Download Power Delivery Basics Presentation, December 3, 2009

Salt Lake Electrical Plan
Task Force
December, 2009
Power Delivery Basics
1
Voltage & Current
V=IxR
Voltage (volts) = Current (amps) x Resistance (ohms)
– Voltage is a measure of electrical “pressure.”
 Think of voltage (V) as water pressure in a hose.
 The pressure at the source is greater than the pressure at
the outlet.
 The pressure at the end of a 500’ hose is less than the
pressure at the end of a 50’ hose.
– Think of resistance (R) as being like the friction inside the
hose
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Voltage & Current
– Current (I) is the movement of electrons through a conductor,
measured in amperes or amps.
 Current is analogous to flow in a hose (gallons)
 A 1” diameter hose can provide more flow than a 5/8”
diameter hose
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Power
P=VxI
Power (volt-amperes) = Voltage (volts) x Current (amps)
Power has two components: Watts, Vars
For our discussion we will only use Watts
Power (watts) = Current (amps) x Voltage (volts)
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Power
– The basic unit of measure for power is the watt (W)
 1,000 watts = 1 kilowatt = 1 kW
 1,000,000 watts = 1 megawatt = 1 MW
– The maximum amount of power a transmission line can carry is
referred to as capacity. Capacity is a function of the voltage and
the wire size.
 P=VxI
 The higher the voltage, the more power a line can carry.
 The higher the current (the larger the wire – or conductor),
the more power a line can carry.
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Quick Quiz
1. Which conductor can carry the most power?
A.
B.
2. For the conductor in figure B above, which voltage can
provide the most power?
A. 46,000 volts (46 kV)
B. 138,000 volts (138 kV)
P (power) = V (volts) x I (amps)
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Energy
 Energy is the measure of power used over time.
 The basic unit of measure for electrical energy is the watt-hour.
 1,000 watt-hours = 1 kilowatt-hour = 1 kWh
 1,000,000 watt-hours = 1 megawatt-hour = 1 MWh
 Your power bill at home shows energy usage in kilowatt-hours
(kWh).
 A 100 watt light bulb operated for 10 hours uses 1,000 watthours or 1 kWh. That would cost about 8 cents.
 Average Utah residential customer uses 800 kWh per month
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Capacity versus Energy
– An electrical system is designed to provide:
 Capacity (kW)
 Energy (kWh)
– Capacity is the maximum amount of electricity a line (or other
electrical equipment) can carry at any instant. The electrical
system must have the capacity to serve the demand placed on it
by the customer(s) at any given time. Typically the peak demand
for Wasatch and Summit counties occurs in the winter.
– Energy describes the flow of power over a period of time.
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Highway Analogy
– Draw a line across a highway.
– In one direction, only one car can cross this line at a time. So the
capacity of the highway at any instant is one car.
– This is like the capacity of a wire measured in kilowatts.
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Highway Analogy
– If we add time to the equation and a total of 500 cars that cross the
line in one hour, we can say we have accommodated 500 carhours.
– If 500 cars per hour cross the line for two hours we have 1,000
car-hours.
– This is analogous to kilowatt-hours of energy.
– When more people need to travel the highway we must increase
the number of lanes to accommodate additional traffic = $$$.
10
Load Growth
– As customer demand grows, Rocky Mountain Power can:
1. Increase system capacity to provide more power
 New lines and substations
 Increase capacity of existing facilities where possible
2. Decrease load during peak hours so less capacity is needed.
This is called demand response/control.
3. Decrease load via energy efficiency.
– Rocky Mountain Power uses all three options
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Power Delivery and Utility Components
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Power Delivery and Utility Components
Substations
– A substation transforms or changes voltage levels and contains
equipment to protect utility components.
– Substations can contain the following:
 Transformers – cell phone chargers contain transformers
 Switches – think of light switches in your house
 Circuit breakers – think of the circuit breakers in your house
– Substations do not generate power
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Power Delivery and Utility Components
Substations
– Major substations: Convert power from high voltage transmission
lines (230 kV, 345 kV) to sub-transmission voltages (46 kV, 138
kV)
– Regional substations: Convert power from sub-transmission lines
(46 kV, 138 kV) to other sub-transmission voltages and
distribution voltages (12.5 kV, 25 kV)
– Local substations: Convert power from sub-transmission lines (46
kV, 138 kV) to distribution voltages (12.5 kV, 25 kV)
 When local substations are added, we must ensure there is
capacity at regional and major substations as well.
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Major
substation
Legend
Regional
substation
345 kV
138 kV
46 kV
12.5 kV
Local
substation
Local
substation
Power Delivery and Utility Components
Transmission Lines (Main Grid)
Energy is transmitted via high voltage lines
(230kV, 345kV) from the power generators to
major substations
High voltage is used for long distance, bulk
energy transmission.
High voltage transmission lines are to electricity
as an interstate freeway is to transportation.
There are few off-ramps or exits (substations).
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Legend
345 kV
138 kV
46 kV
12.5 kV
Main Grid
Transmission Lines
= Freeways
Power Delivery and Utility Components
Sub-transmission Lines (Local Transmission)
– Sub-transmission
voltages – 46 kV and
138 kV.
– Used to transmit energy
from major substations
to regional and local
substations.
– Sub-transmission = state
highway or arterial road
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Local Transmission
= 4 Lane Hwy
Legend
345 kV
138 kV
46 kV
12.5 kV
Lower Voltage Local
Transmission = 2
Lane Hwy
Main Grid = Freeway
Power Delivery and Utility Components
Distribution Lines (Feeders or Circuits)
– Distribution voltages range from 7.2
kV to 25 kV.
– These lines deliver electricity to
your neighborhood.
– Distribution line = residential street
– Delivery (residential, commercial)
voltages range from 120 V to 480 V.
– Transformed to residential voltage
by transformers in the neighborhood
– Service drop = driveway
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Local Transmission
= 4 Lane Hwy
Legend
345 kV
138 kV
46 kV
12.5 kV
Local Transmission
= 2 Lane Hwy
Main Grid = Freeway
Distribution =
Surface Streets