutrons (gray). Electrons (blue) surround the nucleus, forming an electron cloud. The number of electrons in an electrically stable atom is always equal to the number of protons in the nucleus.

 

Electric Charge

  A curious thing happens between protons and electrons: a proton and an electron are always attracted to one another, while a proton will repel other protons, and an electron will repel other electrons. This behavior is caused by something called the electric force. Protons are said to have a positive electric charge, while electrons have a negative electric charge. Two objects with the same type of charge push away from each other, while two objects with opposite charges attract to each other. Since a proton and an electron have opposite electric charges, they are attracted to each other. Two protons, however, move away from each other because of their equal electric charges. The same is true of two electrons, which push away from each other because of their equal negative charges.

Electric Balance

 Most matter contains an equal number of protons and electrons. The negative electrons balance out the positive protons, and the matter has no overall electrical charge. The word overall is important, since the charges are still there, bouncing around inside the matter. Electrical charges are everywhere, but we just can't sense them because they are in balance. In fact, if you take chemistry, you'll learn that the electric force is the very thing that holds matter together. The next time you pick something up, just think that whatever you are holding is literally filled with electric charge. This is an important fact that many people miss when they study electricity.

Static Electricity

 Let's say we steal an electron from one atom and give the electron to another atom. One atom will have an overall positive charge and the other will have an overall negative charge. When this happens, the two atoms are called ions. Because ions have an overall electric charge, they can interact with other charged objects. Since like charges repel and opposite charges attract, a positive ion will attract negatively charged objects, such as electrons or other ions, and will repel positively charged objects. A negatively charged ion will attract positively charged objects, and will repel other negatively charged objects.
The same is true for larger objects. If you take electrons from one object and place them on another object, the first object will have an overall positive charge while the second will have an overall negative charge. Depending on the types of objects and the amount of charge involved, the electric force may be enough to cause the objects to stick together. This phenomenon is often referred to as "static electricity."
There are several ways to steal electrons from one object and give them to another. Some of the ways include chemical reactions, mechanical motion, light, and even heat. If you rub a glass rod with silk, the electrons in the glass rod will be knocked off and collected on the silk. The glass rod gains an overall positive charge, and the silk gains an overall negative charge. In a battery, chemical reactions are used to force electrons from the positive terminal and place them on the negative terminal.

Measuring Charges

The amount of overall electric charge possessed by an object is measured in coulombs. One coulomb is roughly equal to the amount of charge possessed by 6,000,000,000,000,000,000 (six billion billion) electrons. While this may seem like a huge number at first, it is not really that much, since electrons are so tiny. Just to give you an idea, one coulomb is roughly the amount of charge that flows through a 12-watt automotive light bulb in one second.
If the amount of charge possessed by two objects and the distance between them are known, it is possible to calculate the amount of force between the objects using a formula known as Coulomb's law. This law was discovered by Charles Augustin de Coulomb in 1784, and states that the force between two charged objects varies directly as the charges of the objects and inversely as the square of the distance between them. Coulomb's law is given below in formula form:

F is the force, in Newtons.
q and q' are the charges of the two objects, in coulombs.
r is the distance between the objects, in meters.
k is a constant equal to 8.98755×10⁹ N m² C^-2

Voltage

Whenever electrons are taken from one object and placed on another object, causing an imbalance of charge, we say that a voltage exists. That is what somebody means when they say that something has so many volts of electricity. They are describing a difference of charge in two different places. A standard AA battery has a difference of 1.5 volts between its positive and negative terminal, while car battery has a difference of 12 volts between its two terminals, and the everyday type of static electricity that causes things to stick together and occasionally gives you a jolt when you touch a metal object is usually measured in thousands of volts.
Another way to understand voltage is to think of an "electric field." Imagine a plate with positive charge next to a plate with negative charge. If I place a positive charge between these plates, the plates’ electric field will attract the charge to the negative side. Imagine that I place a 1 coulomb positive charge next to the negative plate, and then pull it towards the positive plate. Because the electric field creates a force in the opposite direction, moving the charge requires energy. The amount of energy depends on the distance between the plates and the strength of the electric field created by the plates. We call this energy the electric field’s "voltage." One volt is the amount of energy in joules required to move 1 coulomb of charge through an electric field. Mathematically, 1Volt = 1Joule / 1Coulomb.
Volts are useful, because they neatly describe the size and strength of any electric field. Visualizing the electric field between two simple plates is easy, but visualizing the field in a complicated circuit with batteries, motors, light bulbs, and switches is very difficult. Voltage simplifies circuits like these by describing the entire electric field with a single number.

