How Does A Simple Lightning Conductor Protect A Building?

How Does A Simple Lightning Conductor Protect A Building?

Lightning conductor or Lightning rod is a metal rod or wire that fixed to an uncovered part of a building roof or other tall structure to collect lightning destruction and divert harmlessly into the ground.

Fig-1: Lightning Stroked at tallest building in a city center

Lightning conductor or Lightning rod is the same thing, in UK people say Lightning conductor on the other hand US & AUS people call it Lightning rod.

So, the name lightning conductors recommends that it conducts the electric charge which come from cloud and hits on the building.

This simple equipment attract like magnetic action to lightning charges, harvest them and send to the ground through the wire connected with roof top lightning rod and buried metal plate at bottom.

Do you interested to know more detail about 

Difference Between Lightning and Surge Arrester? 

also may like 

Specification of high voltage Surge Arrester.

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How Does Lightning Work?

Lightning rod or lightning conductor does not allow the electric charge to pass through the building material.

No any metal in the building touches the lightning rod or conductor connected between rod and buried earthing plate, it must be isolated form other material of structure.

The lightning rod and conducting wire must be made of a good conducting material, like- Copper, Aluminum etc.

The lightning conductor is extended till the ground where a plate of conducting material is placed underground. The connection with the ground sets the potential at zero and hence offers the easiest path for the charge to pass through.

The conductor is typically raised above the building in sufficient height that can absorb the shock before the lightning can strike the building.

Lightning rod height should be measure such that to cover the maximum protected area. Draw 45 degree straight line from top of the rod, the covered area by the straight line is the protected area from lightning strike.

Fig-2: Maximum area that a lightning rod can protect

As the lightning strikes the rod, it passes through rod and connected conducting wire into the ground that save the building structure from any damage due to the flow of such high charge.

To know more details and understand the Developing Thunderstorm and Lightning in Space read the different article.

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Who Invented the Lightning Conductor First?

In the USA, credit is normally given to Benjamin Franklin, who write of them between 1749 and 1760. The odd thing about all this is that Franklin’s famous “kite string” experiment was supposed to have been carried out in 1782.

As per Popular Science Monthly/Volume 42/January 1893/The Inventor of the Lightning-Rod "Prokop Diviš was experimenting with similar ideas in the Czech area at around the 1740s, and there are reported devices in India and China from much earlier.

HOW CALCULATE CAPACITANCE OF TWO PARALLEL CABLES

How Calculate Capacitance of Underground Power Cable?

 Capacitor is nothing but a two parallel metal plate separated by a dielectric that store electrical energy; formally we can define capacitor is a passive two terminal electrical component that used to store energy electrostatically in electric field, it also known as condenser. Practically a capacitor usually used a thin films of metal, aluminum foil or disks, etc.

The property of capacitor is known as capacitance, means the capacitance is the ability of a body to store an electric charge. The unit of capacitance is farad, symbol of farad is F, mostly common is micro farad µF.

The formula to calculate the capacitance between two cables is as

C = (Permittivity*Area)/D,

Where, A is the area is that of one cable, D is the distance between the center of the cable and the permitivity is that of the material between the cables.

Capacitance may measure as

C= Q/V= Charge/Potential difference.

How Calculate Single Core Cable

Let,r = radius of the inner conductor and d = 2rR = radius of the sheath and D = 2Rε0 = permittivity of free space = 8.854 x 10-12εr = relative permittivity of the mediumConsider a cylinder of radius x meters and axial length 1 meter. x be such that, r < x < R.Now, electric intensity Ex at any point P on the considered cylinder is given as shown in the following equations.Then, the potential difference between the conductor and sheath is V, as calculated in equations below.After that, capacitance of the cable can be calculated as C= Q/V

Capacitance Between Two Parallel Cables

Practically in electrical transmission lines both in overhead and underground cable system. Simply we can find two wire system both in dc or ac type. If the transmission system so long and voltage is high, charging current drawn by the metallic line conductor due to their capacitance property between two conductors.

If two conductor A & B are placed apart distance between d, consider r is radius of  each conductor, Q is the charge in conductor/meter (if +Q at A & –Q at B); then electric intensity

= Q/ (2π€₀€_rx) V/m

How Calculate Capacitance Of Three Core Cable 

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Consider a three cored symmetric underground cable as shown in the following figure (i). Let Cs be the capacitance between any core and the sheath and Cc be the core to core capacitance (i.e. capacitance between any two conductors).

In the above figure (ii), the three Cc (core to core capacitance) are delta connected and the core to sheath capacitance Cs are star connected due to the sheath forming a single point N. The circuit in figure (ii) can be simplified as shown in figure (iii). Outer points A, B and C represent cable cores and the point N represents the sheath (shown at the middle for simplification of the circuit).

