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How many amps on power lines Amp rating on power lines Ampacity of power line If you draw grid
power during a hot day, it costs more to deliver than on a cool day
when the grid can run more efficiently.
Wait until cooler times to run HVAC, clothes dryer, other 240 and 120 volt loads. |
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 Resource: See full list of wires and ampacity/ pdf Table 1 Table 1 shows amp ratings for one type of stranded, bare aluminum conductor exposed to different ambient conditions ... 77° to 104°F with sun and wind conditions. Direct sun causes more heat on the power line, increasing resistance on the aluminum conductor, and reducing the total amp capacity (ampacity) of power line. Wind has a cooling effect, and so ampacity on power line goes up. The table shows that Heat works against electric transmission and distribution. Volts and amps Amperage is the current of electrons that is being pushed through the matrix, or atomic structure, of a conductive material by voltage. Voltage on power lines remains relatively steady, while amperage varies by demand from end users. For example, when more businesses are open, and all the lights are on, the amperage flowing on power lines goes up. As businesses begin to close at end of day, and lights are turned off, then the amperage starts to fall. Voltage doesn't change throughout the day or night, except for brief surge events caused by large inductive loads, lightning strikes etc. Resistance and heat Conductive materials, like aluminum power lines, always offer resistance to the movement of electrons. Resistance is like friction ... it causes heat. As more electrons are getting pushed down the wire, then the higher the resistance ... and the higher the resistance, the higher the heat caused by friction. If heat on the power line exceeds capacity, then breakers located at substations can trip off. The power company must install a power line that can meet the heat caused by flow of amperage during peak demand, and also meet the expected ambient weather conditions that effect power line ampacity. Resource: Power generation: from power plant to end user The grid is a balance of cost and function Aluminum is chosen for power lines because it is workable within a wide range of temperatures, abundant, relatively inexpensive, lightweight, strong, durable, resistant to deterioration when exposed to weather ... and aluminum is a conductive metal with low resistance against the movement of electrons (amperage) .... this makes aluminum and aluminum alloy conductors the best choice for transmission and distribution lines. Other metals, such as copper, silver and steel are also used as electric conductors. Steel alloys are used for smaller wires ... for areas with low demand that require many miles of low-cost distribution line. Steel alloy is also used for guy wires (to support poles), and as a core for many types of aluminum power line. Using a steel core adds strength to long spans. However steel is not used for large power lines because of weight. Steel is much heavier than aluminum. The poles would have to be set closer together, and poles engineered for for higher loads. Copper and silver are too expensive, and too soft for the long spans of wire that are needed for power lines. Copper conductors are used for ground wires on each power pole, and used for household wiring because it will not expand and contract as much as aluminum ... making copper easier to install and safer than using aluminum conductors inside homes and businesses. Silver is soft and expensive, and is used primarily for electronic circuits. Resource: Power line design .pdf kcmil from row 2, Table 1 1 kcmil = 0.5067 square millimeters. A mil is 1/1000 inch, so 266.8 kcmil wire is 266.8/1000th of an inch = .26" or about 1/4" diameter Typical distribution line might be 900 kcmil or about 7/8" diameter. |
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  Chart
above shows amp rating for one type of 37
strand bare aluminum alloy wire that is among the commonly used
distribution lines is about 7/8" diameter. The line can carry 500-1000 amps depending on ambient weather conditions. Cooler temperatures, clouds, and wind help lower resistance, so the voltage can push more electrons (amperage) through the conductor matrix. Photo taken during installation of power lines. NEVER touch a power line without 100% certainty the line is not carrying electricity. Single-phase and 3-phase Current or amperage draw from power lines The current (I) is inversely proportional to both voltage (E) and number of turns on the transformer's primary and secondary windings. E volts N turns I amps (amps is current or flow of electrons). Resource: Single-phase transformer explained  Single-phaseIf primary volts E1 are 7200 volts on the distribution wire. Primary volts is the volt rating of power company line that distributes power to home. The secondary volts E2 for household single-phase service is 240 volts. Secondary volts are the volts that go from transformer to the household breaker box, or service panel. Resource: From power pole to breaker box Now lets; suppose the main breaker is 250 amps then I2 is 250 amps, and the maximum amount that the breaker box can supply for household usage is 250 amps. If the draw is greater than 250 amps, the main breaker will trip off. With residential single-phase transformer, the turns ratio is 30:1. We know this because incoming voltage from distribution line is 7200 volts, and voltage supplied to house is 240 volts. Calculate the turns ratio and it's 30:1  So primary amperage (I1) can be calculated: for 250 amp by dividing 250 by 30 = 8 amps. This means the 7200 volt primary line must be able to deliver 8 amps to the primary coil on the transformer ... but only during maximum usage of household amperage (which would be rare). Voltage remains unchanged, except for brief surges and anomalies ... so voltage is relatively steady 7200 on the primary side and steady on the 240 volts on the secondary side ... and voltage remains steady no matter how many amps are pulled by the household. Significant voltage drop does not occur during ordinary residential usage because all electric circuits are wired in parallel, not in series. The means each power pole, light or outlet on a circuit breaker receives generally the same voltage. For example, every outlet in the home receives same 120 volts, no