Electric Current

 The word current comes from the Latin word currere, which means to run or to flow. An electric current is nothing more than the flow of electric charges. Electric charges can only flow through certain materials, called conductors. Although the electrons in most materials are confined to fixed orbits, some materials, including most metals, have many loose electrons which are free to wander around through the material. Materials with this property act as conductors. When a conductor is placed between two charged objects, these loose electrons are pushed away by the negatively charged object and are sucked into the positively charged object. The result is that there is a flow of charge, called a current, and the two object's charges become balanced. The amount of current flowing through a conductor at any given time in measured in amperes, or amps for short. When you read that something uses so many amps, what you are being told is the amount of current flowing through the device. One ampere is equal to the flow of one coulomb of charge in one second.

Batteries and Current

 In the previous paragraph, we looked at how current flows from one charged object to another, canceling out the charges of the two objects. Once the charges were canceled, the current stopped. If current were always this short-lived, it would be very impractical. Imagine a flashlight that only lasted a fraction of a second before needing to be recharged! While current does tend to cancel out charges on two objects and then stop flowing, if a charge can be placed on the objects faster than the current can drain the charge, it is possible to keep a current flowing indefinitely. That is what happens in a battery. Chemical reactions within the battery pump electrons from the positive terminal to the negative terminal faster than the device connected to the battery can drain them. The battery will continue to supply as much current as the device requires until the chemicals within the battery are used up, at which point the battery is dead and must be replaced.

Resistance

All conductors offer some degree of resistance to the flow of electric current. What happens is this: As electrons travel through the conductor, they bump into atoms, losing some of their movement in jiggling the atom. The result is that the current flowing through the conductor is slowed down, and the conductor is heated. The amount that a given conductor resists the flow of electric current is measured in ohms.

Power

Whenever current flows, work is done. A conductor may be heated, a motor may be spun, a bulb might give off light, or some other form of energy may be released. There is a simple law that tells exactly how much work may be done by a flowing current. The amount of work done is equal to the voltage of the supply times the current flowing through the wire. This law is expressed in the form P=IV, where P is the power in watts, I is the current in amps, and V is the voltage in volts. For example, if we find that a light bulb draws half of an amp at 120 volts, we simply multiply the 120 volts by half an amp to find that the bulb draws 60 watts of power.

Ohm's Law

 Let's say you have a six volt battery and you need to draw two amps of current. What resistance should you make the conductor? Or let's say you have a three volt power supply and a thousand ohm resistor. How much current would flow through the resistor if you were to connect the resistor to the power supply? In order to find the answers to these questions, all you need to do is to use a simple mathematical formula called ohm's law. Ohm's law states that the amount of current flowing through a conductor times the resistance of the conductor is equal to voltage of the power supply. This law is often expressed in the form V=IR, where V is the voltage measured in volts, I is the current measured in amps, and R is the resistance measured in ohms.

electric circuit, unbroken path along which an electric current exists or is intended or able to flow. A simple circuit might consist of an electric cell (the power source), two conducting wires (one end of each being attached to each terminal of the cell), and a small lamp (the load) to which the free ends of the wires leading from the cell are attached. When the connections are made properly, current flows, the circuit is said to be “closed,” and the lamp will light. The current flows from the cell along one wire to the lamp, through the lamp, and along the other wire back to the cell. When the wires are disconnected, the circuit is said to be “open” or “broken.” In practice, circuits are opened by such devices as switches, fuses, and circuit breakers (see fuse, electric; circuit breaker; short circuit). Two general circuit classifications are series and parallel. The elements of a series circuit are connected end to end; the same current flows through its parts one after another. The elements of a parallel circuit are connected so that each component has the same voltage across its terminals; the current flow is divided among its parts. When two circuit elements are connected in series, their effective resistance (impedance if the circuit is being fed alternating current) is equal to the sum of the separate resistances; the current is the same in each component throughout the circuit. When circuit elements are connected in parallel, the total resistance is less than that of the element having the least resistance, and the total current is equal to the sum of the currents in the individual branches. A battery-powered circuit is an example of a direct-current circuit; the voltages and currents are constant in magnitude and do not vary with time. In alternating-current circuits, the voltage and current periodically reverse direction with time. A standard electrical outlet supplies alternating current. Lighting circuits and electrical machinery use alternating current circuits. Many other devices, including computers, stereo systems, and television sets, must first convert the alternating current to direct current. That is done by a special internal circuit usually called a power supply. A digital circuit is a special kind of electronic circuit used in computers and many other devices. Magnetic circuits are analogous to electric circuits, where magnetic materials are regarded as conductors of magnetic flux. Magnetic circuits can be part of an electric circuit; a transformer is an example. Equivalent circuits are used in circuit analysis as a modeling tool; a simple circuit made up of a resistor, and an inductor might be used to electrically represent a loudspeaker. Electrical circuits can also be used in other fields of studies. In the study of heat flow, for example, a resistor is used to represent thermal insulation. Operating electric circuits can be used for general problem solving (as in an analog computer).

