Table of Contents
Advertisement
1MRK 505 288-UEN A
7.2.7.2
Technical manual
larger than the set operation current and the step is used in non-directional mode a
signal from the comparator for this step is set to true. This signal will, without delay,
activate the output signal STx (x=step 1-4) for this step and a common START signal.
Internal polarizing
A polarizing quantity is used within the protection in order to determine the direction
to the earth fault (Forward/Reverse).
The function can be set to use voltage polarizing, current polarizing or dual polarizing.
Voltage polarizing
When voltage polarizing is selected the protection will use either the residual voltage
3U
or the negative sequence voltage U
0
The residual voltage can be:
1.
directly measured (when a dedicated VT input of the IED is connected in
PCM600 to the fourth analog input of the pre-processing block connected to
EF4PTOC function input U3P). This dedicated IED VT input shall be then
connected to open delta winding of a three phase main VT.
2.
calculated from three phase voltage input within the IED (when the fourth analog
input into the pre-processing block connected to EF4PTOC analog function input
U3P is NOT connected to a dedicated VT input of the IED in PCM600). In such
case the pre-processing block will calculate 3U
the pre-processing block by using the following formula:
UPol =3U0 =(UL1+UL2+UL3)
IECEQUATION2407 V1 EN
where:
UL1, UL2 and UL3
In order to use this, all three phase-to-earth voltages must be connected to three IED VT
inputs.
The residual voltage is pre-processed by a discrete fourier filter. Thus, the phasor of
the fundamental frequency component of the residual voltage is derived.
The negative sequence voltage is calculated from the three-phase voltage input within
the IED by using the pre-processing block. The preprocessing block will calculate the
negative sequence voltage from the three inputs into the pre-processing block by using
the following formula:
×
U =(UL1+alpha UL2 + alpha UL3)/3
2
GUID-87DA8E2C-B3E5-42D6-B909-59EA3F9309D8 V1 EN
as polarizing quantity U3P.
2
are fundamental frequency phasors of three individual phase voltages.
×
Section 7
Current protection
from the first three inputs into
0
(Equation 9)
(Equation 10)
95
Advertisement
Table of Contents
