ABB REL 356 Current Differential Protection
4-5
Measuring Elements and Operational Logic
Relay Functions
Direct Transfer Trip
The REL 356 data frame provides for an independent transfer trip command to be sent to the remote relay by activating
an opto-isolated dc voltage input, DTT KEY. When the remote relay receives the Direct Transfer Trip command for > 10
msec, a trip command is issued and the trip output contacts are closed.
When REL 356 is supplied with the optional output board, transfer trip can be selected to trip all 6 contacts, 4 additional
contacts, or 2 of the additional contacts.
Change Detector Supervision
The REL 356 has sensitive change detectors, forming the signal CD. The current change detectors will operate for a
12.5% change of the sample value in any phase or ground as compared to the same sample one cycle earlier. The
voltage change detectors will operate for a 12.5% change of the sample value in any phase as compared to the same
sample one cycle earlier. The change detector operation, CD, can be selected to use current only (CD =
D
I) or current
OR voltage (CD =
D
I
D
V).
The change detector CD supervises differential trip and is used for triggering DFR records. Current sensing only is
suitable for most applications. For weak feed conditions, however, the
D
I
D
V setting may be preferable.
Open Breaker Function
REL 356 will sense a local open breaker condition by either the 52b contact or by a current sensing element IE or both.
Note that the minimum setting of IE is 0.04 x In (0.2 A for a 5 A relay) why this setting option can not be used on short
lines. As an Open Breaker logic condition will be set when the current is below the IE setting, the line charging current
has to be larger than this setting.
When the local REL 356 detects an open breaker condition, it sends this information to the remote end. If there is a fault
on the line, the remote end REL 356 will then trip from the low set phase and ground overcurrent elements, IPL and IGL,
after a set time delay, SOBT.
The relay at the end with the open breaker will not trip as the differential trip is supervised by the change detector, CD.
The Open Breaker function can be disabled by setting OPBK = OUT. Note that this will disable the Open Breaker
function in the remote end as no open breaker code will be received there.
Figure 4-5. Open Breaker Trip
Stub Bus Trip
The stub bus trip is using the same logic as the Open Breaker function. When a binary input senses that the line
disconnect is open, the local and remote relay will be enabled to trip from the low set overcurrent elements, IPL and IGL.
The relay at the non-faulted section of the line will not trip as the differential trip is supervised by the change detector,
CD.
Summary of Contents for REL 356
Page 23: ...ABB REL 356 Current Differential Protection 1 10 Product Overview and Specifications ...
Page 83: ...ABB REL 356 Current Differential Protection 3 36 Settings and Application ...
Page 127: ...ABB REL 356 Current Differential Protection 5 28 Testing ...
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