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I.L. 40-201.9
1.2.
"Quiescent" Mode of Operation of FSK Data Communication Equipment.
Frequency shift (FSK) DCE shifts carrier frequency in response to the modulating signal IKEY.
Under certain conditions (i.e. to prevent PLC from interfering with other communication equip-
ment) it is necessary to prevent continuous frequency shift under normal load condition. The
constant frequency, present on the line will be that corresponding to SPACE (IKEY=0).
The frequency shift must be, of course, resumed during system faults.
As explained in sections 3 and 5 there are two ways of achieving this goal:
Please remember that:
IT = C1I1 + C2I2 + C0I0
The user must be aware that this approach, while eliminating the line load, also makes
the protection system less sensitive to balanced three-phase faults .
2.
SIGNAL POLARITY CONSIDERATIONS
REL 352 phase comparison logic convention (in the microprocessor software) expects logical
"1" state on the transmitted IKEY signal to correspond to logical "1" state on the MARK and log-
ical "0" state on the SPACE signals received at the far end of the protected line.
REL252 hardware (optoisolated inputs and outputs) and some types of data communication
equipment such as TCF-10B introduce polarity inversions.
REL252 interface electronics provides signal polarity configuration (normal-invert) on the inter-
connect module, appendix B.
The signals affected by these jumpers are:
Channel Fail
MARK2
SPACE2
The diagram below explains the signal flow polarity:
Please note that the jumper positions:
JMP 6 inverted
JMP 4 inverted
JMP 5 inverted
Result in logical "1" applied to remote IKEY corresponding to logical "1" on the MARK and a
logical "0" on the SPACE inputs on the local terminal.
The Channel Failure (CF) input to the microprocessor is logical "0" i.e., low for channel failure
condition.
Therefore: if data communication equipment provides a logical "1" (high) state for failed chan-
nel, REL 352 must be in "Normal" position as shown on the diagram.
If the channel failure input to REL 352 is intentionally not connected to data communication
equipment (floating input) than JMP1 in normal position results in CF being false (logical "1").
K-2
• Setting IKEY above line load
• Setting C1 - (positive sequence coefficient) low enough to reduce the contribution of
load to combined-sequence output IT
-
JMP1
-
JMP 2
-
JMP 3
- Remote IKEY
- Local MARK
- Local SPACE
Power Automation and Protection Division
MARK1
-
SPACE1
-
KEY OUT
-
REL 352 Version 1.00
JMP 4
JMP 5
JMP 6
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