CABLE SIZE & CURRENT CARRYING CAPACITY OF CABLE

 

How to Find The Suitable Size of Cable & Wire for Electrical Wiring Installation? With Examples

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How to Find The Suitable Size of Cable & Wire for Electrical Wiring Installation? With Examples

Remember that it's far very crucial to choose proper wire size while sizing a wire for electrical installations. An inappropriate size of wire for heavy loads current can also create chaos which results in failure of the electrical system, hazardous fire and serious injuries.

Voltage Drop in Cables

Whenever the current flows through the conductor, there will be a voltage drops in that conductor. Normally, voltage drop may be neglected for small length of conductors but in case of a lower diameter and long length conductors we should consider a significant voltage drops for proper wiring installation and future load management.

According to Institute of Electrical and Electronics Engineers (IEEE) rule B-23, at any point between a power supply terminal and installation, voltage drop should not increase above 2.5% of provided (supply) voltage 

Example:

Let us assume , the supply voltage is 230V AC, then the value of permissible voltage drop should be;

• Permissible Voltage Drop = 230 x (2.5/100) = 5.75V

Similarly, if the supply voltage is 110V AC, the Permissible Voltage Drop  should be not more than 2.75V ( 110V x 2.5%).

In electrical wiring circuits, for sub circuits the value of voltage drop should be half of that permissible voltage drop.

Normally, the voltage drop is expressed in Ampere per meter (A / m)

Tables & Charts for Proper Cable & Wire Sizes

Below are the important tables which you should follow for determining the proper size of cable for Electrical Wiring Installation

How to calculate Voltage Drop in a Cable?

Step no. 1:         Calculate the maximum allowable  voltage drop.

Step no. 2:          Calculate the load current

Step no. 3:          After finding the load current select a proper cable from table 1

Step no. 4:          from table 1 find the voltage drop of the cable and multiply with the length of cable

Step no. 5:          Now multiply this calculated value of volt drop by load factor where;

Load factor = Load Current to be taken by Cable/ Rated Current of Cable given in the table.

                          This is the value of Volt drop in the cables when load current flows through it.

Step no. 6:          If the calculated value of voltage drop is less than the value calculated in step (1)                                   (Maximum allowable voltage drop), than the size of selected cable is proper

Step no. 7:          If the calculated value of voltage drop is greater than the value calculated in step (1)                               (Maximum allowable voltage drop), than calculate voltage drop for the next (greater in                             size) cable and so on until the calculated value of voltage drop became less than the                                 maximum allowable voltage drop calculated in step (1).

Example :

For Electrical wiring in a building, Total load is 5kW and the length of the cable from Main panel to sub circuit is 40 feet. Supply voltages is  230V and temperature is 40°C. Find the suitable size of cable which is going through conduits .

Solution:-

    Ø Total Load = 5kW

Ø                           Let us assume at max 20% overload occurs i.e. 1.2*5kW=6kW or 6000W

Now for 6000W load current will flow i.e. 6000/230= 26.08A

ØNow we have to select the size of cable from table 1 for 26.08A current which is 7/0.036 (28                      Amperes). It means we can use 7/0.036 cable according to table 1.

Ø                         Now check the selected (7/0.036) cable with temperature factor in Table 3, so the temperature                factor is 0.94 (in table 3) at 40°C  and current carrying capacity of (7/0.036) is 28A, therefore,                current carrying capacity of this cable at 40°C (104°F) would be

Current rating for 40°C  = 28 x 0.94 = 26.32 Amp.

                  Maximum current carrying capacity is 26.32 A and actual is 26.08A.Hence   this size of cable                  (7/0.036) is also suitable.

Ø                          Now find the voltage drop for 100 feet for this (7/0.036) cable is 7V, But in our case, the length of cable                 is 40 feet. Therefore, the voltage drop for 40 feet cable would be;

                Actual Voltage drop for 40 feet = (7 x 40/100) x (26.08/28) = 2.608V

                And Allowable voltage drop = (2.5 x 220)/100 = 5.5V

             Here The Actual Voltage Drop (2.608V) is less than that of maximum allowable voltage drop of 5.5V.                  Therefore, the most suitable cable size is (7/0.036) for that given load.

