Infrastructure Development Standards
PART 8.3:
AUTOMATIC TRANSFER SWITCH
PART 1 - GENERAL
I
DESCRIPTION
A.
II
This section describes design, materials and testing of the automatic transfer switch
(ATS) shown on the drawings. The contact transfer time in either direction shall not
exceed 1/6th (one - sixth) of a second.
SUBMITTALS
A.
Submit shop drawings to the City for review and approval.
B.
Submit four (4) copies of ratings, circuit diagrams, dimensional data, weights, conduit
entry restrictions, anchor bolt locations, protective relaying, and Bill of Material.
C.
Drawings are subject to approval. Construction is not to begin until all drawings are
approved.
D.
After approval, the vendor shall furnish one (1) set of reproducible tracings of final
certified drawings and six (6) sets of all drawings and data sheets or manuals that
include the following.
1.
2.
3.
4.
5.
6.
7.
8.
9.
III
Plan and elevation.
Dimension outlines including weights.
Terminal arrangements, type and location of accessories.
Assembly details.
Complete bill of material.
Any and all other drawings required for erection and installation of the
equipment.
Complete power and control wiring diagrams including all accessories.
Operations, maintenance and installation instruction books.
Spare parts list.
STANDARDS
A.
The design, fabrication and performance of the equipment shall conform to the applicable
requirements of the following standards and codes.
1.
2.
3.
4.
5.
6.
7.
B.
Underwriters Laboratories - UL1008
Standard for Emergency and Standby Power Systems - NFPA110
IEEE - IEEE Standard 4 (Orange book)
IEEE - IEEE Standard 241 (Gray Book)
American National Standards Institute (ANSI)
National Electrical Manufacturer's Association (NEMA) ICS2-447-AC
National Electrical Code (NEC) NFPA
Any conflict between the above mentioned documents and this specification shall be
referred to the Engineer for clarification before proceeding with the fabrication of the
affected parts.
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Infrastructure Development Standards
PART 2 - PRODUCTS
I
II
III
STRUCTURE DESIGN & CONSTRUCTION
A.
The ATS unit shall be enclosed in a NEMA 4X stainless steel enclosure.
line-up.
the switchboard
B.
The ATS manufacturer shall maintain a local service center capable of emergency service
or routine preventive maintenance and shall offer preventive maintenance contracts.
MECHANICALLY - HELD TRANSFER SWITCH
A.
The transfer switch unit shall be electrically operated and mechanically held in both
normal and emergency side, solenoid operated momentarily energized to minimize power
consumption and heat generation. The switch shall be positively locked and unaffected
by voltage variations or momentary outages so that contact pressure is maintained at a
constant value and temperature rise at the contacts is minimized for maximum reliability
and operating life. The switch shall be mechanically interlocked to ensure only one of
two possible positions--normal or emergency and with programmed transition.
B.
All main contacts shall be silver composition. Switches rated 600 amperes and above
shall have segmented, blow-on construction for high withstand current capability and be
protected by separate arcing contacts. ATS utilizing components of contactors or parts
thereof which have not been intended for continuous duty, repetitive switching or
transfer between two active power sources are not acceptable.
C.
The transfer switch shall be designed to match the voltage and wiring configuration of
the control panel.
D.
Inspection of all contacts (movable and stationary) shall be possible from the front of the
switch without disassembly of operating linkages and without disconnection of power
conductors. A manual operating handle shall be provided for maintenance purposes.
The handle shall permit the operator to stop the contacts at any point throughout the
entire travel to properly inspect and service the contacts when required.
MICROPROCESSOR CONTROL MODULE
A.
The control module shall direct the operation of the transfer switch. The module's
sensing and logic shall be controlled by a built-in microprocessor for maximum reliability,
minimum maintenance, and inherent digital communications capability. The control
module shall be connected to the transfer switch by an interconnecting wiring harness.
The harness shall include a keyed disconnect plug to enable the control module to be
disconnected from the transfer switch for routine maintenance.
B.
The control module shall be completely enclosed with a protective cover and be mounted
separately from the transfer switch unit for safety and ease of maintenance. Sensing and
control logic shall be provided on plug-in printed circuit boards for maximum reliability.