Kirchhoff's laws

  

Kirchhoff's laws [for Gustav R. Kirchhoff], pair of laws stating general restrictions on the current and voltage in an electric circuit. The first of these states that at any given instant the sum of the voltages around any closed path, or loop, in the network is zero. The second states that at any junction of paths, or node, in a network the sum of the currents arriving at any instant is equal to the sum of the currents flowing away.

inductance

  

inductance, quantity that measures the electromagnetic induction of an electric circuit component; it is a property of the component itself rather than of the circuit as a whole. The self-inductance, L, of a circuit component determines the magnitude of the electromagnetic force (emf) induced in it as a result of a given rate of change of the current through the component. Similarly, the mutual inductance, M, of two components, one in each of two separate but closely located circuits, determines the emf that each may induce in the other for a given current change. Inductance is expressed in henrys (for Joseph Henry). An inductor is a device designed to produce an inductance, e.g., a coil; an ideal inductor, i.e., one having no resistance or capacitance (see impedance), is often called an inductance.

Hukum Ohm menyatakan bahwa besar arus yang mengalir pada suatu konduktor pada suhu tetap sebanding dengan beda potensial antara kedua ujung-ujung konduktor   I = V / R   HUKUM OHM UNTUK RANGKAIAN TERTUTUP   I =     n E            R + n rd I =      n           R + rd/p n = banyak elemen yang disusun seri E = ggl (volt) rd = hambatan dalam elemen R = hambatan luar p = banyaknya elemen yang disusun paralel RANGKAIAN HAMBATAN DISUSUN SERI DAN PARALEL   SERI R = R1 + R2 + R3 + ... V = V1 + V2 + V3 + ... I = I1 = I2 = I3 = ... PARALEL 1 = 1 + 1 + 1R    R1  R2   R3 V = V1 = V2 = V3 = ... I = I1 + I2 + I3 + ...   ENERGI DAN DAYA LISTRIK ENERGI LISTRIK (W)  adalah energi yang dipakai (terserap) oleh hambatan R. W = V I t = V²t/R = I²Rt   Joule = Watt.detik KWH = Kilo.Watt.jam DAYA LISTRIK (P) adalah energi listrik yang terpakai setiap detik. P = W/t = V I = V²/R = I²R

HUKUM KIRCHOFF I : jumlah arus menuju suatu titik cabang sama dengan jumlah arus yang meninggalkannya.

S Iin = Iout

HUKUM KIRCHOFF II : dalam rangkaian tertutup, jumlah aljabar GGL (e) dan jumlah penurunan potensial sama dengan nol.

Se = S IR = 0

ALAT UKUR LISTRIK TERDIRI DARI
 

1. JEMBATAN WHEATSTONE	digunakan untuk mengukur nilai suatu hambatan dengan cara mengusahakan arus yang mengalir pada galvanometer = nol (karena potensial di ujung-ujung galvanometer sama besar). Jadi berlaku rumus perkalian silang hambatan : R1 R3 = R2 Rx
2. AMPERMETER	untuk memperbesar batas ukur ampermeter dapat digunakan hambatan Shunt (Rs) yang dipasang sejajar/paralel pada suatu rangkaian. Rs = rd 1/(n-1) n = pembesaran pengukuran
3. VOLTMETER	untuk memperbesar batas ukur voltmeter dapat digunakan hambatan multiplier (R-) yang dipasang seri pada suatu rangkaian. Dalam hal ini R. harus dipasang di depan voltmeter dipandang dari datangnya arus listrik. Rm = (n-1) rd n = pembesaran pengukuran

TEGANGAN JEPIT (V.b) :
adalah beda potensial antara kutub-kutub sumber atau antara dua titik yang diukur.

1. Bila batere mengalirkan arus maka tegangan jepitnya adalah:

Vab = e - I rd

2. Bila batere menerima arus maka tegangan jepitnya adalah:

Vab = e + I rd

3. Bila batere tidak mengalirkan atau tidak menerima arus maka
    tegangan jepitnya adalah .

Vab = e

Dalam menyelesaian soal rangkaian listrik, perlu diperhatikan :
1. Hambatan R yang dialiri arus listrik. Hambatan R diabaikan jika tidak
    dilalui arus listrik.