How domestic earthing can done

 https://www.youtube.com/watch?v=T5zymgvNwug&t=58s

MCB

Current Transformer

Why Capacitors bank is connected parallel with a load to improve power factor

we can improve the power factor by connecting the capacitor bank in parallel or series.If we connect the capacitor bank in parallel that means additional installation and O&M costs can be saved. In fact when we connect the capacitor bank to the series there is a decrease in the power of those capacitors in the series, a distance between 10-20% of the minimum transmission voltage. So power outages are not a major issue. The real problem is protection and the resulting cost: in the event of a short-circuit fault in the load there is a chance that all the transmission voltage will be applied to those capacitors and may fail. As we know it can be protected from over voltage voltages by using appropriate switch switches and split gap sparks. It therefore means additional installation and O&M (operation and maintenance) costs that can be avoided simply by connecting the capacitors accordingly.

Another great advantage is that when we connect it seamlessly you separate your installation, which makes it easier to repair. For example, if you need to replace some bank capacitors, or add others, to the corresponding series you need to do to disconnect the bank throughout the network, instead of the whole facility if you were connected to a network. series.

Just for the record, there are cases where capacitors are connected in series, but not in the load terminals and do not affect the compensating capacitor banks that are active (well, not really). These are the conditions in which it is desired to increase the natural strength of the transmission line. They are also connected to the series to minimize the reaction of the long line (not to be confused with its feature). Therefore, increasing its current capacity and consequently increasing its capacity and stability.This measure is mainly used for long transmission lines, i.e. 500 km and more.

11KV PLINTH MOUNTED TRANSFORMER SUBSTATION

TRANSFORMER MAINTENANCE GUIDELINES

TRANSFORMER MAINTENANCE GUIDELINES

Following specific checking and maintenance guidelines as well as conducting routine inspections will help ensure the prolonged life and increased reliability of a transformer. The frequency of periodic checks will depend on the degree of atmospheric contamination and the type of load applied to the transformer.

Routine checks and resultant maintenance

Sl No	Inspection Frequency	Items to be inspected	Inspection Notes	Action required if inspection shows unsatisfactory conditions
1.1	Hourly	Ambient Temperature	-	-
1.2	Hourly	Oil & Winding Temperature	Check that temperature rise is reasonable	Shutdown the transformer and investigate if either is persistently higher than normal
1.3	Hourly	Load (Amperes) and Voltage	Check against rated figures	Shutdown the transformer and investigate if either is persistently higher than normal
2.1	Daily	Oil level in transformer	Check against transformer oil level	If low, top up with dry oil examine transformer for leaks
2.2	Daily	Oil level in bushing
2.3	Daily	Relief diaphragm		Relief diaphragm
3.1	Quarterly	Bushing	Examine for cracks and dirt deposits	Clean or replace
3.2	Quarterly	Oil in transformer	Check for dielectric strength & water content	Take suitable action
3.3	Quarterly	Cooler fan bearings, motors and operating mechanisms,	Lubricate bearings, check gear boxes, examine contacts	Replace burnt or worn contact or other parts
4.1	Yearly	Oil in transformer	Check for acidity and sludge	Filter or replace
4.2	Yearly	Oil filled bushing	Test oil	Filter or replace
4.3	Yearly	Gasket Joints	-	Tighten the bolts evenly to avoib uneven pressure
4.4	Yearly	Cable	boxes Check for sealing arrangements for filling holes.	Replace gasket, if leaking
4.5	Yearly	Surge Diverter and gaps	Examine for cracks and dirt deposits	Clean or replace
4.6	Yearly	Relays, alarms & control circuits	Examine relays and alarm contacts, their operation, fuses etc. Test relays	Clean the components and replace contacts & fuses, if required.
4.7	Yearly	Earth resistance		Take suitable action, if earth resistance is high

IR testing:

The transformer should be de-energized and electrically isolated with all terminals of each

winding shorted together. The windings not being tested should be grounded. The meg-ohmmeter

should be applied between each winding and ground (high voltage to ground and low voltage to

ground) and between each set of windings (high voltage to low voltage). The meg-ohm values

along with the description of the instrument, voltage level, humidity, and temperature should be

recorded for future reference.

