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arun_sdm
Participant

Join Date: Nov 2011
Posts: 4

Offset MHO Relay

11/21/2011 11:18 AM

Hi everybody,

I am having some queries regarding offset mho relay used in loss of field generator protection.

Here relay operation is based on Impedance Z.If calculated impedance and its angle enters the circle, relay issues trip.

Offset is distance from origin towards -X, which is normally set as -0.5 * X'd(Direct axis transient reactance).

Circle diameter is equal to direct axis synchronous reactance, Xd

It is clear that relay operation is based on impedance, which is measured in ohm.

Then why the protection named as offset mho ?

why not offset ohm.

Pl explain

Regards,

Arun
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lyn
Guru

Join Date: Oct 2008
Posts: 42355
Good Answers: 1693
#1

Re: Offset MHO Relay

11/21/2011 12:11 PM

Because it's not.

Siemens (unit) - Wikipedia, the free encyclopedia
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arun_sdm
Participant

Join Date: Nov 2011
Posts: 4
#2
In reply to #1

Re: Offset MHO Relay

11/21/2011 11:26 PM

Hi Lyn,

Impedance (Z) is calculated from resistance and impedance, where its unit is ohm

Admittance (Y) is calculated from conductance and susceptance, where its unit is mho/siemens

Here offset mho relay works on calculation of Impedance (Z).

Kindly clarify me

Thanks & Regards,

P.S.Arun kumar
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arun_sdm
Participant

Join Date: Nov 2011
Posts: 4
#3

Re: Offset MHO Relay

11/21/2011 11:28 PM

Hi Lyn,

Impedance (Z) is calculated from resistance and impedance, where its unit is ohm

Admittance (Y) is calculated from conductance and susceptance, where its unit is mho/siemens

Here offset mho relay works on calculation of Impedance (Z).

Kindly clarify me

Thanks & Regards,

P.S.Arun kumar
Register to Reply
arun_sdm
Participant

Join Date: Nov 2011
Posts: 4
#4

Re: Offset MHO Relay

11/25/2011 11:00 AM

Hello all,

Pl clarify my doubt.

Regards,

Arun
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