2. Hambatan R umumnya tetap, sehingga lebih cepat menggunakan
    rumus yang berhubungan dengan hambatan R tersebut.

3. Rumus yang sering digunakan: hukum Ohm, hukum Kirchoff, sifat
    rangkaian, energi dan daya listrik.

Contoh 1 :
Untuk rangkaian seperti pada gambar, bila saklar S1 dan S2 ditutup maka hitunglah penunjukkan jarum voltmeter !
Jawab :
Karena saklar S1 dan S2 ditutup maka R1, R2, dan R3 dilalui arus listrik, sehingga :

1    =  1  +  1  Rp       R2    R3 Rp = R2 R3 = 2W       R2 + R1 V = I R = I (R1 + Rp)I = 24/(3+2) = 4.8 A

Voltmeter mengukur tegangan di R2 di R3, dan di gabungkan R2 // R3, jadi :
V = I2 R2 = I3 R3 = I Rp
V = I Rp = 0,8 V
Contoh 2:
Pada lampu A dan B masing-masing tertulis 100 watt, 100 volt. Mula-mula lampu A den B dihubungkan seri dan dipasang pada tegangan 100 volt, kemudian kedua lampu dihubungkan paralel dan dipasang pada tegangan 100 volt. Tentukan perbandingan daya yang dipakai pada hubungan paralel terhadap seri !

Hambatan lampu dapat dihitung dari data yang tertulis dilampu : RA = RB = V²/P = 100²/100 = 100 W Untuk lampu seri : RS = RA + RB = 200 W Untuk lampu paralel : Rp = RA × RB = 50 W                                     RA + RB

Karena tegangan yang terpasang pada masing-masing rangkaian sama maka gunakan rumus : P = V²/R

Jadi perbandingan daya paralel terhadap seri adalah :
Pp = V² : V² = Rs = 4
Ps    Rp    Rs    Rp    1
Contoh 3:
Dua buah batere ujung-ujungnya yang sejenis dihubungkan, sehingga membentuik hubungan paralel. Masing-masing batere memiliki GGL 1,5 V; 0,3 ohm dan 1 V; 0,3 ohm.Hitunglah tegangan bersama kedua batere tersebut !
Jawab :
Tentakan arah loop dan arah arus listrik (lihat gambar), dan terapkan hukum Kirchoff II,

Se + S I R = 0 e1 + e2 = I (r1 + r2) I = (1,5 - 1) = 5  A     0,3 + 0,3    6

Tegangan bersama kedua batere adalah tegangan jepit a - b, jadi :

Vab = e1 - I r1 = 1,5 - 0,3 5/6 = 1,25 V

1= e2 + I R2 = 1 + 0,3 5/6 = 1,25 V

Contoh 4:
Sebuah sumber dengan ggl = E den hambatan dalam r dihubungkan ke sebuah potensiometer yang hambatannya R. Buktikan bahwa daya disipasi pada potensiometer mencapai maksimum jika R = r.
Jawab :

Dari Hukum Ohm : I = V/R =       e                                          R+r Daya disipasi pada R : P = I²R =        e  ²R                                              (R+r)²

Agar P maks maka turunan pertama dari P harus nol: dP/dR = 0 (diferensial parsial)

Jadi e² (R+r)² - E² R.2(R+r) = 0
               (R+r)4
e² (R+r)² = e² 2R (R+r) Þ R + r = 2R
                                        R = r (terbukti)
ARUS/TEGANGAN BOLAK-BALIK
Arus/tegangan bolak-balik adalah arus/tegangan yang besarnya selalu berubah-ubah secara periodik.  Simbol tegangan bolak-balik adalah ~ dan dapat diukur dengan Osiloskop (mengukur tegangan maksimumnya).

NILAI EFEKTIF KUAT ARUS/TEGANGAN AC
Nilai efektif kuat arus/tegangan AC adalah arus/tegangan AC yang dianggap setara dengan kuat arus/tegangan AC yang menghasilkan jumlah kalor yang sama ketika melalui suatu penghantar dalam waktu yang sama.
Kuat arus efektif :          Ief = Imaks / Ö2
Tegangan efektif :         Vef = Vmaks / Ö2
Besaran yang ditunjukkan oleh voltmeter/amperemeter DC adalah tegangan/kuat arus DC yang sesungguhnya,sedangkan yang ditunjukan oleh voltmeter/amperemeter AC adalah tegangan/kuat arus efektif, bukan tegangan/kuat arus sesungguhnya.

