ET3480 Power Systems David Morrisson MS,MBA Week 1

ET3480

Power Systems

David Morrisson MS,MBA

Week 1

Analyze the overall function of a typical residential and commercial electrical power distribution system.Unit Learning Outcomes1. List the basic elements of an electrical power distribution system.2. List the apparatus and safety devices in a typical residential or commercial

power riser diagram.3. Label the various phase and line voltages in a typical three-phase electrical

service diagram.4. Explain the significance of the National Electrical Code (NEC) in establishing

standards for design, safe installation, and maintenance of electrical wiring, apparatus, and equipment.

5. Calculate the NEC minimum demand loads for a residential or commercial occupancy using load diversity.

6. Determine the monthly power bill using the peak power demand, power usage, and power rate schedule.

Key Concepts

1. Electrical components, apparatus, and safety devices2. Riser diagrams (residential/commercial)3. Three-phase electrical service diagrams4. Electrical planning (load demand), design documents, and

installation5. Power bill

The Power Grid

From Generation to the Home

The Basics

• Every power grid in the U.S. has a few essential components.

• These components include the following:• A source: the power plant• A transmission system• A hub: the substation• A distribution system• A user: the home or business

5

The Source: The Power Plant

• Essentially, there are only a few ways to generate AC electricity.

• For the vast majority of electricity in the U.S. a fuel (coal, natural gas, a nuclear reaction) is used to create electricity.

• In addition, solar, wind and hydroelectric methods are used to generate electricity.

6

The Heart: The Steam Turbine

• Once a fuel has created sufficient heat, steam is created.• Pressure from the steam is used to rotate the steam

turbine. • The turbine has magnets attached to the end. • These magnets rotate within coils, thus generating an AC

signal.

7

8

Electrical Generation:Coal, Natural Gas, & Diesel

Nuclear Generation

9

Transmission and Distribution

• Once produced, electricity must be distributed.• The main device used to achieve this is the transformer.• Transformers convert AC voltages.

• Step-up transformers convert from low to high voltages.• Step-down transformers convert from high to low voltages.

10


• Power plant transformers step up voltages to reach substations and are sent at approximately 550kV.

• Once at the substation, transformers are used to step down voltages to approximately 13kV.

• These 13kV voltages are sent via distribution lines to your neighborhood home or business.

• Once in the neighborhood, transformers are used (on poles or set on the ground) to step down the electrical voltage to 120/240.

11


• From the power plant, via transmission lines to the substation.

• From the substation, via distribution lines to the home.• All through the use of the transformer.

12

The Entire System

13

14

The Source: The Power Plant

• Essentially, there are only a few ways to generate AC electricity.

• For the vast majority of electricity in the U.S. a fuel (coal, natural gas, a nuclear reaction) is used to create electricity.

• In addition, solar, wind and hydroelectric methods are used to generate electricity.

15

The Heart: The Steam Turbine

• Once a fuel has created sufficient heat, steam is created.• Pressure from the steam is used to rotate the steam

turbine. • The turbine has magnets attached to the end. • These magnets rotate within coils, thus generating an AC

signal.

16

Electrical Generation:Coal, Natural Gas, & Diesel

17

Relevant Links

• http://www.earthlyissues.com/nuclearplants.htm

• http://www.southerncompany.com/learningpower/powerinfo_5.aspx

http://www.earthlyissues.com/nuclearplants.htm



http://www.southerncompany.com/learningpower/powerinfo_5.aspx



18

Nuclear Generation

ELECTRICAL COMPONENTS

SMALL COMPONENTS

Circuit Protection

Circuit Protection

Types of Fused Protection

How to pull them

Fuses

•Auto-fuse (blade type and Color coded)

•Mini-fuse •Maxi-fuse

A. TEST HOLESB. REMOVAL

Maxi-fuses•Combination blade / cartridge•Protects main circuits•Safer than fusible link•Cover fewer circuits than a fusible link

•Often in Power Distribution box

Ceramic and Glass

• Rated by current failure level• Three letter code for type and size• Glass style replaces ceramic• Caution in pulling

Two reasons for blowing

Where do they blow?

New Circuits

• What size of fuse should I install?

• Use Watts law. Watts divided by volts

?

