CHAPTER 5: SETTINGS SYSTEM SETUP
D30 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL 5-145
5
5.5.3.3 Disturbance detectors (internal)
The disturbance detector (ANSI 50DD) element is a sensitive current disturbance detector that detects any disturbance on
the protected system. The 50DD function is used directly in some elements in the relay, for example VT Fuse Failure
detector or Fault Report. It can also be used to supervise current-based elements to prevent maloperation as a result of
the wrong settings or external CT wiring problem. A disturbance detector is provided for each source.
The 50DD function responds to the changes in magnitude of the sequence currents. The disturbance detector logic is as
follows.
Figure 5-66: Disturbance detector logic
The disturbance detector responds to the change in currents of twice the current cut-off level. The default cut-off threshold
is 0.02 pu; thus by default the disturbance detector responds to a change of 0.04 pu. The metering sensitivity setting
(
PRODUCT SETUP  DISPLAY PROPERTIES  CURRENT CUT-OFF LEVEL) controls the sensitivity of the disturbance detector
accordingly.
5.5.3.4 Example for use of sources
An example of the use of sources is shown in the following figure. A relay can have the following hardware configuration:
This configuration can be used on a two-winding transformer, with one winding connected into a breaker-and-a-half
system. The following figure shows the arrangement of sources used to provide the functions required in this application,
and the CT/VT inputs that are used to provide the data.
Increasing slot position letter -->
UR CT/VT module 1 CT/VT module 2 CT/VT module 3
B30, B90, C70, F35, N60, T35 8 CTs 4 CTs, 4 VTs 4 CTs, 4 VTs
C60, D60, G30, G60, L30, L90, M60, T60 CTs VTs not applicable
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