As we know generation plants are very far from the consumer because of availability of resources eg water, coil and petrol so some sort of system is required to connect consumer with the generating station
Power system is divided into 3 type
1.Generating station
2. Transmission system
3, Distribution system
TRANSMISSION SYSTEM
A Electric line which is used to transmit power from generating station to the load centers is known as transmission system
DISTRIBUTION SYSTEM
Transmission line voltage is stepdown by using stepdown transformer ans then provided to different consumers like industrial , utility
TYPICAL POWER SUPPLY SCHEME
1.Generating station
Generating station is a place where electric power is generated , mostly the generation is done at 11 kv, then generated voltage is step up by step up transformer and given to primary transmission line
2.Primary Transmission line
Generated voltage can be step to different voltage levels maximum step up voltage which is mostly used in pakistan is 512 kv but 132 and 212 kv are also used in some places ,the step up voltage is supplied to Load centres
3.Secondary Transmission
The line which is connected with receiving station is known as secondary transmission,In receiving station voltage is step down upto 132 kv and then supply this voltage to different substation
4.Primary Distribution
In primary distribution the voltage is stepdown upto 11 kv , and then given to other distribution substation or a consumer whose demand is higher than 500 kva a direct 11 kv line is given to them
5.Secondary Distribution
Electric power of primary substation given to secondary substation where voltage is again stepdown upto 400(three phase) and then given to consumer
ELEMENTS OF DISTRIBUTION SYSTEM
FEEDER
Lines which is used to connect substation with the distributor is known as feeder , these lines has same current
DISTRIBUTOR
Distributor have different tapping of voltage and currrent, LOad is connected to these tappings according to the demand of a consumer
SERVICE MAIN
The line which is connected between distributor and consumer is known as Service main
PURPOSE OF TRANSMISSION LINE
As discussed earlier that generating stations are very far from consumer permisses so some sort of line is needed to connect generating stations with the load
Following rules must be obeyed for transmission line system
1.Choice of Frequency
In america the frequency is 60 hz while in Pakistan and some other countries the pre determined frequency is 50 hz ,higher frequency has some advantages over lower some of them are discussed below
1.the rpm of motor at 60hz is 3600 while at 50 hz its 3000 hz
2.In distribution transformer secondary voltage depends on frequency and flux linkage
In transmission line lower frequency is favorable because low frequency means low inductive reactance and high capacitance so high load can be connected to that transmission line
2.Choice of Voltage
By Increasing the voltage the losses and conductor size can be decrease but it also have some disadvantageous like "insulation cost increased, substation cost increased , transmission line end transformer cost increased "
so voltage level can be increased upto certain level , every transmission line has its optimum value
3.Choice of conductor
A conductor size depends on voltage level as voltage level increased conductor level will be decreased and cupper losses will also be decreased
In long transmission line bundle conductors are used in transmission system ,In Pakistan for 220kv twin bundled conductors are used while for 512 triple bundled conductors are used
4.Choice of Circuits
Grid or substation size depends on load of load requirement is low so single busbar is favorable while at high load double busbar scheme is selected
RING SYSTEM OF AC TRANSMISSION LINE
In ring type generating station is connected with substation,
The reason behind this ring form is fault occur in one generating station so another generating station will provide supply to the same substation , it is used where power required at any time
Ring system is of two type
1. Transmission Ring System
In transmission ring system generation station are connected with each other
2.Distribution Ring System
In Distribution ring substation is connected with generating station
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