Toshiba GRZ100-211B, Instruction Manual

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Scheme Logic
Figure 2.4.10.3 shows the scheme logic of the broken conductor protection. BCD element outputs
trip signals BCD TRIP through a delayed pick-up timer TBCD.
The tripping can be disabled by the scheme switch [BCDEN] or the PLC signal BCD BLOCK.
BCD
BCD_TRIP
0.00 - 300.00s
&
TBCD
t 0
"ON"
[BCDEN]
+
1 BCD_BLOCK
1848
766
767
Figure 2.4.10.3 Broken Conductor Protection Scheme Logic
Settings
The table below shows the setting elements necessary for the broken conductor protection and
their setting ranges.
Element Range Step Default Remarks
BCD 0.10 – 1.00 0.01 0.20 I
2
/ I
1
TBCD 0.00 – 300.00s 0.01s 1.00 s BCD definite time setting
[BCDEN] Off / On Off BCD Enable
Minimum setting of the BC threshold is restricted by the negative phase sequence current
normally present on the system. The ratio I
2
/ I
1
of the system is measured in the relay continuously
and displayed on the metering screen of the relay front panel, along with the maximum value of
the last 15 minutes I
21
max. It is recommended to check the display at the commissioning stage.
The BCD setting should be 130 to 150% of I
2
/ I
1
displayed.
Note: It must be noted that I
2
/ I
1
is displayed only when the positive phase sequence current
(or load current ) in the secondary circuit is larger than 2 % of the rated secondary circuit
current.
TBCD should be set to more than 1 cycle to prevent unwanted operation caused by a transient
operation such as CB closing.
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