he
power quality issues.
AEP discussed the situation with Cooper
Power Systems sales engineer Tony
Talavera. Tony recommended a new
Automatic Source Transfer (AST) system
offered by Coopers Systems Integration
Group (SIG) a solution he thought
would be perfect for this situation.
The AST system works by
integrating two of
Cooper Power Systems
most advanced products,
the Form 6 recloser con-
trol, and PeerComm proprietary peer-to-peer
communications proto-
col, which allows pro-
tective relays and
recloser controls to
share information. Two
Form 6 controls are
placed on either side of
a critical load as shown
in Figure 1.
The controls are con-
nected by some type of
communication medi-
um: either fiber optic,
twisted pair, or radio.
Each control needs to
have voltage sensing on
its source side. This can be accom-
plished with either PTs or internal voltage
sensors in the case of the NOVA
recloser (up to 27 kV).
The recloser on the preferred feeder,
Device 1, is normally closed, providing
service to the critical load. The recloser
on the alternate feeder, Device 2, is
normally open, waiting for the opportunity
to provide service to the critical load in
case the preferred feeder has a power
quality issue. When a power quality issue
arises, Device 1 opens. Once Device 1
has fully opened, it will communicate
through PeerComm to Device 2 to tell it to
close, thus serving the critical load again.
The AST system also has three restoration
modes. Manual restoration mode will not
transfer back to the preferred feeder
without line personnel manually closing
the preferred recloser and opening the
alternate recloser. Automatic restoration
manual initiation will also not automati-
cally transfer back to the preferred
feeder without manual intervention.
However, in this mode once the alter-
nate source is opened, or the preferred
source is closed, the other device will
perform the necessary action to return the
AST system to the normal configuration.
Finally, the
automatic
restoration
automatic
initiation
mode returns the AST system to the
normal configuration without any
intervention upon restoration of the
preferred line voltage for a specified
amount of time.
There are several other features that the
AST system includes. One of these features
is the ability to change which feeder is the
preferred and which is the alternate, via
the swap preferred push button. There are
also unique Sequence of Events (SOEs)
that come with the AST system to aid in
system analysis. Eight unique target lights
identify the status of the AST system.
There is also a real time one-line diagram
that can be displayed
through a ProView applica-
tion software connection to
the AST system.
AEP Corpus Christi was
intrigued by the concept of
the AST and agreed to order
a system to resolve the
power quality disturbances
the carbon plant was experi-
encing. The system they
ordered utilizes two NOVA
three-phase reclosers and a
RS-485 twisted pair wire as
the communication medium,
since the reclosers would
only be one pole span apart.
The NOVA reclosers were a
good choice since speed is of
critical importance here, and
the NOVA recloser can make
and break load in two to
three cycles. Furthermore, the use of
physical connection media, such as RS-
485, RS-232, or fiber optic cable for the
PeerComm connection allow for faster
communications speeds than radio com-
munications.
Innovative AST Application
Provides Dramatic Improvement
to Carbon Plants Power Quality
by Dale Crisman, AEP Corpus Christi and Dan Landreman,
Senior Power Systems Engineer
Source
Source
Device #1
Device #2
Normally
Closed
Normally
Open
Critical
Load
Preferred
Feeder
Alternate
Feeder
Figure 1
Two Form 6 controls are placed on either side of a critical load as shown in
Figure 1. Once Device 1 has fully opened, it will communicate through PeerComm to
Device 2 to tell it to close, thus serving the critical load again. T H E L I N E / A p r i l 2 0 0 5 1 1
2 0 0 5 Tr a i n i n g C l a s s e s
Voltage Regulator Training
Regulator Traditional Training
May 3-5
October 4-6
Regulator Tap Changer and Troubleshooting
June 14-16
Regulator CL5/CL6 Control Training
Sept 13-15
Recloser & Control Training
Single & Three Phase Recloser Training
May 10-12
FULL!
