Neutralpoint Connection Module (Ncm); Voltage Limiting Module (Vlm); Figure 3-6 Ncm; Figure 3-7 Vlm - ABB PCS6000 User Manual

3.2.2.1. Neutralpoint connection module (NCM)

PCS6000 converter's neutral point NP is connected to earth through an RC combination to
limit the dv/dt of the converter against earth. This allows the converter to operate with a
single earth fault for limited period of time. Normally, an earth fault is detected and the
converter switched off immediately.
A second function of the NCM is to discharge the DC-Link via high resistance in the case that
the VLM does not work properly.
Figure 3–6 NCM

3.2.2.2. Voltage limiting module (VLM)

The VLM has an IGCT stack. If the DC-Link voltage exceeds a certain limit, the VLM closes the
current path through the braking resistor to dissipate excessive energy.
Another function is discharging DC-Link during shut down of converter.
DC+
1
NP
2
3
DC-
Figure 3–7 VLM
1) VLM
PRODUCT
PCS6000
DOCUMENT KIND
User manual
2) Braking resistor
DOCUMENT ID.
3BHS600000 E40
PRODUCT DESCRIPTION
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