Interfacing relays shall be industrial control grade plug-in type with dust covers. All
relays shall be identical to minimize the number of unique parts.
C.
The control panel shall meet or exceed the voltage surge withstand capability in
accordance with IEEE Standard 472-1974 (ANSI C37.90a-1974) and the impulse
withstand voltage test in accordance with the proposed NEMA Standard ICS 1-109.
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Infrastructure Development Standards
D.
IV
An in-phase monitor shall be provided.
OPERATION
A.
Three-phase control for three-phase power sources. Three-phase controls shall include a
selector switch to enable temporary operation on single-phase power sources.
B.
The voltage of each phase of the normal source 1 shall be monitored, with pickup
adjustable from 85 to 100% and dropout adjustable from 75 to 98% of pickup setting,
both in increments of 1%, and shall be fully field-adjustable without the use of any tools,
meters or power supplies. Repetitive accuracy of settings shall be +/-2% or better over
an operating temperature range of -20C to 70C. Factory set to pick up at 90% and
dropout at 85%.
C.
Three phase voltage sensing of the emergency source shall be provided, with a pickup
adjustable from 85 to 100% (and dropout fixed at 84 to 86% of pickup), and frequency
sensing with pickup adjustable from 90 to 100% (and dropout fixed at 87 to 89% of
pickup). Both pickup settings shall be fully field-adjustable in 1% increments without the
use of any tools, meters or power supplies. Repetitive accuracy of settings shall be +/2% or better over an operating temperature range of -20C to 70C. Factory set to pick
up at 90% voltage and 95% frequency.
D.
The control module shall include four time delays that are fully field-adjustable in
increments of at least 13 steps over the entire range as follows:
- Time delay to override momentary normal source 1 outages to delay all transfer switch
and engine starting signals. Adjustable from 0 to 6 seconds. Factory set at 1 second.
- Transfer to emergency source time delay. Adjustable from 0 to 5 minutes. Factory set
at 0 minutes, unless indicated otherwise on the plans.
- Retransfer to normal 1 time delay. Time delay is automatically bypassed if emergency
source fails and normal source is acceptable. Adjustable from 0 to 30 minutes. Factory
set at 30 minutes.
E.
A momentary-type test switch shall be provided to simulate a normal source 1 failure.
Also, terminals for a remote contact which opens to signal the ATS to transfer to
emergency and terminals for remote contacts which open to inhibit transfer to
emergency source and/or retransfer to normal source 1 shall be provided.
F.
Output terminals to signal the actual availability of the normal and emergency sources, as
determined by the voltage sensing pickup and dropout settings for each source, shall be
provided.
G.
One set of auxiliary contacts shall be provided rated 10 amps, 480 VAC consisting of one
contact closed when the ATS is connected to normal 1 and one contact closed when the
ATS is connected to emergency source. Also, one set of signal lights to indicate when
the ATS is connected to normal source 1 and when the ATS is connected to emergency
source shall be provided.
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Infrastructure Development Standards
V
INCOMING AND OUTGOING CONNECTIONS
A.
VI
The incoming line terminals shall be sized to accommodate the number and size of
copper, non-shielded cables per phase as shown on the drawings. Incoming line cables
may enter the cubicles from overhead or underground as shown. Terminals shall be
made of copper. Outgoing cables will exit the ATS from above or below as shown.
TESTS AND CERTIFICATION
A.
All production units shall be subjected to the following factory tests:
- The complete ATS shall be tested to ensure proper operation of the individual
components and correct overall sequence of operation and to ensure that the operating
transfer time, voltage, frequency and time delay settings are in compliance with the
specification requirements.
- The switch shall be subjected to a dielectric strength test per NEMA Standard ICS1109.21.
B.
Upon request, the manufacturer shall provide a notarized letter certifying compliance with
all of the requirements of this specification included compliance with the above codes and
standards, and withstand current ratings. The certification shall identify, by serial
number(s), the equipment involved. No exceptions to the specifications, other than those
stipulated at the time of submittal, shall be included in the certification.
PART 3 - EXECUTION
I
INSTALLATION
A.
Automatic Transfer Switch to be installed as shown on the drawings.
END OF SECTION
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