September 20-22
Technician/Engineer Form 6 Recloser
Control Training
June 21-23
November 8-10
Basic Form 6 Control & Troubleshooting
Training
October 11-13
System Integration Workshops
Power Engineering Basics
November 7-8
Symmetrical Components
November 9-10
Fundamentals of Power Distribution
April 19-21
June 7-9
Distribution Automation
April 26-28
November 1-3
Capacitor Applications & Protection
May 10-12
Distribution OverCurrent Protection
May 24-26
September 20-22
Distribution Voltage Regulation
June 21-23
Power Quality (PQ)
September 13-15
Distributed Generation
October 18-20
For further information on Systems Integration
classes, contact banalesv@umr.edu,
573-341-4278.
For a complete listing of Cooper training
classes, visit
www.cooperpower.com/EventCalendar.
AEP wanted to see the AST in action
before they installed it on their system.
They set up an actual AST system,
complete with NOVA reclosers, in their
service department and invited Tony and a
SIG representative to witness the testing.
The first few tests showed that the critical
load experienced a loss of service of
nearly 10 cycles. Standard adjustments,
such as baud rate increases, were made
to the AST system. The next few tests
showed transfer times between eight and
a half and nine cycles. While this was
close to the goal of eight cycles needed
for the carbon plant, it was not good
enough to solve the problem.
It was then proposed that instead of
waiting for confirmation that Device 1
had opened, Device 2 should close as
soon as the power quality issue on the
preferred feeder was detected. In essence,
this would set up a race between Device
1 opening and Device 2 closing.
This modification was made to the AST
programming and the tests were run again.
This time the critical load was only with-
out power for between four-and-a-half
and five cycles. AEP personel were very
pleased with this dramatic improvement.
If speed was not such a critical issue for
this particular AST application, the fast
option of closing Device 2 before there is
confirmation that Device 1 had opened
would not be recommended. Often, the
very reason for the power quality issue
is that there is a fault upstream of the
critical load on the preferred feeder,
collapsing the voltage. If Device 2 were
to close before Device 1 opens, then the
alternative feeder would be exposed to
the same fault condition that caused the
power quality issue.
This fast option still does have a mecha-
nism that should prevent Device 2 from
closing before Device 1 opens. Since the
power quality issue is detected by
Device 1, it will tell its NOVA recloser to
open at the same time this information is
transmitted via PeerComm to Device 2.
Device 2 then issues a close command
to its NOVA recloser. Since there is an
inherent delay in the communication
network of roughly one cycle, this gives
Device 1 a headstart over Device 2. As
long as both NOVA reclosers are in good
working condition, then the NOVA
recloser associated with Device 1 should
always open before the NOVA recloser
associated with Device 2 closes. Below
are two tables that give the operations
times associated with both the standard
and fast AST operation.
While the AST fast operation mode was
the perfect solution for this specific
application, it is not intended for all
types of operations. This is why there are
other AST operation modes available as
standard. A Cooper SIG representative
can determine the appropriate AST mode
for any particular installation.
The AST system has now been in service
protecting the carbon plant for more than
six months. The system has operated
dozens of times in that period, saving the
carbon plant hundreds of thousands of
dollars, more than justifying the capital
costs of the equipment. Standard AST Operation
Action
Time in Cycles
Detection of power quality event
1
Opening of Device 1 (NOVA recloser)
3
Confirmation that Device 1 Opened
1
Transmission of situation to Device 2 via PeerComm 1
communication protocol
Closing of Device 2 (NOVA recloser)
3
Total time to restoration of critical load
9
Fast AST Operation
Action
Time in Cycles
Action
Time in Cycles
Detection of Power Quality Event
1
Transmission of situation to
1
Opening of Device 1
3
Device 2 via PeerComm (NOVA recloser)
communication protocol
Closing of Device 2 (NOVA recloser)
3
Total time to restoration of critical load
5