Thinkerz Engineer'z issue

Tunaweka mitego (Portable earthing kit au temporary earthing) tunapofanya kazi kwenye distribution lines kwa sababu kuu zifuatazo:

1. Kuhakikisha Usalama wa Wafanyakazi

Mitego (au “temporary earths”) husaidia kusafisha mabaki ya voltage kwenye nyaya ambazo zimezimwa lakini zinaweza kuwa na voltage kutokana na:

Induction kutoka kwenye nyaya zilizo karibu na zenye voltage.

Backfeed kutoka kwenye vifaa vya wateja (mfano: generators).

Switching errors au human mistake ya ku-supply line wakati kazi inaendelea.

2. Kutoa Njia Mbadala ya Umeme kwenda Ardhi

Endapo umeme utarudi kwenye line kwa bahati mbaya, mitego hutoa njia ya haraka ya kupeleka umeme ardhini (ground path), badala ya kupita kwa mfanyakazi aliye kwenye line hiyo. Hii husaidia kupunguza hatari ya mshtuko wa umeme (electric shock).

3. Kuthibitisha Line Imekatika Kabisa

Kuweka mitego ni sehemu ya utaratibu wa "Test, Tag, and Ground" ili kuhakikisha line haibebi umeme kabla ya kazi kuanza. Ni sehemu ya taratibu za Lockout–Tagout (LOTO).

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Hitimisho:

Mitego ni hatua ya kiusalama inayolenga kuzuia ajali wakati wa matengenezo au kazi nyingine kwenye distribution lines. Bila mitego, wafanyakazi wako kwenye hatari kubwa ya kupata mshtuko wa umeme au hata kufa kwa kuguswa na nyaya zenye mabaki ya voltage.

Umeme wa AC (Alternating Current) - Umeme unaobadilika mwelekeo.

Nini AC?
Umeme wa AC ni aina ya umeme ambao mwelekeo wa mkondo wa elektroni hubadilika mara kwa mara ndani ya sekunde. Hii ina maana kwamba sasa umeme hutiririka kwenye waya kwa mwelekeo mmoja, halafu hubadilika na kutiririka kwa mwelekeo mwingine, na tena hubadilika tena, na hivyo kuendelea.

Jinsi AC unavyofanya kazi:
AC huendeshwa kwa mzunguko wa voltage unaobadilika kutoka thamani chanya (positive) hadi thamani hasi (negative) mara nyingi kwa sekunde. Kwa mfano, TANESCO hutuma umeme wenye frequency ya 50 Hz Tanzania, yaani mzunguko huu unarudiwa mara 50 kwa sekunde.

Kwa nini AC?
AC ni rahisi kusambaza umbali mrefu bila kupoteza nguvu nyingi. Kwa kutumia transformers, voltage ya AC inaweza kuongezwa au kupunguzwa kwa urahisi, hivyo kuifanya yawezekane kupeleka umeme kutoka vituo vya nguvu hadi nyumba zako.

Matumizi ya AC:
AC hutumika sana kwa umeme wa nyumbani, viwandani, ofisini na sehemu nyingine nyingi kwa sababu ya usambazaji wake mzuri.

Umeme wa DC (Direct Current) - Umeme unaotiririka kwa mwelekeo mmoja

Nini DC?
DC ni umeme ambao mkondo wa elektroni hutiririka kwa mwelekeo mmoja tu bila kubadilika. Hii ina maana kuwa voltage ni thabiti na haitabadilika k**a AC.

Jinsi DC unavyofanya kazi:
Elektroni hutiririka moja kwa moja kutoka sehemu yenye voltage ya juu kwenda sehemu yenye voltage ya chini bila kubadilisha mwelekeo wake.

Chanzo cha DC:
Vifaa k**a betri, seli za jua (solar cells), na baadhi ya aina za adapter za umeme hutengeneza DC.

Matumizi ya DC:
DC hutumika kwenye vifaa vya umeme vidogo k**a simu, kompyuta, taa za magari, na vifaa vya elektroniki vinavyohitaji voltage thabiti.

Mfano wa Maisha Halisi

AC: Umeme unaokuja nyumbani kwako kutoka TANESCO ni AC, unaendesha taa, mashine za kuosha, TV, na vifaa vingine vikubwa.

DC: Betri ya simu yako, kompyuta ya laptop, au taa ya gari hutumia DC.

Which of these kills during an electric shock..

