Fourth Year Gas Transformers

Front 1

Transformers are alternating current devices that transfer energy from one circuit to another with no mechanical device ( no moving parts)

What type of current is used in transformers

Back 1

AC ( alternating currents)

Front 2

A transformer transfers energy from one AC current to another in an action called mutual induction.

This transfer of energy is called mutual induction and is measured in Hertz.

How many Hertz are standard in North America ?

Back 2

60 Hz

Front 3

Transformers are 95-98% efficient w/losses due to the inefficiency of the Iron Core.

Some of the magnetic Flux does not travel through the iron core.

This is called __________

Back 3

Flux leakage

Front 4

Induced electromotive force is produced in the Coil when there is a change in the magnetic flux linked with that coil.

The current looks like a whirlpool. What are these currents called?

Back 4

Eddy Currents

Front 5

With a soft Iron core and changing magnetic flux, Eddy currents can cause ________

Back 5

Transfer losses

Front 6

There are 3 types of XFMR construction. What are they are which 2 are used in gas appliances?

Back 6

Core

Shell

H-Types ( not common)

Front 7

Core and Shell type Transformers are common in gas appliances. The core is magnetic quality ( silicon steel) to reduce Hysteresis losses and laminated to prevent ______losses.

Back 7

Eddy

Front 8

What are the 2 functions of a transformer?

Back 8

To isolate one circuit from another

To change the voltage of a circuit ( either Step up or Step down)

Front 9

If the primary and secondary coils have the same oniony of wrappings, what is the transformers function?

Back 9

To isolate one circuit from another.

Front 10

What do you call a transformer, reducing voltage from 120v to 24 v , where the primary Coil has many more windings than the secondary coil?

Back 10

Step down transformer

Front 11

If we have a step up transformer, taking the volts from 24 to 120 V, how to the windings differ?

Back 11

In the case the secondary coil has many many more windings

Front 12

Which type transformers have the most leakage?

Back 12

Core type

Front 13

Why is terminal identification important on a transformer designed to change voltage ( step up or step down ) ?

Back 13

So there is no chance of confusing the high voltage side with the low voltage side

Front 14

What is the high voltage side identified with?

Back 14

H

Front 15

What is the low voltage side identified with?

Back 15

X

Front 16

Subscript numbers are used used to describe the individual terminals. What would H1 describe?

Back 16

Line 1, Hot

Front 17

Subscript numbers are used used to describe the individual terminals. What would H2 describe?

Back 17

Line 2 , neutral

Front 18

Subscript numbers are used used to describe the individual terminals. What would X1 describe?

Back 18

Line 1, R, Hot

Front 19

Subscript numbers are used used to describe the individual terminals. What would X2 describe?

Back 19

Line 2 , C (common), neutral

Front 20

Transformers that have more H and X terminals are called what?

Back 20

Multi-winding terminals

Front 21

On a step down 480/240 multi winding transformer, what would the voltage be on the H3,H4, X3,X4 be rated at in volts?

Back 21

H3 240 volts

H4 240 Volts

X3 120 Volts

X4 120 Volts

Front 22

In an ideal transformer , the voltage ratio is exactly equal to the the turn ratio, there is no significant impedance in the windings so there are no significant_________

Back 22

Voltage drops

Front 23

Since all turns of the windings are subject to the same flux the same voltage is induced in each turn. If there are 100v and 100 turns, how many volts in 1 turn?

Back 23

1 volt

Front 24

If the primary winding has 100 Volt AC on 100 turns, and the secondary winding only has 10windings, what is the voltage of the secondary coil?

Back 24

10 AC

Front 25

The Flux created in the iron core will induce voltage in both the primary and secondary coils. According to Lenz’s Law, the polarity of the induced voltage is _________of what caused it.

Back 25

Opposite

Front 26

Transformers under 1000va are rated in Volt Amperes. What are transformers over 1000 va rated in?

Back 26

Kilo Volt-amperes

Front 27

How many amps in a transformer rated as such:

120vac/24vac — 40 VA

Back 27

40VA / 24 v = 1.6 amps

Front 28

If a 120v is applied to a primary winding of a transformer with 240 turns of wire how many volts are across each turn?

How many windings would he needed for 24v on the secondary?

Back 28

0.5 Volts

48 turns

Front 29

What are regulation turns or wraps ?

Back 29

Additional turns to make up for drop in voltage under normal operating conditions.

