Schweitzer Engineering Laboratories SEL-2020 - Page 73

Date Code Code 20010518 Installation 3-9
SEL-2020 Instruction Manual
satisfied. If the data response has not been completed before the same message trigger condition
occurs again, the second trigger will be missed completely. The SEL-2020 will acknowledge this
missed trigger by setting a delay bit in the port register, which is reported in the SEL-2020 status
report.
Although both exception and periodic data collection can encounter this type of delay, you can
control the periodic collection period, and thereby minimize the possibility of collection delays,
and missed triggers. You should consider first, if the attached device is capable of transferring
data in binary format, or only in ASCII character format, and second, the type of data you plan to
request, i.e., meter, target, demand, or another type.
Table 3.3 presents some general guidelines regarding minimum data collection periods you
should use to collect various types of data from SEL relays in binary or ASCII format. The
guidelines in this table assume the relay is using a baud rate of 2400 or above and is not busy
processing events or communicating on more than one port. As this table shows, there is a
dramatic difference between the minimum collection period for a relay that has Fast Meter
(binary data transfer) capability, and one that can transfer data only in ASCII format.
When connecting to SEL 100 and 200 series relays that have Fast Meter binary data capability,
always connect to Port 2 on the relay. Binary data transfer is not supported on Port 1 of these
relays.
Table 3.3: SEL-2020 Minimum Data Collection Period (in Seconds)
Command Binary Data Format
(Fast Meter)
ASCII Data Format
(no Fast Meter)
20METER 1 10
20DEMAND 1 10
20TARGET 1 20
1
20STATUS N/A 10
20BREAKER N/A 10
20HISTORY N/A 20
2
20EVENT N/A 120
20EVENTS N/A 120
20EVENTL
3
N/A 300
Notes:
1
SEL-321 Relay requires one minute.
2
SEL-321 Relay requires 30 seconds. The SEL-BFR and SEL-2BFR Relays require
40 seconds.
3
Only supported on SEL relays that support 16 sample/cycle event reports.