Electricity

High voltage?

- Can cause arcing through the air which restricts use of high voltages to utilities in industrial applications and electrical services buildings

Specific result of having harmonic distortions?

- Causes the load to heat up creating high voltages and currents that could potentially short circuit the system.

Basic concept of a current transformer?

- Convert large primary currents into smaller secondary currents and therefore must be voltage step up transformers

What is a prime factor in determining the selection of voltage?

- Degree of access to equipment - High voltage must be locked

Transfer switches?

- Double throw, multiple pole devices - May be manual or automatic - Used to select alternate circuits

Describe what the magnetic lines of flux do when AC current passes through a conductor.

- Field sets up around the conductor - Field alternates with the current, building up in one direction then collapsing into the conductor and building up in the opposite direction

Terminal/Connection diagrams?

- Illustrate locations and markings of each terminal and the interconnection required.

Risers Diagrams?

- Indicates the distribution of electrical systems in a multi storied structure by means of single lines and simplified symbols

Rules for high voltage lines?

- Lines must be interconnected and grounded - Disconnect switches must be locked open before maintenance

Location of these 2 things are important if the system or portions of the system have to be shut off at any time.

- Load center - Motor control center

The division of supply through multiple feeders is done on the basis of?

- Locale - Load type - Emergency supply

How often should a transformer be inspected?

- Once or twice a year (low maintenance) - Check for loose or hot connections

Important area of responsibility in relation to electrical distribution circuits?

- Operating equipment - Deciding what maintenance should be done - Isolating equipment for maintenance - First response to fire or accident

Concept of an Auto Transformer?

- Part of its windings common to both the primary and the secondary

Connection/wiring Diagram?

- Physical arrangement of components including all wiring and connections

Core Type transformer?

- Primary and secondary windings are split into two equal parts with one half of each wound on each of the 2 legs of the transformer.

Benefits/Disadvantages of Auto transformers?

- Reduced amount of copper - Limited to small ratios of transformation due to an open circuit in part of the primary and secondary windings.

Through normal load conditions, how does the flux of a transformer virtually remain constant?

- Secondary current flows produce a magnetic flux which opposes and reduces primary flux - Secondary flux reduces the self-inductance in the primary allowing more primary current to flow, which brings the main flux back to its original value

Voltage ranges can vary how much due to load variances?

5%

If the consumer owns the supply transformer and high voltage is brought into the building, how much of a reduced rate will they get?

5% - 10% lower

Schematic (elementary) Diagrams?

- Shows function, sequence and electrical relationships through graphical symbols of a specific circuit - Does not portray any relation to size positioning, shape or location of component devices, parts or terminals.

What are Eddy Currents?

- Small currents induced in the core material by the alternating flux - Generate heat and waste energy - Can be reduced by laminating the core

Examples of certain specifications that could be conveyed in a building?

- Special circuitry - Equipment quality - Manufacturer - Aesthetics - Coding systems - Terminal markings

Other than forced cooling, what else is done to improve the kVa rating of a transformer?

- Submerse the core in an oil which has a much higher specific heat than air

Dangers of Current Transformers?

- The secondary is permanently short circuited by a 5 A ammeter - If secondary is open circuited, voltage across the primary will suddenly increase producing a much higher voltage * Secondaries of current transformers should never be opened in active circuits *

In a three phase system, what device could replace a three phase transformer?

- A bank of single phase transformers - Single phase banks are more expensive and less efficient than 3 phase transformers, but provide a certain convenience

What is ' Self Inductance ' ?

- An opposing voltage which combines with the resistance of the coil to give a total resistance

Extra Low Voltage?

- Below 30 V - Low voltage extremely susceptible to voltage drop (load must be in close proximity to the source) - Not suitable nor economical for power loads of any size

One line diagrams?

- Best for illustrating supply and distribution systems - Each line represents all conductors of a circuit - Portrayed by symbols in sequence on a line - Does not show connections, exact circuitry or complex control circuits

Locale?

Equipment in close proximity is often connected to one feeder to reduce installation costs

What benefit do voltage and current transformers have on Voltmeters and Ammeters?

Lets them be standardized to 125 V and 5 Amps

Load type?

Loads of similar operation and voltage sensitivity are grouped.

