WEG ECW500 - Limiters; Underfrequency Limiter (LUF)

Functional Description .
ECW500 | 45
Table 6.3 Required conditions to change operating modes.
Transition
Required Condition
1
OFF → MTVC: Digital Input Turn ON Excitation
(Offline operating mode must be in MTVC)
MTVC → OFF: Digital Input Turn OFF Excitation
2
OFF → MECC: Digital Input Turn ON Excitation
(Offline operating mode must be in MECC)
MECC → OFF: Digital Input Turn OFF Excitation
3
MECC → MTVC: Digital Input MTVC
MTVC → MECC: Digital Input MECC
4
MTVC or MECC→ MTVC DROOP: Digital Input ENABLE PARALLEL
MTVC DROOP → MTVC or MECC: Digital Input DISABLE PARALLEL
(ECW500 changes to MTVC or MECC mode depending on the configuration of the offline operating mode).
5
MTVC → MRPC: Digital Input ENABLE PARALLEL + Digital Input ENABLE ONLINE (simultaneously)
(Online operating mode must be in MRPC)
MRPC → MTVC: Digital Input DISABLE PARALLEL + Digital Input DISABLE ONLINE (simultaneously)
(Offline operating mode must be in MTVC)
6
MECC → MPFC: Digital Input ENABLE PARALLEL + Digital Input ENABLE ONLINE (simultaneously)
(Online operating mode must be in MPFC)
MPFC → MECC: Digital Input DISABLE PARALLEL + Digital Input DISABLE ONLINE (simultaneously)
(Offline operating mode must be in MECC)
7
MECC → MRPC: Digital Input ENABLE PARALLEL + Digital Input ENABLE ONLINE (simultaneously)
(Online operating mode must be in MRPC)
MRPC → MECC: Digital Input DISABLE PARALLEL + Digital Input DISABLE ONLINE (simultaneously)
(Offline operating mode must be in MECC)
8
MTVC → MPFC: Digital Input ENABLE PARALLEL + Digital Input ENABLE ONLINE (simultaneously)
(Online operating mode must be in MPFC)
MPFC → MTVC: Digital Input DISABLE PARALLEL + Digital Input DISABLE ONLINE (simultaneously)
(Offline operating mode must be in MTVC)
9
MRPC → MTVC DROOP: Digital Input DISABLE ONLINE
MTVC DROOP → MRPC: Digital Input ENABLE ONLINE
(Online operating mode must be in MRPC)
10
MPFC → MTVC DROOP: Digital Input DISABLE ONLINE
MTVC DROOP → MPFC: Digital Input ENABLE ONLINE
(Online operating mode must be in MPFC)
11
MPFC → MRPC: Change the online operating mode to MRPC.
MRPC → MPFC: Change the online operating mode to MPFC.
NOTE!
The commands of the table are represented for the digital inputs, but they can be done by the HMI
or by the supervisory communication too.
6.6 LIMITERS
There are in ECW500 four limiting functions to avoid the synchronous machine operations in inappropriate
conditions. The limiting functions are the Underfrequency limiter, excitation overcurrent limiter, excitation
undercurrent limiter and limiter of overcurrent at the synchronous machine terminals (stator). The limiters
features are described in the following sections.
6.6.1 Underfrequency Limiter (LUF)
The ECW500 has two types of underfrequency limiters, selected through parameter 30122.
The underfrequency limiter type U/f actuate when the system frequency drops below a preconfigured value.
When operating on the MTVC or MTVC DROOP mode, the voltage reference is automatically set so that the