Setting Guidelines - ABB RET670 Applications Manual

1MRK504116-UUS C
3.10.1.2
Application manual
For big and important machines, fast protection against inadvertent energizing should,
therefore, be included in the protective scheme.
The protection against inadvertent energization can be made by a combination of
undervoltage, overvoltage and overcurrent protection functions. The undervoltage
function will, with a delay for example 10 s, detect the situation when the generator is
not connected to the grid (standstill) and activate the overcurrent function. The
overvoltage function will detect the situation when the generator is taken into operation
and will disable the overcurrent function. The overcurrent function will have a pick-up
value about 50% of the rated current of the generator. The trip delay will be about 50 ms.

Setting guidelines

When inverse time overcurrent characteristic is selected, the operate
time of the stage will be the sum of the inverse time delay and the set
definite time delay. Thus, if only the inverse time delay is required, it is
of utmost importance to set the definite time delay for that stage to zero.
The parameters for the general current and voltage protection function (CVGAPC) are
set via the local HMI or Protection and Control Manager (PCM600).
The overcurrent steps has a IMinx (x=1 or 2 depending on step) setting
to set the minimumpickup current. Set IMinx below PickupCurr_OCx
for every step to achieve ANSI reset characteristic according to
standard. If IMinx is set above PickupCurr_OCx for any step the ANSI
reset works as if current is zero when current drops below IMinx.
Directional negative sequence overcurrent protection
Directional negative sequence overcurrent protection is typically used as sensitive
ground-fault protection of power lines were incorrect zero sequence polarization may
result from mutual induction between two or more parallel lines. Additionally, it can be
used in applications on underground cables where zero-sequence impedance depends
on the fault current return paths, but the cable negative-sequence impedance is
practically constant. It shall be noted that directional negative sequence OC element
offers protection against all unbalance faults (phase-to-phase faults as well). Care shall
be taken that the minimum pickup of such protection function shall be set above
natural system unbalance level.
An example will be given, how sensitive-ground-fault protection for power lines can
be achieved by using negative-sequence directional overcurrent protection elements
within a CVGAPC function.
Section 3
IED application
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