ABB RELION 620 Series Technical Manual page 220

Section 4
Protection functions
214
Directional operation is not allowed (the setting Allow Non Dir is "False") when the
measured polarizing or operating quantities are not valid, that is, their magnitude is below
the set minimum values. The minimum values can be defined with the settings Min trip
current and Min trip voltage. In case of low magnitudes, the FAULT_DIR and
DIRECTION outputs are set to 0 = unknown, except when the Allow non dir setting is
"True". In that case, the function is allowed to operate in the directional mode as non-
directional, since the directional information is invalid.
The RCA_CTL input is used in compensated networks where the compensation coil
sometimes can be disconnected. When the coil is disconnected, the compensated network
becomes isolated and the Characteristic angle setting (φRCA) must be changed. This can
be done automatically with the RCA_CTL input. Note that the RCA_CTL input only works
when the Characteristic angle setting is set to exactly -90 degrees or 0 degrees. The value
of the input affects the Characteristic angle setting in the following way:
Table 161: Characteristic angle control in phase angle operation mode
Characteristic angle setting
-90°
0°
Iosin(φ) and Iocos(φ) criteria
A more modern approach to directional protection is the active or reactive current
measurement. The operating characteristic of the directional operation depends on the
grounding principle of the network. The I
network, measuring the reactive component of the fault current caused by the ground
capacitance. The I cos(φ) characteristics is used in a compensated network, measuring the
0
active component of the fault current.
The operation criteria Iosin(φ) and Iocos(φ) are selected with the Operation mode setting
using the values "IoSin" or "IoCos" respectively.
In isolated networks, I sin(φ) does not differ from the phase angle criterion, since the
0
phase angle of the operating quantity is fairly close to -90 degrees. Furthermore, in
completely compensated networks the fault current is usually mostly resistive. Therefore,
the phase angle and I cos(φ) criteria are equally sensitive. However, if the fault is in the
0
background network, the fault current of a sound and healthy line is almost fully
capacitive and its phase angle is close to the operation area of the component. Therefore,
the I cos(φ) characteristic is recommended, since the risk of faulty operation is smaller
0
than with the phase angle criterion.
The angle correction setting can be used to improve selectivity. The setting decreases the
operation sector. The correction can only be used with the Iosin(φ) or Iocos(φ) criterion.
The RCA_CTL input is used to change the Io characteristic:
RCA_CTL = "False"
φRCA = -90°
φRCA = 0°
sin(φ) characteristics is used in an isolated
0
1MAC504801-IB E
RCA_CTL = "True"
φRCA = 0°
φRCA = -90°
620 series ANSI
Technical Manual