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)
