Question 1

The clamp-on ammeter does not have different range settings.

Accepted Answer

The clamp-on ammeter does have different range settings for measuring current. It typically has multiple settings, such as 10A, 100A, and 1000A, depending on the specific model.

Question 2

Current transformers are used to change the full-scale range of ____.
A) wattmeters
B) voltmeters
C) AC ammeters
D) DC ammeters

Accepted Answer

Current transformers are used to change the full-scale range of AC ammeters, as they convert a high primary current to a lower secondary current, which can be measured by an ammeter. Current transformers cannot be used with wattmeters, voltmeters, or DC ammeters.

Question 3

CTs are designed to operate with ____ winding shorted.
A) the secondary
B) the primary
C) both the primary and secondary
D) neither

Accepted Answer

CTs (Current Transformers) are designed to operate with the secondary winding shorted to ensure safety and accuracy. If the secondary winding is open-circuited while the primary is energized, dangerously high voltages can develop, potentially causing damage or injury.

Question 4

Transformer formulas can be used to determine the number of secondary turns needed to produce desired ranges.

Accepted Answer

That is correct. Transformer formulas such as Ns/Np = Vp/Vs can be used to calculate the number of secondary turns needed to produce a desired voltage output.

Question 5

The turns ratio of the transformer can be changed by looping the power wire through the opening in the transformer to produce a primary winding of more than one turn.

Accepted Answer

By looping the power wire through the opening in the transformer, we can create a primary winding with multiple turns, which will change the turns ratio of the transformer.

Question 6

The number of turns needed for a full-scale range of amperes can be calculated using the formula ____.
A) NS / NP = IS / IP
B) NP x NS = IS / IP
C) NP / NS = IS / IP
D) NP / NS = IP / IS

Accepted Answer

The formula for calculating the number of turns needed for a full-scale range of amperes is NP / NS = IS / IP, where NP is the number of turns in the primary coil, NS is the number of turns in the secondary coil, IS is the maximum current in the secondary coil and IP is the corresponding maximum current in the primary coil. Therefore, option C is the correct choice.

Question 7

A(n) ____ transformer is a transformer constructed with a hollow core, similar to a donut in that it has a hole in the middle.
A) solenoid
B) eloid
C) toroid
D) winoid

Accepted Answer

A transformer with a hollow core is called a toroidal transformer.

Question 8

____ of a current transformer must be connected in series with the load.
A) The primary winding
B) The secondary winding
C) Both the primary and secondary windings
D) Either the primary winding or the secondary winding

Accepted Answer

Only the primary winding of a current transformer needs to be connected in series with the load in order to measure the current flowing through it. The secondary winding is used to produce a proportional current that can be measured by a separate instrument or device.

Question 9

Assume that an ammeter provides range values of 5 A, 2.5 A, 1 A, and 0.5 A. Also, assume that the meter movement requires a current flow of 100 mA (0.100) to deflect the meter full scale and that the primary of the current transformer contains 5 turns of wire. The number of turns needed for a full-scale range of 5 amperes is ____ turns.
A) 5
B) 25
C) 125
D) 250

Accepted Answer

The answer of Assume that an ammeter provides range values...

Question 10

When the secondary winding of a CT is opened when there is power applied to the primary, this will cause the transformer to produce a step-down in voltage that could still be high enough to kill anyone who comes in contact with it.

Accepted Answer

When the secondary winding of a Current Transformer (CT) is opened while there is power applied to the primary, it does not produce a step-down in voltage. Instead, it can lead to dangerously high voltage across the open secondary due to the transformer trying to maintain its magnetizing current, potentially causing insulation breakdown or harm to anyone coming into contact with the open secondary terminals.

Question 11

The secondary winding of a CT should never be opened when there is power applied to the primary.

Accepted Answer

Opening the secondary winding of a CT while power is applied to the primary can result in a dangerous voltage surge in the secondary that can cause damage to the CT or injury to personnel. It is important to de-energize the primary circuit before working on the CT.

Question 12

The clamp-on type of AC ammeter uses a current transformer to operate.

