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GENERAL
The automatic source transfer control (ATC) is designed to
work with G&W SF6 and solid dielectric switchgear to perform
basic automatic transfer operations for a distribution switch
installed in a primary selective or bus-tie system configuration.
The control monitors two separate source voltages and their
respective switch positions. When the source voltage is dead,
the control automatically transfers electrical power to minimize
the duration of power outages.
OPERATION
Primary-Selective System: The load(s) are
combined on one solid bus and are all normally fed from a
single source. The first source switch feeding the load(s)
is normally closed and the second source switch (acting as
the alternate, or backup source) is normally open. When the
first source is lost, the control will open its switch and
close the second switch, thereby restoring power to the load(s)
from the alternate source.
Bus-Tie System: The loads are divided between
the two sources and the bus is split with a normally open
tie switch. The first source switch is normally closed and
feeds load 1; while the second source switch is normally closed
and feeds load 2. The loads are sized such that if either
of the two sources are lost, the controller will open its
switch and close in the bus tie switch; thereby feeding both
loads from the one live source. ATC 201 only.
Emergency Return Function: If the preferred
source is lost, the control transfers over to the alternate
source. After some time, the preferred source returns and
the control begins the return transfer delay timer (or waits
for the time-of-day window setting). During this timing process,
the alternate source is lost. Under this circumstance, the
control will ignore the remainder of the return transfer delay
timer and will immediately transfer back to the preferred
source in an open transition mode (open the alternate source
before closing the preferred source switch) - regardless of
how the normal return or initial transfer operation sequence
is set.
SETTINGS FEATURES
The control logic parameters are field selectable and determine
the specific operation sequence, timing, and source preference
for the auto transfer operations. The parameter selections
are as follows:
System Configuration Selection: User selects
between a Primary-Selective (Combined Load) and a Bus-Tie
Configuration. ATC 201only.
Preferred Source Selection: The choices for this
setting are: SOURCE 1, SOURCE 2, or NONE. When a source is
selected as "Preferred," the control will always
try to serve the load from this source (as long as this source
is healthy). If the preferred source is lost, the control
will transfer to the alternate source (as long as that source
is healthy). If the user selects NONE in this setting, the
control will only perform initial transfers.
Operation Sequence Selection Initial and Return Transfers:
The choices for these setting are: "OPEN before CLOSE"
or "CLOSE before OPEN." The selection determines
if the sources will be paralleled or not during an operation
sequence.
Initial and Return Transfer: Delay Timers
and Time-of-Day Window
The user selects a countdown timer setting to add a delay
from the time the voltage is dead and the time the switch
begins the transfer. In the ATC 201, the user selects between
a countdown delay timer and a time-of-day window for the return
transfer operation.
Paralleling of Sources Setting: The user
will be able to select between Yes and No. A Yes setting will
allow the control to have both source switches closed at the
same time. If a No is selected, the user will not be able
to close both switches at the same time.
Auto/Manual Mode Setting: If the user selects
the Auto Mode, the automatic transfer logic is enabled. No
manual electrical open or close operations are allowed, and
the control will only respond to the automatic transfer logic.
The Manual Mode disables the automatic transfer logic and
(in combination with the Local setting) allows the user to
use the local electronics to open and close the switches manually.
In combination with the Remote Mode setting, the user is allowed
to open and close the switches via remote SCADA.
Local/Remote Setting: If the user selects
the Local Mode, all remote access is blocked from the unit.
If the user selects the Remote Mode access to the control
is allowed.
Test Mode Setting: While in the Test Mode,
the user is able to simulate the loss and return of both sources,
simulate a low dielectric condition, and simulate an overcurrent.
If the motors can be decoupled, the test mode will also operate
the motors to test the complete system, without actually operating
the switches.
Overcurrent Lockout: If the overcurrent lockout
input is activated, the control is blocked from performing
any local, remote, or automatic operations. The overcurrent
inputs will come from either a digital (ATC 101 and ATC 201)
or analog source (ATC 201 only) that will activate when this
device detects a downstream fault. The condition is reset
locally at the control once the fault condition has been removed.
Low Dielectric Condition: This feature is
applicable for SF6 switches only. If the low dielectric input
is activated, the control is blocked from performing any local,
remote, or automatic operations and will automatically reset
itself once the low dielectric condition is removed.
Voltage Sensing: Three-phase voltage monitoring
is required on both sources. This control will accept either
digital (ATC 101 and ATC 201) or analog (ATC 201 only) voltage
sensing for each source. If any one of the 3 phases is lost,
the source will indicate dead. All 3 sources need to be live
for a live source indication.
Generator Source Feature: The user will have
the ability to set Source 1, Source 2, or NONE as a generator.
In this case, when the preferred source is lost and the initial
transfer delay timer has expired, the control will activate
(close) the Generator Start Contact. The customer will connect
this contact to their generator. Once the generator is up
and running, its voltage sensors will activate as a good source.
The control will then initiate the transfer from the utility
source to the generator alternate source. Once the preferred
source returns and the return transfer delay timer expires,
the control will:
1. Initiate the return transfer to the preferred source; and
2. Begin the Generator Cool Down Timer.
When the timer expires, the control will activate the Generator
Stop Contact.
Events Recorder: Each ATC 201 shall have
an internal sequence of events recorder. The most recent events
are logged with a time/date stamp. The sequence of events
recorder is an option for the ATC 101.
USER-INTERFACE AND FRONT PANEL
For the ATC 101, all settings and operations of the control
shall be viewed and adjusted without the use of a keypad/display
or any other tools. The ATC 201 shall have a keypad/LCD interface.
Both ATC controls shall provide system status, parameter settings,
local manual operation, test mode operation, and SCADA outputs
all integral in one control.
ENCLOSURE
The standard enclosure shall be padlockable and rated NEMA
4. NEMA 4X and 6P enclosures shall be available as options.
STANDARDS
The ATC package shall be rated for -30ºC to +65ºC.
The control shall meet applicable sections of the following
standards:
• ANSI/IEEE C37.90.2
• ANSI/IEEE C37.90.1
• IEC 60255-22-2
• IEC 60255-21-1 First Edition – 1998
• IEC 60255-21-2 First Edition – 1998
SCADA OUTPUTS
This control shall have a pre-wired terminal block for easy
access and connection to an external RTU. The terminal block
shall have all of the digital status points available from
the control and control outputs so the user can remotely take
control over the switch and operate the two switch mechanisms
open or closed.
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