Transformers which are used to reduce the hazards of high voltages to allow measurement of these high voltage circuits are called?

Instrument transformers

What is Electro-magnetic Induction?

As long as there is movement between a conductor and a magnetic field, an induced voltage is created.

What is meant by "pancake" or "sandwich" windings?

The High voltage windings cover the low voltage windings in a three phase transformer.

Range of branch circuit amperage?

May range from 10A to several hundred amps

" EpIp = EsIs " - What does this equation determine?

This means that the primary and secondary power factors are pretty much the same (losses are negligible)

Three phase transformers are similar to single phase transformers except that windings are wound on each of three legs. True or False?

True

High voltage is not often used as a utilization voltage. True or False?

True, with the exception of large pumps or compressors.

What is more popular... Having services of different voltages, or supply service at a higher voltage and use transformers to drop the voltages?

Use transformers to drop the voltages.

Two units of transformers?

VA and kVA

Riser Feeders?

Vertical feeder ducts.

Magnetic Hysteresis?

- When magnetic domains are forced to re-align - If Current flow reverses, it must build up to some level before the residual magnetism drops to zero and the energy to cancel this magnetism gets lost - Materials like silicon steel have a low retentivity to reduce this loss

Approximately how thick are the laminations that make up the Field Poles?

1 mm thick.

What are 2 ways Iron and Steel can effectively become magnetized?

1) Rubbing the metal with a magnet 2) Inserting an iron or steel bar inside a current-carrying coil.

Two main sections of a DC Generator?

1) Stator: The Stationary part 2) Rotor: The Rotating part

________ _______ to the circuits of AC power systems that demand the use of what special type of transformer?

- Harmonic Distortions - K type transformers (trap harmonics on the PRIMARY windings)

What is the result of Overcorrection beyond Unity Power Factor?

- High voltage - Poor Voltage regulation - Increased Line current

What are 3 things that factor in when considering strength of magnetic flux around an Electromagnet?

- The amount of current travelling through the coil - The number of turns in the coil - The Permeability of the core

What does a Commutator consist of?

- The commutator itself is usually made of copper and divided into segments - Each segment is divided by an insulating material which is usually Mica.

What is meant by a transformer "breathing"?

- The constant heating and cooling of the transformer causes it to conceive and expel air which can lead to the device being covered in sludge and acidity (cause of many failures)

What is Direct Current Flow?

- The flow of electrons from a Negative terminal to a Positive terminal (electron flow) in one continuous direct.

What is Lenz's Law?

- The law of electro magnetic induction - " When a magnetic flux changes and by its change is responsible for inducing a voltage, the direction of the voltage is such that it tends to oppose the action producing a flux change. "

How do Interpoles Work?

- They are smaller, auxiliary magnetic poles that offset the effect of armature reaction - They are placed half way between the main poles and wounded so there polarity is the same as the next main pole in the direction of rotation.

Why is a Voltmeter designed to offer a high resistance to current flow?

- To measure full scale Voltage there must be a small amount of current permitted through the device - A high resistance prevents a current drain which would affect the measurement of the Voltage.

Waterproof Motors?

- Totally enclosed housing - A check valve or drain is installed for draining purposes - Used in applications such as cooling tower fans.

Clamp-On Ammeters?

- Use a basic Current transformer Principle - The intensity of the magnetic flux is proportional to the current flow through the conductor - A coil is installed inside the Ammeter

What is the name for the total lines of force in a magnetic field?

The magnetic flux

What reduces the production of Eddy Currents in the armature core?

The multiple laminations that make up the armature core.

What determines the type of Compound-Wound Generator?

The number of Series fields VS Shunt Fields in the generator will determine the type.

The best diagram for showing supply and distribution of a system is...

The one line diagram.

What is Wattless (reactive) Power?

The power that surges back and forth in an AC circuit and lags behind the Voltage.

What happens if one of three single phase transformers blows within the bank?

The remaining two will supply three phase loads at 58% normal capacity allowing for the damaged transformer to be changed.

What determines the characteristics and type of a particular generator?

The specific winding construction.

2 distinct sections of the service?

The supply service and the consumers service

To actually measure the Power used by the load, what is measured in the kWh meter?

The torque produced on the revolving disk.

What determines the magnitude of flux in a magnet?