Front 30

Class 2 XFRM’s are Smaller transformers ( under 1000v) that have a higher internal impedance so even when the secondary circuit is short circuited the current is very low. These are used for operating gas controls and the 24v control circuit of a furnace. The CEC limits class 2 transformers to a max output of ____v. They do not require _______.

Back 30

100v

Over current protection

Front 31

Current limiting transformers ( class 2) design includes an air gap that comes into effect when the secondary coil attempts to deliver for current than it is rated for. At this point the air gap is near saturation and an increase in magnetic lines of force is___________.

Back 31

Not possible.

Front 32

What information is needed to determine the size of a control transformer?

Back 32

The load voltage,

the load current/amperage draw

Available line voltage

Front 33

VA = Volts X Amps

KVA = ?

Back 33

Volts X Amps divided by 1000

Front 34

What are the 2 basic physical characteristics of XFRMs?

Back 34

Open XFRM

Totally enclosed XFRM

Front 35

What is an open transformer?

Back 35

Transformers with visibly open electrical connections that are screwed, slip on blade, or wire pigtail in configuration. Must be installed inside the cabinet of an appliance.

Front 36

What are totally enclosed transformers?

Back 36

Transformers contained within a metal or plastic enclosure that can be mounted anywhere

Front 37

What are two types of testing equipment to troubleshoot transformers?

Back 37

Test lights

Multi meters

Front 38

What are 2 types of multimeters?

Back 38

Analog

Digital

Front 39

Analog meters have multiple scales. What must we be sure of before testing?

Back 39

They must be zeroes before every resistance reading.

Make sure That the scale referenced is the same that the meter lead and selector switch have been set for.

Front 40

What does a resistance multiplier on the selector switch indicate?

Back 40

That the meter reading must be multiplied

Front 41

When taking a reading of amps or volts , the meter must be set up for AC, otherwise what will happen?

Back 41

A meter set for DC won’t read AC

Front 42

What are the digital clip on ammeters actually reading to measure amperage?

Back 42

The magnetic field around a wire

Front 43

What happens if your clip on amp reader camps around 2 wires?

Back 43

Will result in a zero reading

Front 44

Voltmeters are connected in ______ with the power _____

Back 44

Parallel with the power on

Front 45

Ammeters are connected in ______ with the power _____

Back 45

Series

On

Front 46

Ohmmeters are connected in ______ with the power ______

Back 46

Parallel

Off

Front 47

What is the difference in how an analog multimeter is used for an amperage reading when compared to the way it’s used for a voltage reading?

Back 47

Amperage taken in series, voltage in parallel

Front 48

Why is it important to zero an analog meter each time you are going to make a resistance reading?

Back 48

This check establishes the condition of its internal batteries

Front 49

How can you avoid a parallax error when reading an analog meter scale?

Back 49

Move your eye over the pointer so the reflected image and the pointer line up and the reflection can no longer be seen

Front 50

How do better analog meters help you to avoid parallax errors when you are establishing circuit value?

Back 50

Include a reflective section in the meter face

Front 51

How will you know which scale of an analog multimeter is the one you should be reading?

Back 51

Compare the scale to the selector switch

Front 52

How will you know what units are being measured with a digital multimeter?

Back 52

The LCD readout includes the operation being performed and the range selected

Front 53

What are two ways a transformer can be short circuited?

Back 53

Overheating

Overloading

Front 54

What do manufactures recommend as a max loading factor of the devices that are connected to the secondary side of a dry transformer used for controls?

Back 54

80%

Front 55

How are laminations of a transformer core kept electrically separate from each other?

Back 55

Varnishing each section or place paper between the layers and varnish the sections.

Front 56

What is the purposes of laminating the core of a dry transformer?

Back 56

It keeps Eddy losses to a minimum

Front 57

Which of the following conditions is most likely to be the cause of primary windings opening in a step down transformer?

Back 57

High current flow in the secondary windings

Front 58

What is reactive power in relation to the output of a transformer?

Back 58

Power is used to create an electromagnetic field

Front 59

What is the maximum permissible amperage draw of the secondary side of a transformer with 24 volt output and a 60 va rating?

Back 59

60/24= 2.5 amps

Manufacturers suggest 80% so 2 Amps

Front 60

What the manufactures suggested max circuit resistance be for the transformer with a 24 v output and 60va rating? 2 Amps

Back 60

E ( 24 volts)

I ( 2 amps) R

24/2 = 12 ohms

Hint 60

Ohms law.