ABB RELION Series, Technical Manual

Page: 388 / 804

I G j B U I j I
o stab ostab ostab baseres oCosstab oSinsta
1 1 1 1
= + ⋅ ⋅ = + ⋅
( )
b b
1
GUID-5E6BA356-F1BE-42D6-A6A1-308F93255F7E V1 EN
(Equation 41)
I
o stab
1
The stabilized fundamental frequency residual current estimate, which is obtained (after
conversion) from the corresponding admittance value by multiplying it with the system
nominal phase-to-earth voltage value.
I
o Cosstab
1
The real-part of stabilized fundamental frequency residual current estimate.
I
o Sinstab
1
The imaginary-part of stabilized fundamental frequency residual current estimate.
The main advantage of the filtering method is that due to the admittance calculation,
the resulting current value does not depend on the value of fault resistance, that is, the
estimated current magnitude equals the value that would be measured during a solid
earth fault (R
f
= 0 Ω). Another advantage of the method is that it is capable of
estimating correct current magnitude also during intermittent or restriking faults.
The setting Min operate current defines the minimum operate current.
Setting Operating quantity defines whether the current magnitude supervision is
based on either the “Adaptive” or “Amplitude” methods.
When “Adaptive” is selected, the method adapts the principle of magnitude
supervision automatically to the system earthing condition. In case the phase angle of
accumulated sum admittance phasor is greater than 45 degrees, the set minimum
operate current threshold is compared to the amplitude of
I
o stab
1
(see Figure 199 ). In
case the phase angle of accumulated sum admittance phasor is below 45 degrees, the
set minimum operate current threshold is compared to the resistive component of
I
o stab
1
. This automatic adaptation of the magnitude supervision enables secure and
dependable directional determination in compensated networks, and it is also valid
when the network is unearthed (compensation coil is switched off).
In case operation direction is set to reverse, the resistive and amplitude sectors are
mirrored in the operation characteristics.
When “Amplitude” is selected, the set minimum operate current threshold is
compared to the amplitude of
I
o stab
1
. This selection can be used in unearthed networks.
In compensated networks, setting Operating quantity should be set to
“Adaptive”. This enables secure and dependable directional
determination on compensated networks and it is also valid when
compensation coil is switched off and network becomes unearthed.
Section 4
1MRS758755 A
Protection functions
382 REC615 and RER615
Technical Manual