IEEE PES T&D Conference & Exposition 2022 - 128

especially where there are communications bandwidth limitations.
These networks provide high-performance data
channels for 87L protection because they are deterministic
and time-synchronized, and they have minimal jitter
(latency variation).
Packet-Switched Communications
The most common packet-switched communications
technology today is multiprotocol label switching. Utility
communications put into service today provide all the
required communications services, such as teleprotection,
alarm, supervisory control and data acquisition, energy
management system, metering, voice, engineering access,
and so on.
Packet-based systems are less deterministic than TDM
since the exchange of data packets is not time-synchronized.
Packet-switched communications must be carefully designed
since 87L schemes typically require latency, asymmetry, and
failover times of less than 5 milliseconds. High values of
latency, jitter, and channel asymmetry can affect the performance
of these schemes and cause undesired or delayed relay
operations. Long fault-clearing times mean more damage to
equipment. Furthermore, 87L schemes require low failover
times to a redundant communications channel to minimize
the impact of channel failures.
Typically, 87L channels cannot be directly implemented on
packet-based networks, except for relays that can work properly
on ethernet channels over software-defined networks. Figure
5 shows a method for an 87L scheme to properly function
on an ethernet network. The solution includes OT edge nodes
that provide an IEEE C37.94 interface to the relays and ethernet
line modules to achieve the determinism requirements of
87L schemes.
Wavelength-Division Multiplexing
Fiber-optic links are valuable assets of electrical utilities. In
some applications, ultra-high-speed protection requires pointto-point,
direct fiber-optic communications channels. The
fiber-optic asset can be shared with other services by using
WDM and wavelength-division demultiplexing (WDD), as Figure
6 illustrates. In our example, the WDM multiplexers combine
signals with wavelengths
mmm and 4m to exchange
123
,,,
data between the two terminals with bandwidths in the order of
one Gbps or higher.
Traditional Impedance-Based
Fault Locating
Line protective relays are expected to have fault-locating functionality.
Due to the nature of overhead transmission lines,
faults can occur at any location along the transmission line
path. For example, an atmospheric discharge may induce an
overvoltage and insulation flashover, resulting in a short circuit
that is detected by line protective relays. Once the breakers at
both ends of the line open, control schemes in the substation
reclose the breakers to restore the operation of the line. If the
flashover results in permanent insulation failure, the fault will
still be present and the breakers will be open permanently. If
the insulation failure is transient, the line returns to its pre-fault
Ethernet Packet-Based Network
OT Edge Node
Line Current
Differential
Relay
IEEE
C37.94
Interface
Line
Module
Ethernet
Ethernet
OT Edge Node
Line
Module
IEEE
C37.94
Interface
Line Current
Differential
Relay
figure 5. Line current differential protection scheme over a packet-switched ethernet network.
λ1
λ1
Relay
Other
Services
λ2
λ3
λ4
λ1, λ2, λ3, λ4
WDM/WDD
WDM/WDD
λ2
λ3
λ4
Relay
Other
Services
figure 6. Protective relays and utility services share a fiber-optic connection through the use of WDM/WDD.
128
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