Therefore, the whole three core cable is equivalent to three star connected capacitors each of capacitance Cs + 3Cc as shown in fig. (iii).The charging current can be given as,I_c = 2πf(Cs+3Cc)V_ph      A

Measurement Of Cs And Cc

In order to calculate Cs and Cc we perform various experiments like:

1. First, the three cores are connected together and capacitance between the shorted cores and the sheath is measured. Shorting the three cores eliminates all the three Cc capacitors, leaving the three Cs capacitors in parallel. Therefore, if C₁ is the now measured capacitance, Cs can be calculated as, Cs = C₁/3.
2. In the second measurement, any two cores and the sheath are connected together and the capacitance between them and the remaining core is measured. If C₂ is the measured capacitance, then C₂ = 2Cc+Cs (imagine the above figure (iii) in which points A, B and N are short circuited). Now, as the value of Cs is known from the first measurement, Cc can be calculated.

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CAPACITANCE

Transformer Winding Resistance Test by DC Current

How Do You Do Transformer Winding Resistance Test by DC Current?

Considering the basic principle of operation is to inject a DC current through the transformer winding to be measured, and then read the voltage drop across that winding. 

We may refer to formula for DC voltage across the transformer  is, V = I * R  

where, 

V= DC voltage across transformer winding;

I = DC current through transformer winding; &

R = desired calculated resistance of the transformer winding.

Fig: Connection Diagram of Transformer Winding Resistance Test

How Prepare for Transformer Winding Testing?

1. Selecting the Proper Current Range, transformer manufacturers typically recommend that the current output selected should not exceed about 10% of the rated winding current;
2. Cause erroneous readings due to heating of the winding; 
3. Always choose the highest current output possible for the expected resistance value; 
4. Typical ranges are 0.1-10 % of rated winding current;
5. The temperature of the winding shall be assumed to be the same as the temperature of the insulating liquid;
6. It should not be assumed that the winding are at the same temperature as the surrounding air;
7. For star connected winding, the resistance shall be measured between the line and neutral terminal;
8. For delta connected winding, measurement of winding resistance shall be done between pairs of line terminals.

As in delta connection the resistance of individual winding can not be measured separately, the resistance per winding shall be calculated with the following formula: 

Resistance per winding = 1.5 x Measured value 

he resistance is measured at ambient temperature and then converted to resistance at 75˚C or 85˚C  for all practical purposes of comparison with specified design values, previous results and diagnostics.

Winding Resistance at reference temperature of 75° C or 85° C 

R = Rm (234.5 + Ref. Temp)/(234.5 + Meas. Temp) 

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How Measure Winding Resistance at Delta Side?

Average of the (3) Phase measurements multiplied by 9/2 or 4.5. This is the 3-phase sum resistance at the temperature the resistance was measured.  

Resistance measured: H1-H3 = 0.665, H2-H1 = 0.664, H3-H2 = 0.666 at an oil

temperature of 26°C.  

The average resistance of the (3) phases is 0.665. This (0.665) multiplied by 4.5 equals 2.993. The unit is a 55/65 rise transformer, therefore to correct the resistance to the reference temperature 75°C, use the correction formula: 

 (234.5 + 75) / (234.5 + 26) = 1.1881

So the corrected 3-phase sum resistance is, 2.993 * 1.1881 = 3.554 ohms;

Working backwards from the test report: HV position 3 resistance reported on the  test report is 3.554. Determine oil temperature of transformer at time of resistance measurement (say its 26°C again).   3.554 / 1.1881 = 2.991  

2.991 / 4.5 = 0.665  

The measured resistance between two bushings (one phase) should be approx. 0.665 ohms.  

How Measure Winding Resistance at Star or Y-Side?

 If measuring between L-N, then add each of the L-N measurements together. This is the 3-phase sum resistance at the measured temperature. The resistance needs to be corrected the same as for the Delta connection above.

If measuring a Wye connection L-L, then add each of the L-L measurements and divide by 2. This is the 3-phase sum resistance at the measured temperature. Correct resistance to reference temperature as above. 

How Measure Line to Neutral Resistance?

Resistance measured between X1-XO = 0.0394, X2-XO = 0.0393, X3-XO = 

0.0397 at an oil temperature of 26°C. The 3-phase sum is:

0.0394 + 0.0393 + 0.0397  = 0.1184;

Corrected to 75°C: 

0.1184 * 1.1881 = 0.1407 ohms. 

How Measure Line to Line Resistance?

Resistance measured between X1-X2 = 0.0782, X2-X3 = 0.0783, X3-X1 = 0.0785

at an oil temperature of 26°C. The 3-phase sum is: 

(0.0782 + 0.0783 + 0.0785) / 2 = 0.1175;

Corrected to 75°C”

0.1175 * 1.1881 = 0.1396 ohms .

The 3-phase sum of the resistance between the L-N and L-L measurements are 

slightly different because the L-N measurement has the XO lead cable in the circuit. 

How Confirm the Measurement is Correct?