The total number of lines of force within the magnetic field of that object.

Types of Insulation for motor housings are divided into classes to specify what?

There ability to withstand high operating temperatures. (which is the most important factor when choosing an Insulation)

What is a unique characteristic of the energy dials on a kWh meter?

There may be 4-5 energy dials but they are organized so they alternate according to which way their dials turn. (clockwise, counter-clockwise)

What is said about Atoms that have GREATER THAN 3 electrons in their Outermost Shell?

They are not good conductors and are referred to as Insulators. Atoms with electrons in the range between 1-3 in their outer shell are said to be 'Semiconductors'.

What is said about Atoms that have only 1 electron in their Outermost shell? (copper and silver)

They are said to be good conductors of electricity.

What are kWh Meters used for?

They are used to register the amount of Power used in a period of time.

One advantage of Auto-Transformers?

They can use less copper

What does the term 'Self Excited" mean?

This means part of current thats generated is supplied as an exciting current to the windings.

Assigned numbers are designated to Motors to serve what purpose?

To display a specific set of External dimensions. * Frame Numbers are not used to indicate electrical characteristics *

Why is the Mica insulation between the segments of the commutator machined out about 0.8 mm's?

To ensure that the mica insulation does not interfere with the brush contact on the commutator segments.

What is the purpose of dipping the poles in varnish after the windings have been put on?

To increase the Insulation value.

Why is Insulation Testing done?

To test for electrical leakage which would indicate a fault. ex) A motor will water inside of it.

A conductors resistance is Inversely proportional to its cross-sectional area. True or False?

True

A DC generator will run as a DC motor when connected as a DC motor. True or False?

True.

A DC motor will generate electricity when connected as a generator. True or False?

True.

A conductors resistance is INVERSELY proportional to its cross sectional area. True or False?

True.

A doorbell is an example of an extra low voltage device. True or False?

True.

Every atom of a common element will have the same definite number Protons, Neutrons and Electrons. True or False?

True.

Every conductor carrying current has a magnetic field around it. True or False?

True.

In a coil which has an applied AC voltage, self inductance will limit the amount of current that will flow through the coil even though the electrical resistance is low. True or False?

True.

In some cases, even the Power Engineer may not be authorized to perform duties even something simple as changing a light bulb. True or False?

True.

The size of the conductor is proportional to the amount of the current. True or False?

True.

Tie breakers must be the same size as the main breakers. True or False?

True.

By purchasing larger then needed capacity Induction motors for a system, a low Power factor can be achieved. True or False?

True. However, operating costs for large induction motors are most efficient when fully loaded, and efficiency would be lost since the motor would never run at full load.

On a pretransformer rate, the consumer is responsible for energy losses from the transformers. True or False?

True. Maybe amount to several thousands of dollars a year.

2 ways that a Motor may display its Power Rating?

Under Load and at Peak Power performance.

How would you produce a strong magnetic flux, as required in large DC machines?

Use electro-magnets.

Describe the basic operation/construction of a Kilowatt-hour meter.

Uses a small motor which its speed is proportional to to power consumed. Specific Components include: Voltage coil, Current coil, Compensating coil, Revolving disk and a Registering Mechanism.

What are the proper units used to express the power supplied to a circuit by inductance or capacitance?

Volt-Amps or Kilovolt-Amps. (The product of Voltage X Current)

What is the most common type of Electrical Measurement?

Voltage Measurement

What are the units when expressing actual Power?

Watts or Kilowatts since Actual power = (Voltage X Current) X Power Factor

What is mutual inductance?

When a magnetic flux produced by one coil induces an EMF in a second coil.

When is maximum Voltage generated in a DC generator?

When the conductor is cutting the magnetic lines of force at 90 degrees. When the conductors move parallel with the lines of force NO VOLTAGE is produced.

When are Series motors preferred?

Whenever a large starting torque is required as well as when a motor is firmly coupled to a load whose torque decreases with speed. (hoists, cranes, fans, vehicle starters)

When are Compound Motors preferred?

Where high starting torques are required.

Atoms that have very few electrons orbiting in their outer shell are considered to be what?

good conductors

What are transformers rated in?

kVa (kilovolt amps)

In order for a 2 pole alternator to produce 60 Hz power, how many turns must the rotor turn per second? Per Minute?