matter many loads are plugged in and turned on.. Only the amps vary, with more amps (or current) flowing when a load is on. Since electricity is dynamic, and delivered on demand, then 8 amps would be consumed off the primary coil of the transformer only when the home was using the maximum 250 amps ... for example if home has whole house tankless pulling 120 amps, plus the 23 amp clothes dryer, two 40 amp air conditioners, the 50 amp oven and 25 amp stove top .... the usage would be 295 amps. The 250 amp main breaker in household panel would be trip off, and home might need to downsize usage, switch to heat pump water heater, and stagger air conditioner usage, or install 300+ amp service. Since the effect of usage at one home is multiplied when a distribution line supplies power to 1000s of homes and businesses, I recommend downsizing usage to ensure the grid remain stable and operable for all folks. Compare the same amp draw for 3-phase Primary volts E1 are the same 7200 volts, because the distribution line carries power to both residential and commercial services. With commercial 3-phase, 3 Hot wires and 1 Neutral are pulled from the 3 hot distribution lines. With residential single-phase, 1 Hot line and a Neutral are pulled from the 3 hot distribution lines. Difference between single-phase and 3-phase Let's suppose the main breaker at the 3-phase commercial panel is 250 amps so E2 is 250. So the main breaker are same for both residential single-phase example and commercial 3-phase example. But let's change the secondary voltage at the commercial service E2 to 480 volts commonly found in a commercial 3-phase service. The turns ratio would be 15:1. This means primary amperage I1 can be calculated: 250 amp divided by 15 = 16 amps. So the 7200 volt primary line must be able to deliver 16 amps to the primary coil. Each leg of the 3-phase circuit pulls 16 amps, from 3 separate wires at staggered times as the generator rotates. Unlike single-phase that pulls 8 amps from 1 of the 3 Hot wires. Overall, the effect of higher amp draw results in more power, more kVA or Kilo Volt Amps or Kilowatts. Kva is a static number used to compare amount of power (watts) delivered to HVAC, motors etc. Kva is not to be confused with Kwh, which a measure of billable consumption of watts of (power). Difference between single-phase and 3-phase |
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Power transformer. Other parts include bushings, tap changers, power cable connectors, gas-operated relays, thermometers, relief devices, dehydrating breathers, oil level indicators, and other controls. LPTs (larger power transformer) found at generating station or regional substation have capacity rating greater than or equal to 100 MVA Power transformer is much smaller and found at local substations. Transformers are rated by voltage, and by how fast they cool after heavy demand period. Extra high voltage (EHV), 345 to 765 kilovolts (kV); High voltage, 115 to 230 kV; Medium voltage, 34.5 to 115 kV; and Distribution voltage, 2.5 to 35 kV.... kV is kilovolts or volts x 1000 |
 Larger imagePower transformer at local substation Transformers are designed to step-up or step-down voltage on the transmission and distribution lines, and to provide electrical isolation between the primary windings (coils) and the secondary windings located inside transformer. Each time the voltage is raised or lowered, the amperage is affected. Basic formula: Volts x amps = watts shows that volts and amps are inversely proportional. When volts are raised, amps are lowered. Wires with 500,000 volts have low amps and low heat which is good for long-distance transmission. But the switchgear and wiring for 345,000-500,000 etc volts is too large, expensive and dangerous for use inside home and business. Using transformers, the power company changes volt-amp ratio to accomplish different objectives. The result is households and businesses receive low volt, high amp power. It works nicely because 120-240 household voltage can be safely controlled by small switches, relays, cell phone chargers etc contained within steel and plastic enclosures, while the amperage (heat) is controlled by circuit breakers and then distributed to outlets, switches, dryer etc using correctly sized wire to match amp rating of breaker. |
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Chart on left shows
Transformer kV and MVA ratings. Incoming and outgoing power lines are installed to carry specific voltage. kV is kilovolts ... each kilovolt is 1000 volts. So 230Kv power line carries 230,000 volts on the primary side, and the 300MVA transformer reduces voltage to 115kV on secondary side. Power transformers are rated by power or wattage. MVA is mega volt amps .... volts x amps x 1,000,000 Volts x amps = watts (power) So 300MVA transformer can deliver maximum 300 million watts of power. Read .pdf manual So if a 230kV power line, delivers 230,000 volts to a power transformer that produce up to 300,000,000 watts ... then divide to get approximate amp flow = 1304 amps on the power line. Power line might be 2500-3000 kcmil (1/1000 circular mil) or 2.0-2.4" diameter. 
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recommended to use more than one ampere per one square millimeter
of the aluminum (1 A / 1 mm2). kcmil = 0.5067 square millimeters. A mil is 1/1000 inch. A wire 200 mils in diameter is 40 MCM. MCM is generally used for very large-diameter wire. The reason for this is the power loss. If the resistance (dissipation) is getting higher the active power is increased significantly. This means that higher resistance increases power losses |
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Oil Type Transformers Single-phase and three-phase transformers for the range above 16 kVA and up to 72.5 kV. These units are designed for power centers, substations and networks; also for pad-mounts. They are used in public distribution systems, commercial buildings and industrial complexes. For the range 30 kVA to 30 MVA with primary operating voltages up to 41.5 kV and secondary operating voltages up to 36 kV. These units are designed for operation in difficult conditions – environmental contamination, fire hazard, high humidity or extreme climates. 161/13.8/13.8 kV, 56/28/28 MVA ∆I SinΦ (Circulating current) ∆I SinΦ (S) (circulating current principal for different KVA/MVA ratings of transformer) 220/66 kV, 50 & 100 MVA |
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