Alternating Current Fundaments ( Unit 34

Primary winding with 4 turns at 1 volt = what in the secondary winding

1 turn and 0.25 volts 2 turns and .5 volts 3 turns and .75 volts

4 common low voltage systems are available for consumers : list em

1. 240 single phase , 60 hz 2. 240 three phase , 60 hz 3. 208 V , three phase , 60 hz 480V , three phase , 60 hz

All HVACR equipment is manufactured to operate satisfactorily on voltages of plus or minus ____ percent of the rated voltage unless otherwise specified.

10 percent

In residencies , _____ V ac is used to power most small appliances.

120 V

Construction of a basic motor has _____ coils wrapped around ________ cores called _____ poles

2 coils wrapped around stationary cores called stator poles

Transformers are used to step down the line voltage to ___ volts for the _______ used in HVACR units.

24 volts for the controls used in HVACR units.

Large appliances such as electric stoves and residential AC units use _____ V

240

The most common service supplied to residential and small commercial users is the ________ V ______ phase , ___ hz systems , it uses 3 wires , 2 ____ and 1 ____

240 V , single phase , 60 hz system 2 hot and 1 grounded

For larger motors , generally 5 __ and above __________ phase power is normally used .

5 horsepower and above, three phase.

A simple capacitor consists of

A dialectic placed between two plates of highly conductive material .

Electrical current can be produced by either ?

A generator or an alternator .

A generator rotates coils of wire ______________ a _______ field

A generator rotates coils of wire inside a magnetic field

When current passes through a conductor , what is produced?

A magnetic field

when the coil is energized , the plunger provides?

A path for the flux

If a conductor is moved through a magnetic field , what is induced in the conductor?

A voltage

As on plate leaves and accumulates on the other plate of a capacitor, a _____ begins to develop across the capacitor , This difference is created by current flow and therefore ____ the current

A voltage begins to develop across the capacitor, this difference is created by current flow and therefore lags the current.

DC power can be used for control systems and solid state modules for defrost and over current protection ,f or these applications Dc power is often converted from

AC power through a rectifier .

Electrical power provided to residdential and commercial customers is ___________ with a frequency of _______________

AC with a frequency of 60 hertz

Types of power sources ? ( 2 )

Alternating Current and Direct Current

An Alternator rotates a ___________ field _________ coils of wire

An alternator rotates a magnetic field inside coils of wire

Relays and contactors act as

Automatic switches to turn loads on and off .

Inductance means to

Cause or create

The capacitor _______ when source voltage is applied

Charges

240 V Three phase 60 HZ , Delta systems are commonly used for

Commercial and industrial installations.

Three phase power requires the addition of one more ____- to the generator?

Conductors

Define capacitive Reactance

Describes a capacitors opposition to alternating current , somewhat like resistance , can be used to control the current in a circuit.

Many electrical testing instruments operate on ________ power

Direct current

The polarity of an induced voltage in a conductor is affected by the direction of the ______ and the direction of the _______ field

Direction of the conductor ( up or down ) and the direction of the magnetic field .

Importance of fuse and/or circuit breaker sizing ?

Ensures that in case of an overcurrent event the wiring is protected. Wire often runs through varoius combustible building materials , hot wires could start a fire.

The amount of voltage produced is proportional to how _____ the coils of wire move and how ______ the magnetic field is

Fast the coils of wire move and how strong the magnetic field is.

Commercial and industrial customers normally use ______ voltages in single _______ and three _____ systems

Higher voltages in single phase and three phase systems

Transformers are used to -

Increase or decrease incoming voltages to meet the requirements of the load .

Transformers contain a single _____ that is wrapped with two coiled conductors known as _______ and _______ windings.

Iron core . Two coiled conductors known as primary and secondary windings.

Only time when windings are connected in a transformer is when ?

It has been overheated and the insulation has broken down.

Primary reason for AC current as a standard is ?

It is easily transformed from one voltage to another.

What happens to the plunger when energized ?

It is pulled upward to a magnet which causes the valve to open

If the wiring isn't large enough to carry the current , what might happen?

It may overheat and cause a fire, become hot enough to melt the insulation, allowing wire to come into contact with equipment, which could cause an electrical shock to anyone touching the charged metal .

Advantages of 3 phase power over single phase

Less power loss to transformers , motors are less expensive, more reliable , more efficient Don't require capacitors

A magnetic field transmit outward in all directions from magnetic materials . The invisible lines of force as known as ?

Magnetic Flux

If more electrons spin in one direction than the other , a _________ field is developed

Magnetic field

As current flows through the coils in an Ac motor, the stator poles are ?

Magnetized

All HVACR residential and commercial units are located inside ________ that are designed to withstand an ________ _______ fire

Metal Cabinets .they are designed to withstand an internal component fire.

Advantages of single phase over 3 phase

More readily available Larger variety of equipment types and sizes Often kept in stock at supply houses.

If an iron bar is placed inside the coil , the current flow through the coil will concentrate the flux , this creates a _____ and ____ Polarity , which can be revered by changing the direction of ________ flow through the coil

North and South Polarity , and can be reversed by changing direction fo current flow through the coil

Multiple impedances in a circuit can't be added because the currents in Inductive, capacitive and resistance loads are _______

Out of phase with each other.

Step down transformers are often used to ?

