Chapter No. 04 Distribution Substations: Dr. Intesar Ahmed, Engr. Kashif Imran, Engr. Muhammad Shuja Khan
Chapter No. 04 Distribution Substations: Dr. Intesar Ahmed, Engr. Kashif Imran, Engr. Muhammad Shuja Khan
Chapter No. 04 Distribution Substations: Dr. Intesar Ahmed, Engr. Kashif Imran, Engr. Muhammad Shuja Khan
04 Distribution Substations
Dr. Intesar Ahmed, Engr. Kashif Imran, Engr. Muhammad Shuja Khan
Distribution Substations
Purpose: To lower the voltage from the high voltage transmission and sub-transmission levels to a voltage that can be safely installed on the streets.
13.2 inches for 12.5kV for rigid buses with fixed supports.
4.1.2) Load:
The size of the load to be served determines the
capacity of substation.
Industrial and commercial loads are served by large
by how critical the loss of power is to the load. Loss of power to a hospital or to industrial and commercial areas can result in severe damages, both to human life and economy. Fault removal must be fast Automatic switching should be used to decrease the repair time.
Wood:
Wood pole substations are inexpensive.
Lattice Steel:
It provides structures of low weight and hidg strength.
Unit:
It is a recent development. It is factory built and tested.
to unqualified individuals.
large substations economically. Maximum economy is realized when low voltage feeder mileage is kept as low as possible. Smaller substations allow a lower loss mix of high and low voltage lines, more economical, simpler, design, construction and relaying is easier.
level for all insulation in the station. Bring all equipment and devices to that insulation level. Lightening protection is set at least 20% below this level, but above normal peak operating voltages.
such that a fixed tap can not keep its voltage between allowed limits.
Most popular scheme for voltage regulation is the use
of automatic tap changer, but voltage level of all the feeders from transformers are changed simultaneously.
breaker maintenance.
breakers. Primary switch must be able to break the transformer excitation current. Two sources used which allow service to restored quickly upon a sub-transmission circuit fault.
disconnect the bus if it faults and each feeder has over current relaying.
4.6.4)Automatic Switching(ThrowOver)
In this type, Service outage time is reduced. Each circuit breakers has disconnects on either side to isolate it during maintenance. Each feeder breaker probably has a bypass switch. Well protected with over current protection on transformer secondaries.
expand.
Bus or feeder fault can easily be isolated while station
remains in service.
Three circuit breakers are required for every two
4.7) Faults:
A fault is a malfunction in the system. Mast faults are result of lightning and wind storms.
3.
4.
5.
Line to ground( about 70 %) Line to line(about 15%) Double line to ground(about 10%) Three-phase faults to ground(less than 1%) Open circuits(Very few)
small substations.
a given relay set is its zone of protection. Feeders breaker zone of protection is the individual feeder. Bus zone of protection is the bus and connections to the bus. Over current protective devices must be coordinated to assure that only the faulted substation section is taken out of service.
protected. Transformer must have a minimum of: 1. Secondary over current relaying 2. Primary fusing 3. Sudden pressure relay(Attached to a valve on the transformer tank)
Linear coupler (LC) system, which works by eliminating the iron core of CTs. 2. Multi-restraint, variable percentage relays (CA-16) 3. High impedance voltage operated differential relays(KAB)
1.
protection. Economical requirements may lead to combine these two. HU relays are used for this purpose.
reference voltage for protection systems. Grounding system of a substation consists of a ground mat. Grid wires are about 20 feet apart but spacing varies with the conductivity of soil. Soil must be tested at each location. All substations structures are to be constructed within the perimeter of the grid.
Thank you