The minimum megaohm value for a winding should be 200 times the rated voltage of the winding

divided by 1000. For example, a winding rated at 13.2kV would have a minimum acceptable value

of 2640 megaohms ([13,200V x 200] / 1000). If previously recorded readings taken under similar

conditions are more than 50% higher, the transformer should be thoroughly inspected, with

acceptance tests performed before reenergizing.

Turns ratio testing:

 The transformer turn ratio is the number of turns in the high voltage winding divided by the

number of turns in the low voltage winding. This ratio is also equal to the rated phase voltage of

the high voltage winding being measured divided by the rated phase voltage of the low voltage

winding being measured.

Transformer turns ratio measurements are best made with specialized instruments that include

detailed connection and operating instructions. The measured turns ratio should be within 0.5% of

the calculated turns ratio. Ratios outside this limit may be the result of winding damage, which has

shorted or opened some winding turns.

Insulation PF testing:

Insulation PF is the ratio of the power dissipated in the resistive component of the insulation

system, when tested under an applied AC voltage, divided by the total AC power dissipated. A

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perfect insulation would have no resistive current and the PF would be zero. As insulation PF

increases, the concern for the integrity of the insulation does also. The PF of insulation systems of

different vintages and manufacturers of transformers varies over a wide range (from under 1% to

as high as 20%). As such, it's important that you establish a historic record for each transformer

and use good judgment in analyzing the data for significant variations.

Acceptance testing

Acceptance tests are those tests made at the time of installation of the unit or following a service

interruption to demonstrate the serviceability of the transformer. This testing also applies to drytype

units. The acceptance tests should include IR testing, insulation PF measurement, and turns

ratio testing, all as described under periodic tests. In addition, winding resistance measurements

should be made and excitation current testing done.

Winding resistance measurement:

Accurate measurement of the resistance between winding terminals can give an indication of

winding damage, which can cause changes to some or all of the winding conductors. Such

damage might result from a transient winding fault that cleared; localized overheating that opened

some of the strands of a multi-strand winding conductor; or short circuiting of some of the winding

conductors.

Sometimes, conductor strands will burn open like a fuse, decreasing the conductor cross section

and resulting in an increase in resistance. Occasionally, there may be turn-to-turn shorts causing

a current bypass in part of the winding; this usually results in a decrease of resistance.

To conduct this test, the transformer is de-energized and disconnected from all external circuit

connections. A sensitive bridge or micro-ohmmeter capable of measuring in the micro-ohm range

(for the secondary winding) and up to 20 ohms (for the primary winding) must be used. These

values may be compared with original test data corrected for temperature variations between the

factory values and the field measurement or they may be compared with prior maintenance

measurements. On any single test, the measured values for each phase on a 3-phase

transformer should be within 5% of the other phases.

Excitation current measurement:

The excitation current is the amperage drawn by each primary coil, with a voltage applied to the

input terminals of the primary and the secondary or output terminals open-circuited. For this test,

the transformer is disconnected from all external circuit connections. With most transformers, the

reduced voltage applied to the primary winding coils may be from a single-phase 120V supply.

The voltage should be applied to each phase in succession, with the applied voltage and current

measured and recorded.

If there is a defect in the winding, or in the magnetic circuit that is circulating a fault current, there

will be a noticeable increase in the excitation current. There is normally a difference between the

excitation current in the primary coil on the center leg compared to that in the primary coils on the

other legs; thus, it's preferable to have established benchmark readings for comparison.

Variation in current versus prior readings should not exceed 5%. On any single test, the current

and voltage readings of the primary windings for each of the phases should be within 15% of each

other.

Applied voltage testing:

 The applied voltage test is more commonly referred to as the "hi-pot test." This test is performed

by connecting all terminals of each individual winding together and applying a voltage between

windings as well as from each winding to ground, in separate tests. Untested windings are

grounded during each application of voltage.

This test should be used with caution as it can cause insulation failure. It should be regarded as a

proof test to be conducted when there has been an event or pattern in the transformer's operating

history that makes its insulation integrity suspect.

