ABB ret650, Applications Manual

Page: 180 / 392

The setting of DU> should be set high (approximately 60% of UBase ) and the
current threshold DI< low (approximately 10% of IBase ) to avoid unwanted
operation due to normal switching conditions in the network. The delta current and
delta voltage function shall always be used together with either the negative or zero
sequence algorithm. If
USet
prim
is the primary voltage for operation of dU/dt and
ISet
prim
the primary current for operation of dI/dt, the setting of DU> and DI< will
be given according to equation 44 and equation 45 .
DU
USet
UBase
prim
> =
100
.
EQUATION1523 V3 EN-US
(Equation 44)
DI
ISet
IBase
prim
< =
100
.
EQUATION1524 V4 EN-US
(Equation 45)
The voltage thresholds UPh> is used to identify low voltage condition in the
system. Set UPh> below the minimum operating voltage that might occur during
emergency conditions. A setting of approximately 70% of UBase is recommended.
The current threshold IPh> shall be set lower than the IMinOp for the distance
protection function. A 5...10% lower value is recommended.
10.2.3.6 Dead line detection
M13683-78 v4
The condition for operation of the dead line detection is set by the parameters
IDLD< for the current threshold and UDLD< for the voltage threshold.
Set the IDLD< with a sufficient margin below the minimum expected load current.
A safety margin of at least 15-20% is recommended. The operate value must
however exceed the maximum charging current of an overhead line, when only one
phase is disconnected (mutual coupling to the other phases).
Set the UDLD< with a sufficient margin below the minimum expected operating
voltage. A safety margin of at least 15% is recommended.
Section 10
1MRK 504 169-UEN A
Secondary system supervision
174 Transformer protection RET650 2.2 IEC
Application manual