SUBSTATION DESIGN:
The main considerations taking into account during the design process are:
1. Reliability
2. Cost (sufficient reliability without excessive cost)
3. Expansion of the station, if required.
Selection of the location of a substation must consider many factors:
1. Sufficient land area
2. Necessary clearances for electrical safety
3. Access to maintain large apparatus such as transformers.
4. The site must have room for expansion due to load growth or planned transmission additions.
5. Environmental effects( drainage, noise and road traffic effects.
6. Grounding must be taking into account to protect passers-by during a shortcircuit in the transmission system
7. The substation site must be reasonably central to the distribution area to be served.
LAYOUT DESIGN
The first step in planning a substation layout is the preparation of a one-line diagram which shows in simplified form the switching and protection arrangement required, as well as the incoming supply lines and outgoing feeders or transmission lines.
One-line diagram should include principal elements: Lines ,Switches ,Circuit breakers and Transformers
Incoming lines should have a disconnect switch and a circuit breaker.
A disconnect switch is used to provide isolation, since it cannot interrupt load current.
A circuit breaker is used as a protection device to interrupt fault currents automatically
Both switches and circuit breakers may be operated locally or remotely from a supervisory control center.
Following the switching components, the lines are connected to one or more buses.
An electrical bus, derived from bus bar, is a common electrical connection between multiple electrical devices.
The arrangement of switches, circuit breakers and buses used affects the cost and reliability of the substation. For important substations a ring bus or double bus.
Substations feeding only a single industrial load may have minimal switching provisions.
Once having established buses for the various voltage levels, transformers may be connected between the voltage levels. These will again have a circuit breaker in case a transformer has a fault.
A substation always has control circuitry to operate the various breakers to open in case of the failure of some component.
SWITCHING FUNCTIONS
Switching is the operation of connecting and disconnecting of transmission lines or other components to and from the system.
Switching events may be "planned" or "unplanned".
A transmission line or other component may need to be deenergized for maintenance or for new construction.
To maintain reliability of supply, it is not cost efficient to shut down the entire power system for maintenance.
All work to be performed, from routine testing to adding entirely new substations, must be done while keeping the whole system running.
Also, a fault may develop in a transmission line or any other component. The function of the substation is to isolate the faulted portion of the system in the shortest possible time.
LOAD
The size of the load to be served determines the capacity of the substation.
The load must be distributed such that it can be served with reasonable feeder loss or more.
Critical loads (industrial districts) are served by more complex substations, designed for maximum reliability and speed of power restoration compare to the ones used in residential areas where a short time power loss is usually not a disaster.
Other substations in the area influence the design of a new substation.
The presence of the other substations will increase the overall power capacity and as a result can satisfy the demand for heavy loads.
Substations for critical loads usually use more than one transformer so that the load is served even if one transformer is out.
Otherwise a single large three-phase transformer is used because it costs less per kVA of capacity, and requires less room, bussing, and simpler protective relaying.
The main considerations taking into account during the design process are:
1. Reliability
2. Cost (sufficient reliability without excessive cost)
3. Expansion of the station, if required.
Selection of the location of a substation must consider many factors:
1. Sufficient land area
2. Necessary clearances for electrical safety
3. Access to maintain large apparatus such as transformers.
4. The site must have room for expansion due to load growth or planned transmission additions.
5. Environmental effects( drainage, noise and road traffic effects.
6. Grounding must be taking into account to protect passers-by during a shortcircuit in the transmission system
7. The substation site must be reasonably central to the distribution area to be served.
LAYOUT DESIGN
The first step in planning a substation layout is the preparation of a one-line diagram which shows in simplified form the switching and protection arrangement required, as well as the incoming supply lines and outgoing feeders or transmission lines.
One-line diagram should include principal elements: Lines ,Switches ,Circuit breakers and Transformers
Incoming lines should have a disconnect switch and a circuit breaker.
A disconnect switch is used to provide isolation, since it cannot interrupt load current.
A circuit breaker is used as a protection device to interrupt fault currents automatically
Both switches and circuit breakers may be operated locally or remotely from a supervisory control center.
Following the switching components, the lines are connected to one or more buses.
An electrical bus, derived from bus bar, is a common electrical connection between multiple electrical devices.
The arrangement of switches, circuit breakers and buses used affects the cost and reliability of the substation. For important substations a ring bus or double bus.
Substations feeding only a single industrial load may have minimal switching provisions.
Once having established buses for the various voltage levels, transformers may be connected between the voltage levels. These will again have a circuit breaker in case a transformer has a fault.
A substation always has control circuitry to operate the various breakers to open in case of the failure of some component.
SWITCHING FUNCTIONS
Switching is the operation of connecting and disconnecting of transmission lines or other components to and from the system.
Switching events may be "planned" or "unplanned".
A transmission line or other component may need to be deenergized for maintenance or for new construction.
To maintain reliability of supply, it is not cost efficient to shut down the entire power system for maintenance.
All work to be performed, from routine testing to adding entirely new substations, must be done while keeping the whole system running.
Also, a fault may develop in a transmission line or any other component. The function of the substation is to isolate the faulted portion of the system in the shortest possible time.
LOAD
The size of the load to be served determines the capacity of the substation.
The load must be distributed such that it can be served with reasonable feeder loss or more.
Critical loads (industrial districts) are served by more complex substations, designed for maximum reliability and speed of power restoration compare to the ones used in residential areas where a short time power loss is usually not a disaster.
Other substations in the area influence the design of a new substation.
The presence of the other substations will increase the overall power capacity and as a result can satisfy the demand for heavy loads.
Substations for critical loads usually use more than one transformer so that the load is served even if one transformer is out.
Otherwise a single large three-phase transformer is used because it costs less per kVA of capacity, and requires less room, bussing, and simpler protective relaying.
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