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Figure A.1 – Non-directional circular characteristic with directional supervision

Figure A.1 – Non-directional circular characteristic with directional supervision

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IEC 60255-121:2014 © IEC 2014



– 103 –



While in conventional electromechanical relays the MHO characteristic is a circle, in

microprocessor based relays in order to achieve better performance under different conditions

the MHO circle is used with additional blinders.

The characteristic used here should accommodate all characteristics in use as shown in

Figure A.2.

X

PsReactAng



PsReactRch

PsImpRch

PsImpAng

PsRisRch

OfsImpRch



DirChrAng1



PsRisAng



R



PsImpRch

PsImpAng



Positive Impedance Reach

Positive Impedance Angle



OfsImpRch

OfsImpAng



Offset Impedance Reach

Offset Impedance Angle



PsRisRch

PsRisAng



Positive Resistive Reach

Positive Resistive Angle



PsReactRch

PsReactAng



Positive Reactance Reach

Positive Reactance Angle



DirChrAng



Directional Characteristic Angle



OfsImpAng

IEC



0178/14



Figure A.2 – MHO characteristic

Polar reach

PsImpRch: The polar reach defines the reach of the MHO circle and corresponds to the

percentage of line impedance which is protected by the zone. For MHO circles without offset,

this represents the diameter of the circle. The reach is set with the two parameters:





PsImpRch and the PsImpAng are the two settings that define the polar reach.







PsImpAng is measured from the positive R-axis counter clockwise.



Offset

For setting an offset on the MHO circle the two parameters OfsImpRch and OfsImpAng are

used. OfsImpAng is measured from the positive R-axis counter clockwise.

Blinders

In some relays the MHO characteristic is combined with blinders which will limit the resistive

reach as well as the reactive reach of the MHO characteristic. The positive resistive blinder is

built by a line which crosses the R-axis at PsRisRch. The slope of the resistive blinder is set

with the setting via PsRisAng. PsRisAng is measured counter clockwise from the R-axis. The

area right from the blinder is excluded from the operating area.

Resistive reach scaling (loop based or phase based) needs to be identified .

The negative resistive blinder is built by a line which crosses the R-axis at NgRisRch. The

slope of the resistive blinder is set with the setting via NgRisAng. NgRisAng is measured

counter clockwise from the R-axis. The area left from the blinder is excluded from the

operating area.

The reactive reach blinder is built by a line which crosses the X-axis at PsReactRch.



– 104 –



IEC 60255-121:2014 © IEC 2014



The slope of the reactive blinder is set with the setting via PsReactAng. PsReactAng is

measured counter clockwise from the horizontal. The area above the blinder is excluded from

the operating area as shown in Figure A.2.

PsImpRch is the impedance reach of the bend point – the point on the horizontal line going

through the impedance reach tip where in some relays the reactive reach line can bend or tilt.

PsImpAng is the impedance angle with respect to the R-axis.

ImpRad is the radius of a circle with the centre at the impedance point – the midpoint of the

line between PsImpRch and OfsImpRch points on the circle.

ImpAdd indicates if this adds to or subtracts from the operating area of the characteristic

(True/False).

An active quadrant may be needed in some cases to limit the operating area of the distance

characteristic.

Polarization method

In many relays the polarization method is fixed. On other relays the polarization method is

dynamically selected based on certain conditions. The standard parameter set cannot

describe this internal selection logic. However, the settings needed to set the polarization

method(s) can be described here.

A.1.4



Quadrilateral/polygonal



Quadrilateral/polygonal is a characteristic that is used in many multifunctional transmission

line protection relays. It can have a different shape depending on the basic shape, number of

lines used and the settings of the relay.

The characteristic described in this annex as shown in Figure A.3 is an abstract characteristic

that can be used to represent most existing quadrilateral/polygonal characteristics using a

subset of the characteristic elements defined.



PsReactAng2



X



PsImpRchAng2



Z



PsReactRch



PsImpRchAng1



PsReactAng1

PsImpRch



PsImpAng



NgRisAng1



r



PsRisAng1



NgRisRch DirCharAng2

PsRisRch



NgRisAng2



DirChrAng1



NgImpAng

NgReactRch

NgImpRch

NgImpRchAng2



x

z



R



PsRisAng2



NgImpRchAng1



PsRisRch

PsRisAng1

PsRisAng2



Positive Resistive Reach

Positive Resistive Angle 1

Positive Resistive Angle 2



PsReactRch

PsReactAng1

PsReactAng2



Positive Reactance Reach

Positive Reactance Angle 1

Positive Reactance Angle 2



NgRisRch

NgRisAng1

NgRisAng2



Negative Resistive Reach

Negative Resistive Angle 1

Negative Resistive Angle 2



NgReactRch

NgReactAng1

NgReactAng2



Negative Reactance Reach

Negative Reactance Angle 1

Negative Reactance Angle 2



PsImpRch

PsImpAng

PsImpRchAng1

PsImpRchAng2



Positive Impedance Reach

Positive Impedance Angle

Positive Impedance Reach Angle 1

Positive Impedance Reach Angle 2



NgImpRch

NgImpAng

PsImpRchAng1

PsImpRchAng2



Negative Impedance Reach

Negative Impedance Angle

Negative Impedance Reach Angle 1

Negative Impedance Reach Angle 2



DirChrAng1

DirChrAng2



Directional Characteristic Angle 1

Directional Characteristic Angle 1

IEC



Figure A.3 – Quadrilateral/polygonal characteristics



0179/14



IEC 60255-121:2014 © IEC 2014



– 105 –



PsRisRch



Positive Resistive Reach – defines the positive resistive reach to limit the

coverage for fault resistance and at the same time to limit the

encroachment of the load impedance into the characteristic. The setting

determines the reach on the R-axis.



