ABB RER620, Техническое руководство

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Section 4
1MAC309294-MB F
Protection functions
198 RER620
Technical Manual
4.3.2.3 Functionality
The three-phase undervoltage protection (27) is used to disconnect from the network
devices, for example electric motors, which are damaged when subjected to service under
low voltage conditions. The 27 function includes a settable value for the detection of
undervoltage either in a single phase, two phases, or three phases.
The function contains a blocking functionality. It is possible to block function outputs,
timer, or the function itself, if desired.
4.3.2.4 Operation principle
The function can be enabled and disabled with the Operation setting. The corresponding
parameter values are Enable and Disable.
The operation of the three-phase undervoltage protection can be described by using a
module diagram. All the modules in the diagram are explained in the next sections.
Figure 90: Functional module diagram
Three Phase Mode
The fundamental frequency component of the measured three phase voltages are
compared phase-wise to the set
Pickup value . If the measured value is lower than the set
value of the Pickup value setting, the level detector enables the phase selection logic
module. The Relative hysteresis setting can be used for preventing unnecessary
oscillations if the input signal slightly varies above or below the Pickup value setting. After
leaving the hysteresis area, the pickup condition has to be fulfilled again and it is not
sufficient for the signal to only return back to the hysteresis area.
The Voltage selection setting is used for selecting the phase-to-ground or phase-to-phase
voltages for protection.
For the voltage IDMT mode of operation, the used IDMT curve equations contain
discontinuity characteristics. The
Curve Sat relative setting is used for preventing
unwanted operation.
For more detailed description on IDMT curves and usage of Curve Sat
Relative setting, see the General function block features section in this
manual.
V _ A _ A B
V _ B _ B C
V _ C _ C A
B L O C K
P h a s e
s e le c tio n
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L e v e l
d e te c to r
t
T im e r
t
O P E R A T E
S T A R T
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