Pencemaran Lingkungan, Udara, NOx, SOx,

Pencemaran Lingkungan
Perkembangan teknologi dan industri dapat berdampak positif atau negatif bagi kehidupan manusia. Dampak positif (menguntungkan), yaitu dampak yang diharapkan dalam rangka meningkatkan kualitas dan kenyamanan hidup. Dampak negatif (merugikan), yaitu dampak yang dapat menurunkan kualitas/kenyamanan hidup. Dampak ini tidak diharapkan karena menimbulkan masalah yang harus diatasi, yaitu masalah kerusakan atau pencemaran lingkungan.
a. Pengertian Pencemaran Lingkungan
Pencemaran adalah peristiwa penyebaran bahan kimia dengan kadar tertentu yang dapat merubah keadaan keseimbangan pada daur materi dalam lingkungan (keseimbangan lingkungan) baik keadaan struktur maupun fungsinya sehingga dapat mengganggu kesejahteraan manusia. Pencemaran lingkungan meliputi pencemaran udara, pencemaran air, dan pencemaran tanah (daratan).
Lingkungan dapat tercemar karena:
1) Kecepatan hilangnya senyawa tertentu dari lingkungan lebih besar daripada kecepatan masuknya senyawa pengganti.
2) Rusaknya atau putusnya alur siklus biokimia.
3) Kecepatan masuknya senyawa ke dalam lingkungan lebih besar daripada kecepatan pengambilannya.
4) Masuknya senyawa yang tidak terdegredasi ke dalam lingkungan.
b. Daur Pencemaran Lingkungan
Pencemaran lingkungan dapat disebabkan karena ulah manusia dan pada akhirnya dampaknya juga akan dirasakan oleh manusia, baik secara langsung maupun tak langsung.


Pencemaran Udara
Udara akan tercemar jika ada bahan-bahan atau zat asing di dalam udara yang menyebabkan perubahan susunan atau komposisi udara dari keadaan normalnya.
a. Penyebab Pencemaran Udara
1) Faktor internal (secara alamiah), misalnya:
• debu beterbangan oleh tiupan angin
• abu atau debu dan gas-gas volkanik dari letusan gunung berapi
• proses pembusukan sampah
2) Faktor eksternal (karena ulah manusia), misalnya:
• pembakaran bahan bakar fosil
• debu atau serbuk dari kegiatan industri
• pemakaian zat-zat kimia yang disemprotkan ke udara
b. Sumber Pencemar Udara
• transportasi
• industri
• pembuangan sampah
• pembakaran stasioner, dan lain-lain
c. Komponen Pencemar Udara
• Karbon monoksida (CO)
• Oksida nitrogen (NOx)
• Oksida belerang (SOx)
• Hidrokarbon
• Partikel (particulate), dan lain-lain
d. Dampak Pencemaran Udara
1). Dampak Pencemaran oleh Karbon Monoksida (CO)
Gas CO tidak berbau dan tidak berwarna. Pada keadaan normal konsentrasinya di udara ± 0,1 ppm, dan di kota dengan lalulintas padat ± 10 - 15 ppm. Dampak pencemaran oleh gas CO antara lain:
• Bagi manusia dampak CO dapat menyebabkan gangguan kesehatan sampai kematian, karena CO bersifat racun metabolis, ikut bereaksi secara metabolis dengan hemoglobin dalam darah (Hb) :
Hb + O2 ⎯→ O2Hb (oksihemoglobin)
Hb + CO ⎯→ COHb (karboksihemoglobin)
COHb 140 kali lebih stabil daripada O2Hb.
Kadar CO :
Waktu kontak :
Dampaknya bagi tubuh :
≤ 100 ppm
± 30 ppm
± 1000 ppm
± 1300 ppm
> 1300 ppm
sebentar
8 jam
1 jam
1 jam
1 jam
dianggap aman
menimbulkan pusing dan mual
pusing dan kulit berubah kemerah-merahan
kulit jadi merah tua dan rasa pusing yang hebat
lebih hebat sampai kematian

Tanda-tanda keracunan gas CO adalah: pusing, sakit kepala dan mual. Keadaan yang lebih berat lagi adalah: kemampuan gerak tubuh menurun, gangguan pada sistem kardiovaskular, serangan jantung, sampai dengan kematian.
• Bagi tumbuhan, kadar CO 100 ppm pengaruhnya hampir tidak ada khususnya tumbuhan tingkat tinggi. Kadar CO 200 ppm dengan waktu kontak 24 jam dapat mempengaruhi kemampuan fiksasi nitrogen oleh bakteri bebas terutama yang terdapat pada akar tumbuhan.

