Electrical symbol used in house wiring

Electrical symbol used in house wiring

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 C_nH_2n+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

CaTio_{3 –} Calcium Titanate

SrTio_{3  -S}tantium Titanate

BaTio_{3 –}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

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.