60 Revs/second OR 3600 Revs/min

The housings of grease lubricated bearings should be filled up how much if the shaft being used is 75mm and smaller? Larger than 75 mm?

75mm and smaller = 40% of the housing capacity larger than 75mm = 60% of the housing capacity

Maximum allowable working temperature for a Class A insulation working in 40 degree ambient temperature?

80-90 deg.C

What kind of system is a 120/208 V system?

A 3-phase, 4 wire system

Power factor correction capacitors are typically sized to yield what value of Power factor?

A Power factor of 0.95 is common.

Clamp on Ammeters measure current flow using what?

A basic transformer principle

What is a "Shunt Resistance"?

A built in resistance within the Ammeter (individual resistors)

Compound Windings?

A combination of Shunt and Series windings.

Typically generators are driven by a constant speed driver and the number of conductors on an armature is fixed. What is regulated on the generator to control the output Voltage?

A field regulator which varies the strength of the field by controlling the current to the electromagnets of the poles.

What is a Mega-ohmeter composed of?

A high voltage DC generator which is hand operated, and a sensitive ammeter.

What would cause a Low Power Factor?

A large number of Induction Motors and other Inductive equipment connected in a Central AC distribution system.

Practically speaking, a Commutator on a generator acts the same as what other common device used to convert AC to DC?

A mechanical rectifier.

In a Double Pole Switch, what kind of material is used to connect the 2 poles?

A non-conductive material.

What is an instrument transformer used to measure voltage called?

A potential transformer.

The load current has no affect on the field excitation of what kind of generator?

A separately excited generator

Most conductors tend to increase in resistance with increase in what?

temperature

Which device is connected in series with the shunt field winding to control the amount of current flowing?

A variable resistor (Rheostat). Through changing the field current , the output Voltage of the generator is controlled.

How much resistance does an Ammeter have?

A very low resistance so it won't affect the reading of how many Amps are actually flowing through the circuit.

Do transformers step up/step down DC or AC voltage?

AC voltage

Function of the service?

Act as an electrical supply or source to the building

How would you find the total resistance in a series circuit?

Add them up to find the sum.

Current flow direction and intensity through a conductor will affect what?

Affect magnetic field direction and intensity

What is the most common cooling method for Motors?

Air cooling.

What type of cooling do Dry Transformers rely on?

Air-convection (forced cooling)

Shell Type transformer?

All of the primary and secondary is wound on the centre leg. The entire winding is then surrounded by a shell of iron.

A few turns of wire wrapped around a soft iron core has a current of electricity passed through it. What do you have?

An electro-magnet

What exactly does a Current measurement give you?

An indication of the amount of Power a device is using.

What relationship do Capacitive Reactance and Inductive Reactance have with each other?

Capacitive reactance cancels out Inductive reactance and power factor correction is accomplished by placing capacitors in parallel with inductive circuits.

What is a popular material that has a negative temperature coefficient?

Carbon. As the temperature of carbon increases the resistance decreases. Most materials however have a positive temperature coefficient.

Branch circuits?

Circuits that extend beyond the final overcurrent device. Utilization is the function of branch circuits.

Shunt Windings?

Consists of many turns of fine wire.

Series Windings?

Consists of relatively few turns of heavy wire.

Shunt DC Motors?

Constant speed.

Construction of High Speed (3600 rpm) Poles?

Constructed of Cylindrical Casting. Slots are cut in the casting for the rotor windings and the windings are held in place by wedges.

Role of self-inductance in an AC circuit?

Continually changing current makes it so self inductance is always a factor in limiting current through the coil.

2 types of single phase transformers?

Core type and Shell type

The rotating field of an Alternator is produced by applying what to the rotor?

DC POWER

What is the major difference between an AC and DC generator?

DC generators have commutators, and AC generators have slip rings

What is the soul purpose of using the Right Hand Rule?

Determine the direction of induced current flow.

Medium of communication between equipment designers and equipment users?

Diagrams.

From each energy dial to the next, how much is 1 full revolution relevant to the dial beside it?

Dial 1 = 1 revolution > Dial 2 = 1/10 of a revolution Dial 2 = 1 revolution > Dial 3 = 1/10 of a revolution and so on...*** ALWAYS ROUND TO THE SMALLER NUMBER ***

Function of the feeders?