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DC applied voltage tests are often conducted in the field because DC test sets are smaller and

more readily available than AC applied voltage sets. With DC tests, the leakage current can be

measured and is often taken as a quantitative measure. However, DC leakage current can vary

considerably from test to test because of creepage across the complex surfaces between

windings and between windings and ground.

The use of AC voltage is preferable since the transformer insulation structures were designed,

constructed, and tested with the application of AC voltage intended.

Impedance testing:

An impedance test may be useful in evaluating the condition of transformer windings, specifically

for detecting mechanical damage following rough shipment or a service fault on the output side

that caused high fault currents to flow through the transformer windings. Mechanical distortion of

the windings will cause a change in their impedance. To maximize the effectiveness of this test, a

measurement should be taken during the transformer's initial installation to establish a benchmark

value.

An impedance test is performed by electrically connecting the secondary terminals together with aconductor capable of carrying at least 10% of the line current and applying a reduced voltage to

the primary windings. This is easily accomplished by applying a single-phase voltage to each

phase in succession. The applied voltage is measured at the primary terminals and the current

measured in each line.

These values shall be recorded and then calculate the ratio of voltage to current for each phase.

This ratio should be within 2% for each phase and should not vary more than 2% between tests.

A variation of more than 2% indicates the possibility of mechanical distortion of the winding

conductors, which should be investigated as soon as possible.

GUIDELINES FOR INSTALLING TRANSFORMERS

GTRANSFORM INSTALLATION UIDELINES

When your transformer arrives on site, various procedures must be performed to ensure effective operation. The efficiency of the transformer depends on the correct installation as well as on the design and production quality. The instructions stated in the manufacturer's manual or in the Standard will be followed to ensure adequate safety for personnel and tools. This section will provide general guidelines for installing and testing both dry and liquid-filled transformers for installation.

Typical transformer tests for each unit include the following:

· Estimation, of voltage relation;

• Polarity of single and 3 phase units (because transformers in single phase are sometimes present

connected in parallel and sometimes in a 3-phase bank);

• 3-phase unit relationships (important if there are two or more transformers

working in tandem);

• Excitation current, which is related to efficiency and ensures that the contextual design is accurate;

• No-load core loss, which is also related to efficiency and optimal content design;

• Resistance, in calculating the rotating temperature

• Impedance (by checking the short circuit), which provides the information needed for the breaker

and / or integrate measurement and disruption measurement and coordination of transfer schemes;

• Loss of load, which is also directly related to the efficiency of the transformer;

• Regulation, which stipulates the reduction of electricity when loading; and

• Used and attracted energy, which ensures dielectric strength.

There are additional tests that may work, depending on how and where the transformer will be used. Additional tests that may be performed include the following:

• Impulse (where lightning and power fluctuations are common);

• Noise (important for applications in residential and office areas and can be used as

comparisons with future sound tests to identify any underlying problems);

• Increased coil temperature, which helps to ensure that design limits are not exceeded;

• Corona of medium (MV) and high-voltage (HV) units, which helps determine

the insulation system is efficient;

• Resistance to insulation installation (meg-ohmmeter test), which determines the drying of the installation and

it is usually done after childbirth to serve as a benchmark against the future

reading; and

• The embossing force, which is applied to the first installation and every few years thereafter

to help determine the aging process of insulation.

Site considerations

When planning an installation, a location is selected, which corresponds to all current security codes

does not interfere with the normal movement of employees, equipment, and materials. Location

should not expose the transformer to potential damage from cranes, trucks, or moving objects.

Initial test for the receiver of the transformer If received, the transformer should be inspected for damage during shipment. The inspection must be done before removing it from the train or truck, and, if there is any apparent damage or misconduct, the claim must be lodged with the carrier immediately and the manufacturer informed. Later, the covers or panels should be removed and the internal inspection should be done for damage or removal of parts, loose or broken connections, dirt or foreign material, and the presence of water or moisture. When the transformer is moved or when available

stored before installation, this test should be repeated before placing the transformer in service.

Plan to prevent contamination

Create a process to develop all the tools, hardware, and any other tools used in

test, assembly, and transformer testing. A test sheet should be used to record everything

items, and verification should be done so that these items are properly calculated

completion of work.