1: current
2: voltage

And why ❓

Ramadhan Kareem

Understanding Electricity:
Any appliances that we use in our daily lives such as household appliances, office equipments and industrial equipments, almost all of those things take electricity. Therefore, we should understand electricity.
The first question that we will find out the answer is "where does electricity come from?"
All matters are made up of atoms. Then ask the next question, "What are atoms?"
Atoms are the smallest part of an element. They are composed of nucleus and electrons, electrons surround nucleus. Elements are identified by the number of electrons in orbit around nucleus of atoms and by the number of protons in nucleus.
Nucleus is made up of protons and neutrons, and the number of protons and neutrons are balanced. Neutrons have no electric charge, protons have positive charges (+) and electrons have negative charges (-). A positive charge of proton equals a negative charge of electron.
Electrons are bound in their orbit by attraction of protons, but electrons in the outer band can become free of their orbit by some external forces. These are referred to as free electrons, which move from one atom to the next, electron flows are produced. These are the basis of electricity. Materials that allow many electrons to move freely are called conductors and materials that allow few free electrons to move are called insulators.
All matters are made up of atoms that have electric charges. Therefore, they have electric charges. For the matter that has a balanced the number of protons and electrons, positive charge force and negative charge force are balanced. It is called neutral state of an atom. (The number of protons and electrons remains equal.)
"Static electricity" represents a situation that all things are made up of electric charges. For example, the rubbing of material against another can cause the static electricity. Free electrons of one material move forcefully till they are freed of their orbits around nucleus and move to another. Electrons of one material decrease, it presents positive charges. At the same time, electrons of another increase, it has negative charges.
In general, charge producing of the matter means the matter has electric charges. It has positive and negative charges, which is expressed in coulomb.
Current, Voltage and Resistance
What is Current?
An electrical phenomenon is caused by flow of free electrons from one atom to another. The characteristics of current electricity are opposite to those of static electricity.
Wires are made up of conductors such as copper or aluminum. Atoms of metal are made up of free electrons, which freely move from one atom to the next. If an electron is added in wire, a free electron is attracted to a proton to be neutral. Forcing electrons out of their orbits can cause a lack of electrons. Electrons, which continuously move in wire, are called Electric Current.
For solid conductors, electric current refers to directional negative-to-positive electrons from one atom to the next. Liquid conductors and gas conductors, electric current refers to electrons and protons flow in the opposite direction.
Current is flow of electrons, but current and electron flow in the opposite direction. Current flows from positive to negative and electron flows from negative to positive.
Current is determined by the number of electrons passing through a cross-section of a conductor in one second. Current is measured in amperes, which is abbreviated "amps". The symbol for amps is a letter "A".
A current of one amp means that current pass through a cross-section of two conductors, which are placed in parallel 1 meter apart with 2x10-7 Newton per meter force occur in each conductor. It can also mean charges of one coulomb (or 6.24x1018 electrons) passing through a cross-section of a conductor in one second.
What is voltage?
Electric current is flow of electrons in a conductor. The force required to make current flow through a conductor is called voltage and potential is the other term of voltage. For example, the first element has more positive charges, so it has higher potential. On the other hand, the second element has charges that are more negative so it has lower potential. The difference between two points is called potential difference.
Electromotive force means the force which makes current continuously flows through a conductor. This force can be generated from power generator, battery, flashlight battery and fuel cell, etc.
Volt, abbreviated "V", is the unit of measurement used interchangeably for voltage, potential, and electromotive force. One volt means a force which makes current of one amp move through a resistance of one ohm.
What is resistance?
Electrons move through a conductor when electric current flows. All materials impede flow of electric current to some extent. This characteristic is called resistance. Resistance increases with an increase of length or decrease of cross-section of a material.
The unit of measurement for resistance is ohms and its symbol is the Greek letter omega (Ω). The resistance of one ohm means a conductor allows a current of one amp to flow with a voltage of one volt.
All materials are difference in allowing electrons flow. Materials that allow many electrons to flow freely are called conductors such as copper, silver, aluminium, hydrochloric solution, sulphuric acid and saltwater. In contrast, materials which allow few electrons to flow are called insulators such as plastic, rubber, glass and dry paper. Another type of materials, semiconductors have characteristics of both conductors and insulators. They allow electrons to move while being able to control flow of electrons and examples are carbon, silicon and germanium, etc.
The resistance of conductor depends on two main factors as the followings:
1. Types of material
2. Temperature of material
How to measure current
The instrument used to measure current is called ampere meter or ammeter.
•
Steps for current measurement Connect a small light bulb to a dry cell. Measure current that passes through light bulb by connecting positive terminal (+) of ammeter to negative terminal (-) of a dry cell.
•
Safety instructions for current measurement;
1. Estimate current that required measuring then choose a suitable ammeter, since each ammeter has different limit of current measurement.
2. Be sure that the connection to positive terminal (+) and negative terminal (-) of ammeter are correct.
3. Do not directly connect ammeter terminals to dry cell terminals. Since it can damage the meter.
How to measure voltage
The instrument used to measure voltage, difference potential or electromotive force is called voltmeter.
•
Steps for voltage measurement
Connect a small light bulb to a dry cell. A voltmeter is wired in parallel with the light bulb to measure voltage across the light bulb. Connect positive terminal (+) of voltmeter to positive terminal (+) of a dry cell and connect negative terminal (-) of voltmeter to negative terminal (-) of a dry cell.
•
Safety instructions for measuring voltage;
1. Estimate voltage that required measuring then choose
a suitable voltmeter, since each voltmeter is designed with
the limit of voltage measurement.
2. Be sure that the connecting of positive terminal (+) and negative terminal (-) of voltmeter are correct.
How to measure resistance
The instrument used to measure resistance is called test meter or multimeter. The multimeter or test meter is used to make various electrical measurements such as current, voltage and resistance. It combines the functions of ammeter, voltmeter and ohmmeter.
•
Steps for resistance measurement
Turn the face dial to a position for required measuring, resistance, then touch both of terminals of multimeter (see figure 1) and adjust the meter range to 0 Ω. Touch both of terminals of meter to a resistance and take the reading.