Distribution.

Magnetic field build with...

Each turn of wire around the coil

2 possible losses due to the magnetization of the core?

Eddy currents and Magnetic Hysteresis

Emergency supply?

Emergency equipment grouped on one feeder.

What is comprised of the Rotating Field in an AC machine?

Exciting windings are installed on the rotor with DC power supplied through a pair of slip rings. The stationary conductor is called the Stator.

The strength of the magnetic field in a SHUNT wound generator can be described as what?

Fairly constant

A conductors resistance is DIRECTLY proportional to its diameter. True or False?

False, a conductors resistance is proportional to its length. The longer the conductor, the greater its resistance.

Copper has very good magnetic characteristics. True or False?

False, copper cannot be magnetized

As the frame number increases the Power Rating and size of the motor tends to decrease. True or False?

False, the motor size and power rating tend to increase with increase in frame number. The frame number is indicated on the identification tag attached to the motor.

Amperages must be equal in synchronizing generators. True or False?

False. Voltages must be in phase, Phase rotations must be the same, Voltages must be equal, and Frequencies must be equal.

The utilities responsibility does not go beyond the customers ....

First OVER CURRENT device

The direction of _____ due to motor action can be determined using Flemings Left hand rule.

Force

How are transformers usually cooled?

Forced air cooling using fans

On the OUTSIDE of a magnet, in which sequence do the magnetic lines of force travel?

From North pole to South Pole.

On the INSIDE of a magnet, in which sequence do the magnetic lines of force travel?

From South pole to North Pole.

What is Conventional Current flow?

From positive to negative

Compound Wound DC generator?

Has a combination of Shunt and Series characteristics, depending on the predominance of each type of winding

Relevant to Generators, what did Michael Faraday discover in 1831?

He discovered that an induced voltage is produced in a conductor when the conductor is moved across a magnetic field.

Series DC motors?

High speed at Low load, Low Speed at High Load.

Important characteristic of Transformer cooling oil?

Higher specific heat than AIR

Transformers require MORE or LESS maintenance than most other machinery?

Less

What is considered to be a Low Power Factor that could result in penalizations from the Utility?

Less than 0.8 is considered to be low. (1 is considered Unity)

An Ammeter must offer High or Low resistance to an electrical circuit?

Low resistance

Magnetic Flux V.S. Magnetic Field?

Magnetic Flux is the sum of magnetic lines of force about a magnet. Magnetic field is the space around the magnet the lines of force are expected to travel.

Alternators must run at frequent speed to maintain what?

Maintain the Alternators frequency.

A current carrying conductor being moved by a magnetic field illustrate what principle?

Motor Action.

Recommended distance to keep away from high voltage conductors?

Not less than 2 meters

When would you use a Mega-ohmeter?

On Insulators.

How often should transformer be inspected?

Once or twice a year

Why is it important not to overload a motor?

Overloading a motor can cause high current flows in the magnetic field or in the armature which can damage the windings.

Utility companies have a surcharge to their customers based on what?

Peak Power demand

What is the property that determines whether or not a material will be easily magnetized?

Permeability.

Atoms that have greater numbers of electrons orbiting around their outer shell are considered to be what?

Poor conductors?

Arc tracking?

Pumps and compressors collect moisture and dirt, and could spontaneously energize

What is a term used to describe a materials resistance to magnetic flux?

Reluctance.

What is the quantity used to measure Permeability?

Reluctance. * Iron and Steel have a very low Reluctance and Air and Glass have a very high reluctance *

Proper way of reading dials on a Power Meter?

Right to Left

Construction of Low Speed (1800 rpm) Poles?

Salient Pole Construction: Rotor windings are wound around the poles.

The 3 main types of DC generators are all...

Self Excited

Ammeters are connected in series or parallel?

Series

If high voltage is used in commercial and residential applications, its usually restricted to what area?

Service entrance and some feeders.

Distribution system is composed of what 3 things?

Service, feeders and branch circuits

Instead of one big coil winding, what is used in a large DC machine?

Several individual coils are laid in slots on the Armature.

What material is the Stator of an AC alternator built of?

Silicon Steel laminations mounted in a frame.