Creating active links

A connection will be made, between the transformer terminals and the incoming one

outgoing conductors, carefully following the instructions given on the nameplate or

communication diagram. Check every tap jumper for proper positioning and durability. Re-tighten

all bolts hold the cable after the first 30 days of service. Before the connection works do

assurance that all safety measures have been taken. Adequate support systems will be put in place

inlet / outlet connecting cables, so that no machine pressure is applied

transformer bushings and connections. Such stress can cause a tree to crack or a

connection fails.

Noise control

All transformers, once powerful, produce an audible sound. Although there are no moving parts

in a transformer, the spine produces sound. In the presence of a magnetic field, the core

side laminations and contract. This occasional mechanical movement creates noise

120 Hz basic vibration frequency and harmonic harmony output of this key.

The location of the transformer is directly related to the volume of its sound. Because

for example, if the transformer is installed in a quiet hallway, clear hum will be recognized. If the unit

installed in the area shared with other equipment such as motors, pumps, or compressors,

transformer hum will not be detected. Some applications require reduced volume, such as

a large unit in a commercial building with people working near it. Occasionally, installation

some form of noise reduction will be required.

Make sure the transformer is low

Laying is required to remove any standing stagnant charges and is needed as a protection if the transformer windows accidentally come in contact with the context or enclosure (or tank of wet types). Note that in MV transformers, secondary neutrality is sometimes based on restriction. Make sure all basic or integration plans meet the NEC and local codes.

What is the reason for choosing frequency 50 or 60 hz not more than this

The choice of high power frequency depends on three factors; two that change over time and one that does not change:

A specific application.

Technology.

Basic laws of physics.

Let's start with # 3. The efficiency of telephone transmission decreases with increasing volume for two main reasons:

The skin effects force the AC currents to the top of the conductor.

Cables emit energy efficiently in high frequency waves. This is good for building antennas, not so good for building a transmission line.

So from a basic physics point of view, the frequency of the appropriate AC power line is zero Hz, that is, DC.

DC also has a peak-to-RMS volume ratio of 1: 1. Since the electrical insulation must withstand its high voltage, DC uses insulation insulation more effectively than AC. (Yes, the square-wave AC also has a voltage ratio of 1: 1 up to RMS, but this includes carrying an infinite number of harmonics - which re-introduces the recently reported disadvantages of high frequencies.)

Now why has DC not become a standard despite basic physics? As a result of considerations # 1 and # 2. The advantages of high power efficiency and (comparatively) low current transmission apply to both AC and DC, but during the Current War between Edison's DC and Westinghouse's AC there was no active DC transformer. So AC won automatically.

But what is the frequency of AC? It's too low, and the lights will flash. (Without DC, of ​​course, but that was not an option without an active transformer.) High frequency transformers are also lighter and smaller than the low frequency AC transformer with the same power, which is why the unusually high frequency of 400 Hz became standard in aviation. Aircraft are also much smaller than the earth's power grid, so transmission losses are not a major problem.

Large electric motors work very well at low AC frequencies, especially the “AC / DC” brush type which has long been used in power grids (railways) due to the need for continuous speed variation. Many power lines live in low frequencies for this reason, e.g., 25 Hz of the Southern Northeast Corridor in the US and 16 2/3 Hz in most of central Europe. DC is even better, and many urban trains (e.g., subways and trams) use it, but also the benefits of high power AC wins when significant distances are involved.

But 50 and 60 Hz were both logical issues for many users for general purposes, which is why they became international standards. Why not one? Because one was as good as the other, and there was no real reason to throw away so many wonderful things that could last so long.

If we could do it again and again from the beginning with modern technology, the strongest case could be made that power systems could and should be completely DC. Thanks to the high power of semiconductor electronics, we now have an effective “DC transformer”. In fact, they “cut” the DC into AC at a very high frequency so that it can be lowered up or down by a transformer (very small and light), and then quickly converted back to DC at a new voltage.

This has already been done for decades on some long-distance transmission lines, especially those that carry very high distances for long distances, below sea level or below.

The same electronics make it possible to drive a simple and powerful AC import engine at any speed you want from a power source at any frequency, including DC. This technology is the basis of modern electric and hybrid vehicles, and it has taken over the railways.