Comparing the factory value or factory standard and  the previous measured value can help to confirm the measured value is satisfactory or not.

So, note the below points and compare:

1. Comparing to original factory measurements
2. Comparing to previous field measurements
3. Comparing one phase to another 
4. Industry standard (factory) permits a maximum difference of  0.5% from average of three phase wingdings.  
5. Field readings may vary slightly more than this due to the many  variables. If all readings are within 1% of each other, they are  acceptable. 

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When Do Need to Carryout the Transformer Winding Resistance Test?

Test In the factory: 

1. To know the manufacturing is correct or not;
2. To calculate conductor losses; 
3. Calculations of DC component of conductor losses;
4. Calculation of winding temperature at the end of a temperature test cycle. 
5. Measuring the  resistance of the winding assures that the connections are correct and the resistance  measurements indicates that there are no severe mismatches or opens. 

Test on Site:

To evaluate possible winding damage, such as short circuits between  winding or between turns; open circuits; contact problems; condition of the tap changer. 

Test at Installation:

1. Risk of damage is significant whenever a transformer is moved damage will often involve a current carrying component such as the LTC,  DETC or a connector,
2. Serves as a verification of the manufacturers work,
3. Installation measurements should be filed for future reference 

Transformer Routine Maintenance:

Transformer routine maintenance is required to verify operating integrity and to assure reliability. 

1. To detect damage to the transformer;
2. To determine if it is safe to re-energize;
3. To determine if corrective action is necessary;
4. To establish priority of corrective action. 

At Internal Transformer Inspections: 

Internal inspections are expensive due primarily to the cost of oil processing. When such opportunities do present themselves the inspection should be  planned and thorough. 

QUALITY ASSURANCE INSPECTION AND TESTING FOR POWER TRANSMISSION LINE CABLE PROJECT

The Inspection and Testing Procedure to Ensure Quality

The underground power cable transmission line, whole Plant supplied and works constructed under the contract should be subject to inspection and testing by the Engineer, by the Employer or, where appropriate by an approved inspection authority should they so require, during manufacture the equipment, erection the plant and after completion the installation works.

The inspection and testing should include but not be limited by the requirements of this article of the specification and of the detailed inspection. Prior to inspection and testing the plant and equipment should undergo pre-service cleaning and protection as specified in the section of the specification.

Following Inspection and Test should be carryout in the underground power cable transmission line project:

·     FAT or Factory Acceptance Test, before shipment the plant or equipment this test must be completed;

·  PLI or Post Landing Inspection, after arrived the plant or equipment this inspection should carry out;

·  SAT or Site Acceptance Test, during installation or erection the plant or equipment this test should carry out to satisfy the employer;

· Pre-commission, before final commissioning the plant satisfactory pre-commissioning should carry out;

·       Commission, final commissioning test must be carry out before energize the plant.

What Standard Should Follow to Ensure Quality

Where no test is specified then the various items of plant, materials and equipment should be tested in accordance with the relevant British, American or National Standards acceptable to the Engineer. Where no appropriate standard is available, tests should be carried out in accordance with the manufacturer’s standard practice which must meet with the prior approval of the Engineer. 

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Notification for Inspection and Testing

Fourteen days notice of the readiness of plant for test or inspection and every facility should be provided by the service provider and sub-service provider to enable the Engineer to carry out the inspection and witness the test.

Equipment should be packed, prepared for shipment, or dismantled for the purpose of packing for shipment only when it has been inspected and approved (or inspection has been waived) and written instructions have been received from the Engineer.

Within 30 days of acceptance of the agreement the service provider should submit a quality assurance program and a work quality program for the Engineer’s approval.

Responsibility for Quality Assurance

The Engineer should have the right to supervise and witness tests of all materials to be used and all workmanship employed in connection with manufacture.

Each part of the work should be commenced after prior approval from the Engineer. This should not relieve the service provider from any liability or obligation under the agreement and he should be responsible for the acts, defaults and neglects of any sub-supplier, his agents; employees or workmen as if they were the acts, defaults, or neglects of the service provider.

Quality Assurance Plan

For control of the quality of manufacture, material control and documentation, the service provider and each main sub-service provider should submit a copy of his manufacturing program and three unparsed copies of all guidelines and sub-guidelines from the Engineer. 

These documents will be examined and classified according to the extent of expediting, quality audit or inspection required. The approved manufacturing program should be integrated with the Engineer’s Quality Department work program. 

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Manufacturing Capacity

The Service provider should furnish evidence that he and his sub-service providers have supplied other equipment of a similar type and size that should have been in commercial operation successfully for a minimum of four years.

Engineer require reviewing and approving any manufacturing capacity; the Service provider should secure permission for such reviews to be made by the Engineer.

To ensure the inspection and testing for power transmission underground power cable project, each and every test and inspection standard and safety measure must comply with international and local or national standard.

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