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 earthing principle of the network. The Iosin(φ) characteristics is used in an
isolated network, measuring the reactive component of the fault current caused
by the earth capacitance. The Iocos(φ) characteristics is used in a compensated
network, measuring the 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.
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:
Table 409: Relay characteristic angle control in the IoSin and IoCos operation
criteria
Operation mode:
RCA_CTL
= "False"
RCA_CTL
= "True"
IoSin
Actual operation criterion: Io-
sin(φ)
Actual operation criterion: Io-
cos(φ)
IoCos
Actual operation criterion: Io-
cos(φ)
Actual operation criterion: Io-
sin(φ)
When the Iosin(φ) or Iocos(φ) criterion is used, the component indicates a forward-
or reverse-type fault through the
FAULT_DIR
and
DIRECTION
outputs, in which 1
equals a forward fault and 2 equals a reverse fault. Directional operation is not
allowed (the
Allow non dir setting is "False") when the measured polarizing or
operating quantities are not valid, that is, when their magnitude is below the set
minimum values. The minimum values can be defined with the
Min operate current
and
Min operate voltage settings. In case of low magnitude, 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 calculated Iosin(φ) or Iocos(φ) current used in direction determination can be
read through the I_OPER monitored data. The value can be passed directly to a
decisive element, which provides the final start and operate signals.
The I_OPER monitored data gives an absolute value of the calculated
current.
The following examples show the characteristics of the different operation criteria:
Example 1.
Iosin(φ) criterion selected, forward-type fault
=> FAULT_DIR = 1
1MRS757644 H
Protection functions
620 series
Technical Manual
403
