ION9000 2CT wiring and configuration

[joel_mora_soati]

Hello Experts,

I have an ION9000 wired as 4W-WYE system with 3 CTs. I had an issue with the L2 current and my customer is asking me to change the ION configuration to work with 2CT.

I have done this configuration with low cost meters as PM5000 not in an ION9000. If I look at the basic parameters I don't see the option to select just 2CT.

Can you help me to understand the requierents of wiring and configuration?

Thanks. 

[Charles_Murison]

Hello @joel_mora_soati ,

If you look at the image you shared, you can see that the 2 CT method using the I1 and I3 feed into I2 "backwards". What this does on a physical level is give -(I1+I3) signal into the input of I2. The result is in system with only 3 current paths (I1,I2,I3), I2 would be the equivalent to what a CT would give. When you have 4 current paths (I1+I2+I3+N) you cannot use this method. You need 1 less CT than path minimum for accurate readings.

Regards,

Charles

[joel_mora_soati]

Thanks @Charles_Murison.

Just to confirm there is no aditional configuration in meter parameters?

[Charles_Murison]

Hello @joel_mora_soati ,

I want to mention again that the 2 CT method is intended for Delta systems where there are only 3 current conductors. If you use the 2 CT method as shown in the diagram, the meter will not be able to detect any neutral current. 

The meter's Volts mode will be the only configuration that would change based on how the meter is wired.

Regards,

Charles

[DanL · Accepted solution]

correct, there is no additional configuration in meter parameters because the meter still sees three currents. The I2 secondary signal is the wired inverted summation of I1 and I3 (aka. residual current).

In a 4-WYE system, if there really is a 4th wire (ie. neutral) connected to the loads then using only 2 CTs may not result in accurate readings. See Blondel's theorem for more information:

https://en.wikipedia.org/wiki/Blondel%27s_theorem