Manufacture Of Electric Power Cables and Chronological Development

Underground Power Cable Installation

This Video Clip shows how to install underground power cables. 

This is not used in modern equipment and technology.

You could see the initial technology for the oilfield underground power cable and its installation and erection procedure. 

Electron Drift Velocity Basic

What is the definition of Electron Drift Velocity?

Drift velocity is the average velocity with which electrons 'drift' in the presence of an electric field. It's the drift velocity (or drift speed) that contributes to the electric current. In contrast, thermal velocity causes random motion resulting in collisions with metal ions.

The definition of drift speed can be understood by imagining randomly moving electrons in a conductor. Free electrons move in a conductor with random speeds and random directions. When we apply an electric field through a conductor, randomly moving electrons experience an electric force in the direction of the field.

Electron Drift Velocity Calculation

The calculation of the electron drift velocity formula or equation is as below:

We start with the acceleration of the electrons, 

a = F/m = eE/m. 

The average velocity gained, i.e. the drift velocity, due to this acceleration = a*t = eEt/m.

The density of conduction electrons in copper. or 0.15 mm/s! Compare this to the random thermal speed, of the electrons which is about 106 m/s or about 1010 times faster!.

So we learned that when an external field is applied across the conductor the free electrons acquire a net velocity opposite to the direction of the electric field. The average velocity acquired by them is called drift velocity.

The density of charge carriers:

The density of charge carriers, n, is the number of free electrons per unit volume. It tells how good a conductor the material is. A lower value of n means that the electrons will have to move faster in order to produce the same current.

Conductors, like metals, have high values of n – around 10²⁸per m³

Insulators, such as plastic, will have very low values of n – these may be close to 0

Semiconductors, for example, silicon, have values of n in between the two – this means they conduct better than insulators but not as well as conductors.

How to Calculate Fuse Rating for Electrical Appliances?

Different Rating's Fuses

Fuse Rating Calculating Guide

The function of a fuse is to break a circuit when a current threshold is exceeded. It’s a single-function device, and historically single-use. Calculating the rating of very basic protection equipment fuse, we use the thump rule just select a fuse rated 150% - 200% of the normal operating current of the specific circuit. But actually, there are numerous calculations are involved in determining an appropriate fuse rating. Frequently necessary to consider other factors- including ambient temperature, available energy during a fault, inrush current, etc.

In order to select the proper rated fuse protective device, the following parameters and criteria need to be considered:

1.    What is the normal operating current of the circuit?

2.    What is the operating voltage?

3.    Is the circuit AC or DC?

4.    What is the operating ambient temperature?

5.    What is the available short-circuit current?

6.    What is the maximum allowable I²t?

7.    Are there in-rush currents available?

8.    Is the protective device being used for short-circuit protection, over-load protection, or both?

9.    What are the physical size limitations?

10.Is the PCB surface mount or thru-hole?

11.Does the fuse need to be "field-replaceable"?

12.Is reset ability an issue?

13.What safety agency approvals are needed?

14.How will I mount the device?

15.What are the cost considerations?

Formula to Calculate the Fuse Rating

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There is a simple and basic formula for working out the fuse rating, voltage or wattage for each appliance:

P=VxI

Where,

P for power in Watts;

V for voltage in volt);

I for current in Amps.

The fuse rating can be calculated by dividing the power used by the appliance by the voltage going into the appliance.

I (Amps) = P (Watts) ÷ V (Voltage).

Fuse Rating Calculation for Motor

A fuse for a machine is rated on the load that the machine carries when running. For example, a 1-HP (746W) motor operating at 115V would draw 746/115 = 6.5A at full load, so theoretically a 10A fuse would be sufficient.

What is Fusing Factor?

Fusing Factor is the ratio of minimum fusing current and current rating of fuse.

Therefore, fusing factor = Minimum fusing current or current rating of the fuse.

The value of fusing factor is always more than 1.

Fuse Size Calculation Formula

Fuse Wire Rating: The melting point and specific resistance of different metals used for fuse wire is as below:

Metal	Melting point	Specific Resistance
Aluminium	240oF	2.86 μ Ω – cm
Copper	2000oF	1.72 μ Ω – cm
Lead	624oF	21.0 μ Ω – cm
Silver	1830oF	1.64 μ Ω – cm
Tin	463oF	11.3 μ Ω – cm
Zinc	787oF	6.1 μ Ω – cm

Many times we have to face some physical places limitation to choose the fuse or circuit breaker mounting sizes.

It is this reason that fuse and circuit breaker manufacturers have created a wide selection of components with varying physical sizes. Typically however, there are a trade-offs that the engineer must consider.

Generally speaking, the smaller the fuse, the less current and/or capabilities that the fuse or circuit breaker may have. For example, a sub-miniature fuse maybe limited to 15A whereas the larger 1/4" x 1 1/4" glass tube fuse can accommodate up to 40A.

Additionally, although the fuse can be smaller, the corresponding fuse holder maybe substantially bigger adding to the consideration.

Get download the pdf copy of full guide to calculate the fuse ratings:

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Read the article details on different type of Fuses and their uses

Why DC System Is More Dangerous Than AC System?

Which Voltage DC or AC is Dangerous for Shocking?

Which one is more dangerous either DC or AC power, especially when it shocks a human body. Other way we can say, if we can take the same amount of AC and DC current onto our body which one would hurt us more?

The answer- DC (Direct Current) is more dangerous than AC (Alternating Current), but why DC is more dangerous than AC?.

Before we find the answer for dangerousness of DC or AC, let we know the basic definition of DC and AC:

What is DC System?	What Is AC System?
DC or Direct Current could be defined as the one direction or unidirectional flow of current. Current does not change its flowing direction, only flows in one direction. The amplitude of voltage and current may vary over the time but flow of direction always unchanged. Plot of Direct Current Waveform	AC or Alternating Current could be define as opposite the DC, changes direction periodically. Not only changes, periodically reverse direction. The amplitude of voltage and current vary and reverse over the periodic. Plot of Alternating Current Waveform

Why DC Shock is More Dangerous than AC Shock?

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It would be difficult to mentioned DC is more dangerous than AC for electric shock. But, if we consider the same amount of DC an AC current flowing through a human body for a certain period of time from a same voltage difference, then could say the DC is more dangerous than AC or not.

If you look at the both waveform (red mark lines in above figures) for DC and AC: for DC the amplitude or amount of current is same in respect to time variation.

On the other hand, for AC the amplitude or amount of current is varying, it is increasing from zero to positively and after maximum it is again decreasing up to zero and up to negative maximum and again coming positive maximum through zero.

Now, comparing the DC and AC waveform there is a zero amplitude in AC system that is not presence in DC system. This zero amplitude is known as "zero voltage crossover point" in AC system.

This zero amplitude for a period in AC system is giving a chance to release  from the touching live conductor. This is the secret of AC is less dangerous than DC for electric shocking.

Does Really DC is Safer Than AC Voltage?

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It is still debatable and there is no conclusive research on safety of one over other because this cannot ethically tested on humans. People who would say that AC is more dangerous because it's pulsating nature disturbs the nervous system;

On the other hand, some would say that AC is safer because it gives time for nervous system to react during Zero-voltage crossover points in AC.

Actually both AC and DC current and voltage are dangerous. People who speak of AC is less dangerous than DC are, but statistics of electricity shocking accident says most of the peoples are dying in AC system though there is zero current passing point which lets you to go or leave your muscle to relax.

Keep electricity safe rising the safety awareness, as far as safe voltage levels are concerned some UL standards consider 42 V AC/DC to be safe and some ECMA standards even consider up to 60V DC to be safe.