Protective Elements
I2>G – Generator Unbalance Protection [46G]
The 46G function has an inverse time element.
The relation of CTprim/FLA should be less than 2.
46G – Inverse Time Generator Unbalance Protection Element
The condition for a trip of this module is that the negative sequence current I2 is above the set threshold »I
2/FLA«
.
The module initiates a trip if this condition is fulfilled for a specific tripping delay time.
The rating value »I
2/FLA«
is the permitted continuous unbalanced load current of the protected generator.
The principle of the module is as follows:
• The protective device permanently calculates the heat (thermal) energy
θ
of the generator. This happens
all the time, independent of any alarm or tripping decisions.
The module trips if for the tripping delay time t
trip
– which is dependent on
θ
– the following conditions are all
fulfilled:
1. The negative sequence current
I2
is above the set threshold »I
2/FLA«
and
2. the calculated thermal energy
θ
exceeds a maximum value
θ
max
,, which is calculated based on the
setting
K
for the thermal load capability.
• For
θ = 0
the tripping delay time is calculated as follows:
t
trip
= tripping delay in seconds
K
= thermal load capability of the generator while running
with 100% unbalanced load current.
This is an intrinsic property of the generator, and
therefore it must be specified as a setting value (Setting Group parameter »
K
«).
It should be possible to obtain this value from the data sheet of the generator.
FLA
= Full Load Amperage
I
2
= unbalanced load current
I2
(calculated from measured current values).
• In case of a still present residual heat,
θ > 0,
the tripping delay t
trip
is reduced accordingly, so that an earlier
tripping occurs.
• As long as the unbalanced load current
I2
is
greater
than the threshold »I
2/FLA«
it is assumed that the
generator is
heating up
. During this phase, the heat (thermal) energy is calculated by an integration of the
current value
I2
:
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