112 GC250 Technical Manual
EAAM057608EN
generator during the supply phase. As engine protection, the maximum power protection must
be used, that is independent from the load type.
A maximum current threshold and the maximum time the generator can work with this current
are defined. If the current is lower than the defined threshold, the protection does not activate.
If the current rises above the threshold, the protection activates with a time inversely
proportional to the over current. In order to correctly set the thresholds, perform the following
steps:
Define the system rated current. It can be inferred from the the system rated power
(P.0106 generator rated power kVA) and rated voltage (P.0102 Genset rated voltage):
o
Single-phase system:
𝐼
𝑛𝑜𝑚
=
𝑃.0106×1000
𝑃.0102
o
Three-phases system:
𝐼
𝑛𝑜𝑚
=
[
(𝑃.0106×1000)
3
⁄ ]
(𝑃.0102
√3
⁄
)
For example, on the three-phase system at 400 V out of 200 kVa, the rated
current is approximately 289 A.
When the parameter P.0106
“Generator rated power kVA” is set after
correct configuration of parameters P.0101
“Number of generator
phases” and P.0102 “Generator rated voltage”, the display shows the
rated current.
Set the maximum current threshold with the parameter P.0309, as a percentage of the
rated current. In the previous example, setting a 350 A maximum threshold, requires
entering 121 (%) in parameter P.0309.
Set the action time in the parameter P.0310: the protection will be activated within time
set if the current is constantly equal to the threshold P.0309 multiplied by
√2
. In the
previous example, if you set 10 s, the protection will activate in10 seconds with approx
495 A of constant load; in a shorter time if the current is higher; in a longer time if the
current is lower; and it will never do if the current is lower than 350 A.
In order to calculate the intervention time for a preferred current, please use the following
formula:
𝑡
1
=
𝑃. 0310
(
𝐼
𝑃. 0309
)
2
− 1
Where
I
is the current in the circuit.
Please remember that the protection is performed by performing the integral of the current
value during time; therefore, current values above the rated threshold all concur to define the
intervention time, with their instant weight resulting from the above formula. Thus, only way to
experimentally verify this formula is to switch instantaneously from a normal load situation to
an overload situation.
The following graph shows the curve used for enabling protection, with a value of P.0310 set
to 60 seconds (I is the maximum current):
