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Functions
160
The thermal characteristic is prespecified by 8 value pairs concerning the U/f
overexcitation (related to nominal values) and the t trip time. In most cases, the
specified characteristic related to standard transformers provides for sufficient
protection. If this characteristic does not correspond to the actual thermal behavior of
the object to be protected, each desired characteristic can be implemented by entering
customer-specific trip times for the specified U/f overexcitation values. Intermediate
values are determined by a linear interpolation within the device.
The characteristic resulting from the device default settings is shown in Figure 4-13 in
the Technical Data, Section 4.18. Figure 2-74 illustrates the behaviour of the
protection on the assumption that within the framework of configuration the setting for
the pickup threshold (parameter 4302 U/f >) was chosen higher or lower than the
first setting value of the thermal characteristic.
Pickup threshold U/f > (parameter 4302)
T
1. Setting value of
thermal characteristic
t 1.05
T U/f >>
1.0
1.05
1.10
Pickup threshold U/f > (parameter 4302)
t
1. Setting value of
thermal characteristic
t 1.05
T U/f >>
1.0
1.05
1.10
Figure 2-74
Tripping Time Characteristic of the Overexcitation Protection
Tripping area
Thermal
trip stage
Overexcitation
trip stage U/f >>
1.20
1.30
1.40
U/f >>
(Setting of
stepped characteristic)
Tripping area
Thermal
trip stage
Overexcitation
trip stage U/f >>
1.20
1.30
1.40
U/f >>
(Setting of
stepped characteristic)
a) Pickup threshold U/f >
is less than the
1st setting value of the
thermal characteristic
F#
b) Pickup threshold U/f >
is greater than the
1st setting value of the
thermal characteristic
U/f
7UM62 Manual
C53000-G1176-C149-3
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