Instrument for Reading Sequence Components

An oscilloscope could probably do it.

positive peak detector, negative peak detector, and zero cross over detector, coupled with three different event counters, should work.

This should work..

http://www.hobbylab.us/default.aspx

Rakesh

This method follows along with your comments. However I am not sure I understand how you measure the Zero component. Can you explain more detail.

Eagle

That looks like an expensive hobby lab.

Eagle

Every time wave form crosses zero line a trigger pulse can be generated with zero cross over detector, some of examples can be seen on this page.

Rakesh,

just try to do it by some bunch of diodes and capacitors and pulse counter

I understand that but does it give you a zero sequence component or zero sequence current/voltage?

its just by the way you design the circuit. Diodes, Capacitor & pulse counter will do irregardless of magnitude (voltage/current) if you are just to find the sequence.

Yes, but it is not as simple as most previous posters have incorrectly assumed.

Symmetrical components is a mathematical artifice created long before digital computers existed, a time when slide rules and nomograms were the only way to do complex calculations and vector math. These parameters do not exist in physically realizable network elements however physically realizable network components can be interconnected to create a Symmetrical Component Network Element whose measured parameters will correspond to the calculated values. The "Sequence Filters" in the Wikepedia article are those elements. Modern digital computational methods do the matrix math on the measured waveforms as described here (you could probably build a decent meter based upon this info)...

www.must.edu/Publications/AFSLS.pdf

From Wikipedia, the free encyclopedia....

In electrical engineering, the method of symmetrical components is used to simplify analysis of unbalanced three phase power systems under both normal and abnormal conditions.

In 1918 Charles Legeyt Fortescue presented a paper^[1] which demonstrated that any set of N unbalanced phasors (that is, any such polyphase signal) could be expressed as the sum of N symmetrical sets of balanced phasors, for values of N that are prime. Only a single frequency component is represented by the phasors.

In a three-phase system, one set of phasors has the same phase sequence as the system under study (positive sequence; say ABC), the second set has the reverse phase sequence (negative sequence; CBA), and in the third set the phasors A, B and C are in phase with each other (zero sequence). Essentially, this method converts three unbalanced phases into three independent sources, which makes asymmetric fault analysis more tractable.

By expanding a one-line diagram to show the positive sequence, negative sequence and zero sequence impedances of generators, transformers and other devices including overhead lines and cables, analysis of such unbalanced conditions as a single line to ground short-circuit fault is greatly simplified. The technique can also be extended to higher order phase systems.