PsRisAng1



Positive Resistive Angle in the first quadrant. This angle is measured

counter clockwise from the R-axis. The area right from the blinder is

excluded from the operating area.



PsRisAng2



Positive Resistive Angle in the fourth quadrant. This angle is measured

clockwise from the R-axis.



PsReactRch



Positive Reactance Reach – defines the positive reactive reach to limit the

coverage for fault reactance. The setting determines the reach on the Xaxis.



PsReactAng1



Positive Reactance Angle 1 to the right of the line impedance. This angle is

measured clockwise from the horizontal line going through the reactive

reach on the X-axis. The area above the line is excluded from the

operating area.



PsReactAng2



Positive Reactance Angle 2 to the left of the line impedance. This angle is

measured counter clockwise from the horizontal line going through the

reactive reach on the X-axis. The area above the line is excluded from the

operating area.



NgRisRch



Negative Resistive Reach – defines the negative resistive reach. The

setting determines the reach on the R-axis.



NgRisAng1



Negative Resistive Angle 1 in the second quadrant. This angle is measured

counter clockwise from the R-axis. The area left from the blinder is

excluded from the operating area.



NgRisAng2



Negative Resistive Angle 2 in the third quadrant. This angle is measured

counter clockwise from the R-axis. The area left from the blinder is

excluded from the operating area.



NgReactRch



Negative Reactance Reach – defines the reactance reach in the reverse

direction.



NgReactAng1



Negative Reactance Angle 1. This angle is measured clockwise from the

horizontal line going through the negative reactance reach on the X-axis.

The area below the line is excluded from the operating area.



NgReactAng2



Negative Reactance Angle 2. This angle is measured clockwise from the

horizontal line going through the negative reactance reach on the X-axis.

The area below the line is excluded from the operating area.



PsImpRch



Is the impedance reach of the quadrilateral/polygonal characteristic. In

many cases the impedance or reactive reach line is a horizontal line. In

some relays it also can be the bend point – the point on the horizontal line

going through the impedance reach tip where the reactive reach line can

bend or tilt with an RsImpRchAng angle. In some relays there can be one

tilt angle on the right of the impedance line (PsImpRchAng1) and another

tilt angle on the left of the impedance line (PsImpRchAng2). The reactive

reach line can also tilt instead at the intersection of the reactance axis X

and the reactive reach line. The tilt in this case will be defined by

PsReactAng1 and in some cases PsReactAng2.

The same may apply on the negative reach of the quadrilateral/polygonal

characteristic.



PsImpAng



Positive Impedance Characteristic Angle – this is the line impedance angle

in the forward direction (first quadrant). This angle is measured counter

clockwise from the positive R-axis.



NgImpAng



Negative Impedance Characteristic Angle – this is the impedance angle in

the reverse direction (third quadrant). This angle is measured counter

clockwise from the negative R-axis.



– 106 –



IEC 60255-121:2014 © IEC 2014



DirChrAng1



Directional Characteristic Angle 1 – this is the directional characteristic

angle in the fourth quadrant. This angle is measured counter clockwise

from the positive R-axis.



DirChrAng2



Directional Characteristic Angle 2 – this is the directional characteristic

angle in the second quadrant. This angle is measured counter clockwise

from the positive R-axis.



A.2

A.2.1



Example characteristics

General



The following are examples based on the models described above.

A.2.2



Non-directional circular characteristic (ohm)



The non-directional circular characteristic is shown in Figure A.4.



jX



ImpRch



R



IEC



0180/14



Figure A.4 – Non-directional circular characteristic (ohm)

The following setting is applicable to this characteristic:





ImpRch is the setting of the distance element.



A.2.3



Reactive reach line characteristic



The reactive reach line characteristic is shown in Figure A.5.



IEC 60255-121:2014 © IEC 2014



– 107 –



X

Z

PsReactAng1



PsReactRch



R



IEC



0181/14



Figure A.5 – Reactive reach line characteristic

The following settings are applicable to this characteristic:





PsReactRch is the Positive Reactance Reach setting of the relay.







PsReactAng1 in the case of a horizontal line will be zero.



A.2.4



MHO characteristic



The MHO characteristic is show in Figure A.6.

X

PsImpRch



PsImpAng



R

IEC



0182/14



Figure A.6 – MHO characteristics

The following settings are applicable to this characteristic:





PsImpRch is the impedance reach setting of the distance element.







PsImpAng is the characteristic angle.



A.2.5



Resistive and reactive intersecting lines characteristic



Resistive and reactive lines intersecting lines characteristic is shown in Figure A.7.



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Figure A.1 – Non-directional circular characteristic with directional supervision

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