Pg 125-130 Electrical Distribution Systems and Grid Fundamentals

Flashcards reviewing distribution line components, underground loop design, customer classifications, voltage designations, and overhead versus underground construction.

What are the three main elements that comprise an electrical distribution line?

The three main elements are Primary, Secondary, and Services.

How is the primary element of a distribution line characterized?

The primary is the high voltage portion of a distribution line, such as $12,470/7,200\,\text{Volts}$.

What is the secondary element of a distribution line, and where does it run?

The secondary is low voltage ($120\text{-}480\,\text{volts}$) and runs from pole to pole on overhead systems or padmount to pedestal in underground systems.

Where do service lines run in overhead and underground systems?

Services run from pole to customer on overhead systems or pedestal to customer in underground systems.

What is a loop design in underground distribution systems?

A design where each transformer can be served from two directions, improving reliability and providing more switching options compared to a radial circuit.

How does a loop feed benefit maintenance on underground systems?

It allows any section of cable or transformer to be taken out of service without affecting adjacent customers.

What factors determine the number of customers on a distribution circuit?

The population density of the area, the type of customers, and the capability (or capacity) of the circuit.

What four classifications do utilities typically use for customers?

Residential (customer dwellings), Commercial (stores, shopping centers, medical facilities), Agricultural (irrigation pumps, grain storage, dairies), and Industrial (large manufacturing plants, refineries).

Which customer classifications make up the bulk of a utility's customer base?

Residential and commercial customers.

How are distribution system voltages designated compared to transmission system voltages?

Distribution system voltages are normally designated by two numbers (a phase-to-ground/neutral voltage and a phase-to-phase voltage), whereas transmission uses one phase-to-phase voltage because it has no neutral.

In a dual-number voltage designation such as 7,200/12,470, what does the smaller number represent?

The smaller number is the voltage from phase to neutral.

What are the most common distribution voltage levels in the United States?

The most common levels are $7,200/12,470$, $7,620/13,200$, $12,000/20,800$, $14,400/24,940$, and $19,900/34,500$.

Within what voltage range are utilities obligated to deliver power at the customer meter?

Utilities are obligated to provide voltage at the meter in an acceptable range of $114$ to $126\,\text{volts}$.

Where can voltage be regulated automatically on a distribution system?

Voltage may be regulated automatically at the substation or somewhere on the distribution circuit.

How does the cost of underground construction compare to overhead construction per mile of line?

Underground systems remain approximately four times more expensive than overhead construction per mile of line.

What are common reasons for choosing underground line construction despite higher costs?

Customer preference (they cannot be seen), city ordinances requiring new lines to be underground, joint installation in residential subdivisions, and protection in areas with extreme weather.