Sel 411L - Figure 3.191 Isolated Ring-Connected Network with Dedicated, Managed Switches; Figure 3.192 Isolated, Star-Connected Network with Managed or Unmanaged Switches; Table 3.145 Impact of Network Performance on 87 L Protection

P.3.278
SEL-411L Relay Protection Manual Date Code 20151029
Protection Functions
87L Communication and Timing
Figure 3.191 Isolated Ring-Connected Network With Dedicated, Managed Switches
Figure 3.192 shows an example of an engineered network topology with star
configuration. While the simplest of the topologies, it exhibits a single point
of failure design.
Figure 3.192 Isolated, Star-Connected Network With Managed or Unmanaged Switches
Table 3.145 provides a cause and effect table that correlates network
performance with 87L performance. Network performance is defined in terms
of various network issues and 87L performance is defined in terms of 87L
element availability. Note that in many cases the failure mode is not unique to
Ethernet communications and the 87L will have the same response when
using a serial communications channel.
Station A
SEL-411L
IRIG-B
Switch
SEL-411L
Switch
SEL-411L
Switch
SEL-411L
Switch
Station B
IRIG-B
Station C
IRIG-B
Station D
IRIG-B
Station A
SEL-411L
IRIG-B
Switch
SEL-411L
Switch
SEL-411L
Switch
SEL-411L
Switch
Station B IRIG-B Station C IRIG-B Station D IRIG-B
Table 3.145 Impact of Network Performance on 87L Protection (Sheet 1 of 2)
Cause Detection Method Limit 87L Recovery time
Lost packets A packet timer starts when a packet
is received and resets when new
packet is received. If timer is not
reset within required time, a lost
packet is declared.
No tolerance. One lost packet
causes 87L unavailability.
Two cycles after the relay receives
the first new packet.
Corrupt packets BCH and CRC and two different
parity checks.
No tolerance. One corrupt packet
causes 87L unavailability.
Two cycles after receipt of first
uncorrupted packet.
Duplicate packets Checks sequence number (SNTX)
of each packet.
No effect—relay ignores dupli-
cate packets.
N/A (relay is unaffected)
Excessive time dif-
ference between
received packets
Jitter
a
variation in channel delay.
The relay expects a new sample
every 1/16th of a power system
cycle. If no data is available when
expected, a failure is declared.
Jitter threshold established by
the 87ETHJT setting.
Two cycles after receipt of next
packet within the tolerable jitter
threshold.