ABB RELION REX640 Technical Manual page 436

Section 4
Protection functions
430
to operate in the directional mode as non-directional, since the directional information
is invalid.
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 485: Relay characteristic angle control in the IoSin and IoCos operation criteria
Operation mode:
IoSin
IoCos
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.
RCA_CTL = "False"
Actual operation criterion:
Iosin(φ)
Actual operation criterion:
Iocos(φ)
1MRS759142 C
RCA_CTL = "True"
Actual operation criterion:
Iocos(φ)
Actual operation criterion:
Iosin(φ)
REX640
Technical Manual