Accepted Answer

The clamp-on type of AC ammeter relies on a current transformer to measure the current in a conductor without the need to physically break the circuit.

Question 13

A current transformer has a ratio of 600:5. If the primary power wire is inserted through the opening, it will require a current of 600 amps to deflect the meter full scale. If the primary power conductor is looped around and inserted through the window a second time, the primary now contains two turns of wire instead of one. It requires ____ amps of current flow in the primary to deflect the meter full scale.
A) 125
B) 200
C) 300
D) 600

Accepted Answer

When the primary conductor is looped twice, the effective turns ratio is halved, so it requires 300 amps to deflect the meter full scale.

Question 14

To use the clamp-on type of AC ammeter, clamp the jaw of the meter around ____ of the conductors supplying power to the load.
A) only one
B) one or two
C) two
D) all

Accepted Answer

Clamp-on type AC ammeters are designed to measure the current flowing through a conductor by clamping around only one of the conductors. This allows the meter to measure the magnetic field around the conductor without direct electrical contact, providing a current reading. Clamping around more than one conductor would result in inaccurate measurements due to the cancellation of magnetic fields.

Question 15

A problem with many clamp-on ammeters is that ____.
A) changing the turns ratio is limited to wrapping two turns of wire around the jaw of the ammeter
B) their mid-range scale values are inaccurate
C) they can have different range settings by changing the turns ratio of the secondary of the transformer
D) their lowest scale value is too high to accurately measure low-current values

Accepted Answer

Many clamp-on ammeters have a lowest scale value that is too high to accurately measure low-current values. This can lead to inaccuracies and difficulties in measuring lower currents.

Question 16

When current transformers are used, the main power line is inserted through the opening in the transformer. The power line acts as the primary of the transformer and is considered to be two turns.

Accepted Answer

The power line acts as the primary of the transformer but is considered to be a single turn, not two turns, regardless of how it is inserted through the transformer.

Question 17

Current transformers differ from voltage transformers in that the primary winding is generally part of the power line.

Accepted Answer

Current transformers have their primary winding directly connected to the power line for measuring current, while voltage transformers have their primary winding connected in parallel to the power line for measuring voltage.

Question 18

Many electricians use the clamp-on type of AC ammeter.

Accepted Answer

Many electricians use the clamp-on type of AC ammeter, which can measure the current flow in a circuit without the need to disconnect any wires.

Question 19

In-line ammeters (ammeters that must be connected directly into the line) that have multiple-range values cannot use a current transformer to provide the different ranges.

Accepted Answer

In-line ammeters with multiple-range values can use shunts or other methods to extend their range, but they can also be designed to work with current transformers to provide different ranges, especially for high current measurements.

Question 20

An ammeter with a full-scale range of 0-6 amperes would not be able to measure accurately a current flow of 0.2 amperes. The answer to this problem is to ____.
A) wrap just one turn of wire around the jaw of the ammeter to change the secondary-scale value
B) simply change the secondary-scale value setting
C) wrap multiple turns of wire around the jaw of the ammeter to change the secondary-scale value
D) none of the above

Accepted Answer

Wrapping multiple turns of wire around the jaw of the ammeter will change the secondary-scale value and allow for an accurate measurement of a lower current flow. This is because the current is multiplied by the number of turns, effectively creating a higher current reading on the secondary scale. Wrapping just one turn of wire would not provide enough of a change to accurately measure the lower current, and simply changing the secondary-scale value setting would not account for the limitation of the physical meter itself.

Quiz 6: Current Transformers

The clamp-on ammeter does not have different range settings.

Current transformers are used to change the full-scale range of ____.

CTs are designed to operate with ____ winding shorted.

Transformer formulas can be used to determine the number of secondary turns needed to produce desired ranges.

The turns ratio of the transformer can be changed by looping the power wire through the opening in the transformer to produce a primary winding of more than one turn.

The number of turns needed for a full-scale range of amperes can be calculated using the formula ____.

A(n) ____ transformer is a transformer constructed with a hollow core, similar to a donut in that it has a hole in the middle.

____ of a current transformer must be connected in series with the load.