Electricity: Generation>Transmission>Distribution
Before electricity reaches our Household ,it is first generated in generating stations then transmitted to Grid substations , then to Power substations and further it is distributed from power substations to consumer end. Most of the equipment which are used at consumer end uses low voltage to operate, but we step-up this voltage in generating stations and at Grid Sub-Stations for reducing transmission line losses.
Electricity is generated in generating stations like thermal power station, hydel power station, Nuclear power station, & other energy producing stations. Most of the generating stations which are based on conventional sources use steam pressure to rotate alternators which in turn produces electricity.
Power is usually generated in generating stations at 11 kilo-volts ,this voltage level is further stepped up using step up transformers in generating stations to higher voltage levels to reduce transmission line loss and then power is transmitted to Grid substations.
(PC-electricaltechnology.org)
Grid Sub-station (GSS)
Grid Sub-station (GSS) is usually constructed somewhere near load centers (a place where power is consumed like cities, villages etc) usually for voltage level above 33 KV , they can be of rating like 400/220kv ,220/132kv, 132/33kv or other voltage levels. In a Grid sub-station, voltage is stepped down from higher level to lower level using a step down transformer and it is further distributed to other nearby Gss or nearby Power substation.
First numeral in Gss rating denotes voltage in incoming side of Gss and second denotes voltage level of outgoing/Output side of Gss, say if a Gss is of 220/132kv level it means incoming voltage in Gss is 220kv and it is stepped down to 132kv in the Gss and distributed ahead. It is to be noted that 220kv, 132kv, 33kv etc voltages are line voltages i.e they are voltage between any two phase in a 03 phase system.
Power Sub-station (PSS)
From Grid substation power is transmitted to Power sub-stations(PSS) ,they are usually at 66kv or lower voltage level. PSS are very near to load centers ,if a Pss is of 33/11kv level it means that incoming voltage in Pss is 33kv and outgoing voltage is 11kv. From Pss, power is stepped down and usually distributed at 11kv and then it finally reaches the 11kv/415v distribution transformers which are located near our households and colonies and it steps down the voltage from 11kv to 415v.
All above power is transmitted using three phases (R,Y,B). This is how 3 phase, 415v supply reaches near our houses from generating station , now we can connect our houses using single phase supply or may use 2 phase or 3 phase supply depending on our requirement.Power flow analysis is also done to understand where power loss,voltage drop etc is occurring.
Power near consumer end :
Normally people take connection of single phase in houses and 2 phase or 3 phase connection is taken usually for commercial purpose where there is requirement of more power. A low tension line (LT line) is generally of 415v or lower voltage level , this line is of three phases (R,Y and B) also called 3ph, 3wire system or three phases with one neutral wire which is called 3ph,4 wire system.
(PC-Slideshare)
How we get 240v AC supply in our Households:
Ohm’s law states that for electricity to flow we need voltage difference ,therefore in our houses we create this difference by using one phase and one ground (neutral). There are two ways we can get 240V AC supply (240V is Phase to ground voltage) from L.T (Low tension) lines:
1. 3ph,4W system (Three phase four wire system): Three phase and one neutral wire is laid in this system. We can take one phase and neutral from this L.T line and we can easily get 240V Ac supply in our homes.
Vphase=Vline/1.732. (Line voltage is 415V)
Due to extra cost in laying one additional wire for neutral and some operational issues ,we don’t see 3ph,4w distribution system in many countries .
2. 3ph, 3W system (Three phase three wire system):This type of L.T line is very common . In this type of L.T lines consumers have to create neutral (zero potential) in their respective homes, for this earth pit is constructed and earthing rod and charcoal mixture is put inside the pit. This pit acts as zero potential and one phase supply is taken from L.T line to get 240V. If earthing rod is not of good quality and earth resistance of pit is higher we may face low voltage issue due to this.
We can transmit power from generating stations to load centers using either insulated cables or by using bare conductors. Cables are usually laid inside the ground and higher the voltage level more expensive a cable becomes ,also finding fault in underground cable is difficult task, for these reasons underground cables are not considered economical for all voltage levels.
For transmission of power at high voltage levels and longer distance ,bare conductors of different rating is used depending on voltage level and power flow. We use cables for shorter distance or low voltage levels. Cost of bare conductors is comparatively economical to power cables. Bare conductors are placed on transmission towers or electric poles and they are suspended using electric insulators and hardware fittings. Electric poles are used for 33kv or 11kv voltage level, for 33kv and higher voltage levels, transmission towers are erected.
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