Broken Conductor Protection Scheme Logic - Toshiba GRE110 Instruction Manual

Scheme Logic
Figure 2.7.3 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], binary input signal BCD BLOCK.
The broken conductor protection is enabled when three-phase current is introduced.
ICD is the inrush current detector ICD, which detects second harmonic inrush current during
transforomer energisation, and can block the BCD element by scheme switch [BCD-2F]. See
Section 2.9.
81
BCD
[BCD-2F]
+
"Block" &
ICD
[BCDEN]
+
"ON"
BCD BLOCK
Figure 2.7.3 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
BCD 0.10 – 1.00
TBCD 0.00 – 300.00s
[BCDEN] Off / On
[BCD-2F] NA / Block
Minimum setting of the BC threshold is restricted by the negative phase sequence current normally
present on the system. The ratio I
displayed on the metering screen of the relay front panel, along with the maximum value of the last
15 minutes I max. It is recommended to check the display at the commissioning stage. The BCD
21
setting should be 130 to 150% of I
Note: It must be noted that I
(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.
&
0.00 - 300.00s
1
Step Default Remarks
0.01 0.20 I
2
0.01s 0.00 s BCD definite time setting
Off BCD Enable
NA BCD blocked by inrush current
/ I of the system is measured in the relay continuously and
2 1
/ I displayed.
2 1
/ I is displayed only when the positive phase sequence current
2 1
 42 
TBCD
0
t
/ I
1
6 F 2 T 0 1 7 2
138
BCD TRIP