17.16
SEL-400 Series Relays Instruction Manual Date Code 20171006
IEC 61850 Communication
Sampled Values
minimum delays via an Ethernet connection. Fiber-optic based Ethernet connec-
tions are established between SV publishers and SV subscribers for transmitting
SV samples and GOOSE messages. This network is also called the process bus
network. The information exchange between the SV publisher and the SV
subscribing relays is based on a publisher/subscriber mechanism that is similar to
GOOSE messaging. The SV subscribing relay receives the time-stamped SV
messages and checks the timeliness of the samples. Messages are buffered and
then used by the relays.
To promote interoperability and fast deployment of SV, UCA International Users
Group released “Implementation Guideline for Digital Interface to Instrument
Transformers Using IEC 61850-9-2” and described a subset of IEC 61850-9-2,
also known as UCA 61850 9-2LE or simply 9-2LE. The SEL-400 series SV
products are compliant with the 9-2LE guideline, also known as the 9-2LE pro-
file in this manual.
You can configure the SEL-400 series SV products via Architect or using Port 5
settings. See IEC 61850 Configuration on page 17.22 for more information on
SV product configuration.
SV Processing
SV Publication
An SV publisher is an interface to the non-conventional instrument transformers
(NCIT) and traditional instrument transformers. When an SV publisher is con-
nected to a traditional instrument transformer, it is also called a standalone merg-
ing unit. The SV publisher samples the analog data at 8 kHz and down-samples
to 4.8 kHz/4.0 kHz when the nominal frequency is 60 Hz/50 Hz. A time stamp
representation, known as smpCnt, is encoded with each published SV message.
Given the sampling rate and the need to maintain the time coherence of samples
from multiple merging units, merging units must be time-synchronized to high-
accuracy time source. See Section 11: Time and Date Management for time-syn-
chronization methods. The difference between the time encoded by the smpCnt
in an SV message and the time that the message is published at the Ethernet inter-
face is the merging unit processing delay. This delay and the transmitting delay
over a process bus network is the total network delay. See SV Network Delays on
page 17.18 for more about network delay.
SV Dataset
SEL SV publishers can transmit multiple SV data streams. Each SV message
includes four currents and four voltages. For example, the SEL-401 has inputs for
12 analog measurements (6 currents and 6 voltages). This means that the merging
unit function requires at least two streams to send all available voltage/current
inputs. Merging units support as many as seven output streams, allowing
unmatched flexibility with measurement channel assignment and precise routing
of duplicate streams.
Primary/Secondary Scale Factor
The analog measurements inside SV messages represent the primary side of the
instrumental transformer. When connecting a standalone merging unit to a con-
ventional transformer, a scale factor should be applied such that the measured
secondary quantity is scaled to primary values. For example, if the SEL-401 IW
terminal is connected to an ANSI C600 1200/5 CT, the merging unit CT ratio
CTRW should be set as 1200/5 = 240. Once CTRW is set, the measured second-
ary quantity on IW is scaled by CTRW before it is transmitted.
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