Schweitzer Engineering Laboratories SEL-321 - Page 321

Date Code 20011026 Maintenance and Testing 7-51
SEL-321/321-1 Instruction Manual
The resistive reach of the quadrilateral distance element under test is defined by the
RG2 element setting. In this case RG2 = 5.00 secondary ohms. The impedance
measured by the relay for a ground fault is determined by the faulted phase voltage,
faulted phase current, and the residual current multiplied by the zero-sequence
current compensation factor, k0. The SEL-321 Relay uses k01M and k01A settings
to define the zero-sequence current compensation factor for all zones.
The reactance measured by the relay ground quadrilateral distance element for a
Zone 2 fault is defined by the following equation:
()()()
()
()
()
()
[] *ANG1Z1I0kIIIIm
*ANG1Z1I0kIVIm
R
RA0A2A
2
3
RAA
AG
∠⋅⋅++⋅
∠⋅⋅+
=
Equation 7.20
Where:
k0 = k01M ∠ k01A° for Zone 1, 2, 3, and 4
I
A2
= negative-sequence current flowing in A-phase for the fault
I
A0
= zero-sequence current flowing in A-phase for the fault
For a fault on a radial system with no load and when testing a ground distance
element using a single current source, I
A
= I
R
, I
A2
= I
A
/3, and I
A0
= I
A
/3. Equation
7.20 can be simplified:
()()()
()()()
*ANG1Z10k1IIIm
*ANG1Z10k1IVIm
R
AA
AA
AG
∠⋅+⋅⋅
∠⋅+⋅⋅
=
Equation 7.21
Select a value for V
A
. Then it is possible to use Equation 7.21 to calculate the
magnitude and angle of I
A
required to test the Zone 2 ground quadrilateral distance
element resistive reach.
For the example, select V
A
= 40.0 ∠0°. To simplify the resistance calculation, select
the angle of I
A
= 0°. For the Zone 2 element, RG2 = 5.00 Ω, ∠Z1ANG = 83.97°, and
k01 = 0.726 ∠-3.69°.
()()()
()()()
()()()
()()()
()()()
()()()
*42.82725.1IIIm
*42.82725.1I00.40Im
00.5
*97.83155.1725.1IIIm
*97.83155.1725.1I00.40Im
00.5
*97.83169.3726.01IIIm
*97.83169.3726.01I00.40Im
00.5
AA
A
AA
A
AA
A
°∠⋅⋅
∠⋅°∠
=
°∠⋅°−∠⋅⋅
°∠⋅°−∠⋅°∠
=
°∠⋅°−∠+⋅⋅
°∠⋅°−∠+⋅°∠
=
Equation 7.22
Because the angle of I
A
equals 0°, simplify the equation above:
()
() °−∠⋅
°−∠⋅⋅
=
42.82725.1ImI
42.82725.1ImI0.40
00.5
2
A
A