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Instrument Transformers in AC Circuits

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Questions and Answers

What are the two main reasons for using instrument transformers in measurement?

To extend the range of measuring instruments and to isolate them from high-voltage lines (correct)

To increase accuracy and to reduce cost of instruments

To decrease power consumption and to reduce size of instruments

To reduce power loss and to increase the safety of operators

What is the main advantage of using CT over shunts in ac circuits?

CT is cheaper than shunts

CT does not require careful designing of reactance and resistance proportions (correct)

CT is more accurate than shunts

CT is more reliable than shunts

What is a limitation of using shunts for circuits involving large current?

Shunts are not safe for the operator

The power loss in the shunt itself will become prohibitively high (correct)

Shunts are too expensive

Shunts are not accurate for large currents

What is a problem with using multipliers in measurement?

They can introduce errors in measurement due to inherent leakage current Signup and view all the answers

What is an advantage of using instrument transformers with ammeters?

They eliminate the need for careful designing of reactance and resistance proportions Signup and view all the answers

Why are measuring circuits involving shunts or multipliers not safe for the operator?

They are not electrically isolated from the power circuit Signup and view all the answers

What is an advantage of using a suitable multi-range CT or PT with a single-range instrument?

It allows the instrument to cover a wide range of measurement Signup and view all the answers

What is the main difference between a CT and a PT?

A CT is used for measuring current and a PT is used for measuring voltage Signup and view all the answers

What is the main reason why instrument transformers are used in measurement of voltage, current, energy, and power in ac circuits?

To extend the range of measurement and to isolate the measuring instrument from high-voltage lines Signup and view all the answers

What is a disadvantage of using multipliers in measurement?

They can introduce errors in measurement due to inherent leakage current Signup and view all the answers

Study Notes

Instrument Transformers

Used in measurement of voltage, current, energy, and power in AC circuits
Two main reasons for use:
- Extend (multiply) the range of measuring instruments
- Isolate measuring instruments from high-voltage lines

Types of Instrument Transformers

Current Transformer (CT): extends current ranges of instruments
Voltage or Potential Transformer (PT): increases voltage ranges

Advantages of Instrument Transformers

Over Shunts and Multipliers

No need for careful design of reactance and resistance proportions for shunts and meters
Can be used for circuits involving large currents without excessive power loss
No introduction of errors in measurement due to leakage current
No unnecessary heating due to power loss
Electrically isolated from power circuit, ensuring operator safety
Can cover a wide range of measurements with single-range, moderate-sized instruments
Can reduce overall cost by connecting multiple instruments to the same instrument transformer

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Description

Learn about the use of instrument transformers in measuring voltage, current, energy, and power in AC circuits. Understand their importance in extending measurement ranges and isolating instruments from high-voltage lines.