Dampak Pencemaran Oleh Oksida Nitrogen (NOx}
Gas NO tidak berbau dan tidak berwarna. Gas NO2 berbau menyengat, berwarna coklat kemerahan. Sifat racun (toksisitas) NO2 empat kalinya NO. Organ yang paling peka paru-paru, jika terkena NO2 akan membengkak sehingga sulit bernapas sampai kematian. Konsentrasi NO yang tinggi mengakibatkan kejang-kejang, bila keracunan berlanjut mengakibatkan kelumpuhan. NO akan lebih berbahaya jika teroksidasi menjadi NO2.
Oksida nitrogen bagi tumbuhan menyebabkan bintik-bintik pada permukaan daun, bila konsentrasinya tinggi mengakibatkan nekrosis (kerusakan jaringan daun), sehingga fotosintesis terganggu. Konsentrasi NO 10 ppm dapat menurunkan kemampuan fotosintesis 60 – 70 %. Di udara oksida nitrogen dapat menimbulkan PAN (Peroxy Acetyl Nitrates) yang dapat menyebabkan iritasi mata (pedih dan berair). PAN bersama senyawa yang lain akan menimbulkan kabut foto kimia (Photo Chemistry Smog).

Dampak Pencemaran oleh Oksida Belerang (SOx)
SOx sebagian besar berasal dari pembakaran bahan bakar fosil, terutama batubara. Gas buang lebih banyak mengandung SO2 dibanding SO3. Dengan oksigen dari udara SO2 menghasilkan SO3:
SO2 + O2 ⎯→ SO3
Gas SO2 berbau tajam dan tak mudah terbakar. Gas SO3 sangat reaktif. Dengan uap air dari udara:
SO2 + H2O ⎯→ H2SO3
SO3 + H2O ⎯→ H2SO4
Jika ikut terkondensasi di udara dan jatuh bersama air hujan menyebabkan hujan asam.
• Bagi tumbuhan kadar SOx ± 0,5 ppm dapat menyebabkan timbulnya bintik-bintik pada daun. Jika paparan lama daun menjadi berguguran.
• Bagi manusia SOx menimbulkan gangguan pernapasan. Jika SOx berubah menjadi asam akan menyerang selaput lendir pada hidung, tenggorokan dan saluran napas yang lain sampai ke paru-paru. SO2 dapat menimbulkan iritasi tenggorokan tergantung daya tahan masing-masing (ada yang 1 - 2 ppm, atau 6 ppm). SO2 berbahaya bagi anak-anak, orang tua, dan orang yang menderita kardiovaskuler. Otot saluran pernapasan akan mengalami kejang (spasma). Akan lebih berat lagi jika konsentrasi SO2 tinggi dan suhu udara rendah. Pada paparan lama akan terjadi peradangan yang hebat pada selaput lendir yang diikuti paralysis cilia (kelumpuhan sistem pernapasan), kerusakan lapisan ephitelium, akhirnya kematian. Pada konsentrasi 6 - 12 ppm dengan paparan pendek yang berulang-ulang dapat menyebabkan hiperplasia dan metaplasia sel-sel epitel yang akhirnya menjadi kangker.

• Pada benda-benda, SO2 bersifat korosif. Cat dan bangunan gedung warnanya menjadi kusam kehitaman karena PbO pada cat bereaksi dengan SOx menghasilkan PbS. Jembatan menjadi rapuh karena mempercepat pengkaratan.

Spektrofotometr

Spektrofotometri merupakan suatu metoda analisa yang didasarkan pada pengukuran serapan sinar monokromatis oleh suatu lajur larutan berwarna pada panjang gelombamg spesifik dengan menggunakan monokromator prisma atau kisi difraksi dengan detektor fototube.

Spektrofotometer adalah alat untuk mengukur transmitan atau absorban suatu sampel sebagai fungsi panjang gelombang. Sedangkan pengukuran menggunakan spektrofotometer ini, metoda yang digunakan sering disebut dengan spektrofotometri.

Spektrofotometri dapat dianggap sebagai perluasan suatu pemeriksaan visual dengan studi yang lebih mendalam dari absorbsi energi. Absorbsi radiasi oleh suatu sampel diukur pada berbagai panjang gelombangdan dialirkan oleh suatu perkam untuk menghasilkan spektrum tertentu yang khas untuk komponen yang berbeda.

Absorbsi sinar oleh larutan mengikuti hukum Lambert-Beer, yaitu :

A = log ( Io / It ) = a b c

Keterangan : Io = Intensitas sinar datang

It = Intensitas sinar yang diteruskan

a = Absorptivitas

b = Panjang sel/kuvet

c = konsentrasi (g/l)

A = Absorban

Spektrofotometri merupakan bagian dari fotometri dan dapat dibedakan dari filter fotometri sebagai berikut :

1. Daerah jangkauan spektrum

Filter fotometr hanya dapat digunakan untuk mengukur serapan sinar tampak (400-750 nm). Sedangkan spektrofotometer dapat mengukur serapan di daerah tampak, UV (200-380 nm) maupun IR (> 750 nm).

2. Sumber sinar

Sesuai dengan daerah jangkauan spektrumnya maka spektrofotometer menggunakan sumber sinar yang berbeda pada masing-masing daerah (sinar tampak, UV, IR). Sedangkan sumber sinar filter fotometer hanya untuk daerah tampak.