For AC generators, what are used instead of Commutators?

Slip rings.

When using Voltmeters or Ammeters, which scale should you start your measurement on?

Start on a higher scale so you don't risk damaging the Device.

What is Armature Reaction?

The distortion or twisting of the main lines of magnetic force (between the poles) caused by the current developed in the armature windings which in turn create their own magnetic lines of force. The clash of these magnetic lines of force is seen as a shift in the NEUTRAL PLANE.

What part of the system is the consumers responsibility? (consumers service)

The latter - the part of the systems that extends from the supply service to the first circuit breakers

Which hand rule is applied concerning Motor Action?

The left hand rule. " A conductor carrying current in a magnetic field tends to move at right angles to the field. "

What are Field Poles made out of?

Layers of Silicon plates called laminations.

Low voltage systems may have a voltage variation of how much?

+ or - 5%

Drip-Proof Motor?

- An open enclosure where debris is prevented from entering the motor at an angle between vertical and 15 degrees.

Demand Meters?

- Basically a kVh meter but with an extra face and 2 pointers - Red pointer indicates the demand continually but the black pointer indicates the maximum demand during the entire billing period

4 Advantages of having a rotating field?

- Brushes and slip rings only carry the Excitation current which is a considerably lower voltage/current than the current supplied by the Stator. - The rotating mass is reduced since only the rotor spins - Only one pair of slip rings is required for a three-phase ROTATING field alternator - Insulation of the output leads is made easier (good when operating at high voltages)

Three means of producing Electromotive Force? (voltage)

- Chemically (batteries) - A Mechanically driven generator - Photovoltaic Cells

Construction of Knife Switches?

- Consist of one or more copper blades hinged at one end - When the switch is closed, blades are accepted into clips to complete the circuit - Usually installed so upward force is need to close the switch so the force of gravity won't be a threat

Separately Excited DC Generators?

- Constant output voltage at all loads - The load current has no effect on the field excitation since the field current is supplied from a separate source.

Weather Protected Motors?

- Constructed to prevent entry of rain, snow or other particles.

4 Items that are included on an Electric Motors Nameplate?

- Construction information - Application Information - Service Information - Manufacturers Name

4 Pre-cautions to take when using megohmmeters?

- De-energize the equipment - Identify the components in the circuit your testing - Make sure all Capacitors are discharged from the circuit - Do not hold the contacts of the test leads when the meter is energized

Open type Motors?

- Draws cool air in using a fan - The fan can either be an Integral part of the Rotor, or can be separately mounted on the Shaft

How would you increase the magnitude of the Voltage produced in an Electro-magnetic conductor?

- Increase the speed at which the magnetic lines of force are cut - Increase the strength of the magnetic field - Increase the # of conductors cutting the magnetic field with the conductors connected in series with each other

Shunt-Wound Self Excited DC generator?

- Nearly constant output voltage at all loads

Totally Enclosed type Motor?

- Not open to atmosphere - Cooling is either supplied by an outside source or re-circulated inside the motor and cooled by some form of Heat Exchange

5 common motor enclosure types are?

- Open type - Drip-proof - Totally Enclosed - Fan-cooled - Explosion Proof

Series-Wound Self Excited DC generator?

- Output Voltage rises dramatically from minimum load to full load conditions since the armature current generated flows through the series field.

DC generators are seldom used these days, but still find use in specific applications. What are 2 examples?

- Portable electric welding machines - Elevators

A Compound-Wound DC Generator can be sub-divided into what 3 types?

- Rising output voltage VS loaf - Constant output voltage - Decreasing output voltage VS load

Splash Proof Motor?

- Similar to the drip proof motor except the protection against the motor is increased from vertical to 100 degrees from the vertical

What are four popular mechanisms which rely on Magnetism to function?

- Solenoids - Relays - Electric Motors - Generators

What is the Potential difference in a Standard Dry Cell?

1.5 V

How many Volts can be produced in a Meggers generator?

1000 Volts and greater. Most meggers these days are battery operated using double A batteries.

MAWT for a Class B insulation working in a 40 deg.C ambient temperature?

110-120 deg.C

The voltage produced in each phase of a 3 phase generator is displaced by ______ electrical degrees of the other phases.

120 Degrees

What is the maximum voltage that can be accepted by a kW/h meter for proper measurement?

