WEG ECW500, Руководство пользователя

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Functional Description .
ECW500 | 47
6.6.2 Excitation Overcurrent Limiter (LEOC)
This feature is intended to limit the excitation current to an adjusted level, preventing a high current from being
applied to the exciter of the synchronous machine. When the LEOC actuate, it controls only the excitation
current, independent of terminal voltage and current values of the synchronous machine. To ensure proper
dynamic operation, LEOC PI loop gains must be adjusted according to the response desired for application.
The LEOC limiter has two configurable levels with different forms of action:
■ high level (parameter 30132), with immediate action and
■ low level (parameter 30140), with delayed action.
Thus, if the excitation current exceeds the value set as high level, the limiter will act immediately to keep current
at this level. But if the excitation current is above the low level and below the high level, the LEOC will lead the
excitation current to the value defined by parameter 30140 after reaching the integral limit (Ixt), that is defined by
the following equation:
𝐼𝑛𝑡𝑟𝑒𝑔𝑎𝑙 𝐿𝑖𝑚𝑖𝑡 𝐿𝐸𝑂𝐶 = (𝐻𝑖𝑔ℎ 𝐿𝑒𝑣𝑒𝑙
𝐿𝐸𝑂𝐶
− 𝐿𝑜𝑤 𝐿𝑒𝑣𝑒𝑙
𝐿𝐸𝑂𝐶
) × 𝑇𝑖𝑚𝑒 𝐴𝑐𝑡𝑢𝑎𝑡𝑖𝑜𝑛
𝐿𝐸𝑂𝐶
In which:
𝑇𝑖𝑚𝑒 𝐴𝑐𝑡𝑢𝑎𝑡𝑖𝑜𝑛
𝐿𝐸𝑂𝐶
parameter 30134
Once the condition of application allows machine operation below the low level, the limiter will turn off and
returns to the previously active mode control.
Figure 6.17 Behavior of integral actuation for the excitation overcurrent limiter (LEOC)
NOTE!
As a first adjust for this protection, set the low level with the same value of the rated excitation
current (30066) and the high level to 10% above the low level. The LEOC time can be maintained
at default value (10s).
NOTE!
The excitation overcurrent limiter actuates in all operating modes, except on the MECC mode.
It can be disabled by parameter 30142 and a relay can be configured to indicate its operation.