3. Monokromator

Filter fotometere menggunakan filter sebagai monokrmator. Tetapi pada spektro digunakan kisi atau prisma yang daya resolusinya lebih baik.

4. Detektor

- Filter fotometer menggunakan detektor fotosel

- Spektrofotometer menggunakan tabung penggandaan foton atau fototube.

Komponen utama dari spektrofotometer yaitu :

1. 1. Sumber cahaya

Untuk radisi kontinue :

- Untuk daerah UV dan daerah tampak :

- Lampu wolfram (lampu pijar) menghasilkan spektrum kontiniu pada gelombang 320-2500 nm.

- Lampu hidrogen atau deutrium (160-375 nm)

- Lampu gas xenon (250-600 nm)

Untuk daerah IR

Ada tiga macam sumber sinar yang dapat digunakan :

- Lampu Nerst,dibuat dari campuran zirkonium oxida (38%) Itrium oxida (38%) dan erbiumoxida (3%)

- Lampu globar dibuat dari silisium Carbida (SiC).

- Lampu Nkrom terdiri dari pita nikel krom dengan panjang gelombang 0,4 – 20 nm

- Spektrum radiasi garis UV atau tampak :

- Lampu uap (lampu Natrium, Lampu Raksa)

- Lampu katoda cekung/lampu katoda berongga

- Lampu pembawa muatan dan elektroda (elektrodeless dhischarge lamp)

- Laser

1. 2. Pengatur Intensitas

Berfungsi untuk mengatur intensitas sinar yang dihasilkan oleh sumber cahaya agar sinar yang masuk tetap konstan.

1. 3. Monokromator

Berfungsi untuk merubah sinar polikromatis menjadi sinar monokromatis sesuai yang dibutuhkan oleh pengukuran

Macam-macam monokromator :

- Prisma

- kaca untuk daerah sinar tampak

- kuarsa untuk daerah UV

- Rock salt (kristal garam) untuk daerah IR

- Kisi difraksi

Keuntungan menggunakan kisi :

- Dispersi sinar merata

- Dispersi lebih baik dengan ukuran pendispersi yang sama

- Dapat digunakan dalam seluruh jangkauan spektrum

1. 4. Kuvet

Pada pengukuran di daerah sinar tampak digunakan kuvet kaca dan daerah UV digunakan kuvet kuarsa serta kristal garam untuk daerah IR.

1. 5. Detektor 

Fungsinya untuk merubah sinar menjadi energi listrik yang sebanding dengan besaran yang dapat diukur.

Syarat-syarat ideal sebuah detektor :

- Kepekan yang tinggi

- Perbandingan isyarat atau signal dengan bising tinggi

- Respon konstan pada berbagai panjang gelombang.

- Waktu respon cepat dan signal minimum tanpa radiasi.

- Signal listrik yang dihasilkan harus sebanding dengan tenaga radiasi.

Macam-macam detektor :

- Detektor foto (Photo detector)

- Photocell

- Phototube

- Hantaran foto

- Dioda foto

- Detektor panas

1. 6. Penguat (amplifier)

Berfungsi untuk memperbesar arus yang dihasilkan oleh detektor agar dapat dibaca oleh indikator.

1. 7. Indikator

Dapat berupa :

- Recorder

- Komputer

PLTGU 1

SYSTEM PLTGU

PLTU

DEAERATOR

Deaeration of Condensate and Make-up Water

in Steam Turbine and Combined Cycle Power Plants

High oxygen content in the feedwater can cause corrosion of components and piping. The deaerator should be designed to remove the maximum amount of the incondensable gases possible from the boiler feedwater cycle and to achieve an oxygen content of < 7 ppb (=0.005 cc/l) in the feedwater. This protects the boiler and the whole system against corrosion. Depending on the pressure in the feed water tank/deaerator the deaeration process takes place either under vacuum (known as vacuum deaeration) at about 60°C, 0.2 bar, or at pressure above atmospheric pressure (over-pressure deaeration).


Deaeration of Condensate 
If the oxigen content of condensate at the deaerator inlet is not very high, a tray type deaerator can be used (see deaerators Fig. 007).

Tray Type Deaerators:
- Tray type deaerator as horizontal vessel over FWST
- Annular tray type deaerator as vertical dome over FWST (ALSTOM tray type Deaerator)
- Tray type deaerator as vertical dome over FWST (TPT tray type Deaerator).
The water is sprayed at the top of deaerator by means of a spring-operated sprayer or by means of spray nozzles. The sprayer reduced the water to small droplets or to a water film. The water flows down between trays or deflection baffles. The steam enters the deaerator in the lower part of the deaerator and rises to the sprayed water in counterflow to the down-coming water and takes away the gases from the water. The steam condenses practically on the sprayed water and the incoming water is heated to the satturation temperature and deaerated. The apparatus works as DC heater and deaerator.
The freed oxygen is discharged to atmosphere or to the condenser via the vent openings at deaerator top, which may be fitted with throttling organ.

