Transmission  vs Subtransmission  vs Distribution   Image of grid
There are 3 categories of power lines on the grid: Transmission and Subtransmission, which make up the bulk power system, and local Distribution
Read more about the grid

1) 'Transmission-level voltages are usually considered to be 110 kV (110,000 volt) and above.'
Typical transmission lines are 775-500-270 kV, and are attached to steel lattice towers, steel and concrete poles, and are suspended highest off the ground to prevent arcing.
EHV or extra high voltage, is roughly defined as 345,000– 765,000 Volts.
UHV or ultra high voltage is > 800,000 volts.
HVDC or high voltage DC 100,000+ VDC is 'more efficient for long distance transmission over 300 miles' because lower line loss, but requires costly converter stations to change DC (direct current) into AC (alternating current). Image

2) Lower voltages from 110 kV to 33 kV are usually considered sub-transmission voltages.'
Subtransmission lines might be 69,000 Volts (110-69-33 kV), and travel from substation to local substation and are located higher off the ground than local distribution lines.
Transmission and subtransmission make up the bulk power system.

3) 'Voltages less than 33 kV are usually used for distribution.'
Distribution lines travel from local substation to each home and business, and are much lower to the ground and carry less dangerous 12000+ volt, measured between hot wire to hot wire ... and 7200 volts (7.2 Kv) measured between hot wire to ground.

Voltage classes on Distribution line
Typical 'distribution voltage classes can be 5 kV, 15 kV, 25 kV, and 35 kV,' which means distribution voltages vary by need in the area they serve.
Voltages are determined at local substation transformer and vary depending on local demand, distances etc.

Distance of local distribution lines can be up to 20 miles long. Distances can be longer in remote areas with few customers.
Longer than 20 miles and another substation is installed, so grid does not suffer voltage drop.
Substations receive power from transmission and subtransmission lines, then reduce voltage before distributing power to local area..
There are generally 3 categories for distribution: Radial, Loop, & Network. (not discussed further).

Measuring voltages on power line
Voltages are measured across lines on the power pole. For example, 12000+ (12Kv) volt is measured from hot wire to hot wire, and called LINE voltage... while 7200 volts (7.2 Kv) is measured from Hot wire to Neutral, and called PHASE voltage. Phase voltage on 3-phase grid is equal to Line voltage divided by square root 3.
Read more

Why transformers are safe
Transformers used on the grid use magnetic induction to raise and lower voltage. This is called an isolation type transformer where higher voltage wires never come in contact with lower voltage wires.
Using magnetic induction guarantees that lower voltage lines cannot be energized with the higher voltage, and guarantees safe and usable low volt, high amp electricity is supplied to household.
Read more

Isolating the higher and lower voltages using an isolation transformer guarantees that high voltage wires can never come into contact with household wires, and so extremely dangerous 4,500-7,200 volt distribution power will never occur inside household wiring.

It works nicely because household 120-240 volt single-phase can be safely controlled by small switches, relays, cell phone chargers etc contained within steel and plastic enclosures, while the amperage (and heat it causes) is controlled by circuit breakers (overcurrent protection) and then distributed to outlets, switches, clothes dryer etc using correctly sized wire to match amp rating of breaker.