GE D90 Plus Instruction Manual page 191

CHAPTER 7: PROTECTION
Internal disturbance detection
Example use of sources
PLUS
D90 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
Name
Range: up to 20 alphanumeric characters
Default: LINE
This setting specifies a name for the protection source.
Phase CT
Range: None, J1, J4, J1+J4, etc.
Default: J1+J4
This setting selects a phase CT or sum of phase CTs to represent the protection source.
Ground CT
Range: None, J7
Default: J7
This setting selects a ground CT to represent the protection source.
Phase VT
Range: None, J10
Default: J10
This setting selects a phase VT to represent the protection source.
Auxiliary VT
Range: None, J8, J9
Default: None
This setting selects an auxiliary VT to represent the protection source.
The disturbance detection element (ANSI 50DD) is a sensitive current disturbance detector
that detects any disturbance on the protected system. This element is intended for use in
conjunction with measuring elements, blocking of current based elements (to prevent
maloperation as a result of the wrong settings), and starting oscillography data capture. A
disturbance detector is provided for each source.
The disturbance detector responds to the changes in magnitude of the sequence currents.
The disturbance detector also responds to the change in currents of twice the current cut-
off level. The default cut-off threshold is 0.02 pu. As such, the disturbance detector
responds to a change of 0.04 pu by default. The
Settings > Protection > Power System > AC Input - Current menu) controls the metering
sensitivity of the disturbance detector.
The source 1 disturbance detector logic is shown below. The logic is identical for all three
sources.
Figure 160: Disturbance detector logic scheme
Plus
Consider a D90 connected as shown below. This configuration could be used on a
transmission line 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 AC module inputs used to provide the data.
setting (located in the
Current Cutoff
POWER SYSTEM
181