WorksheetsTransformer Fundamentals Worksheet
Total questions: 53
Worksheet time: 27mins
Single phase and three phase loads can be supplied by ______ transformer connections.
Open delta
Delta–delta
Open wye–open delta
Wye–delta
The principle of self‑induction is employed with a:
Step‑up transformer
A.C. generator
Autotransformer
Motor
A bank of transformers that has a low impedance path and high circulating currents will be caused by:
Mismatched transformers
Re‑magnetized transformers
Ungrounded transformers
Loss of one phase
The series‑winding in a step‑down autotransformer has a volt‑per‑turn value of 0.46 volts. The common winding in the same transformer will have a volt‑per‑turn value of:
1.2 volts
0.86 volts
0.46 volts
1.5 volts
The primary neutral current contains a third harmonic with a balanced load and is most apparent with a ______ connection.
Y–Y
Y–Δ
Δ–Δ
Δ–Y
Three 1 kVA single‑phase transformers are connected in a delta‑wye configuration. If the primary line voltage is 480 volts, what is the voltage from A to B on the secondary?
120 volts
208 volts
240 volts
277 volts
On a transformer nameplate, taps labeled with the letters “FCAN” stand for:
Full capacity below normal
Reduced capacity above normal
Full capacity above normal
Reduced capacity below normal
Delta‑wye connected transformers ______ support three‑phase as well as single‑phase loads.
can
cannot
must be reconfigured first
require a tertiary winding to
A lighting ballast is connected for a 208‑volt supply. With the lamp removed from the lamp holder socket and a voltmeter connected to measure the open‑circuit voltage, it would read:
240 V
300 V
480 V
220 V
Polarity and secondary currents are not the same with ______ connected transformers.
Δ–Δ
Y–Y
Δ–Y
Y–Δ
The ______ rating of a breaker indicates the amount of short‑circuit current that it can safely clear.
interrupting rating
ampere rating
thermal rating
demand rating
Three‑phase transformers connected for four‑wire wye have their voltage balance accomplished with the use of a:
phase‑shifting reactor
zig‑zag transformer
isolation autotransformer
neutral grounding resistor
The three phase transformer bank shown is connected in
Y
Δ
Δ-Δ
Y-Δ
if the primary phase voltage is 240v then the secondary line voltage will be....
480V
480VA
960V
960VA
if the primary phase voltage is 240v then the secondary line voltage will be....
480V
480VA
120V
120VA
A transformer has 50 turns on the primary winding. From the bottom of the secondary upward, the taps provide 15 V, then 60 V, and 120 V at the top. With a 120 V supply applied to the primary, how many turns are on the secondary tap that produces 15 V?
400
6.25
15
120
A transformer has multiple secondary windings. If one of the windings has 208V, how much windings would this correspond to when linked to a 24 V supply?
1040|120
12|4
1200|120
208|24
A transformer has multiple secondary windings. If one of the windings has 208V, how much windings would this correspond to when linked to a 24 V supply? what is the coil Ratio.
8.66'
3
10
8.66
A transformer has multiple secondary windings. If one of the windings has 240V, how much windings would this correspond to when linked to a 24 V supply? what is the coil Ratio.
8.66'
3
10
8.66
Transformer taps are usually full capacity, meaning that:
The transformer can deliver its rated kVA only at the nominal tap position.
The transformer can deliver its rated kVA regardless of the tap position.
The transformer can only operate at reduced capacity when taps are changed.
The transformer taps limit the current from the rated value.
What type of connection does the transformer secondary use to deliver voltage to the load/output?
Y
Δ
In a three-phase transformer bank, what is the primary purpose of the power leg on the secondary side?
To reduce current
To provide a neutral point
To balance the load
To increase voltage
When connecting a three-phase transformer bank, which configuration is commonly used to ensure a stable power leg on the secondary side?
Δ-Y
Y-Δ
Δ-Δ
Y-Y
In a transformer with a (YΔ) connection, what is the relationship between the primary and secondary voltages?
Primary voltage is higher than secondary voltage
There is no relationship
Primary voltage is equal to secondary voltage
Secondary voltage is higher than primary voltage
What is the advantage of connecting the primary side of a transformer in Wye (Y) and the secondary side in Delta (Δ)?
Increased efficiency
Ability to handle unbalanced loads
Reduced losses
Improved voltage regulation
What is the nominal declared voltage for a grounded wye connected transformer connection?
Neutral voltage
Grounded voltage
Phase voltage
Line voltage
In a delta connected transformer, what is the nominal declared voltage when it is ungrounded?
Neutral voltage
Phase voltage
Grounded voltage
Line voltage
Which of the following describes the nominal declared voltage for a wye connected transformer?
