Thursday 20 June 2013

Insulating material

INSULATING MATERIAL

Properties of traditional insulating material, SF6, Vacuum, Air, Insulating oil, Ceramics, PVC, PTFF, PMMC, Fiber glass, Polyethylene
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INSULATOR:
Insulators are mounted on the cross arms and the line conductors are attached to the insulators so as to provide the conductors proper insulation and clearances between the conductors and metal work.
Ø  Insulators provide clearances against the highest voltage in worst atmospheric condition to which the line is likely to be subjected.
Ø  Insulators prevent short circuiting between the different phase conductors.
Ø  Insulators provide mechanical support for the line conductors.

Properties of insulating material

§  High mechanical strength so as to bear the load like wind force, ice loading.
§  High relative Permitivity so as to provide high dielectric strength
§  High insulation resistance in order to prevent leakage of currents to earth.
§  High ratio of rupture strength to flash over voltage.
§  Ability to withstand large temperature variation.
Material used should not be porous and should be impervious to the fluids and gases with the
atmosphere. It should be free from internal impurities and cracks etc.

SF6

SF6 (sulphur hexa floride) is a gaseous insulation having high dielectric strength and low liqui- friction temperature; it can be used over a wide range of operating condition.
  It has good arc quenching properties and therefore, widely used as an insulating as well as arc quenching medium in high voltage apparatus such as high voltage cables, current and voltage transformer, circuit breaker and metal enclosed substations.
Dielectric strength- 73KV/cm to 30 KV/cm

VACUUM:
Under vacuum conditions the dielectric loss is low and dielectric strength is high. Hence vacuum or low gas pressure finds application in electronic equipment including capacitors, circuit breaker and electrostatic separator.

AIR:
Air is free gift from god. It has got application everywhere in spite of our consent. It is used as insulation in transmission line. It has high insulation resistance but droppps due to moisture. When using air, there is very less dielectric loss. At high voltage corona effect takes place.
Dielectric strength- 30 KV/cm
Insulating oil mineral insulating oils are hydrocarbons refined from crude petroleum deposit from the ground. It is of hydrocarbon of group CnH2n+2.
Transformer oil is very commonly used as insulating oil for dissipation the heat by convection from winding and core to the cooling surface and for maintaining the insulation of windings. Insulating oil is used in circuit breaker and all those equipments where rate of heat production is high or heat dissipation is required at fast rate.
Dielectric strength- 300KV/cm to 500 KV/cm
Resistivity: 1010W-meter

CERAMICS:
Ceramics are inorganic materials produced by consolidating minerals into monolithic bodies. By high temperature heat treatment. Ceramics can be divided-
Low Permitivity    ®  er <12    as insulator
High Permitivity   ®  er >12    in capacitors and transducers

CERAMICS ARE DIVIDED:

HT Porcelain
LT Porcelain
Alumina
Chemical composition
50% clay
25% feldspar
25% flint
50% clay
25% feldspar
25% flint
95%
Safe temperature (0C)
1000
900
1600
Water Absorption (PPM)
0
0.5-2
0
Dielectric strength (KV/MM)
25
3
16


Ceramics are chemically inert to all alkalis and most of the acids. They are corrosion proof and resistant to contamination. They are used in the fabrication of high current vacuum interrupter and a variant of electrical and ceramic components.
Alumina is used for suspension type insulators and station type post insulators.
High permit ivies ceramics are:
MgTio3-Magnesium Meta titamate
CaTio3 – Calcium Titanate
SrTio3  -Stantium Titanate
BaTio3 –Barium Titanate

EPOXY RESIN

Epoxy resins are thermosetting types of insulating materials; they possess excellent dielectric and mechanical properties. They can be easily cast into desired shapes even at room temperature. They are very versatile and their basic properties can be modified by using fillers.
Resistivity: 75KV/mm
Epoxy resin can be formed into an insulator of any desired shape for almost any type of high voltage application. Insulators, bushings, apparatus etc can be made out of epoxy resin. It can be used for encapsulation of electronic components, generator windings and transformers. It is used for bonding of very diverse materials such as porcelain, wood, metals, plastic etc. It is very important adhesive used for sealing of high vacuum joints.
Glass fiber rein forced epoxy are widely used for overload transmission line insulators, bushing and bus bar insulators.

