Electrical wire

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Electrical wire

Introduction

A Cable is one or more wire or optical fibers bound together. Typically in a common protective jacket or sheath. The individual wires or fibers inside the jacket may be covered or insulated. Combination Cable may contain both electrical wires and optical. Electrical wire is usually copper. Because of its excellent conductivity. But aluminum is sometime used because it costs less.

Working Procedure

RBD (Rod Break down Machine):

Wire draw with annealed is first step- The first step in the manufacturing process takes place at wire draw. Here copper rod from nearby Arizona copper mines are reduced to copper needed wire size. During the wire draw, the copper rod is pulled through a series of synthetic diamond dies, which gradually decrease in size. The rod and dies are flooded with a coolant and a synthetic lubricant to increase copper annealing and the life of the dies and keep the copper wire from overheating.

Twisting and stranding Machine:

In the next step-

The insulated wires are twisted into conductor pairs. It requires two operators to run one stranding machine. The first operator takes the reels of twisted pairs and sets them up on a supply stand in the proper order and twist-length sequence. The pairs are then fed through a rotating, oscillating faceplate that is designed to prevent the same twist patterns from being placed side by side in the finished cable.

Extruder Machine:

Insulation/ Jacketing step-

The outer cable jacket is extruded in the next step. It is usually made from low-density polyethylene. This rugged plastic is the final protection for the enclosed cable against the environmental conditions underground or when strung to utility poles. The jacketed cable then passes through a temperature- controlled water trough, which cools the jacket. The cable is dried, and the top layer of the jacket is heated slightly so that printer markings can be imprinted on it.

Finally this cable is some testing before shipping. Its below the table:

Machine Name	Test name
Tensile tester (For copper/Aluminum)	Elongation percentage & Tensile strength
Tensile tester (Insulation/ Sheath)	Elongation percentage & Tensile strength
Digital micro ohm meter	Conductor resistance & Conductivity
Hot set test @ 200 0C	Under load & Permanent elongation
High voltage tester	AC High voltage test (LT & HT)

Cable and Type of cables

Cable: A Cable is one or more wire or optical fibers bound together. Typically in a common protective jacket or sheath. The individual wires or fibers inside the jacket may be covered or insulated. Combination Cable may contain both electrical wires and optical. Electrical wire is usually copper. Because of its excellent conductivity. But aluminum is sometime used because it costs le

Type of cables:

1. Single core (unsheathed)

2. Single core (Sheathed)

3. Circular twin, three and four core (sheathed)

4. Flat twin with or without (Sheathed)

5. Flat three, four core (Sheathed)

1.2.2 Single core (Unsheathed)

Construction: Plain annealed copper/aluminum conductor and PVC Insulated

Application: Suitable for use in surface mounted or concealed steel conduits or trucking. Also suitable for field protected insulating in lighting ■■■■■■■■ and inside appliances

Single core (Sheathed)

Construction: Plain annealed copper/aluminium conductor, PVC Insulated and Gray PVC Sheathed

Application: Suitable for use in fixed installation in dry or damp premises clipped direct to a surface or on a cable tray unenclosed and also for use in non metallic conduit (PVC)

Circular twin, three and four core (sheathed)

Contraction: Plain annealed copper/aluminum conductor, PVC Insulation, PVC inner sheath and Gray PVC outer Sheathed

Application: Suitable for use in fixed installation in dry or damp premises clipped direct to a surface or on a cable tray unenclosed and also for use in non metallic conduit (PVC)

Flat twin with or without (Sheathed)

Contraction: Plain annealed copper/aluminium conductor, PVC Insulation, core laid in flat form and with or without Gray PVC outer Sheathed

Application: Suitable for use in fixed installation in dry or damp premises clipped direct to a surface or on a cable tray unenclosed and also for use in non metallic conduit (PVC)

Flat three core (Sheathed)

Contraction: Plain annealed copper/aluminium conductor, PVC Insulation, core laid in flat form and Gray PVC outer Sheathed.

Voltage designation

The voltage designation indicated the rated voltage Uo/U for which the cables are designed, where “Uo” is the power frequency voltage between conductor to metallic covering / earth and “U” is the power frequency voltage between conductors.

Service Voltage

It is the voltage which locally exists between the line conductors of a power installation in underground operator at a given place and at a given time.

Permissible service

It is the maximum permissible voltage with which the cable can be used in continuous undisturbed voltage operation.

Nominal Value

It is the value by which a quantity is designed which must be maintained within the tolerance as laid down in corresponding standard.

Approximate value

It is the value which is neither guaranteed nor checked, but it should lie within commercially accepted tolerances or tolerances governed by the method of manufacture. Approximate values may, for instance, be used as a basis for the computation of dimension.

Chapter 2

Properties and Construction of Conductors and Insulations, Materials

Conductor

The conductor shall be composed of plain annealed high conductivity copper & aluminum wires.

