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2.12.2 Setting Hints
General
2.12.2.1 Differential Protection for Generators and Motors
Precondition
Increase of Pickup
Value on Startup
7UM62 Manual
C53000-G1176-C149-3
The differential protection is only effective and accessible if the type of protected
object for this function was set within the framework of the protective function
configuration (Section 2.2, address 0120, DIFF. PROT. = Generator/Motor or
Three-phase trans.). Only the relevant parameters for that object are offered, all
others are hidden. Disabled is set if the function is not required. At the address
2001 DIFF. PROT. the user can switch the function ON or OFF, or only block the trip
command (Block Relay).
Note:
When the device is delivered, the differential protection function is switched OFF. This
is because this protection function must not be used before at least the vector groups
and matching values have been correctly set. Without these settings the device may
show unpredictable behaviour (e.g. tripping)!
The primary rated current I
rated current I
of the object to be protected. However, at least the following
N, Object
condition should be observed with regard to the upper limit of the linear zone of the
7UM62, which is 20 ⋅ Ι
N
>
I
p, CT
A precondition for the functioning of the generator or motor differential protection is
that during configuration at the address 0120 DIFF. PROT. = Generator/Motor
has been set.
One important setting is the location of the CT starpoints on both sides of the protected
object (addresses 0201 STRPNT->OBJ S1 for side 1 and 0210 STRPNT->OBJ S2
for side 2, see Section 2.3).
Also, the nominal values (S
protected, and the primary and secondary nominal currents of the main CTs on both
sides must be entered. The settings are referred to these values. They are also used
e.g. for determining the primary measured values.
Information as to the treatment of the starpoint on both sides is required for the
measured value monitoring; it has already been entered during configuration at the
addresses 0241 STARPNT SIDE 1 and 0244 STARPNT SIDE 2 (see Section 2.3.2).
For additional security against overfunctioning when a non-energized protection
object is switched in, an increase of the pickup value on startup can be set at address
2005 INC.CHAR.START. On delivery of the device, this function is switched OFF.
The associated parameters can be found at addresses 2051A, 2052A and 2053.
Address 2051A I-REST. STARTUP is used to set the pickup value for startup
detection. The function is disabled by setting I/I
the increase factor of the pickup values on startup. For generator and motor
protection, a setting of 2052A START-FACTOR = 2.0 is recommended.
Differential Protection (ANSI 87G/87M/87T)
of the used CTs should normally be higher than the
p, CT
:
⋅
0.75 I
N, Object
, U
N GEN/MOTOR
N GEN/MOTOR
) of the machine to be
= 0. The START-FACTOR specifies
nO
89
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