Electric Energy T&D - Index

Electric Energy T&D - EE Magazine March / April - Index

Building on part 1 of this article in the previous issue, this second
installment illustrates the issues and impacts of implementing
substation integration in harmony with the utility’s organization
and operations using a standards-based approach. The engineering
process implemented by Black & Veatch at a Northeastern U.S. utility
is presented here in case study fashion. This project began in 005
with the addition of a new substation.
The utility wanted to move their substation design from a mix of
electromechanical relays and other IEDs to an integrated substation
that supports automation. However, they were not starting with a blank
sheet of paper. They were already extending their corporate WAN to
their substations, so they knew they wanted Ethernet; but how do
you install Ethernet in substations? They knew what microprocessor
relays they wanted, but what protocol was the best choice of the three
supported protocols (DNP3, Modbus, and IEC 61850)?
Recognizing the need from previous experience, the utility began with
substation integration training to introduce personnel from across the
enterprise to the equipment, concepts and issues, reasons, costs, risks,
benefits, and process of substation integration. Once the initial training
was completed, functional requirements for performance were defined
as outlined in the first article, and the process was under way.
Input and Outputs
Substation inputs and outputs (I/O) include measurements, status, and
control. By defining an I/O scheme that shows the substation data sources
(See Figure 1), several underlying issues were uncovered and resolved.
figure 1 – Example I/O Scheme for 15 kV Breakers
Making Substations More Intelligent
by Design
PART TWO: Bringing It All Together at a Northeast Utility
By Craig M. Preuss, Engineering Manager-Utility Automation,
Black & Veatch Corporation
On the distribution side, metering data from relays was considered
accurate enough. Revenue meters were already required on two of three
transmission lines and both transformers. For the remaining transmission
line, it was discovered that metering values from the primary relay were
accurate enough. While metering values could have been obtained from
primary and backup devices, the utility decided that multiple sources
added unnecessary complexity to system design and operation.
Besides standard metering quantities, other examples of analog
quantities gathered from other substation IEDs are tap position,
battery DC voltage, control house temperature, transformer dissolved
hydrogen level, and transformer winding temperature.
For wiring the approximately 70 hard-wired status points, brief
consideration was given to wiring them to relays. Significant concern
was raised because many status points are not associated with relays
and the status of equipment still in service would be lost when an
unassociated relay was taken out of service. By hardwiring breaker
status and other status points to an IED dedicated to that purpose, the
source of status and controls is readily known and easily isolated. For
these reasons, a distributed I/O device was selected for status inputs.
Initial discussions surrounding controls had the SCADA controls assigned
to the primary relays and local HMI controls assigned to the backup relay.
In addition, the utility wanted a manual way to perform controls outside
of the relays and to also manually disable controls. Performing controls
through relays resulted in the difficult association of some control points
with relays and the loss of control when a relay is out of service. By using
dedicated distributed I/O, the utility was able to directly trip the breaker
without the use of interposing relays, but careful consideration of contact
output ratings was required (See Figure ).
vENDoR DEScRIpTIoN
figure 2 – Comparison of Distributed I/O Control Output Ratings
March-April 2008 Issue I
1 10A at 30 Vdc,½A at 1 5Vdc
3
Make: 30 A @ 50 Vdc per IEEE C37.90
Continuous Carry: 6 A @ 70°C; 4 A @ 85°C
Break: 4 V 0.75 A;48 V 0.50 A;1 5 V 0.30 A
Heavy duty protective relay-grade 10A for direct connection
to circuit breaker trip coils
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