Insulation

The insulation shall be of PVC, XLPE, PE Compound

Filters:

The fillers shall consist of vulcanized rubber, un-vulcanized rubber and thermoplastics compound. The fillers materials shall be suitable for operating temperature of the cable and compatible with other components of the cable. Theses shall not be ■■■■■■ than PVC used for insulation and sheath.

Binder tape

Binder tape shall consist of plastic or proofed textile material.

Sheath

The sheath shall consist of PVC compound. This sheath for cables with improved fire performance.

Thickness of insulation

The average thickness of insulation shall be not less than the nominal value.

Tolerance on thickness of insulation

The smallest of the measured values of thickness of insulation shall not fall below the nominal value (ti) specified in specified in the relevant tables by more than (0.1 mm +0.1 ti)

Application of insulation

The insulation shall be so applied that it fits closely on the conductor and it shall be possible to remove it without damage to the conductor.

Core identification

Cores shall be identified by different coloring of PVC insulation. The color scheme as given in below the table shall be adopted.

No. of cores	Color
1-Core	Red, Black, Yellow, Blue, White or Grey
2-Core	Red and Black
3-Core	Red, Black, Yellow
4-Core	Red, Yellow, Blue and Black
5-Core	As agreed to between the purchaser and the supplier

Flat twin cables (With ECC)

Two with a bare ECC shall be laid side by side in the same plane (ECC occupying the central position) For core cables the ECC shall be placed between yellow and blue cores in same plane.

Circular twin, three and four cores cables

Tow, three or four cores shall be laid together with a suitable right-hand lay. The interstices between the cores may be filled with fillers. A binder tape may be applied over the laid-up cores.

SHEATHING

The sheath shall be so applied that it fits closely on the laid-up cores and it shall possible to remove it without damage to the insulation

The sheath, where applicable, shall applied by extrusion. It shall be applied

a. Over the insulation in case of single- core cables, and

b. Over the lade-up cores in other cases.

The color the sheath shall be black or any other color as agreed to between the purchaser and the supplier. Cables for outer use, the color of sheath shall be black or grey only

Thickness of sheath

The thickness of PVC sheath, determined by taking the average of a number of measurement, shall be not less than the nominal value (ts) and the smallest of the measured values shall not fall below the nominal value (ts) by more than 0.2 mm + 0.15 ts.

Overall dimensions

The mean overall dimensions of the cables shall not exceed the limits.

Ovality

The difference between maximum and minimum measured value of overall diameter of sheathed circular cables shall not exceed 15parcent of the maximum measured value at the same cross- section.

Physical & Electrical properties of Copper & Aluminum

Copper and aluminum are used in their highly refined from for the conductors of cables. The total impurities contained in high conductivity copper should be less than 0.1% and for aluminum less than 0.5%. The measured conductivity of these metals will have its highest value when they are annealed. Hard drawn conductors have conductivity that is several percentage points lower than the annealed value. Note that casting made of these materials will generally have conductivity slightly lower than their rolled and drawn forms. The presence of oxygen in the form of oxides is the most common impurity. It slightly reduces the conductivity, malleability and ductility of the metal.

Following table: shows some of the electrical and physical properties of these two metals. For use in most power cable applications these metals are formed into annealed conductors.

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Continuing the discussion from Electrical wire:

Example 10. Calculate the resistance at the working temperature of 75° C of a 4-pole, lap
connected armature winding from the following data :

Number of slots …100
Conductors per slot …12
Mean length of turn …3 m
Cross-section of each conductor …1.5 cm × 0.2 cm
Specific resistance of copper of 20° C … 1.72 × ohm metre
Temperature co-efficient of resistivity at 0°C … 0.00427/° C.

Solution. Total number of conductors, Z = 100 × 12 = 1200
Length of each conductor, l = = 1.5 m

Cross-sectional area of each conductor = 1.5 cm × 0.2 cm = 0.3 = 0.3 ×
Specific resistance of copper at 20° C, ρ20 = 1.72 × ohm-metre.
Temperature co-efficient of resistivity at 0°C, α0 = 0.00427/°C
If ‘a’ is the number of parallel paths,
Resistance of each parallel path, R0 =
As there are such ‘a’ paths in parallel, hence equivalent resistance,

R0 = …(i)
Also,
1.72 × 10–8 = (1 + 0.00427 × 20) = 1.0854

or = = 1.585
Now by substituting the different values in eqn. (i), we get,

R0 = = 0.0594
Resistance of winding at 75° C,
= (1 + × 75)
= 0.0594 (1 + 0.00427 × 75) = 0.0784 Ω
Hence resistance of winding at 75° C = 0. 0784 Ω. (Ans.)

