Chapter 9 Flashcards
Distribution
How can the Distribution System be visualized?
A series of local “streets”
How is the Distribution System different from the Transmission?
The direct delivery of power is more localized.
Distribution lines are not typically longer than __ miles
50
How are Distribution lines recognized?
Shorter poles located more closer together with more equipment mounted on the poles.
What kind of lines do Distribution lines typically have?
Aluminum Conductors
On average, about how far apart are Distribution structures?
300’
What is the primary function of the Distribution System?
To receive electric power from the Transmission System and distribute it to customers at voltage levels that can be utilized by various types of customers.
How must the power be delivered?
Safely with acceptable quality and reliability.
How must the Distribution System equipment work?
It must allow the amount of electrical energy consumed by customer to be accurately measured, so the serving utilities can bill the customers.
What’s another function of the Distribution System?
Deliver power with a minimum of loss.
What is the Dist. System almost entirely, AC or DC?
AC
Why might DC be used in a Dist. System?
In larger cities, for special applications such as elevators in high-rise structures.
Where does the Dist. System start?
At the substation with individual circuits leaving the station and going out in the service area to deliver power to the customers.
What is the Dist. System similar to?
A House
How s the Dist. System similar to a house?
Where there is a main panel with several circuits delivering power to various rooms. Each circuit has its own breaker, and come circuits deliver more power than others
What is an energized wire referred to as?
A Phase
How is a main line Dist. circuit composed?
- 3 Phases, 1 Neutral
- 3 Phases
What do circuits in a Dist. System consist of?
Main Lines and Tap Lines
What are Main Lines also referred to?
Feeder Mains
Properties of Main Lines?
- Always Three Phase
- Start at the station and radiate to the end of the line or tie to another circuit.
- Main route used to supply power to the Tap Lines and customer along he main lines
- Larger conductors than Tap Lines
How are Main Lines and Tap Lines easily distinguished?
By conductor size and destination
What is the majority circuit type?
4 Wire (Three-Phase & a Neutral) Also called WYE
What is common for the WYE System?
- For both single and 3-Phase lines to be tapped off the main line
- To tap two phases and the neutral to serve light three phase loads (Sometimes referred to as “V” Phase Cons.
What are three wire circuits with no neutral conductor called?
WYE or DELTA
On DELTA circuits what is required of the transformer?
Single-Phase Transformers require two phases for the proper connection.
What are the 3 main elements of a Dist. Line?
- ) Primary - High Voltage
- ) Secondary - Low Voltage (Pole to Pole)
- ) Services - Low Voltage (Pole to Customer)
How are Underground Systems usually designed?
So each transformer can be served from two directions
Why use the Loop Design?
It improves the reliability and makes it more convenient for line crews to work on the systems.
How is the number of customers on a circuit determined?
- Density of the Area
- Type of Customer
- Capability of the Circuit
How are customers typically classified?
- Residential
- Commercial
- Agricultural
- Industrial
Give me a circuit comparison
One industrial customer or 5,000 Residential Customers
What is circuit voltage level typically based on?
Existing System Voltages
Voltage levels are normally ______ on longer circuits.
Higher
What are the two numbers usually referred on a Dist Line?
- Phase to Ground
- Phase to Phase
What are the most common voltage levels in the US?
- 7,200/12,470
- 7,620/13,200
- 12,000/20,800
- 14,400/24,940
- 19,900/34,500
What are utilities obligated to provide?
Voltage at the meter in an acceptable range (114-126) so customer equipment will run efficiently and not be damaged.
How may the voltage be regulated?
Automatically at the substation o somewhere on the Dist. circuit.
How may some circuit be installed?
Entirely overhead or underground; However, most circuits have both types of construction.
How many more times expensive is underground than overhead?
4x
What new passed ordinances have many cities required?
All new lines to be underground.
How are almost all residential subdivisions installed?
Underground jointly with other utilities
Why else may a utility install underground rather than overhead?
In areas with extreme weather
Where are overhead lines particularly installed?
Rural Areas
What is one common project in overhead construction?
To upgrade or increase the capability of a line so more power can be delivered to the customers.
What similar components do all Dist. Line share?
