Current Measurement Using Current Transformer

Published Sep 05, 2018

Apache-2.0

13 hours to build

Intermediate

arduino

This project is for to measure the current using current transformer and Arduino.

Components Used
INA199A2DCKR Current Sense Amplifiers INA199A2DCKR	X 1
Variable Transformer Variable Transformer	X 1
Digital Multimeters Digital Multimeters Fluke 87V MAX DMM and PVLEAD1 MC4 Test Leads Bundle	X 1
Resistor 20 Ohms Metal Film Resistors - Through Hole 20 OHM 1/4W 1%	X 2
Resistor 1 Ohms Metal Film Resistors - Through Hole 1 OHM 1/4W 1%	X 2
Capacitor 10 µF Aluminium Electrolytic Capacitors - Radial Leaded 100V 10uF 85C 2k Hour Radial	X 1
Capacitor 100nF Multilayer Ceramic Capacitors MLCC - Leaded K 50V 100NF +/- 10 % X7R AMMO E3	X 5
Resistor 1 kOhms Metal Film Resistors - Through Hole 1K ohm 1/4W 1%	X 1
Current transformer Current Transformers PACT SPC-20-1A-D13	X 1
Rheostat	X 1

Description

Basics of Current Transformer

A current transformer is a device that produces a reduced current in its secondary winding accurately proportional to the current flowing in its primary winding. The secondary current flows through the secondary winding usually called as burden resistor.

Classes of CT

0.1 or 0.2 for precision measurements.
0.5 for high grade kilowatt hour meters for commercial grade kilowatt hour meters.
3 for general industrial measurements.
3 or 5 for lower accuracy commercial measurements.

Here I’m used class 0.1 with the 2500 Turns Ratio of current transformer.

Selection of Burden Resistor

CT turns ratio is 2500:1 then the secondary current is 1/2500 of the primary current.

In a typical application, the secondary current is applied to a resistor (usually defined as the “burden resistor”) of a few ohms in order to generate a voltage signal.

Following Ohm’s law, the resulting voltage V across the burden resistor R is:

Vout=(ILoad/N)R burden

Where,

N = turn’s ratio and

I Load = primary load current.

Note: The optimum burden resistor value is specified by the CT manufacturer. If the burden resistor value is too high, the output becomes non-linear.

Selection of CT

The selection of a current transformer includes factors such as range of current being measured, turns ratio and the class. The resultant accuracy depends on these parameters. Subjecting a current transformer to load currents above the manufacturer’s rated current specification will saturate the core and may cause mechanical failures due to an excessive temperature rise. On the other hand, a current transformer that is rated much higher than the target load current might be restrictively too large and too expensive for its purpose. A typical rule of thumb is to select a current transformer which is rated approximately 20% above the expected maximum load current.

Basic Formulas

Secondary current calculation