WorksheetsTransformers
Total questions: 40
Worksheet time: 23mins
Name this Autobot
Ratchet
Optimus Prime
Megatron
bumble Bee
Which two (2) of the following methods are used to insulate LV (dry) transformers
Cellulose insulation with mineral oil
Vacuum pressure Impregnated (VPI)
Cast resin (CRT)
Mineral oil only
An isolating transformer installed in accordance with AS/NZS 3000 must have
one leg of the primary winding connected to the secondary winding
both legs of the primary winding connected to the secondary winding
the primary winding separated from the secondary winding by double insulation
an earthed metal shield installed between windings and bonded to both windings
According to AS/NZS 3000, where a transformer secondary winding supplies equipment via a cable that has a current rating equal to or greater than the transformer secondary winding:
a HRC fuse must be used to protect the cable
circuit protection is not required for the cable
a circuit-breaker must be used to protect the cable
either a circuit-breaker or a fuse must be used to protect the cable
What type of winding arrangements is used in this transformer construction
side by side
Concentric
Sandwich
LT-HT-LT-HT
Which two (2) of the following methods are used to insulate LV (dry) transformers
Cellulose insulation with mineral oil
Vacuum pressure Impregnated (VPI)
Cast resin (CRT)
Mineral oil only
Which of the following insulation methods is the most preferred to insulate HV (wet) transformers?
Vacuum pressure impregnated (VPI)
Cast resin (CRT)
Mineral oil only
Cellulose insulation with mineral oil
What is the cooling type used on this transformer
Oil Forced air forced
oil natural air forced
Oil Natural air natural
Oil forced water forced
Who is the leader of the Decepticons?
Shockwave
Laserbeak
Megatron
Shockwave
Which Autobot is known for his expertise in military tactics, bravery, and being Optimus Prime's loyal second-in-command?
Ironhide
Wheeljack
Bumblebee
Ratchet
Laminated transformer cores are constructed using magnetic materials which primarily contain:
stainless steel
aluminium
iron
copper
Which two (2) of the following are the most relevant industry standards relating to transformers?
AS 60076
AS 2374.1.2
ISO 9001
AS/NZS 3019
AS3017
What is the typical output rating of a potential transformer used for monitoring high voltage?
12 volts
110 volts
120 volts
230 volts
Which three (3) of the following are advantages of an auto-transformer
More efficient for the same VA rating
Smaller in size compared to double wound transformers of the same VA rating
Improved safety due to common section of winding
Reduced cost
Increased short-circuit performance
Which two (2) of the following are disadvantages of an auto-transformer?
Complexity of construction
Only useful for moderately smaller voltage changes
Increased cost
No electrical isolation between the windings
Larger short circuit current
What is the safety risk if the common section of an auto-transformer winding is open circuited?
Primary voltage will increase to load value
Primary current may equal secondary current
The secondary voltage could become equal to the primary voltage
The secondary current might reach short circuit values
Which four (4) of the following are recommended precautions for the connection and disconnection of potential (instrument) transformers?
The primary and secondary must be electrically interconnected to ensure mutual induction
The load on the secondary should be within the capacity of the transformer rating
The primary and the circuit under test must be connected in parallel
The PT should be tested and inspected to ensure compliance with specifications before use
The secondary side of the potential transformer must never be short-circuited
Which three (3) of the following are typical applications of an auto-transformer?
Compensate for volt-drops in long cable runs
Dropping voltages in d.c. circuits
Changing speed of a.c. fans
Reducing starting voltages of synchronous and induction motors
Increasing currents for spot welders
What cooling arrangement is this?
ONAN
OFAF
OFWF
ONAF
Name this cooling arrangement
OFAF
ONAN
OFAN
ONAF
What is the typical rated output current of a current transformer
1A or 3A
5A or 10A
3A or 10A
1A or 5A
What would be the secondary voltage of a transformer with a 50:100 turns ratio and the input voltage to the primary is 240 volts
415
480
120
110
What would be the secondary current of a ideal transformer with a 10:200 turns ratio and the input current to the primary is 1000 amps
20000 amps
50 amps
10000 amps
100 amps
Which of the following tests can be used to determine the variable (copper) losses of a transformer?
No-load test
Polarity test
Short circuit test
Insulation test
Which two (2) of the following are possible causes of secondary voltage variations in a transformer
Back emf
Increased load
Incorrect connections
Transformer bushings
Primary voltage fluctuations
What is the percentage voltage regulation of a supply transformer with a no-load secondary voltage of 125V and a full-load secondary voltage of 110V
0.88%
13.6%
12%
1.14%
Which two (2) of the following are affected by the percentage impedance (Z%) value of a transformer?
Transformer output rating
Prospective short-circuit current
Transformer input rating
Voltage regulation
Turns ratio
Which test would you use to determine percentage impedance of a transformer?
Insulation test
Open circuit test
Short-circuit test
Full load test
What is the percentage impedance of a 4 MVA, 33/11kV transformer that has 4.37kV primary voltage during a short circuit test?
12.1%
13.2%
39.7%
33.3%
What is the percentage impedance of a 16 MVA, 66/3.3kV transformer that has 3.78kV primary voltage during a short circuit test?
0.87%
5%
34.36%
5.73%
Which three (3) of the following are reasons for connecting transformers in parallel
Get Mad max current
easy to fix
in case of fire we still got power for the WIFI
Improve the power factor
looks heaps cool
Which three (3) of the following parameters need to be the same if two transformers are to be successfully paralleled and to share load equally
Insulation resistance
Same Z%
Same polarity
our turns to ratio is same
same brand
What is the effect of the circulating currents that result if two transformers are incorrectly paralleled?
Hectic Voltages
Increase the output current supplied to the load
Set the windings on fire/overheat
increased power factor
Z% increases
In Transformers, Bumblebee originally appears as a dilapidated...
1968 Ford Mustang Fastback
1977 Chevrolet Camaro
1978 Chevrolet nova
1967 chevrolet impala
An ideal single-phase autotransformer has a turns ratio of 1.75:1 and a primary voltage of 240V.
Calculate the Secondary voltage based on a secondary load current of 20A.
420V
137V
35V
12V
An ideal single-phase autotransformer has a turns ratio of 1.56:1 and a primary voltage of 300V.
Calculate the Primary current (I1) based on a secondary load current of 33A.
51.48A
192.3A
21.15A
468A
An ideal single-phase autotransformer has a turns ratio of 1.25:1 and a primary voltage of 125V.
Calculate the The current in the common section of the winding based on a secondary load current of 14A and a primary of 7.5Amps.
11.2A
6.5A
9.375
6
What type of transformer is this?
Toroidal
Shell
Core
cylindrical
What type of transformer is this?
Shell
Toroidal
Core
Cube
equal sides
Calculate the maximum secondary current for a 66v/33v 100VA transformer
3.03A
2A
1.5A
15A
