GE T35 UR Series, Instruction Manual

Page: 201 / 568

GE Multilin T35 Transformer Protection System 5-79
5 SETTINGS 5.2 PRODUCT SETUP
5
The operand shall be configured to drive an output contact, user-programmable LED, or selected communication-based
output. Latching and acknowledging conditions - if required - should be programmed accordingly.
The CRC alarm function is available on a per-channel basis. The total number of direct input and output messages that
failed the CRC check is available as the
ACTUAL VALUES

STATUS

DIRECT INPUTS

CRC FAIL COUNT CH1
actual
value.
• Message count and length of the monitoring window : To monitor communications integrity, the relay sends 1 message
per second (at 64 kbps) or 2 messages per second (128 kbps) even if there is no change in the direct outputs. For
example, setting the
CRC ALARM CH1 MESSAGE COUNT
to “10000”, corresponds a time window of about 160 minutes at
64 kbps and 80 minutes at 128 kbps. If the messages are sent faster as a result of direct outputs activity, the monitor-
ing time interval will shorten. This should be taken into account when determining the
CRC ALARM CH1 MESSAGE COUNT
setting. For example, if the requirement is a maximum monitoring time interval of 10 minutes at 64 kbps, then the
CRC
ALARM CH1 MESSAGE COUNT
should be set to 10 × 60 × 1 = 600.
• Correlation of failed CRC and bit error rate (BER) : The CRC check may fail if one or more bits in a packet are cor-
rupted. Therefore, an exact correlation between the CRC fail rate and the BER is not possible. Under certain assump-
tions an approximation can be made as follows. A direct input and output packet containing 20 bytes results in 160 bits
of data being sent and therefore, a transmission of 63 packets is equivalent to 10,000 bits. A BER of 10
–4
implies 1 bit
error for every 10000 bits sent or received. Assuming the best case of only 1 bit error in a failed packet, having 1 failed
packet for every 63 received is about equal to a BER of 10
–4
.
c) UNRETURNED MESSAGES ALARM CH1(2)
PATH: SETTINGS

PRODUCT SETUP

DIRECT I/O

UNRETURNED MESSAGES ALARM CH1(2)
The T35 checks integrity of the direct input and output communication ring by counting unreturned messages. In the ring
configuration, all messages originating at a given device should return within a pre-defined period of time. The unreturned
messages alarm function is available for monitoring the integrity of the communication ring by tracking the rate of unre-
turned messages. This function counts all the outgoing messages and a separate counter adds the messages have failed
to return. When the unreturned messages counter reaches the user-definable level specified by the
UNRET MSGS ALARM
CH1 THRESHOLD
setting and within the user-defined message count
UNRET MSGS ALARM CH1 COUNT
, the
DIR IO CH1 UNRET
ALM
FlexLogic operand is set.
When the total message counter reaches the user-defined maximum specified by the
UNRET MSGS ALARM CH1 MESSAGE
COUNT
setting, both the counters reset and the monitoring process is restarted.
The operand shall be configured to drive an output contact, user-programmable LED, or selected communication-based
output. Latching and acknowledging conditions, if required, should be programmed accordingly.
The unreturned messages alarm function is available on a per-channel basis and is active only in the ring configuration.
The total number of unreturned input and output messages is available as the
ACTUAL VALUES

STATUS

DIRECT
INPUTS

UNRETURNED MSG COUNT CH1
actual value.

UNRETURNED

MESSAGES ALARM CH1
UNRET MSGS ALARM CH1
FUNCTION: Disabled
Range: Enabled, Disabled
MESSAGE
UNRET MSGS ALARM CH1
MESSAGE COUNT: 600
Range: 100 to 10000 in steps of 1
MESSAGE
UNRET MSGS ALARM CH1
THRESHOLD: 10
Range: 1 to 1000 in steps of 1
MESSAGE
UNRET MSGS ALARM CH1
EVENTS: Disabled
Range: Enabled, Disabled