PVC:
PVC= polyvinyl chloride.
PVC is obtained from polymerization of gaseous vinyl chloride. Vinyl chloride has the following molecular structure
                       H   H
                       I      I
                       C=C
                       I      I
                       H   H
Since the vinyl chloride molecular posses a dipole moment its loss tangent is higher. PVC is hard and brittle. Its resistance to moisture, acid, alkalis, oils and alcohols is quite satisfactory. PVC is widely used for making various plastic and rubber like articles for insulating telephone and other wires for protecting electric and frost resistant, plasticisers liquid with high boiling points are added.
It is resistant to the action of sunlight, water and oxygen.

PTFE

Poly –tetra- fluro-ethylene is obtained through the polymerization of tetra fluro ethylene and has a linear molecular structure
                       F   F     F
                       ½I  ½    ½
                    -  C- C –C -
                       ½    ½    ½
                       F   F     F
PTFE possesses exceptionally valuable properties. Some of these properties are extreme heat resistance to almost all chemical reagents, non-hygroscopic and excellent insulating properties over a wide range of temperature and frequency. Its volume resistivity is more than 1010W-cm. Its Permitivity is 1-9-2-2 and loss tangent is 0.00001 to 0.0003. Its electrical strength drops sharply when subjected to a continuous ac voltage PTFE has a low radiation resistance. The application of PTFE is as capacitors dielectrics, insulators for all kind of windings, as conductor insulation of cables and wires as heat resistant material. 
 

PMMC

Plastics (polymeric materials) used for electrical insulation purpose consists of long chain macromolecules with repeating monomer units. A polymer is named by putting the prefix poly in front of the monomer.
PMMC stand for poly-methyl-meta-crylate plastics are very widely used as insulating materials because of their excellent dielectric properties.
Properties:
Dielectric strength- 170-280KV/cm
Volume resistivity  -1016W-meter
Tand (50 Hz to106 Hz)  -0.0002


FIBRE GLASS:
It is made from material, which is a free alkali metal oxide, which may form a surface coating that may attack the glass silicates. Glass does not absorb moisture volumetrically, but may attract
It by capillary action between the fine filaments. Tapes and clothes woven from continuous filament yarns of glass have a high resistivity, thermal conductivity and tensile strength and from a good class B insulation.
The dielectric strength of glass varies from 3000 5000 KV/Cm decreases with increase with temperature, reaching half the value at 1000C. Glass is used as a cover and for internal support in electric bulb, electronic valve, mercury arc switches, X-ray, equipment capacitors and as insulator in telephone.


POLYETHYLENE:
Polyethylene is a thermoplastic material that combines unusual electrical process, high resistance to moisture and chemical, easy process ability and low cost. It has got high resistivity and good dielectric properties at high frequencies and therefore, is widely used for power and coaxial cables, telephone cables multi-conductor control cable, TV lead in wire etc.
Electrical properties of polyethylene

Properties
Low density
Medium density
High density
Irradicated polyethylene
Volume resistivity
W-Cm
>1016
>1016
>1016
>1016
Dielectric strength- KV/cm
170-280
200-280
180-240
720-1000
Dielectric constant 50 Hz to106 Hz
2.3
2.3
2.35
2.3
Tand (50 Hz to106 Hz
0.0002
0.0002
0.0002
0.0005
Arc resistance
Melts
Melts
Melts
Melts


 

Classification of solid insulation materials

Organic material
Inorganic material
Synthetic polymers
Thermo plastic
Thermosetting
Amber
Cotton
Paper
Pressboard
Rubber
Wax
Wood

