Measure negative sequence currents.

[Audun]

I'm wondering if anybody has a setup for measuring negative sequence currents. (using 5A CTs)
Anything analoge, not digital please.

Audun

 

[dpc]

It is possible to configure passive elements (reactors and resistors) in such a way as to develop a voltage that is proportional to negative sequence current.

If you have a copy of the Westinghouse "Applied Protective Relaying", there is an example schematic shown in Figure 3-8. Older electro-mechanical 46 relays operated on this principle.

 

[busbar]

One possible “out-of-the-box” capability is a Basler BE1-46N with analog output option

http://www.basler.com/downloads/udj7bull.pdf

The text, A R Van Warrington, "Protection Relays Their Theory and Practice"

 

[Audun]

I know there is a way of using passive components, and this
is what I want. I don't have the book dpc refers to, so please describe it in detail...

Audun

 

[busbar]

However seemingly inconvenient, libraries are wonderful places.

 

[electricpete]

Well, there are plenty of negative sequence current meters (used on generators) and relays on the market. Some of the relays based on electromechanical.

HCB-1 pilot wire relay includes negative sequence filter. Manual is available here but very slow. I don't know if the diagram is in there:

http://www.abb.com/global/abbzh/abb...6312A&e=us&c=E7EF0335F231D88285256AB900400274

 

[electricpete]

Well, the hcb flyer finally loaded and nothing there.

I hate to try to think about reinventing the wheel since it's already been done. But... I'm just thinking about how you would do it starting from the definition.... something like I- = Ia + A*Ib + A^2*Ic where A is exp(j*120 degrees)... and you might switch the B and C coefficients depending upon your power system phase rotation.

So... how to shift the phase of a current. Well certainly putting it through an RC or RL network could develop that phase shift on the voltage... then how to add the voltages? Hmmm.

 

[Bung]

Alstom's old PRAG, now available online at relaylounge.com.

Bung
Life is non-linear...

 

[jbartos]

Suggestion: Reference:
1. C. Russell Mason "The Art and Science of Protective Relaying," John Wiley and Sons, Inc., 1956,
page 189 figure 22 A positive-phase-sequence-current filter and relay.
By interchanging the leads in which Ib and Ic flows, the filter becomes a negative-phase-sequence-current filter.