EGRID CH 9 distribution

What is the primary function of a distribution system?

To receive electric power from the transmission system and deliver it to customers at usable voltage levels.

How long are distribution lines typically?

Distribution lines are typically not longer than 50 miles.

How far apart are distribution structures on average?

About 300 feet apart

What are two main distribution circuit types?

Overhead and underground construction.

What are common distribution pole materials?

Wood, fiberglass, and steel. Wood poles remain the most popular choice.

What is the typical height range of most distribution poles?

35 to 55 feet.

What is the purpose of an insulator?

The chapter identifies insulators as distribution-line components. Post insulators provide more contact area and are used with larger conductors. Polymer insulators are commonly used at dead-end structures.

Where are the largest distribution conductors used?

On main lines, which begin at the substation.

Where are smaller distribution conductors usually used?

On tap lines, which generally serve fewer customers.

What is the purpose of a pole-mounted distribution transformer?

To reduce voltage to a level that customers can use.

What are the four main types of distribution protective equipment?

Fused cutout switches, reclosers, sectionalizers, and lightning arresters.

What does a fused cutout switch protect?

It protects equipment such as transformers and protects the main line from faults on a tap line.

What happens when a cutout fuse operates?

The fuse burns, and the fuse holder automatically falls open, helping lineworkers locate the fault.

What is the purpose of a recloser?

A recloser can close the line again after a temporary fault, reducing outage time.

How many times can a recloser reclose to determine whether a fault is temporary or permanent?

Up to four times.

What is the purpose of a sectionalizer?

It clears a faulted section of line. It opens while the line is de-energized by a recloser when a permanent fault occurs.

What does a lightning arrester do?

It diverts a lightning surge to ground to protect lines and equipment.

How is a lightning arrester connected?

One end is connected to the phase, and the other end is connected to ground.

What is the purpose of a voltage regulator?

It automatically adjusts voltage up or down to keep voltage within acceptable limits.

By how much can the regulator described in the chapter adjust input voltage?

It can increase or decrease input voltage by 10%.

What is the purpose of a capacitor on a distribution line?

It improves circuit efficiency by introducing capacitive reactance that counteracts the negative effects of inductive reactance.

What is a gang-operated switch used for?

It redirects power or sectionalizes part of a line. It can open all three phases at the same time during regular line load.

What limitation applies to gang-operated switches?

Their ability to break all three phases at once applies to regular line load, not fault currents.

What are the two classifications of underground equipment?

Above-ground or padmounted equipment, and below-grade or subsurface equipment.

What is one advantage and one disadvantage of underground distribution?

It is less affected by high winds, ice, and trees, but it is costly to install and maintain.

What type of conduit is most commonly used for underground installations?

PVC conduit

What are manholes used for?

Larger concrete manholes are typically installed in cities to house heavy cables and equipment.

What are pedestals used for?

Pedestals are above ground and are used to splice low-voltage secondary and service conductors.

What is a riser?

A pole where an overhead circuit transitions to an underground circuit, or an underground circuit transitions to an overhead circuit.

What is a radial circuit design?

Independent circuits radiate into the service area. If a permanent fault occurs, power cannot be restored from another source.

What is a radial-tie circuit design?

Circuits are connected at one or more points so power can be supplied from another circuit when needed.

What is a network grid design?

Circuits and step-down transformers are connected to form a low-voltage grid network.

Where is a network grid design typically used?

In larger cities with high-rise buildings.

What voltage systems are identified for the network grid design?

Three-phase 120/208-volt or 277/480-volt low-voltage networks.

Which distribution design is the most reliable and most expensive?

The network grid design.

How many conductors do almost all distribution circuits have?

Four: three phase conductors and one neutral conductor.

What is the primary portion of a distribution line?

The high-voltage portion.

What is the secondary portion of a distribution line?

The low-voltage portion running from pole to pole on overhead systems, or from padmount to pedestal in underground systems.

What are services?

The low-voltage portion running from the pole to the customer on overhead systems, or from the pedestal to the customer on underground systems.

What legal agreement is commonly used when a utility installs facilities in a city or county?

A franchise agreement.