GE C70 Instruction Manual page 347

CHAPTER 5: SETTINGS
5.5.3.2 AC input actual values
The calculated parameters associated with the configured voltage and current inputs are displayed in the current and
voltage sections of actual values. Only the phasor quantities associated with the actual AC physical input channels display
here. All parameters contained within a configured source are displayed in the sources section of the actual values.
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.
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
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:
UR
B30, B90, C70, F35, N60, T35
C60, D60, G30, G60, L30, L90, M60, T60
C70 CAPACITOR BANK PROTECTION AND CONTROL SYSTEM – INSTRUCTION MANUAL
Figure 5-66: Disturbance detector logic
) controls the sensitivity of the disturbance detector
Increasing slot position letter -->
CT/VT module 1 CT/VT module 2
8 CTs 4 CTs, 4 VTs
CTs VTs
SYSTEM SETUP
CT/VT module 3
4 CTs, 4 VTs
not applicable
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