5-138 G30 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUALPRODUCT SETUP CHAPTER 5: SETTINGS5DIRECT OUTPUT DEVICE ID: “2”DIRECT I/O CH1 RING CONFIGURATION: “Yes”DIRECT I/O CH2 RING CONFIGURATION: “Yes”For UR-series IED 3:DIRECT OUTPUT DEVICE ID: “3”DIRECT I/O CH1 RING CONFIGURATION: “Yes”DIRECT I/O CH2 RING CONFIGURATION: “Yes”In this configuration the following delivery times are expected (at 128 kbps) if both the rings are healthy:IED 1 to IED 2: 0.2 of power system cycleIED 1 to IED 3: 0.2 of power system cycleIED 2 to IED 3: 0.2 of power system cycleThe two communications configurations can be applied to both permissive and blocking schemes. Take speed, reliability,and cost into account when selecting the required architecture.5.3.17.2 CRC alarm CH1(2)SETTINGS PRODUCT SETUP DIRECT I/O CRC ALARM CH1(2)The G30 checks integrity of the incoming direct input and output messages using a 32-bit CRC. The CRC alarm function isavailable for monitoring the communication medium noise by tracking the rate of messages failing the CRC check. Themonitoring function counts all incoming messages, including messages that failed the CRC check. A separate counteradds up messages that failed the CRC check. When the failed CRC counter reaches the user-defined level specified by theCRC ALARM CH1 THRESHOLD setting within the user-defined message count CRC ALARM 1 CH1 COUNT, the DIR IO CH1 CRC ALARMFlexLogic operand is set.When the total message counter reaches the user-defined maximum specified by the CRC ALARM CH1 MESSAGE COUNTsetting, both the counters reset and the monitoring process is restarted.Configure the operand to drive an output contact, user-programmable LED, or selected communication-based output.Latching and acknowledging conditions—if required—are programmed accordingly.The CRC alarm function is available on a per-channel basis. The total number of direct input and output messages thatfailed 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 1message 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 minutesat 64 kbps and 80 minutes at 128 kbps. If the messages are sent faster as a result of direct outputs activity, themonitoring time interval shortens. Take this into account when determining the CRC ALARM CH1 MESSAGE COUNTsetting. For example, if the requirement is a maximum monitoring time interval of 10 minutes at 64 kbps, then the CRCALARM CH1 MESSAGE COUNT is set to 10 × 60 × 1 = 600.• Correlation of failed CRC and bit error rate (BER) — The CRC check can fail if one or more bits in a packet arecorrupted. Therefore, an exact correlation between the CRC fail rate and the BER is not possible. Under certainassumptions an approximation can be made as follows. A direct input and output packet containing 20 bytes resultsin 160 bits of data being sent and therefore, a transmission of 63 packets is equivalent to 10,000 bits. A BER of 10–4implies 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 . CRC ALARM CH1 CRC ALARM CH1FUNCTION: DisabledRange: Enabled, Disabled CRC ALARM CH1MESSAGE COUNT: 600Range: 100 to 10000 in steps of 1 CRC ALARM CH1THRESHOLD: 10Range: 1 to 1000 in steps of 1 CRC ALARM CH1EVENTS: DisabledRange: Enabled, Disabled
