Correct MHO relay wiring

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mbrooke

mbrooke

Batteries Included
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Technician
Question, is the wiring for the restraint coil transformer correct for the relay at the far right or should it be like the other two on the left? If it is indeed meant to be different, is this to produce an offset zone 3 or does it serve another purpose? I'm clueless on this one.
 

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MBrooke...

Actually it's simpler than you think! But first, I'm advising you.. DO NOT MESS WITH MFG'S WIRING! They are different by design! Define "Mho" and I will reveal why!

Phil
 
Last edited:
Phil Corso said:
MBrooke...

Actually it's simpler than you think! But first, I'm advising you.. DO NOT MESS WITH MFG'S WIRING! They are different by design!
Click to expand...

Ok- but I still want to know from a physics or theory standpoint. I can't think of any reason why it would be wired that way, not even to achieve an offset.




Define "Mho" and I will reveal why!

Phil
Click to expand...


In simple terms Z=V/I. Voltage is the restraint current is the operate.

The idea is that you trip at about the same location regardless of your source impedance- meaning you do not exhibit under reach and over reach as fault current levels change as you would with conventional over current relays.
 
MBrooke, et al

Definition:
Mho (Admittance) is the inverse of Ohm (impedance! And now, the rest of the story!

History
Early in the history of protection schemes, transmission line-protection was relegated to current-monitoring devices, i.e., instantaneous, time-overcurrent, directional-instantaneous, distance, etc! But, as lines grew longer and voltages higher, it became more difficult to implement the equations (based on impedance) with hardware (relays). Furthermore, fault-clearing times became intolerable as other systems, like radial feeders (which led to the 3-zone concept) and tapped-bus, were introduced! As early as the 30’s, protection schemes using “admittance-based” equations made it easier to implement with hardware! Additionally, fault-clearing times were improved to less than 1-cycle!

Today
Fuggedaboudit. It's all done by software!

Reason Against Re-wiring
The diagram submitted by MBrooke must not be changed! Each section, purported to be ‘miswired', are intentionally designed to energize the four-poles of a mini ‘2-phase motor’! Thus, sufficient torque is developed to actuate the trip-contact pertinent to the zone in which the fault occurs

Reference
“Silent Sentinels”, Messer’s J.L. Blackburn and G.D. Rockefeller, 1964 (Prof. Blackburn was my teacher and mentor)
(An aside, the cost of the book was $3.00 when I purchase it in school!)

Regard, Phil Corso
 
Last edited:
Phil Corso said:
MBrooke, et al

Definition:
Mho (Admittance) is the inverse of Ohm (impedance! And now, the rest of the story!
Click to expand...


yup-

as conductance is the reciprocal or resistance, admittance the reciprocal of impedance and suseptance is the reciprocal of inductance and reciprocal of capacitance is elastance (daraf).


History
Early in the history of protection schemes, transmission line-protection was relegated to current-monitoring devices, i.e., instantaneous, time-overcurrent, directional-instantaneous, distance, etc! But, as lines grew longer and voltages higher, it became more difficult to implement the equations (based on impedance) with hardware (relays). Furthermore, fault-clearing times became intolerable as other systems, like radial feeders (which led to the 3-zone concept) and tapped-bus, were introduced! As early as the 30’s, protection schemes using “admittance-based” equations made it easier to implement with hardware! Additionally, fault-clearing times were improved to less than 1-cycle!
Click to expand...


I think they mean trip decision time. Even the best HV breakers today take about 2 cycles to open, 5 if not operated for some time. So 3 to 6 cycles total.

Today
Fuggedaboudit. It's all done by software!
Click to expand...

True, but you still have a MASSIVE base of eletromechanical relays in existence.

Reason Against Re-wiring
The diagram submitted by MBrooke must not be changed! Each section, purported to be ‘miswired', are intentionally designed to energize the four-poles of a mini ‘2-phase motor’! Thus, sufficient torque is developed to actuate the trip-contact pertinent to the zone in which the fault occurs
Click to expand...

Ok- but why the difference in wiring? What does it do? I can't find anything that will explain the reason.
 
MBooke...

My 'but' in response to your "true but"...

Yes... but, did you know that a massive're (meaning greater than massive) portion of our protection systems use soft-ware provided by foreign companies! :weeping:

Phil
 
Phil Corso said:
MBooke...

My 'but' in response to your "true but"...

Yes... but, did you know that a massive're (meaning greater than massive) portion of our protection systems use soft-ware provided by foreign companies! :weeping:

Phil
Click to expand...

Explain... I know thw hardware (SEL) is US based.
 
Phil Corso said:
MBooke...

My 'but' in response to your "true but"...

Yes... but, did you know that a massive're (meaning greater than massive) portion of our protection systems use soft-ware provided by foreign companies! :weeping:

Phil
Click to expand...

Well...... i guess maybe the bright side is feeling better about all the genny hook ups i do Phil :) ~RJ~
 
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