Reduce line voltage required for motor starters to lower voltages for the controls .

Flux will choose the path of least _____

Reluctance

resistance is also known as ?

Reluctance

Single phase power is commonly used for ________ and ____ commercial systems.

Residential and small commercial systems.

Face shift factors relate to the following ( 3)

Resistive circuits Inductive circuits Capacitive circuits

Sizing of electrical power wiring and overcurrent protection are important for a number of reasons . What is the most important ?

Safety

208 V , Three phase 60hz WYE systems are common in

Schools, hospitals and office buildings where 208 V three phase motors and 120 V single phase lighting and convenience circuits are required.

When AC voltage is applied to the primary winding, the resulting lines of force are carried through the core . These lines create a current flowing through the ________ winding, inducing a ______- in that winding

Secondary winding, inducing a voltage in that winding.

how to fix 60 hertz low frequency noise in motors and transformers?

Secure motor or transformer tightly on mounting brackets , use pop rivets or sheet metal screws if sound is tracked to vibrating sheet metal.

Any electrical appliance that operates on 120 V power is

Single phase equipment

A good example of magnetic induction is the operation of ?

Solenoid valves

Two types of transformers ?

Step down transformers and step up transformers

Alternating current is the most common source of power for most HVACR systems. T OR F

T

The most common source of direct current is ?

The battery

The term power factor is used to indicate

The difference between true power and apparent power in an inductive circuit

2 main factors that affect capacitive resistance

The frequency of current ( and voltage ) and the amount of capacitance

Define impedance ? what unit is used?

The opposition to the current flow in Ac circuit . Represented by Z

What causes an AC motor to run?

The stator field induces an opposing field in the rotor and the principle of attraction and repulsion causes the motor to run.

When a solenoid valve is de energized , the plunger moves downward to close the valve because ?

There is no magnetic force to hold the plunger in the coil

Inductive circuits contain inductive loads such as

Transformers, relays , motors aka loads that are constructed using coils of wire and produce magnetism

The amount of voltage induced in the secondary winding depends on the Ratio of the number of ____ in the primary winding to the Number of turns in the ______ winding

Turns in the primary winding to the number of turns in the secondary .

Magnetic induction is used to generate ______ for ____ and _______ use

Used to generate voltage for commercial and residential use

In a resistive circuit, the current rises and falls with the ______ and are considered " in ___"

Voltage and the two are considered in phase

Wire near the _____ pole will always be_______ while wire near the _______ pole will always be _______

Wire near the north pole will always be negative while Wire near the south pole will always be positive.

What is the impedance of a single phase inductive circuit having a voltage of 240 V and a current flow of 10 A

Z = 240 V / 10 A = 24 ohms

how to calculate impedance

Z = E / I ( impedance = Voltage / Current = Votls/Amps

doubling reactance will reduce the frequency or capacitance

by half

A capacitor is an electrical device that is used to ____ the phase _____ between the ______ and ______

change the phase relationship between the current and voltage

The magnetic field created by current passing through the conductor will intensify if the conductor is _______

coiled

Electrical current is produced by moving __________ of wire through a ________ field .

coils of wire through a magnetic field .

If an iron bar is placed between the two ends of a magnet the flux will ?

concentrate through it

A capacitor is usually connected in _____ with the load

connected in series with the load

Solenoid valves open and close automatically by ?

energizing or de energizing a coil of wire

When the switch is closed ,t he supply voltage is applied across the capacitor . Electrons flow rapidly from the first ____ p to the ____ second____ to the _____ then through the _____

first plate , second plate , the source, then the load .

Doubling the frequency or capacitance will reduce reactance by

half

Air has a _____ reluctance

high

Commercial systems utilize ________ voltages and use ______ power

higher voltages and three phase power

The electricity flowing through a coil of wire _____ a magnetic field that causes another ______ _______ to flow in a parallel coil.

induces a magnetic field that causes another electric current to flow in a parallel coil.

In the inductive circuit, the current ___ or is out of ____ with the voltage

lags or is out of phase

Lines of magnetic flux are always considered to leave the ______ pole and enter the ______ pole of a magnet in ________ loops

leave the north pole and enter the south pole in continuous loops

Because of the current lag , the measured power in an inductive circuit will always be ____ than the calculated power ( E x I )

less

an iron bar would have a _____ reluctance

low reluctance

there is no _________ connection between windings of an induction device such as a transformer

no electrical - mechanical connection .

AC power , certain characteristics affect the power calculation X x I , which are known as

phase shift factors

Voltage and current in circuits containing inductive loads are phase ____ or out of ____

phase shifted or out of phase

Capacitors are broadly categorized as either (3 types)

polarized , non polarized and variable

The resistive circuit contains at least one ?

resistive load , Ex ( heater or lamp_

Step down transformers have more _______ on the _______ coil while step up transformers have ______ windings on the ______ coil

step down transformers have more windings on the primary coil while step up transformers have fewer windings on the primary coil.

Capacitors can be used to increase the _____ of an electric motor

torque /starting power of an electric motor.

HVACR euquipment has a tendency to operate better on max ____

voltage

Local transformer s reduce ______ levels to suit _____ requirements

voltage levels to suit user requirements

Residential service requires lower ______ and single__________ Power

voltages and singe phase power

True power calculation is ?

wattmeter reading / ExI or (true power ) / (apparent power)