Schweitzer Engineering Laboratories SEL-734 - Table 7.5 Minimum Bandwidth Requirements

7.7
Date Code 20090730 Instruction Manual SEL-734 Meter
Time-Synchronized Measurements
Synchrophasor Measurements
Evaluate the Communications Channel Bandwidth
Once you know the frequency and size of the messages, use Equation 7.1 to
determine the rate at which the Fast Messages can be sent:
Equation 7.1
For example, given that PMDATA = A, nn = 96 (60h), L = 12 (worst case), and
the frequency of messages is 5 per second, the required baud rate would be at
least 1.2 • (96 • 2 • 5) = 6912 bits per second. Therefore, the communications
channel speed could be no less than 9600 baud.
Table 7.5 is a partial list of various combinations. If the application does not
require updates more than once or twice a second, then bandwidth should not
be an issue. If the communications system is in place, and the baud rate is
below 38400 baud, then either the message frequency or analog values
included in the packet will need to be adjusted.
Starting and Stopping Synchrophasor Fast Messages
It is important to note that all synchrophasor messages, including the enable
and disable messages, must be transmitted and received through use of a
binary transmission method. Standard terminal emulation software will
decipher the hex data as ASCII, and the meter will not respond as expected.
Enable Synchrophasor Fast Messaging
NOTE: The initial IRIG-B time
synchronization can take up to a
minute to occur.
After evaluating what data will be required, how often the data will be
required, verifying that the communications channels will transfer the data
adequately, and changing the appropriate settings, you are ready to construct
the enable message. Table 7.6 shows the content and format required to enable
the unsolicited synchrophasor binary messages.
where:
nn = message size (bytes)
L = length of message byte (1 start bit, 8 data bits, 2 stop bits,
1 parity = 12)
f = frequency of messages
1.2 = factor to account for system delays
Table 7.5 Minimum Bandwidth Requirements
PMDATA Setting
Transmission Rate
(messages per second)
Minimum Allowable
Baud Rate
V1 20 9600
V1 10 4800
V1 5 2400
V 20 19200
V109600
V 5 4800
A 20 38400
A 10 19200
A 5 9600
A 4 4800
bps 1.2(nn L f )• • =
Courtesy of NationalSwitchgear.com