- Poles
- Supporting Brackets/Crossarms
- Insulators
- Primary Conductors
- Transformers
- Protective Equipment
- Capacitors
- Gang-Operated Switches
Most popular style pole in Dist. Lines?
Wood
What styles poles are used where the long-term benefits outweigh their higher initial cost?
Fiberglass and Steel
Why are Fiberglass and Steel poles used?
When the long-term benefits outweigh their higher initial cost.
What is the standard height of Dist. Poles?
35-55’
What style crossarms remain popular?
Wood Crossarm
What style crossarms are gaining popularity?
Fiberglass
What are other supporting brackets made of?
- Steel
- Fiberglass
- Aluminum
Why are these brackets used?
To mount transformers, cutouts, riser terminations, lightning arresters and insulators.
What are Insulators on a Dist. System made of?
Porcelain or Polymer
Difference between Post and Pin Insulators?
Post Insulators offer more contact area at the point of attachment than pin insulators and are used with larger conductors.
Where are Polymer insulators mot commonly found?
Dead End Conductors
How is the size an type of conductor chosen on a Dist.?
- How much power
- Length of the Line
- Span Lengths
- Weather Environment
- Line Losses
- Cost of the Conductor
What happened on Dist. Lines because of the need to deliver larger amounts of power and reduce line losses?
Conductor sizes have increased over the years.
As the number of customers decreases down the line what happens to the conductors?
Smaller Conductors will be used.
Where are smaller conductors usually found?
On tap lines because they usually serve a limited number of customers
What does the pole-mounted Dist. Transformer do?
It is the key element used to reduce a voltage level that can be used by customers.
What is the ultimate destination of nearly all power lines?
Transformer or Transformer Bank
Which unit is the most popular?
Single-Phase Unit
Why is the single-phase unit most popular?
It can be used to provide single-phase and three-phase service when two or three units are connected in a bank.
What is does the Protective Equipment consist of?
- Fused Cutout Switches
- Reclosers
- Sectionalizers
- Lightning Arresters
- Voltage Regulators
Why is Protective Equipment necessary?
- Service Reliability is EXTREMELY important to Customers
- Commercial and Industrial Customers and experience significant monetary losses when the power goes out
What is the Protective Equipment designed to do?
To distinguish temporary faults from permanent faults.
How are Dist. Systems designed with Protective Equipment?
So that when an outage occurs, as few customer as possible are affected, and outage time to those affected customers is minimized.
Why are Fused Cutout Switches installed?
To protect equipment such as transformers and to protect the main line from fault that occur on a tap line..
How does a Cutout Switch work?
They have a fuse holder, which houses the fuse. When a fault occurs the fuse burns and the fuse holder automatically falls open. Allowing lineman to quickly locate the fault.
How do Reclosers work?
They “Reclose” after a temporary fault, which minimizes outage time. They have the ability to reclose up to 4x to determine if a fault is permanent or temporary. Typically coordinated with fuses or sectionalizers.
What kind of device is a Recloser?
In-Line Device meaning that current must pass through it.
Why are Sectionalizers installed?
To clear faulted sections from the line, and are coordinated with a Recloser.
How does a Sectionalizer work?
It Sectionalizes the line if a permanent fault occurs. The Sectionalizer opens during a monetary period when the line has been de-energized by the recloser.
What are Sectionalizers similar in appearance to?
Reclosers
What is one of the main causes of damage to Dist. Lines?
Lightning
What is installed to protect Dist. lines from lightning?
Arresters take the lightning surge and divert it to the ground.
Where are Arresters commonly found?
Transformer Poles, Riser Poles and other Poles with equipment mounted on them.
How are Arresters installed?
One end is connected to the phase and the other end to ground.
What is installed to automatically control voltage on the line?
Voltage Regulators
Different Installations?
Single-Phase or Three-Phase
How is the desired voltage set?
In a control box connected to the regulator unit. Once set, can increase or decrease the input voltage by 10%
Why are Capacitors used?
To improve the efficiency of the circuit.
What do Capacitors do?
They reduce the flow of power that doesn’t perform any useful function.
What happens when transformers and customer-owned motors are installed on a system, and how would a Capacitor work with it?
