Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
36 Cards in this Set
- Front
- Back
|
What is induction?
|
A property of an electric circuit by which an electromotive force is induced in it by a variation of current.
|
|
|
What is a Field winding?
|
Electromagnets produce magnetic fields when current passes through them forming magnetic poles. The coils of wire around these pole pieces create the magnetic field and so the winding is called the field winding.
|
|
|
What is electricity?
|
Electrons are considered to carry an electrical charge. Electricity is considered to be a flow of electrons which are extremely small particles within the atoms of which matter is composed.
|
|
|
what is voltage or what is also referred to as EMF or potential difference?
|
The relative amount of electric charge at one point in an electric circuit compared with that at another point in the circuit which causes a current to flow through a continuous path between the two points. Also referred to as electromotive force or potential difference.
|
|
|
What is capacitance?
|
That property of a capacitor which determines how much charge can be stored in it for a given potential difference across its terminals.
|
|
|
What is an ohm?
|
The basic unit of electrical resistance. It is the resistance which will allow one ampere of current flow when the voltage across the resistance is one volt. In the electrical circuit the resistance apposes the flow of electrons.
|
|
|
What is torque?
|
Torque is the strength that a motor produces by turning while it is starting or running.
|
|
|
What is horse power?
|
A unit of measuring the power of motors. One horsepower equals 33000 foot-pounds of work per minute.
|
|
|
what is an ampere?
|
Electrical current is measured by the number of electrons that flow past a given point in the circuit in one second. The practical unit of electrical current measurement is the ampere.
|
|
|
What is Alternating current?
|
Alternating current is an electric current that reverses direction sinusoidally. It rises to maximum positive value then swings to a maximum negative value this is one cycle. It has a sinusoidal wave form.
|
|
|
What is direct current?
|
Direct current is a constant voltage. Direct current does not have a sinusoidal wave form.
|
|
|
What is frequency? And what unit of measurement is used to measure it?
|
The number of cycles the voltage undergoes in one second is referred to as its frequency. The unit of measure for cycles per second or frequency is the Hertz (Hz).
|
|
|
What are the two types of magnets used in the HVAC industry?
|
Electromagnet and the Permanent Magnet
|
|
|
What is magnetism?
|
A force causing a magnetic field to attract ferrous metals or where like poles of a magnet repel and unlike poles attract each other.
|
|
|
What is electromagnetism?
|
Magnetism is produced when electrons flow through a conductor. A magnetic field is created around the conductor and the conductor becomes a magnet it is caused by the flow of electric current.
|
|
|
A common unit of electrical power is?
|
The Kilowatt which is 1000 watts.
|
|
|
The flow of electrons is called?
|
Electrical current.
|
|
|
If the Ohm rating of the load changes what will happen to the ampere flow?
|
It will change.
|
|
|
Describe (PSC) Permanent Split Capacitor motor:
|
This starting circuit remains energized the entire time the motor is running. The capacitor is sized such as to pass enough current to provide the required starting torque but not so big that it would cause the starting windings to overheat.
|
|
|
Describe (CSCR) Capacitor-Start Capacitor-Run motor:
|
The running capacitor is in the circuit continuously and it must be designed for continuous operation. Also this type of motor has high starting torque. It is applicable to larger single-phase motors of the range of 1/4 to 5 HP.
|
|
|
Describe a Split-Phase motor:
|
The start & run windings are connected in parallel across the line. The R/W is constructed of a number of turns of relatively heavy diameter wire which causes it to have a low electrical resistance and a high inductance. R/W current lags phase. The start winding heats quite rapidly when energized, to avoid damage it must be electrically disconnected from the circuit when the motor attains approximately 85% of full speed. this is accomplished by means of a relay or centrifugal switch.
|
|
|
Describe (CSIR) Capacitor Start Induction Run motor, and what are the two types of relays used in these motors and which one is N/C and the other N/O?
|
When the motor has attained about 75% of its rated speed the starting relay operates and disconnects the starting winding and the capacitor. The two types of relays used in these motors are (1) Potential Relay N/C & (2) Current relay N/O.
|
|
|
What are the three major parts of a motor?
|
Stator, Rotor, & Armature
|
|
|
Describe three types of motor enclosures:
|
Open type motors, have ventilation openings on the end-bells. Totally Enclosed (Drip proof) motors, are Large motors with external heat-sink fins to get rid of heat, and Hermetic motors, completely sealed usually cooled by refrigerant.
|
|
|
Describe the purpose of a starting relay and what are the four different types of starting relays?
|
Starting relays are used to remove the starting circuit from operation when the motor reaches approximately 75% of its normal running speed.There are four common starting relays: (1) Amperage (current) relay (2) Hot Wire Relay (3) Solid state and (4) Potential (voltage) relay.
|
|
|
Describe a Potential Relay:
|
The Potential relay applies the principle that motors generate a voltage called a counter EMF (Back EMF). The increase of current generated causes the coil to open the N/C switch and drops off the start winding. This relay is used in CSIR motors.
|
|
|
Describe the principle operation of a Current Relay:
|
When power is applied to the motor the motor draws a heavy current, strong enough for the magnetic coil to close the N/O cantacts & complete the circuit through the start winding. As the motor comes up to speed there is a decrease in current. Eventually enough to cause the contacts to open and dropping off the start winding.
|
|
|
At what rate of speed must the motor attain before the start relay disconnects the start winding and capacitor?
|
75% of its rated speed
|
|
|
A power consuming devise is refered to as?
|
A load.
|
|
|
What is a fuse?
|
These are devises used to protect the conductors and connected equipment from heavy overloads and short circuits
|
|
|
What are two types of fuses used in the HVAC industry?
|
Plug and cartridge type fuses
|
|
|
What is a circuit breaker?
|
A Circuit Breaker is a devise used to provide overcurrent protection just as fuses is used. However the circuit breaker is somewhat like a switch which will open or trip under excessive current conditions.
|
|
|
Circuit Breakers operate on one of two principles, what are these two principles?
|
Thermal Trip or Magnetic Trip
|
|
|
The operation of the AC motor is based on what principle?
|
Electromagnetism
|
|
|
One Kilowatt (KW) = ______Horsepower, and One Watt = _____ BTU per hour?
|
One KW equals 1.34 Horsepower and One Watt equals 3.41. Btuh
|
|
|
define Azeotrope:
|
A mixture of two similar refrigerants which has pressure temperature characteristics different than of its individual components.
Azeotropes cannot be seporated by distillation and component ingredients tend to leak from systems in amounts proportional to their mixture content. |
