Chapter 7 Flashcards
Substations
What are other names for Substations?
Power Station or Supply Station
Common description of Substation
Fenced enclosure with large equipment inside and several power lines coming in and out of the station.
Common location of substations
- 1-10 acres of land owned by a utility.
- Geographically located where it can most effectively perform its functions
What are the three major functions of Substations?
- Change the voltage of circuits from one level to another
- Connect or disconnect lines or equipment from each other
- Control the flow of power by adjusting the voltage and current
What are some Substations limited to?
Some Transmission Stations only have equipment that can connect or disconnect lines or equipment from each other and they are commonly referred to as Switching Stations.
What are Generation Stations designed to do?
Generation Stations are designed to Step Up the voltage that is produced by the generators of a power plant so it can be transported to where it will be used.
Where is the Generation Station located?
Adjacent to the Generating Plant
What are Transmission Stations designed to do?
Transmission Stations are typically installed to change the voltage levels to help integrate a system.
Common properties of a Transmission Station?
- Several Transmission lines coming in and out
- 500kV to 230kV
- Large Power Transformers & Circuit Breakers
- Equipment to control the Voltage and Current
Common properties of Subtransmission Stations?
- Typically located near load centers
- Main function is to change voltage from a higher Transmission Line Voltage
- Example 345kV Transmission to 69kV Subtransmission to then be distributed to a Distribution Substation within a load center
Where are Distribution Substations located?
- In the middle of a load center
- Within 4-10mi of each other in densely populated areas
Common properties of Distribution Substations?
- They have transformers that would change Subtransmission Voltages to Distribution Voltages
- Typical station might have two Subtransmission lines supplying the power and 10 Distribution circuits leaving the station to supply power to customers in the area
Substation Functions
- Voltage Change
- Point of interconnection for lines of different ownership
- Power flowing in and out of the substation measured
- Lines coming in and out the station connected and disconnected for routine work or abnormal conditions
- Equipment inside the station connected and disconnected for routine work or abnormal conditions
- Lightning surges and switching surges removed for line and equipment
- Voltage and Current on lines controlled
- Communication circuits connected to lines and equipment
- AC-DC-AC
What are some of the major pieces of equipment easily identified?
- Power Transformers
- Circuit Breakers
- Disconnect Switches
- Current and Potential Transformers
- Capacitors and Reactors
- Voltage Regulators
- Steel Structures
- Control House
- Ground Grid
What are Power Transformers used for?
To change voltage level from one to another
Common properties of Power Transformers
- Large
- Heavy
- Contain mineral oil
- Require special transportation
- Older stations have 3-Single Phase units
- Newer stations have 1-3 Phase unit
- May or may not have a Load Tap Changer (LTC)
What is LTC used for?
To cut in or out a portion of the transformer winding which adjusts the voltage to the conditions.
Common properties of Circuit Breakers?
- Connect and disconnect lines and equipment
- Large in size but not as heavy as transformers
What are Circuit Breakers designed to do?
Interrupt large amounts of current, and typically use oil, air, vacuum, or Sulfur-Hexafluoride Gas
Whats the purpose of installing Disconnect Switches?
- Isolate lines and equipment
- Provide a means to connect or disconnect parts of the station to reroute flow of power
- Normally operated by Switchman
How do Current and Potential Transformers work?
- Provide a reduction in the voltage and current so the power flow can be measured
- Sense abnormal levels of voltage and current which is used to disconnect lines and equipment during trouble conditions
How do Capacitors and Reactors work?
- Assist in controlling the flow of power on the system
- Connected and disconnected from the system based upon the dynamics of the flow of power
What do Voltage Regulators do?
-Automatically adjust the voltage as required
-If the station transformer does not have a LTC a separate regulator may be used
The Regulator may be 3-Single Phase or 1-3 Phase unit
What do Steel Structures in Substations provide?
- Means to terminate lines entering and leaving the station
- Mount switches, disconnects, bus conductors, and other equipment
What is a Control House?
- Houses key control equipment such as relays, meters, and computers
- Contains DC batteries that are used to control key equipment if power to the station is lost
How does the Ground Grid work?
- Provide a path to earth for lightning surges
- Provide a ground reference source for transformers and associated system neutral conductors
- Provide a ground source for other station equipment
- Ensures safety to the workers in the station by limiting ground potential differences
- Ensure the safety of the public who may be near the station fence during a fault condition
- Limit the influence of faults to communications facilities entering the station
What makes up the Ground Grid?
- Large stranded copper wire buried 12-18 inches below the grade and spaced in a grid pattern of 8-20 foot squares
- Supplemented by ground rods as necessary to to further reduce the overall resistance
- Covers the entire footprint and slightly outside the perimeter fence
- The fence is connected to the grid at several locations`
Basic Substation design?
- Enough room for expansion in case more capacity for power delivery is needed
- So equipment can be safely maintained and operated with room for bringing in a mobile substation in case a transformer needs to be taken out of service
What are the Key Elements when talking about Environmental Considerations?
- Appearance of the Station - Attractive Landscaping, Low Structure Profile and Decorative Fencing
- Electromagnetic Fields - Minimize EMF
- Sound - Sound Barriers or Special Design Consideratio
- Oil Spill Containment - Contain released liquid in case of catastrophic failure & have immediate Cleanup Crew
- Fencing - Installed for both human and wildlife safety and Substation equipment security. Must be surrounded by a high fence
