125-130 Distribution Lines and Electrical Grid System

Flashcards covering primary, secondary, and service distribution line components, underground loop design, customer classifications, voltage designations, and overhead versus underground installation costs.

What are the three main elements of a distribution line?

The three main elements of a distribution line are Primary, Secondary, and Services.

How is the Primary portion of a distribution line characterized?

The primary is the high voltage portion of a distribution line.

What is the voltage range and physical routing of Secondary distribution lines?

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

What is the physical routing of Services in overhead and underground systems?

Services are low voltage lines that 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 loop design is an underground layout serving many or commercial customers where each transformer can be served from two directions.

What advantages does an underground loop feed circuit provide over a radial circuit?

It improves reliability for the customer, gives the power company more switching options, and allows any section of cable or transformer to be taken out of service without affecting adjacent customers.

What three factors determine the number of customers on a single electrical circuit?

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

What are the four classifications utilities typically use for customers?

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

How can customer counts on a circuit vary depending on customer type?

A single circuit might serve just $1$ industrial customer while another circuit might serve $5,000$ residential customers.

How are distribution system voltage levels normally designated?

Distribution voltage levels are normally referred to by two numbers: a phase to ground (phase to neutral) voltage and a phase-to-phase voltage.

Why is transmission system voltage referred to by only one number instead of two?

Because there is no neutral on the transmission system, so only one phase-to-phase voltage is used.

In a dual-number distribution voltage designation (such as $2,400/4,160$), what does the smaller number indicate?

The smaller number is always the voltage from phase to neutral.

What are the five 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 $19,900/34,500$.

What acceptable voltage range are utilities obligated to deliver at the meter?

Utilities are obligated to provide voltage at the meter in an acceptable range of $114\text{ to }126\text{ volts}$ so customer equipment runs efficiently and is not damaged.

Where can automatic voltage regulation take place in a distribution system?

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

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

Underground systems remain approximately four times ($4\times$) more expensive than overhead construction per mile of line.

What are three reasons utilities install circuits underground despite higher costs?

City ordinances requiring new lines to be underground, joint installation with other utilities in residential subdivisions, and installation in areas with extreme weather.