120 V. If the voltage is higher than this it must be stepped down first.

The tension for the brushes in Industrial Generators should be approximately _____ kPa.

15 kPa

The service factor indicated permissible overloading for a Motor. What is a common Service Factor?

15% for short periods of time.

To produce 60 Hz power, how fast would a 4-pole alternator have to be rotating?

1800 revs/min since every full revolution completes 2 cycles.

Minimum distance of approach when working with high voltage systems?

2 meters

What is the percent average of a consumers consumption versus the peak demand the utility company can actually provide?

25% of what the utilities can provide.

High amperages are stepped down to ____ A before kW/h meters can be used to measure the amount.

5 A

2 Types of electrical Testing meters?

Analog and Digital.

Flux leakage?

Any flux that does not cut the secondary and does no useful work

What is Back-Electromotive Force?

As the armature spins which is holding the conductors, an induced voltage will be produced within the armature itself. This force will run in the opposed direction to the applied electromotive force in the armature conductor that is driving the motor.

Transformers which have both the primary and secondary windings in common with the coil are called?

Auto transformers.

Why can't an Ammeter be connected in Parallel?

Because by connecting it in parallel you are only adding to the circuit and this would draw more current. Connecting it in series measures all the current that is in the circuit.

Why do Demand Readers use Internal and External Multipliers?

Because the actual voltage and current may be too large to be measured by the meter so transformers are used to step up or step down these measurements.

How many Poles may be installed on a Stator?

Between 2 and 12 poles.

What are the 2 materials alternator slip rings are usually made of?

Brass and Steel

Since conductors are fixed, and speed must be kept constant to maintain Frequency, how is output Voltage varied in AC Alternators?

By adjusting the Field Strength. This is accomplished by adjusting the DC current supplied to the rotating field. (Rheostat or Electronic Control)

What effect do Conventional and Reverse current flow through a circuit have on a conductors magnetism?

By altering which way the current is flowing will reverse the direction the lines of force around the conductor.

Electrical schematic (elementary diagram) portrays what?

By means of graphical symbols the function, sequence, connection and electrical relationship of each circuit

How are the ends of each Armature Coil connected to the commutator segments?

By soldering.

What is the purpose of a Fuse?

If excessive current begins to the through the conductors (overloading) then the Fuse is placed before the Load so it will melt and open the circuit before damage can be done to the Equipment.

What could cause a DC motor to "Run Away"?

If the current to the field coils is lost this will result in magnetic field strength to become weak. With the loss of field current, armature current increases drastically which could boost the speed of the motor. * Once the field current becomes weak, the Back-Electromotive force also becomes weak *

What is Conventional Current Flow?

If the flow of electrons is from a Positive terminal to a Negative terminal.

What would define a well designed transformer?

If the flux produced by the Primary cuts every turn of both the primary and secondary winding, thereby inducing the same voltage in every turn.

Magnetite or Lodestone were recognized to magnetically attract what other metals?

Iron, Steel, Nickel and Cobalt. (Iron being the most magnetic)

What is the purpose of the Yoke in a DC machine?

It contains and supports the main components of the DC machine and is usually made of Cast Steel or Iron or a steel slab rolled into the appropriate diameter.

For every Pole in the generator, how many brushes are there?

It is common to have equally as many brushes as there are poles.

Why are AC machines dominant in Industry these days over DC machines?

It is not economical to build DC machines in large sizes. AC machines are most commonly built with a rotating field and stationary conductors, making for a simpler construction.

A current carrying conductor is in a magnetic field. If the current reverses direction, what happens to the electro-motive force carrying the current?

It reverses direction also

What determines whether a material will be easily magnetized or not?

Its Permeability

What do Watt Meters measure?

TRUE WATTS

A conductor supplied with current while in a magnetic field will do what?

Tend to move at RIGHT ANGLES with the flux lines

What did Michael Faraday discover?

That a conductor will voltage induced if it cuts magnetic flux

What does the Commutator do exactly to maintain Direct Current generator and not Alternating?

The Commutator continually reverses connections between the loop and external circuit, causing current to flow in one direction in the external circuit.

What are the most common type of DC generators used?

The Shunt, Compound and Separately Excited DC generator are most frequent.