And as the incandescent lamp is quickly replaced by CFL and now LED lights, both of which use electricity, DC is also natural - though it can also easily adapt to any AC supply.

Wave Trap

lighting and Protection

ELECTRICAL SAFETY

Electric shock:

It can be described as a sudden and dangerous movement of the nervous system with electrical energy.

ELECTRICAL SHOCK YOU CAN FEEL AS A FOLLOWING: When the body becomes part of the circuit and the current flows in one place and then exits another point; possible -

With both wires of the electrical circuit

With a single wire of a strong circle and ground

 With a piece of metal that has heated itself by touching a strong wire.

Electric shock:

The magnitude of the electrical shock depends on -

The level of energy flow in the body.

The current approach to the body.

The length of time the body is in the ring.

Current frequency.

The stage of the heart cycle when shock occurs.

The physical and mental state of a person

HUMAN RESISTANCE:

REASONS FOR ELECTRICAL SHOCK:

Touching an empty live driver

Touching the improperly installed driver

Open / short circuit due to resource failure

Dry electricity

Lightning

The touch body of the live machine.

EARTH LEAKAGE CIRCUIT BREAKER (ELCB)

The Indian Electricity Regulations 1956 were amended in 1985 to include the use of the ELCB mandatory requirement of more than 5 KW of electrical load to accommodate power leaks that may cause shock.

 The key features of this ELCB are

It is currently in operation

It applies to the principle of core balance current transformer

It works even if it fails moderately.

Travel within 30 million seconds.

Free travel route - i.e. during the reset error is impossible and the trip even if forced to be held in the "ON" area.

Occupational health - more than 20,000 jobs to 63 A and more than 10,000 jobs for 80 A & 1OOAmps.

10 KA short circuit resistance. - Available up to 100A, 2 pole & 4 pole for sensitivity from 30 milli amps onwards. (100 A & 300 A sensitive materials are also available according to need.)

Voltage or current which is more dangerous

The difference between electricity and current is confusing for many people who do not have a background in electrical science / engineering. How many times have we heard the phrase “touch the cable with x volts running”, which discourages electrical engineers.

To understand the difference, consider water. The water itself is like an electric charger, which always does nothing but, if you lift it up to the top, it gets a potent power and wants to flow down; voltage is often referred to as power for a reason. You will only get a flow if you have a difference (possible), in other words a voltage, between a high water tank AND a low surface AND both are connected to a pipe of some kind. High power can only "kill" you if you allow current to flow. A “pipe” can be anything that electricity can flow into, say, a telephone, or it can be your body.

Now, if you connect a small pipe to your high water tank, that pipe has high resistance to flow and you will only get a small squirt of water at the end. The flow rate, "currently" (also called for a reason), is small although the potential difference is high and that small current will not harm it.

If on the other hand you connect a large fat sluice pipe (with "low resistance") to that water tank, you will get a large flow rate and it will drop you to your feet.

So, go back to electricity. Voltage is not something that kills you, it is now. The reason why high voltages are dangerous is because they have great potential to kill you. There is no danger of the current unless you put yourself in the current position by connecting the world's highest energy (or something) with your body.

So 240V (here in the UK) is dangerous because it is connected to your body down to earth with resistance (say) 1,200 ohms or more will push the current 200mA for you enough to kill you. If you happen to be standing on a rubber mat, then you can escape because now the resistance on the road is high so it is currently low even though the voltage is the same.

On the other hand your USB phone charger probably emits about 1A (enough to kill you) but that is not dangerous because a) it passes through the cable and does not pass through you and b) because it is close. 5V therefore, if you plug it into your body resistance which is much higher than your phone, it will produce a small current (about 4mA or less) that will not hurt you at all.

So it is a deadly current but the electrical power is dangerous.

Having said that, birds can safely sit on top of power lines because even though those may be '000s of volts, the air gap resistance between them and the ground is never ending so there is no current flow (backwards. In my water simulation, the water tank is very high). but no pipe is connected to it, the bird is sitting on top with the tank).

I get to think about it about the height of the water and the pipes making it very clear to the average person.