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I.L. 40-201.9
4.4.3. Test Enable
The TEST ENABLE signal on the REL 352 channel logic diagram is provided through the front
panel TEST mode. When the TEST mode TEST or TLDT functions are selected, the TEST EN-
ABLE signal on the REL 352 phase comparison logic diagram is active, otherwise it is disabled.
Oscillographic data storage is triggered, when the ENTER key is depressed, while the TEST
mode TEST function is selected on the front panel.
4.4.4. Channel Delay Time (TEST)
The communication Delay Time (CDT) is computed when the TEST mode TLDT function is se-
lected. The keying level must be set to a minimum IKEY = 0.2 at both ends of the line.
The load current must be present and be greater than the IKEY level. The positive sequence
network coefficient C1 (See Section 3.2 for explanation) must be set high enough to produce
60 Hz square wave at the XMTR KEY (+) signal at the rear terminal TB4-12. Again the C1 co-
efficient must be set the same at both ends of the line.
NOTE:
REL 352 computes the CDT as the time delay between raising edge of the IKEY (transmitted
signal) to the falling edge of the received SPACE signal. Note that a load condition produces
out of phase current relationship of both ends. The CDT is displayed in the value field (range 0
to 1 cycle) in milliseconds.
This value must be subsequently entered as a setting LDT.
High line charging current (long line or HV cable) can introduce measurement errors especially
when load current is low. The following illustrates the current relationship.
The phase angle displacement j introduced by line charging current translates into time error
t
. The time measurements t
c
t
= t
A
D
t
= t
B
D
where t
t
+ t
A
B
t
= t
D
A
Thus the error due to IC is eliminated.
4-8
Coefficients C0 and C2 for simplicity should be set to "0" at both ends.
A
I A
A
+ t
C
- t
C
is communication channel propagation delay adding above equations leads to:
D
= 2 t
D
+ t
D
2
Power Automation and Protection Division
B
I B
I C
and t
at A and B will therefore be:
B
I C
I A
I B
ϕ
REL 352 Version 1.00
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