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INSTRUMENT TRANSFORMER THEORETICAL DISCUSSIONS

INSTRUMENT TRANSFORMER THEORETICAL DISCUSSIONS
Basic theoretical concept of instrument transformers guide

Instrument transformer is the standardized term used for current and voltage transformer.

Theoretical Reminder:

Current Transformers
Current transformers have a similar composition to "conventional" transformers. A magnetic circuit (generally made of an iron alloy) in the shape of a toroid is surrounded by N1 turns on the primary and N2 turns on the secondary. The primary can be reduced to a simple conductor passing through the toroid (n1 = 1) (see figure 6-2).

basic current transformer
General Application Rule
Current transformers feed measuring, control and monitoring devices. Galvanic insulation electrically seperates the primary circuit from the secondary circuit. It allows earthing of the electrical measuring device and thus ensures safety of operating personnel.

The current transformer is designed to give the secondary a current that is proportional to the primary current. The seondary is connected to a low impedance (use in practically short-circuited conditions). In a current transformer, the primary current/secondary current ratio is constant. The secondary current is thus independent of the burden as long as saturation is not reached.

Voltage Transformers



General Application Rule

 The voltage transformer is a transformer connected to a very high impedance (used on an almost open circuit).The electrical operation theory of voltage transformers is analogous with that of power transformers.

A voltage transformer is designed to give the secondary a voltage proportional to that applied to the primary. For a voltage transformer, the primary voltage/secondary voltage ratio is constant. The secondary voltage is independent to the burden.


Specifications and definitions of voltage transformer parameters

The voltage transformer must comply with the network specifications.

As with any device, the voltage transformer must meet requirements relating to the voltage, current and frequency.

Voltage transformer specifications are only valid for normal conditions of use. A derating should be provided for in acordance with the ambient temperature and the altitude.


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  1. UnknownFebruary 18, 2016 at 12:46 PM

    Very good post on CTs, I also have an article regarding types of CTs on my page if anyone is interested in learning more about Current Transformer Theory. Cheers!

    ReplyDelete

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