Functions
2.14 Differential Protection and Its Protected Objects
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
116
The CTs also determine the limits of sensitivity in the case of motors. In asynchronous motors, the startup op-
eration may be modelled in different ways by the CTs, so that major differential currents occur (see also side
title "Increase of Pickup Value on Startup").
2.14.2.2 Setting Notes
Requirement
A precondition for generator or motor differential protection function is that on configuration address 120 DIFF.
PROT. was set to Generator/Motor.
One important setting is the location of the CT starpoints on both sides of the protected object (addresses 201
STRPNT->OBJ S1 for side 1 and 210 STRPNT->OBJ S2 for side 2, see Section P.System Data 1).
Also, the nominal values (S
N GEN/MOTOR
, U
N GEN/MOTOR
) of the machine to be protected, and the primary and sec-
ondary 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 242 STARPNT SIDE 1 and 244 STARPNT
SIDE 2 (see Section 2.5.1).
Pickup Value Increase on Startup
For additional security against overfunctioning when a non-energized protection object is switched in, the in-
crease of the pickup value on startup can be set at address 2005 INC.CHAR.START. On delivery of the device,
this function is switched .
The associated parameters can be found at addresses 2051, 2052 and 2053. Address 2051 I-REST.
STARTUP is used to set the pickup value for detecting a startup. The function is disabled by setting I/I
N Obj.
= 0.
The START-FACTOR specifies the increase factor of the pickup values on startup. For generator and motor pro-
tection, a setting of 2052 START-FACTOR = 2.0 is recommended.
Tripping characteristic
The parameters of the tripping characteristic are set at addresses 2021 to 2044. Figure 2-42 illustrates the
meaning of the different parameters. The numerical values at the characteristic branches are the parameter
addresses.
Address 2021 I-DIFF> is the pickup value for the differential current. The pickup value is referred to the
nominal current of the generator or motor. For generators and motors, a setting between 0.1 and 0.2 is rec-
ommended.
In addition to the pickup threshold I-DIFF>, a second pickup threshold is considered. If this threshold (2031
I-DIFF>>) is exceeded, tripping is initiated regardless of the magnitude of the restraint current (unstabilized
high-speed trip stage). This stage must be set higher than the I-DIFF> stage. Recommendation: Set a value
above the steady-state value of the transient short-circuit current, i.e.:
With values for x
d
’ between 0.15 and 0.35, the resulting setting values for I-DIFF>> are approx. (3 to 7) I
N,
Mach
.
The tripping characteristic comprises two further branches. Address 2041 SLOPE 1 determines the slope of
the first branch, whose starting point is specified in the parameter 2042 BASE POINT 1. This branch considers
current-proportional error currents. These are mainly transformation errors of the main CTs and of the input
CTs. If the CTs are identical, the default setting of 0.25 can be reduced to 0.15.
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