WORKSHEET #4 Flashcards
A device that uses inductors to convert AC voltage from one value to another is known as what?
Transformer
Abbreviation: TX
What are the names of the inductors or windings given to a transformer (TX)?
Primary and Secondary windings
There are 2 different types.
A TX that you apply a lower voltage to the Primary windings, and a higher voltage is expected from the secondary is known as what type?
Step-up Transformer
A TX that you apply a higher voltage to the Primary windings, and a lower voltage is expected from the secondary is known as what type?
Step-down Transformer
A TX that is designed to convert field voltage to a lower voltage to facilitate in the functionality of motors or lighting or other electrical devices, but does not feed the device directly. This description describes what type of TX?
Control Transformer
A TX that is designed to convert a higher voltage to a lower voltage with the intended purpose of supplying a safer lower voltage for the utilization of branch circuits, is known as what type of TX?
Distribution Transformer
A TX that does not transform a voltage difference from the primary to the secondary, meaning it has equal turns ratio (1:1) in both sets of windings, with the sole purpose of reducing electrical noise in the AC waveform such as harmonics is known as what type of TX?
Isolation Transformer
Why is it we can only use transformers to change the voltage of an AC source, and not a DC source?
Transformers require a changing magnetic field to induce voltage, which only occurs in AC.
Why does our power grid use transformed AC voltage and not DC?
AC voltage can be easily transformed to different voltage levels, which is essential for efficient power distribution.
What is the term that dictates the physical reason for the change in voltage from the primary to the secondary?
The term is ‘turns ratio’. It describes the relationship between the number of turns in the primary winding to the number of turns in the secondary winding.
What factors determine the strength of an inductor?
The strength of an inductor is dependent on the number of turns, strength of the magnetic field, and the speed of the cutting action.
What is the only variable that allows for the change in voltage in a transformer?
The number of turns in the winding from the primary versus the number of turns in the secondary.
How do we calculate the applied voltage on the secondary using turns ratio?
We use the turns ratio to determine the voltage change on the secondary, without discussing the actual number of turns.
What would the turns ratio be for a transformer with 600 VAC applied to the primary and 24 VAC on the secondary? Show your math.
Turns ratio = Primary Voltage / Secondary Voltage = 600 VAC / 24 VAC = 25. This is a step-down transformer.
What would the turns ratio be for a transformer with 120 VAC applied to the primary and 24 VAC on the secondary? Show your math.
Turns ratio = Primary Voltage / Secondary Voltage = 120 VAC / 24 VAC = 5. This is a step-down transformer.
If we had 4800 VAC applied to the primary and the turns ratio is 1:30, what would the voltage be on the secondary? Is this a step-up or step-down transformer?
Secondary Voltage = Primary Voltage / Turns Ratio = 4800 VAC / 30 = 160 VAC. This is a step-down transformer.
What is the electrical power rating we use for a control transformer?
We use VA (volt-amperes) as the electrical power rating for a control transformer.
Why do we use VA and not Watts?
We use VA because it accounts for both voltage and current in AC circuits, while Watts only measures real power.
If we add a 5th light to the secondary circuit, will we exceed the electrical ratings of the transformer?
It depends on the electrical ratings of the transformer and the total load of the lights.
Will all 5 lights come on when the switch is closed?
Yes, if the transformer can handle the load.
What would eventually happen if we exceed the electrical ratings of the transformer?
The transformer may overheat or fail.
What is the name of the current limiting device applied to the secondary circuit?
The device is called a fuse or circuit breaker.
What size should the current limiting device be?
The size depends on the load and transformer specifications.
What does CEC, Section 26 rule -240 outline?
It outlines safe installation practices for transformers.
