Current transformer selection....Guidance needed

[tkvenki]

Hi all,

First let me give a brief introduction to the circuitry.
The ade7758 evaluation board can take 22mA current.
But Energy meter manufacturers usually specify their buden as 1A or 5A.
So if we do that, then we have to incorporate an internal CT.

The internal CT will have
Primary current : 0 to 1A.....(or 5A)
secondary current : 0 to 22mA.
Can a get a CT like this??.

Other option is to use a 200:1 CT internally, then
If we specify the burden of our meter as 5A, then we get 25mA, which can be
given to the evaluation board.

But the problem here is I'm unable to find a 200:1 CT with 0.1% accuracy.
The 0.1% is mandatory as the ade7758 is having the same accuracy.

Please help me out by getting me few links for getting a high precision current transformer. I tried out in google....but i did not get the required results. suggest me some good search strings for google.

 

[zachtheterrible]

What kind of board is this? I have no idea what a ade7758 evaluation board is evaluating :lol:
Is the transformer you need a power transformer (from the wall) or a transformer on the board to match impedances, step up voltage . . .?

What's the difference between a current transformer and a regular transformer?

 

[Klaus]

What kind of board is this? I have no idea what a ade7758 evaluation board is evaluating :lol:
Is the transformer you need a power transformer (from the wall) or a transformer on the board to match impedances, step up voltage . . .?

What's the difference between a current transformer and a regular transformer?

Zach, a current transformer is often a toroid shaped core with a large number of current sensing turns around it. The wire ( or busbar) that carries the current to be measured is fed through the core (or loped around it a few times).
The ratio of the windings lets you measure large quite currents with a small scale meter.
These CT's only work for AC, naturally. One precaution is to short the sensing wires before the meter is removed as an open circuit sense coil can develop a dangerous voltage at its terminals.
CT's measure current without having to interrupt the current carrying wire /busbar. The clamp on Ampmeters work on this principle too.
Klaus

 

[Phasor]

What's the difference between a current transformer and a regular transformer?

In a nutshell, whereas a voltage transformer (or power transformer) gives you a ratio of the input voltage, a current transformer gives you a ratio of the input current at the output.

 

[john1]

Hi tkvenki,

don't see a problem with such a CT.

Why do you think there's a problem ... ?

 

[john1]

Unless its the accuracy thats concerning you ... ?
you can make your own small adjustments externally if you are that
concerned about the 1 per cent accuracy.
Most of them would be in that area of accuracy anyway i would think.
Its easy enough for you to check for yourself.

 

[tiger_king]

small adjustments should be made, my design works very well.

 

[grim]

you should be able to get a very accurate ct - at a set point - it's the linearity that is difficult.

here is a link

 

[penoy_balut]

just put a current limiting resistor in your CT secondary

 

[vivek_acharya21]

ADE7758 SPI Cmmunication Register

Please help me how to access the ADE7758 Register.
I interface the ADE7758 with MCU. I wrote SPI Communication program but the outcomes values are inproper.

Please let me know how to proper way access the ADE7758 Register.

If possible please mail me on: vivek_acharya21@yahoo.com or
call to me on +919925226614