Protective Elements
θ
0,cool
= initial value at the beginning of the heating phase,
i. e. the thermal energy at the end of the last cooling-down phase
(or = 0, if the last cooling-down phase has ended, see below,
or if there has not been any cooling-down phase yet),
ƒ
= scaling factor.
• As long as the unbalanced load current
I2
is
less
than the threshold »I
2/FLA«
it is assumed that the
generator is
cooling down
. During this phase, the heat (thermal) energy is calculated based on a cooling-
down constant. This constant is another intrinsic property of the generator, and therefore it must be
specified as a setting value (Setting Group parameter »
τ-cool
«):
θ(t)
= actual value of the thermal energy,
θ
0,heat
= initial value at the beginning of the cooling-down phase,
i. e. the thermal energy at the end of the last heating-up phase
τ
cool
= generator property, setting value »
τ-cool
«.
• The cooling-down phase always continues as long as I2 is below the threshold, i. e.
θ(t)
is calculated
continuously. (Only after
θ(t)
has dropped below
0.01
⋅
θ
max
the calculation ends and
θ
gets reset to
0
, i. e.
a subsequent heating-up phase will start with initial value
θ
0,cool
= 0
.)
The heat (thermal) energy is an auxiliary value that is calculated and
maintained internally, i. e. it can neither be displayed at the HMI nor be
retrieved via any communication protocol.
The parameters described above can be set in the menu [Protection Para/Set(x)/Unbalance-Prot/46G-I.Unbalance].
Moreover, the following parameters can be set:
»Tmin«
: This is the minimum operate time of this element. The element will not operate before this time expires.
This is set to prevent false trips for faults that would be cleared normally by system protections.
»Tmax«
: This is the maximum operate time of this element. This setting can be applied to limit the maximum
tripping time for low level unbalances.
754 MCDGV4 DOK-HB-MCDGV4-2E
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