Distribution Systems : Distribution Systems Presented By: M. Aamir Sohail khan
Dept, of electrical engineering bahaudian zakariya university Multan , Pakistan 1 DEPARTMENT OF ELECTRICAL ENGINEERING UCE&T BZU MULTAN Contents of presentation : Contents of presentation HV Distribution System
Closed Loop System
Open Loop System
Double Supply System
Grid Form Of HV System
Improved Radial System
LV Distribution System 2 primary distribution system : primary distribution system Primary distribution system is that part of the electric distribution system between distribution substation and distribution transformers.
It is made up of circuits called primary feeders or distribution feeders. 3 Radial system : Radial system 4 Radial system : Radial system In this system all the sections/branches of a feeder are fed from a single source in a fixed direction 5 Load Load Load Generator Contd… : Contd… In this it is shown that there are two primary feeders from which further subfeeders supply to there respective loads. If any one of the feeder becomes faulty then supply through that feeder has to cut so no reliability 6 merits : merits 7 Demerits : Demerits 8 Application : Application It is considered more suitable for the areas with low density of load involving long distances and requiring low degree of availability. 9 Slide 10: 10 5
1 Slide 11: Closed loop system What is closed loop system? : What is closed loop system? If a HT line emanating from a Grid station and covering the load area in shape of a loop, finishes at the same Grid station returning to same breaker or another independent breaker it is called closed loop and the system is called closed loop system.
In this system each transformer has two sectinalizers, one on either side of the transformers tap-off point. Typical wapda closed loop system : Typical wapda closed loop system Bus bar Station circuit breaker Sectionalizing switch closed transformer Load Sectionalizing switch closed Merits of closed loop system : Merits of closed loop system This system is more reliable than radial system.
At fault breaker at grid station opens.
After tracing the fault the faulty section is isolated, and supply to remaining section is restored.
The consumers don’t have to wait very long till the rectification of the fault as in the case of Radial system.
In case of two simultaneously faults, the consumers have to wait much till the rectification of the fault of at least one section. But possibility of two simultaneously faults is less.
It is usually preferred that there must be two breakers instead of one.
Less voltage drop, less line losses
As compared to radial system the voltage drop and line losses is less. De merits of closed loop system : De merits of closed loop system This is an expensive system because of the following reasons.
It requires extra length of loop to complete the loop back to sub-station.
Each transformer has to be provided with two sectionalizers , in absence of which the loop does not sere any purpose.
In emergency total load of loop may have to be served from one side of loop, so higher size conductors are required to carry twice the current. Cost increases.
Similarly in low load section the load during emergency must be more than 50%.
They are used for small loops, If loop size is so large then the fault location time may exceed up to 5 to 6 hours. and if consumers are without electricity for this time then there is no justification to install such a system Application : Application It is usually recommended for HIGH density areas where distances are small. preferably for urban areas.
This system can be equally useful for rural areas where economy so permits. But to ensure effectiveness the loop should be of small size. OPEN LOOP DISTRIBUTION SYSTEM : OPEN LOOP DISTRIBUTION SYSTEM UNIVERSITY COLLEGE OF ENGINEERING & TECHNOLOGH, B.Z.U. OPEN LOOP SYSTEM : OPEN LOOP SYSTEM In a closed-loop system with two breakers( one at each end), if one of the two sectionalizers of low-load-section is kept normally open, the system is named as “open-loop system”. COMPARISON b/w CLOSED-LOOP & OPEN-LOOP SYSTEM : COMPARISON b/w CLOSED-LOOP & OPEN-LOOP SYSTEM ADVANTAGES : ADVANTAGES Economical
Availability of service is improved
Locating fault is easy Slide 21: TRANSFORMER SECTIONALIZING SWITCH (OPEN) SUBSTATION BUS SECTIONALIZING SWITCH (CLOSED) STATION CIRCUIT BREAKER OPEN LOOP SYSTEM HRC FUSE Load Slide 22: Double Supply
System Double Supply System : Double Supply System Additional radial feeder is provided side by side to feed the same consumer.
Using automatic change over switches.
‘Duplicate supply system’ or ‘parallel feeders’. Slide 24: Substation Bus Circuit Breaker Sectionalizing switch FUSE TRANSFORMERS LOAD LOAD DOUBLE SUPPLY SYSTEM Merits and Demerits : Merits and Demerits GRID FORM OF HIGH VOLTAGE SYSTEM : GRID FORM OF HIGH VOLTAGE SYSTEM GRID FORM OF H.V SYSTEM : GRID FORM OF H.V SYSTEM In this system all the distribution transformers of a load area, are interconnected providing normally two or more alternatives. while the whole system is fed from two or more bulk supply sources.
But availability can not be improved through manual operation of sectionalizer to isolate faulty section during emergency as it will take quite a considerable time to identify the faulty section and to determine the better alternative.
as manual operation may result in wrong operation due to complexity of the system so to have a real benefit of this system, automatic switching arrangements with sophisticated protection schemes should be provided including establishment of a remote control center. Slide 28: SINGLE LINE DIAGRAM OG GRIF FORM OF H.V-DISTRIBUTION SYSTEM Merits : Merits Most reliable because normally no possibility of failure of supply and availability is almost 100%.
In case of two simultaneous faults, service to the consumers will not be affected at all, or effect will be limited.
It is most costly system. Applications : Applications The system being the most reliable, and at the same time the most costly, is recommended for the areas of highest priority of supply with very high load density.
If the economy for a county is not a problem, this system is considered the most suitable one for urban areas, specially the big cities Improved Radial System : Improved Radial System In this system we use sectionalizers so that in case of fault on one feeder a part of that can fed by other. 31 LV Distribution system : LV Distribution system Usually Radial system is used due to following reasons:
As LT lines feed only one or few consumers so in case of fault only few consumers are affected.
Simplest and cheapest.
In some important areas Open loop and Closed loop systems might also be used. 32