What is comprised of a Stator?

The Yoke and its attached poles make up the Stator. The Armature rotates inside the yoke and is part of the rotor.

What determines the strength of the magnetic field around the conductor?

The amount of current flowing through it, and the direction of the magnetic field depends on the direction of the current flow.

The amount the neutral plane is shifted is proportional to what?

The amount of current flowing through the armature rotor. (the load on the machine)

What defines an Ohm?

The amount of resistance that will allow 1 Ampere of current flow through it when an electromotive force of 1 Volt is applied.

How is Cooling or Air circulation achieved in an Armature shaft?

The armature may have holes punched or drilled through them to permit air circulation for cooling.

How many degrees does the Run Winding lag behind the Start Winding in a Split Phase Motor?

The current lags about 15 degrees behind the Start winding.

What is Wattless (reactive) Current?

The current that surges back and forth in an AC circuit and lags behind the Voltage.

Why should you never clamp more than 1 wire with a Clamp-On Ammeter?

The currents could be flowing in opposite directions and the measurements will cancel out, making for an unsafe situation.

Tie circuit breakers?

Most low voltage system are only fed from one source of power. A tie circuit breaker makes it so if one power source becomes unoperative, power can still be maintained to the switchboard main bus and service will continue.

What is the PRINCIPLE on which a transformer operates?

Mutual Inductance: When magnetic flux produced by one coil cuts the conductors of a second coil, a voltage is induced in the second coil.

How do you calculate transformer efficiency?

Output power/Input power X 100%

Low Voltage?

- Pose a threat to life - Voltages sufficient to supply power loads

How many electrons may the OUTERMOST shell of an Atom contain?

32 electrons

What happens when a conductor moves relative to a magnetic field and it passes through the lines of magnetic flux?

A voltage is induced in the conductor.

How do you maintain proper load distribution?

Balance the loading as well as possible between all conductors. (reduces line losses and energy costs)

The former is the responsibility of the utility as well as the ____ and __________ of the former.

Care and maintenance

2 types of single-phase transformers?

Core type and Shell type. Each type winds the low voltage conductor nearest the iron core first.

Open contacts on a high voltage system ensure the line is de-energized. True or False?

False, downstream conductors may store some amount of capacitance.

As the temperature of a transformer increases during operation, the kVA rating increases. True or False?

False, if the heat is properly dissipated it is able to perform with a higher kVA rating.

How many Electrons may the First Shell of an Atom contain? Second Shell? Third Shell?

First = 2 electrons Second = 8 electrons Third = 18

What enables a transformer to work at a high kVa rating?

If the heat in the transformer can be dissipated at a faster rate lowering the the temperature rise (type of insulation is important)

Distortion increases due to added ______ to the transformer.

Impedance.

In a DC circuit, does self-inductance remain a factor even after the current is at its maximum value?

No, self inductance is no longer a factor. If the circuit opens however, then self inductance again becomes a factor.

Equipment selection in a circuit must conform to what constraints?

Number of phases and voltages.

Role of self-inductance in a DC circuit?

Self inductance delays the build up of current to its maximum value, determined by the value of the applied voltage and the resistance of the coil.

What is it called when AC action cause a counter current in a coil?

Self-inductance.

What replaced PCB in modern day transformers?

Silicone based oils or florinated hydrocarbons.

A three-phase transformer is similar to what type of single-phase transformer?

The Shell type transformer, except the windings are wound on each of the three legs.

Copper losses derive from what in a transformer?

The actual resistance of the copper wire used in the windings.

What prevents electrons from flying away from the Atoms nucleus during Orbit?

The attraction of forces between the Electrons and the Protons.

What gives each element its unique Electrical, Chemical and Physical Properties?

The difference in the structure of the atom.

Step up Transformer?

The number of windings in the secondary is greater than that of the primary inducing a greater voltage in the secondary.

Step down Transformer?

The number of windings in the secondary is less than that of the primary inducing a lower voltage in the secondary.

As current flows through a conductor what is lost?

Total power output is lost. A larger diameter conductor can reduce these losses but bulk, weight and cost increases for that transformer.

What is equally proportional in a transformer?

Voltage is proportional to the number of turns in each winding.

Two types of Instrument transformers:

Voltmeters and Ammeters