ABB REO 517 Applications Manual page 111


Sudden current change function (SCC)
ZnRW- START
SVC- START
SCC-START
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The parameters for the sudden current change function are set via the local HMI or PST
(Parameter Setting Tool). Refer to the Technical reference manual for setting parame-
ters and path in local HMI.
The setting of the operate value for the sudden change current measuring element di/dt
must be greater than highest expected load current change on the protected line. It is
necessary with an additional margin of at least 10% above the declared inaccuracy of
the current transformer and measuring element.
The setting of the recovery delay t for the sudden change current measuring element
must be greater than the set time delay of the zone which activates the ZnRW-TRIP sig-
nal plus the operate time of the tripping signal.
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The current transformer secondary setting current (Is
I
S EC
⋅
Is ------------- - Is
=
SEC
I
PRIM
where I is the secondary rated current of the main CT and I
SEC
ondary rated current of the main CT.
&
>1
en02000512.vsd
) is:
SEC
&KDSWHU 
&XUUHQW
(Equation 47)
is the primary sec-
PRIM
101