It is always lower than delta voltage
It is always higher than delta voltage
It is the same as phase voltage
It is the same as line voltage
What is the relationship between line voltage and phase voltage in a wye connected transformer with a nominal voltage of 480/277V?
Line voltage is equal to phase voltage
Line voltage is higher than phase voltage by a factor of √3
There is no relationship
Phase voltage is higher than line voltage by a factor of √3
What is the nominal declared voltage for an ungrounded wye connected transformer connection?
Both 138V and 230V
Neither 138V nor 230V
230V
138V
What is the significance of the high leg voltage in a grounded delta connected transformer?
It helps in balancing the load
It reduces the risk of electrical shock
It allows for higher phase voltage
It provides a neutral point for grounding
Select subtractive polarity.
Left
Right
Select Additive polarity.
Left
Right
What is the primary function of a control voltage transformer in industrial applications?
To isolate circuits
To provide backup power
To convert high voltage to a lower control voltage
To increase high voltage
When converting 240V to 24V using a control transformer, what is the voltage ratio?
5:1
10:1
8:1
12:1
What type of transformer is used to supply a stable, low-voltage output for operating control devices such as relays, contactors, and indicator lights?
Control voltage transformer.
Control Current transformer.
Control Apparent transformer.
Control Resistance transformer.
In a three-phase transformer bank, what is the effect of connecting the primary side in a delta configuration?
It eliminates the need for a neutral connection
It increases the line voltage
It allows for better load balancing
It reduces the phase current
What is the primary advantage of connecting the primary side of a transformer bank in wye configuration?
Ability to provide a neutral point
Lower voltage drop
Reduced harmonic distortion
Higher efficiency
When the primary side of a three-phase transformer bank is connected in wye, what is the relationship between the line and phase voltages?
Line voltage is equal to phase voltage
Line voltage is higher than phase voltage by a factor of √3
Phase voltage is higher than line voltage by a factor of √3
There is no relationship
What is the typical voltage level on the primary side of a transformer when it is rated at 6900V?
240V
480V
6900V
120V
In a transformer, what does the primary voltage of 6900V indicate about its application?
It is only for residential use
It is suitable for low voltage applications
It is used for medium voltage applications
It is designed for high voltage transmission
When a transformer has a primary voltage of 6900V, what is the expected phase voltage in a wye configuration?
3970V
6900V
4000V
3970V
The current flow in a transformer is called.
Amps
Excitation
Volt Amps
What is the primary cause of excitation in a transformer?
Inductive reactance
Electrical resistance
Magnetic flux linkage
Capacitance
What is the primary principle that allows a single-phase transformer to operate?
Capacitance
Electromagnetic interference
Resistance
Mutual induction
In a single-phase transformer, what happens to the magnetic field when alternating current magnetizes the secondary winding?
It reverses direction
It remains constant
It becomes static
It collapses
What is the main advantage of using a delta-delta transformer connection in industrial applications?
Improved voltage regulation
Ability to provide a neutral point
Reduced harmonic distortion
Higher efficiency under balanced loads
In a wye-delta transformer connection, what is the effect on the phase current when stepping down voltage?
Phase current remains the same
Phase current becomes zero
Phase current decreases
Phase current increases
Which of the following correctly describes the characteristics of a Delta/Wye transformer connection?
Provides line-to-line and line-to-neutral voltages, allows for grounding of the neutral, and can supply both three-phase and single-phase loads.
Provides only line-to-line voltage, cannot be grounded, and is mainly used for low-voltage single-phase applications.
Uses only two transformers to supply three-phase loads and cannot provide a neutral.
Is limited to supplying ungrounded high-voltage systems only.
Which of the following is a disadvantage of a delta-wye transformer connection?
Increased voltage drop
Higher risk of unbalanced loads
Increased harmonic distortion
Requires a neutral connection
Which of the following statements is true about an Open Delta (V-V) transformer connection?
It uses three transformers, can carry the full load, and provides both line-to-neutral and line-to-line voltages.
It uses two transformers, can supply three-phase loads at reduced capacity (~57.7% of full load), and is often used as a temporary or economical solution.
It is identical to a Delta/Wye connection but provides extra capacity for heavy loads.
It is used only for single-phase loads and cannot supply three-phase equipment.
What is the effect of using a four-wire delta transformer connection on the phase current?
It balances the phase current
It has no effect on the phase current
It increases the phase current
It decreases the phase current
What is the primary advantage of using a four-wire delta transformer connection?
It improves load balancing
It reduces harmonic distortion
It allows for higher phase voltage
It provides a neutral point for grounding