TPT Tray type Deaerator: 

 

Inlet condensate: Flow rate Mc, Temperature Tc, oxygen content C1o2
Steam flow rate Ms:     Ms = f(Mc, Tc, Ps)
Dome diameter D:          D = f(Mc, Ms, Ps)
Bypass steam channel ratio:  L/D = f(Ms, Ps)
Venting flow rate Mvent:     Mvent = f(Mc, C1o2, C2o2)
Deflection plats number (baffles) and height H1 are function of O2 content C1o2, C2o2 and Ps.

Design of the TPT Deaerator:The deaerator is laid out in such a way that the main heating steam flows through two by-pass channels and the condensate and flush steam are connected in a counter flow.
For the design of a deaerator the following condensate and steam load capacities are computed:

a) Water load capacity
The water load capacity limit (flood limit) is put at the basis for the maximum condensate mass flow density mc (kg/sm2) through the deaerator dome.
Since steam in the top of the dome condensed and the condensate increases the water load of the deaerator qross-section, for the diameter definition the mass flow density mc is computed from the sum of the condensate flow (Mc) and the steam flow (Ms).

b) Steam load capacity
The load capacity limit (flood limit) for a given deaerator type is a function of the steam flow and the steam pressure or the density of the saturated steam.
With an excess of the Steam load capacity instability with strong steam impacts will arise.

The deaerator masses (dome diameter D, by-pass steam chanels or their distance L, ...) are laid out so that the flood limit is not exceeded. The calculation will be determined for the worst operation case and from the water and steam load capacities of the deaerator (see deaerator sketch 007a).



Deaeration of Make-up Water

Make-up water is usually fully saturated with oxygen (see diagram).
For make-up water with oxygen content of 9000 ppb (9 mg/lit) at deaerator inlet, the oxygen content at the outlet of 5 to 7 ppb (0.005 to 0.007 mg/lit) should be achieved.
For a lower mass flow rate of make-up the water can be sprayed to the cycle in the condenser neck.

Packing Deaerator
for Make-up Water and Condensate 
The deaerator is arranged as cylindrical dome over FWST or as separate deaerator. The mixture of Make-up water and condensate is sprayed at the top of the deaerator (Fig. 007). By means of a distributor the sprayed water is distributed across the dome cross-section. The water trickles down through the mass transfer packing elements and forming a large interfacial area between the water and the surrounding steam phase. A venting system extracts all gases from the vapor phase. The freed non-condensable gases is discharged to atmosphere or to the condenser via the vent openings at deaerator top.

Since the packing elements are expensive, the packing deaerator is used for deaeration of water under extreme parameters (high oxygen content and low pressure).
The disadvantage of this deaerator type (especially in case of vacuum deaeration) that a large packing diameter is necessary because of the large volume flow of the heating steam. The large packing volume leads to higher deaerator costs.




TPT Packing Deaerator
for make-up water and condensate
High performance deaerator for high make-up flow rate and vacuum pressure
The Make-up water is sprayed in a chamber at the top of the deaerator dome. During direct introduction of steam to the upper chamber the water is heated and partly deaerated. The heated water flows downward to the distributor and distributed across the dome cross-section (Fig. 007b).

The condensate can be introduced into the dome by spray nozzles above the Packing or by a spraying valve above the distributor. The make-up water and the condensate trickle down through the packing elements in counter flow to the second steam flow part.
The steam flow through the packing is reduced and thus arises a small packing diameter.
The packing diameter D is laid out so that the flood limit is not exceeded. The calculation will be determined for the worst operation case and from the water and steam load capacities of the deaerator.

Venting System:
By means of a venting system with a venting condenser the gases is extracted from the deaerator through several venting stages. A small bypass make-up flow is selected, which is sprayed by a small nozzle into the vent condenser. By means of openings at the top of the upper chamber and the top of the packing chamber the steam/air flows (Vent 1 and Vent 2) are throttled to the vent condenser. The throttle organs of the vent lines 1 and 2 are adjusted in such a way that the pressure Pv of the vent condenser and the desired steam/air flows (Vent 1 and Vent 2) results in. The non-condensable gases (Vent Mv) is discharged from the vent condenser via a throttle organ to the condenser.

 

Special Packing Deaerators for CCPP:
Patent: EP 077500: Packing Deaerator with counter-flow
Patent: US 5203286: Packing Deaerator with parallel/counter-flow