Charge Controller Sizing:
How to choose the right size charge controller for your solar energy system.

Charge controller sizing is best understood when you grasp what a charge controller does.

Solar Charge Controller Functions:
The function of a charge controller is to regulate the charge going into your battery bank from your solar panel array and prevent overcharging and reverse current flow at night.

It does this by using a transistor to shunt the PV charging circuit. This means, if your battery is full, it stops the charging and if your battery is reaching an unhealthy discharge point, it stops the discharging.

By using a pv charge controller you minimize the use of utility power and maximize the chances of your batteries and other photovoltaic components lasting longer, thus increase the life expectancy and efficiency of your entire solar system.

More sophisticated solar charge controllers make sure the battery is charged by utilizing pulse width modulation (PWM) or maximum power point tracking (MPPT).

By inputting pre-set high and low voltage cut off settings, you can help keep your batteries healthy and efficient, automatically.

Charge Controller Sizing
Sizing charge controllers is pretty simple really. PV charge controllers are rated and sized depending on your solar array's current (amps) and the solar systems voltage (push).

Therefore solar charge controller sizing basically involves "getting a charge controller big enough to handle the amount of power and current produced by your solar energy system".

The most common pv charge controllers come in 12, 24 and 48 volts. Amperage ratings can be between 1-60 amps and voltage ratings from 6-60 volts.

So if your solar system's volts were 12 and your amps were 14, you would need a solar charge controller that had at least 14 amps.

However due to factors such as light reflection, sporadic increased current levels can occur, so you need to factor in an additional 25% bringing the minimum amps that our pv charger controller must have to 17.5 amps.

So we'll need a 12 volt, 20 amp charge controller (rounded up).

It won't hurt anything if your charge controller's amps are higher, in fact it's a good idea just in case you increase the size of your solar energy system in the future.

MPPT Charge Controllers
MPPT stands for Maximum Power Point Tracking and a MPPT charge controller is used in the very common case where your solar array's voltage is higher than your battery bank's voltage.

This is the case with the example solar arrangement diagrams we use in our Solar Panel Wiring Diagrams section, so pay attention to this if you choose to copy any of those arrangements. MPPT charge controllers also work great with systems that have panels with odd voltage ratings, for instance: 56V.

When a MPPT solar charge controller notices a difference in voltage, it will automatically and efficiently convert the higher voltage to the lower voltage so your panels, battery bank and PV charge controller can all be equal in voltage.

So if you had a 900 watt solar array with 48 volts, and your battery bank's voltage was 24 volts...

..you can determine the amps your PV charge controller needs to have by dividing the watts by the lower of the two volts.

Watts / Volts = Amps

So 900W / 24V = 37.5 Amps

Plus you still have to add an extra 25% for unexpected current increases due to factors such as light reflection... and you get 46.87 amps.

So you'll need a 24 volt, 50 Amp MPPT charge controller (rounded up). Learn more about MPPT charge controller sizing.

PV Charge Controller - Upper Voltage Limit
All charge controllers have an upper voltage limit. This refers to the maximum amount of voltage they can handle from the solar array. Make sure you know what the upper voltage limit is and that you don't exceed it or you may end up burning out your solar charge controller.

How to choose the right equipment for my needs:

For simplicity, let's assume you have a 100 watt device that you want to power with free solar energy for 10 hours each night.

To figure out what size solar panel, batteries, charge controller and inverter you need, follow the simple steps below.

1. Calculate how much energy is needed. 100 Watts x 10 hours = 1,000 Watt hours. That is the total energy you will need.

2. Now calculate what size solar panel you will need. Based on a ten hour day of light, the calculation is simple:
1,000 Watt hours / 10 hours sunlight = 100 Watt solar panel.

The reality is that most summer days give about 15 hours of sunlight and winter you get about 4-5 hours of sunlight. Always choose the worst case scenario for
your solar panel. In this case, go with a winter day of 5 hours sunlight.
1,000 Watt hours / 5 hours sunlight = 200 Watt solar panel.

3. Calculate what size batteries you need. 1,000 Watt hours divided by 12 Volts = 83 Amp Hours of reserve battery power.
1,000 / 12 = 83.3
An average marine deep cycle battery will work well here. Select a larger size battery to be sure, say 100 Amp hours capacity.

4. To figure what size solar charge controller is needed, take your solar panel wattage, which is 100 watts divided by 12 Volts.
100 / 12 = 8.3 Amps.
Always go larger, in this case use a 10 Amp solar charge controller.

5. Calculate what size inverter is needed. That's the easy part. You need to power a 100 Watt load, so select an inverter that has
at least 100 Watts continuous power rating.

SENSORS