They introduce inductive reactance, which reduces the amount of power that can be delivered to customers, and the Capacitors introduce Capacitive reactance which counteracts the negative effects of inductive reactance.
How can Capacitors be controlled
Manually or Automatic
How are Gang-Operated Switches used?
They are strategically placed throughout the main line to redirect power or to sectionalize a portion of a line.
What is the advantage of Gang-Operated Switches?
They break load and all three phases open at the same time.
Why would you want all three phases to open at the same time?
It prevents damage to customer’s Three-Phase Equipment.
What most distinguishes Gang-Operated Switches?
The Operating Handle that extends to the ground.
What has became the most popular and reliable way of installing a Dist. Line?
Underground
Why is Underground most popular?
The public prefers the elimination of poles and wires from sight.
What is a benefit of running Underground?
Underground is immune to high winds, ice, trees etc.
How is Underground Equipment commonly classified?
- Above ground or padmounted equipment
- Below grade or subsurface equipment
Differences between above or below ground?
- Public prefers below for its appearance.
- Padmounted is visible and much easier to maintain and operate
Which do utilities usually install?
Both
What did the first underground lines use?
Paper Insulated Lead Cables
How are cables typically made today?
Polyethylene type insulation and are much easier to splice and terminate.
How are larger cables made?
Stranded aluminum or copper
How are smaller cables made?
Stranded or solid
How are most underground installations?
PVC Conduit, Some install cables directly underground.
Where might Steel Conduit be installed?
Certain main feeders in locations like substations or areas where the protection is warranted.
What is Cable in Conduit?
This product is made by extruding a continuous one-piece conduit over the cable. This increases the efficiency of the installation.
What does the term Enclosure mean?
To broadly classify various types of concrete, fiberglass or composite-type housings, which are used to splice cables, terminate cables and house equipment such as switches and transformers.
What is a Manhole?
Larger concrete structure which is typically installed in larger cities to house heavy cables and equipment.
What is a pedestal?
They are above ground and are used to splice low voltage secondary and service conductors.
How are Transformers usually classified?
Padmount or Subsurface
What is common to see in Overhead Construction?
Three Single-Phase Transformers in a Bank to provide Three-Phase Service.
How are Transformers installed in Underground Construction?
A Single Three-Phase Unit
How are Padmounted Transformers installed?
Pad of ether concrete or Polyurethane.
How are Subsurface Transformers installed?
In an Enclosure or a Manhole
How are Switches an Fuses similar to Transformers?
They can be either Padmounted or Subsurface.
Why is it poplar to have a combination of fuses and switches?
It increases the reliability of the circuit
What is a Riser?
Term used to identify a pole where there is a transition from an overhead circuit to an underground circuit or viceversa.
What is common for riser poles to have?
Switches to open the circuit or fuses to protect the line. Also common for riser poles to have lightning arresters.
What is one of the first considerations when building a Dist. Line?
Route of the Line associated with terrain, existing developments etc.
What must a utility obtain to construct a Dist. Line?
Legal Rights
What is done when the utility is serving a city or county?
The typical arrangement to install facilities is a franchise agreement.
What needs to be secured for Dist. Lines on Private Property?
Some form of an Easement from the landowner.
What can Telecom do to poles?
They have the rights to power company’s poles; however, they are required to provide some form of compensation.
How must pole lines be designed?
For the proper strength and clearance of all utilities, as required by the National Electric Safety Code
What is the NESC?
National Electric Safety Code
What are the 3 Dist, Circuit designs?
- ) Radial
- ) Radial Tie
- ) Network Grid Design
Properties of a Radial Design?
- Circuits are independent and radiate into the service area.
- If a permanent fault occurs, there is no opportunity to restore power from another source.
- Transformers are installed individually to supply power to customers at desired voltages.
- Least reliable design.
Properties of a Radial Tie?
- Circuits can be connected automatically or manually at one or more points.
- In case of trouble or need to take a line section out of service, the ability to supply power from other circuits is a significant advantage.
Properties of a Network Grid Design?
- Circuits connected
- Step-Down Transformers connected to form a low voltage grid network
- If one transformer fails it is automatically disconnected and does’t affect service
- Extremely Reliable
- Typically found in larger cities with high-rise buildings
