Instrument Transformer and Uses

What is Instrument Transformer and how does it work?

The Instrument transformers are as same as other conventional transformers but different it is just high-accuracy class electrical devices. Instrument transformers are actually used to isolate or transform voltage or current levels for using metering or controlling signals. 

Operating the instruments for controlling the system or measuring the high-level voltage or current, the instrument transformers are used to decrease to voltage or current level to the measuring level for safely isolating secondary control circuitry from the high voltages or currents. 

Using of Instrument Transformer

So, if you ask what Instrument Transformer is, In simply, we can say that Instrument Transformers are used in AC systems for the measurement of electrical quantities like- voltage, current, power, energy, power factor, and frequency. Instrument transformers are also used with protective relays for the protection of the power system.

Instrument transformer Connection Procedure

The high voltage or high current end of the circuit is connected to the primary winding of the instrument transformer and the meter or relay is connected to the secondary circuit.

Types of Instrument Transformers

Instrument transformers are of two types –

1. Current Transformer (C.T.)
2. Potential Transformer (P.T.)

Read more details on Current Transformer 

Current Transformer and Traditional Transformer

Read more details on Current Transformer 

Voltage Transformer Primary & Secondary Connection

Difference between C.T. and P.T.

Sl. No.	Current Transformer (C.T.)	Potential Transformer (P.T.)
1	Connected in series with power circuit.	Connected in Parallel with Power circuit.
2	The secondary is connected to Ammeter.	The secondary is connected to Voltmeter.
3	Secondary works are almost in short-circuited condition.	Secondary works are almost in open-circuited condition.
4	The primary current depends on the power circuit current.	The primary current depends on the secondary burden.
5	Primary current and excitation vary over a wide range with the change of power circuit current	Primary current and excitation variations are restricted to a small range.
6	One terminal of the secondary is earthed to avoid the insulation break down.	One terminal of the secondary can be earthed for safety.
7	The secondary is never open-circuited.	Secondary can be used in open circuit conditions.

You may know the details about the electrical transformer from the following articles:

 

1. Working Principle of Transformer;
2. Transformer Construction;
3. Core-type Transformers;
4. Shell-type Transformers;
5. Elementary Theory of an Ideal Transformer;
6. E.M.F. Equation of Transformer;
7. Voltage Transformation Ratio;
8. Transformer with losses but no Magnetic Leakage;
9. Transformer on No-load;
10. Transformer on Load;
11. Transformer with Winding Resistance but no Magnetic Leakage;
12. Equivalent Resistance;
13. Magnetic Leakage;
14. Transformer with Resistance and Leakage Reactance;
15. Simplified Diagram;
16. Total Approximate Voltage Drop in Transformer;
17. Exact Voltage Drop;
18. Equivalent Circuit Transformer Tests;
19. Open-circuit or No-load Test;
20. Separation of Core Losses;
21. Short-Circuit or Impedance Test;
22. Why Transformer Rating in KVA?;
23. Regulation of a Transformer;
24. Percentage Resistance, Reactance, and Impedance;
25. Kapp Regulation Diagram;
26. Sumpner or Back-to-back-Test;
    
27. The efficiency of a Transformer;
28. Condition for Maximum Efficiency;
29. Variation of Efficiency with Power Factor;
30. All-day Efficiency;
31. Auto-transformer;
32. Conversion of 2-Winding Transformer into Auto-transformer;
33. Parallel Operation of Single-phase Transformers;
34. Questions and Answers on Transformers;
35. Three-phase Transformers;
36. Three-phase Transformer Connections;
37. Star/Star or Y/Y Connection;
38. Delta-Delta or ∆/∆ Connection;
39. Wye/Delta or Y/ Connection;
40. Delta/Wye or ∆/Y Connection;
41. Open-Delta or V-V Connection;
42. Power Supplied by V-V Bank;
43. Scott Connection or T-T Connection;
44. Three-phase to Two-Phase Conversion and vice-versa;
45. Parallel Operation of 3-phase Transformers;
46. Instrument Transformers;
47. Current Transformers;
48. Potential or Voltage Transformers.