Asbestos
 Ceramic
 Glass
 Mica


Polyethylene
Polypropylene
Poly vinyl chloride
Poly carbonate

Bakelite
Epoxy resin
Cross linked Polyethylene
Phenolics elastomer
Melamine

Sunday 16 June 2013

Indian standard for electricity


Indian standard for electricity
Sr.
Standard no.
Description
1
IS 732-1963
Code of practice for Electrical Wiring installations (system Voltage not  exceeding 650 Volts)
2
 IE RULE 1956 / 50
Medium pressure wiring

3
IE RULE 1956 / 51
Regarding Medium and High pressure wiring
4
IE RULE 1956 /
32(1)(2)
Identification of earthed and Neutral conductors
5
 IE RULE 1956 / 51(1)
6Fixed type metallic boxes
6
IS 375-1963
® Marking and arrangement for switch-gear bus bars, main connections and auxiliary wiring
7
IE RULE 1956 / 33
Earthed termination on consumer premises
8
IE RULE 1956 / 33
Connection with Earth.

9
IE RULE 1956 / 33
Connection with Earth
10
IS 347 / 1952
Varnish Shellac for general purposes
11
IS2309 /  1969
Code of practice for the protection of buildings And allied structures against lightning.
12
IS RULE 1956
Safety procedure.
13
IS CODE 5216 / 1969
Guide for safety procedures and practice in Electrical works.

14
IS 1954 (Part-
I)1976
For working voltages upto and including 1100 Volts
15
IS 1954(Part-
II)1967
For working Voltage from 3.3 KV up to and including 11 KV.

16
IS 692-1973
Paper insulated lead sheathed cables for electricity supply.
17
IS 732-1963
Code of practice for electrical wiring installations (System voltage not exceeding 650 Volts).
18
IS 3961 (PARTII)
1967
Paper insulated lead sheathed cables.
19
IS 3961 (PARTII)
1967
PVC insulated and PVC sheathed heavy duty cables
20
IS 5819--1970
Recommended short circuit rating of high voltage PVC cables.
21
IS 1255-1967
Code of practice for installation and maintenance of Paper insulated power cables ( up to & including 53 KV).
22
 IS 1255-1967
--do—Section II
23
IS 2713 - 1964
Tubular steel poles for O.H. Lines
24
IS 705-1970
Reinforced concrete poles for OH power & Telecommunication lines.
25
IS 876-1970
Wood poles for O.H power and Telecommunications lines.
26
IS 1678-1960
Pre-stressed concrete poles for OH power, traction and
Telecommunications lines.
27
IE RULE 1956/76
Strength of Supports.
28
IE RULE 1956/90
Earthing of poles
29
IS 2141-1979
Galvanized stay strand.
30
IS 1445-1966
Porcelain Insulators for O.H. power lines (below 1000 V)
31
IS 731/1971
Porcelain Insulators for overhead lines (3.3 KV and below).

32
IE RULE 88
Repairing Guard Wire
33
IS 398-1961
Hard drawn stranded "A" and steel-cord "A" conductors for over head power transmission purpose.
34

-do-(Part 8) ---do--

IS 3070-1974 PART(I)

Non-Linear resistor types lighting arrestors
35
IS 3070-1966
Expulsion type Lighting Arrestors.

( PART II)

36
IE RULE 92
Regarding Earthing the lightning arrestors
37
IE RULE 77
Clearance above ground of the lowest conductor
38
IE RULE 79
Clearance from building of low and medium voltage
lines and service lines


--do-- 80 --do—of high & extra high


--do—81 Conductors at different voltage on same supports


--do-- 86 Conditions to supply where Telecommunications lines
and power lines are carried on same supports


--do—87 Lines crossing or approaching each other.
39
IS 2551-1963
Danger Notice Plates.
40
IS 270-1962
Galvanized steel barbed wire for fencing
41
IE RULE 76
Guard of service Line
42
IS 1255-1967
Care of practice for installation and maintenance of paper
insulated power cables (up to and including 33 KV
Section 11.7).
43
IS 429-1954
Methods for testing weights and uniformity of coating on Galvanized iron and steel wires and steel sheets.



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