Conditions for applying Ohm’s law. Ohm’s law is applicable under the following
conditions :

1. Ohm’s law can be applied either to the entire circuit or to a part of the circuit.
2. When Ohm’s law is applied to a part of a circuit, part resistance and the potential difference
   across that part resistance should be used.
3. Ohm’s law can be applied to both D.C. and A.C. circuits. However, in case of A.C. circuits,
   impedance Z, is used in place of resistance.
   Then, I = =
   Electrical power. It is the rate of doing work. In other words, the amount of work done in
   one second is called ‘‘power’’.
   or P = … (8)

where P = The power in watts,
W = The work done in joules, and
t = Time in second.

Power is equal to the product of voltage (V) and current (I) in a particular circuit
i.e., *P = V × I …(9)
The following relations hold good :
(i) *P = VI = R =
(ii) I =
(iii) R =
(iv) V =
Power is expressed in terms of kW (kilowatt = 1000 W) or MW (megawatt = 1000 kW or
106 W).
Electrical energy. It is the total amount of work done in an electric circuit.
In other words, it is measured by the product of power and time.
i.e., W = P × t …(From eqn. (8)]
or W = VI t
= VQ joules

where Q = The quantity of electricity passing through the circuit in coulombs.
The unit of electrical energy is joules or watt-sec.
It is expressed in kWh (kilowatt hours)
1 kWh (commercial unit) = 1 kW × 1 hour = 1000 watt-hours
= 1000 × 60 × 60 watt-sec
= 3.6 × 106 watt-sec. or joules.

Linear and non-linear resistors. A linear resistor is one which obeys ohm’s law.
A circuit which contains only linear components is called a linear circuit.
Such elements in which V/I (volt-ampere) plots are not straight lines but curves are called
non-linear resistors or non-linear elements.
Examples of non-linear elements : Filaments of incandescent lamps, diodes, thermistor and
varistor.
‘‘Varistor (Non-linear resistor)’’ :
It is a voltage-dependent metal-oxide material whose resistance decreases sharply with
increasing voltage.
The zinc oxide-based varistors are primarily used for protecting solid-state power supplies
from low and medium size voltage in the supply line.
Silicon carbide varistors provide protection against high-voltage surges caused by lightning
and by discharge of electromagnetic energy stored in the magnetic fields of large coils.
Limitations of Ohm’s law. Ohm’s law does not apply under the following
conditions :

1. Electrolytes where enormous gases are produced on either electrode.

2. Non-linear resistors like vacuum radio valves, semiconductors, gas filled tubes etc.

3. Arc lamps.

4. Metals which get heated up due to flow of current.

5. Appliances like metal rectifiers, crystal detectors, etc. in which operation depends on the
   direction of current.
   An Electric Circuit
   An ‘‘electric circuit’’ is a conducting path through which either an electric current flows, or is
   intended to flow. It can be divided into four categories :
   (i) Closed circuit (ii) Open circuit
   (iii) Short circuit (iv) Earth or leakage circuit.
   (i) Closed circuit. It is the complete path for flow of electric current through the load.
   Example. The glowing of a bulb.
   (ii) Open circuit. In case any one of the supply wires is disconnected or the fuse burns out,
   then the current will not flow through the bulb, which is an example of open circuit.
   (iii) Short circuit. If the supply mains are connected directly by a piece of wire without any
   load, then the value of current will be much greater than that in closed circuit. Hence, the fuse
   gets
   blown off and this circuit is known as short circuit.
   (iv) Earth or leakage circuit. If any wire of supply mains touches the ‘body of an appliance’,
   then it is known as earth or leakage circuit.
   Depending upon the type of current flowing in it, an electric circuit may be further classified
   as :
   (i) D.C. circuit (ii) A.C. circuit.
   Resistances in Series
   Fig. 9 shows three resistance connected in series. Obviously current flowing through each
   resistance will be same but voltage drop across each of them will vary as per value of individual
   resistance.

Also the sum of all the voltage drops (V1 + V2 + V3) is equal to the applied voltage (V).
i.e., V = V1 + V2 + V3

IR = IR1 + IR2 + IR3 (Using Ohm’s law : V = IR)
i.e., R = R1 + R2 + R3 …(10)
where R is the equivalent resistance of series combination.
Also = + + …[10(a)]
As seen from above, the main characteristics of a series circuit are :

1. Same current flows through all parts of the circuit.

2. Different resistors have their individual voltage drops.

3. Voltage drops are additive.

4. Applied voltage equals the sum of different voltage drops.

5. Resistances are additive.

6. Powers are additive.

Voltage divider rule. Since in a series circuit, same the same current flows in each
of the given resistors, voltage drop varies directly with its resistance. Fig. 10 shows a 24 V
battery connected across a series combination of three resistors.
4 Ω 8 Ω

Total resistance, R = R1 + R2 + R3 = 4 + 8 + 12 = 24 Ω

= V = 24 8V
= V = 24 12V