FUSIBLE LINKS

• Lighter gauge wire than main conductor

• Covered with special insulation• Protect Main circuits• Usually under hood

Fusible Links Repair• Location

• Circuits protected• Insulation

• Visual checks • Installing a new link

• 4 wire sizes smaller (4 numbers larger)

• Soldering

Fuses

Male Pal fuses Female Pal fuses Bolt on Pal Fuses

Circuit Breaker

•Why circuit breakers•Styles•Deterioration

TESTING CIRCUIT PROTECTION DEVICES

• Must inspect closely• Type of failure determines cause• Best to use DVOM• Do not overload circuit by installing to large of fuse or tin foil• Connections must be tight• Do not use un-fused jumper wire

Electrical Components

Switches

• Controls electrical current (N.O. or N.C.)• Single-pole, single throw (SPST)• Momentary Switch• Single-pole, double throw switch (SPDT)• Ganged Switch

Relays

• Electromagnetic Switches (Relays)

• Two Circuits• Control Circuit• Load Circuit

• Magnetic field operates contacts

• Late model relays are universal

TESTING RELAYS

• Can use several methods to test• Must Check both circuits• Be careful using test light if relay is operated by computer• Can bench test if needed• Some relays have schematic on them• Must be correct resistance

SOLENOIDS

• Electromagnetic device with a iron core

• Does mechanical work• Core is moveable and does work• Can test with DVOM

• Usually used to control fan motor speeds

• Resistance is changed by control of switch

• Controls current to change speeds• Thermal fuse

STEPPED RESISTORS

Variable Resistors

• Rheostats• Two terminals• Higher current

• Potentiometer• Three terminals• Lower current

• Many uses for variable types

The three types of circuit defects are:

•Shorts•Grounds•Opens

• poor connections

TESTING FOR CIRCUIT DEFECTS

• DVOM IS BEST TO USE!• Must know circuit operation before can diagnose problem• Must know how to use equipment and which equipment to

use.

See the file: Industrial Electrical

Three-Phase Advantages1. The horsepower rating of three-phase motors and the kVA rating of three-

phase transformers are 150% greater than single-phase motors or transformers of similar frame size.

2. The power delivered by a single-phase system pulsates and falls to zero. The three-phase power never falls to zero. The power delivered to the load in a three-phase system is the same at any instant. This produces superior operating characteristics for three-phase motors.

3. A three-phase system needs three conductors; however, each conductor is only 75% the size of the equivalent kVA rated single-phase conductors.

Three-Phase Circuits


Three-phase power never falls to zero.


Three-phase voltages with 120 degrees of phase shift.


Basic Properties• Three-phase systems have either three or four conductors.• There are three-phase conductors identified as A, B, and C.• The three phases are 120 degrees out of phase with each

other (360 divided by 3).• There is sometimes a fourth conductor, which is the neutral.

Wye Connections• The wye, or star, connection is made by connecting

one end of each of the phase windings together in a common node.

• Each phase winding has a voltage drop known as the phase voltage.

• The line voltage is measured from phase conductor to a different phase conductor.


Wye Connections• In a wye system, the line voltage is higher than the

phase voltage by a factor of the square root of 3 (1.732).

• ELine = EPhase x 1.732• EPhase = ELine / 1.732


Wye Connections• In a wye system, the line current is equal to

the phase current.• ILine = IPhase


Line and phase voltages in a wye connection.


Line and phase currents in a wye connection.


Vector sum of typical wye system voltages.


Delta Connections• In a delta system, the line current is higher than the

phase current by a factor of the square root of 3 (1.732).

• ILine = IPhase x 1.732• IPhase = ILine / 1.732


Delta Connections• In a delta system, the line current is equal to the

phase current.• ELine = EPhase


Delta system voltage and current relationships.


Delta system division of currents.


Three-Phase Power• Three-phase power can be computed in

two ways, using line values or phase values.

• VA = 3 x ELine x ILine

• VA = 3 x EPhase x IPhase

• Note that this is the same on wye or delta systems.


Three-Phase Power• Computing watts requires using the power factor

(PF).• P = 3 x ELine x ILine x PF• P = 3 x EPhase x IPhase x PF• Note that this is the same on wye or delta systems.


Example #1 given values.








Review:

1. The voltages of a three-phase system are 120° out of phase with each other.

2. The two types of three-phase connections are wye and delta.

3. Wye connections are characterized by the fact that one terminal of each of the devices is connected together.


Review:

4. In a wye connection, the phase voltage is less than the line voltage by a factor of 1.732. The phase current and the line current are the same.

5. In a delta connection, the phase voltage is the same as the line voltage. The phase current is less than the line current by a factor of 1.732.


Documents

ET3480 Power Systems David Morrisson MS,MBA Week 1