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Information Sheet 663A-451
Information Sheet 663A-451
S&C Source-Transfer PMH Pad-Mounted Gear
Outdoor Distribution (14.4 kV and 25 kV)
Detailed Functional
Specification Guide
August 4, 2008
©
S&C Electric Company
1.0
GENERAL
1.01
The pad-mounted gear shall be in accordance with the single-line diagram, and shall conform
to the fol lowing specification.
1.02
The pad-mounted gear shall consist of a single self-supporting enclosure, containing
interrupter switches and power fuses with the necessary accessory components, including
sensing, controls, and control power supply, all completely factory-assembled and
operationally checked.
1.03
Ratings

The ratings for the integrated pad-mounted gear shall be as designated below. (Select values
from the table on page 2.)

Nominal Voltage, kV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _________________

Maximum Voltage, kV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _________________

BIL Voltage, kV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _________________

Main Bus Continuous Current, Amperes . . . . . . . . . . . . . . . . . . . _________________

Three-Pole Load-Interrupter Switches

Continuous, Amperes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _________________

Load Dropping Current, Amperes . . . . . . . . . . . . . . . . . . . . . . . . _________________

Two-Time Duty-Cycle Fault-Closing Current,

Amperes, RMS, Symmetrical . . . . . . . . . . . . . . . . . . . . . . . . . . . _________________

Fuses with Integral Load Interrupters

Maximum Current, Amperes . . . . . . . . . . . . . . . . . . . . . . . . . . . . _________________

Load Dropping Current, Amperes . . . . . . . . . . . . . . . . . . . . . . . . _________________

Two-Time Duty-Cycle Fault-Closing Current

Capability, Amperes, RMS, Asymmetrical . . . . . . . . . . . . . . . . _________________

Short-Circuit
Current, Amperes, RMS, Symmetrical . . . . . . . . . . . . . . . . . . . . _________________

MVA, Three-Phase Symmetrical,

at Rated Nominal Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _________________

The momentary and two-time duty-cycle fault-closing ratings of switches, momentary rating
of bus, interrupting ratings of fuses, and two-time duty-cycle fault-closing capabilities of fuses
with integral load interrupters shall equal or exceed the short-circuit ratings of the pad-
mounted gear. 2

S&C Information Sheet 663A-451
S&C Source-Transfer PMH Pad-Mounted Gear
1.04
Certification of Ratings

(a)
The manufacturer of the pad-mounted gear shall be completely and solely responsible
for the performance of the basic switch and fuse components as well as the complete
integrated assembly as rated.

(b)
The manufacturer shall furnish, upon request, certification of ratings of the basic
switch and fuse components and/or the integrated pad-mounted gear assembly
consisting of the switch and fuse components in combination with the enclosure.
1.05
Compliance with Standards and Codes

The pad-mounted gear shall conform to or exceed the applicable requirements of the
following stan dards and codes:

(a)
The applicable portions of ANSI C57.12.28, covering enclosure integrity for pad-
mounted equipment.

(b)
Article 490.21(e) in the National Electrical Code, which specifies that the interrupter
switches in combination with power fuses shall safely withstand the effects of closing,
carrying, and interrupting all possible currents up to the assigned maximum short-
circuit rating.

(c)
All portions of ANSI, IEEE, and NEMA standards applicable to the basic switch and
fuse components.

The following optional feature should be specified as required:

(d)
Canadian Standards Association listing. Fuses rated 200E amperes maximum are also available with
short-circuit ratings of 12,500 amperes RMS symmetrical and 310
MVA at 14.4 kV. When these fuses are specified, the ratings of the
pad-mounted gear are reduced to that level. 29 kV for pad-mounted gear furnished with switches only; also
pad-mounted gear furnished with electronic power fuses. 600-ampere
bushings.
SELECTION OF 60-HERTZ RATINGS
Nominal Voltage, kV
Maximum Voltage, kV
BIL Voltage, kV
14.4
17.0
95
25
27 125
Main Bus Continuous Current, Amperes
600
600
Three-Pole Interrupter
Switches
Continuous Current, Amperes
Load Dropping Current, Amperes
Two-Time Duty-Cycle Fault-Closing Current,
Amperes, RMS, Asymmetrical
600
600
22,400
600
400
22,400
Fuses with
Integral Load Interrupters
Maximum Current, Amperes
Load Dropping Current, Amperes
Two-Time Duty-Cycle Fault-Closing Current
Capability, Amperes, RMS, Asymmetrical
200E, 200K, or 400
200 or 400
13,000
200E, or 200K
200
13,000
Short-Circuit
Current, Amperes, RMS, Symmetrical
MVA, Three-Phase Symmetrical,
at Rated Nominal Voltage
14,000
350
12,500
540 S&C Source-Transfer PMH Pad-Mounted Gear

S&C Information Sheet 663A-451

3
1.06
Enclosure Design

(a)
To ensure a completely coordinated design, the pad-mounted gear shall be con-
structed in accordance with the minimum construction specifications of the fuse and/
or switch manufacturer to provide adequate electrical clearances and adequate space
for fuse handling.

(b)
In establishing the requirements for the enclosure design, consideration shall be given
to all relevant factors such as controlled access, tamper resistance, and corrosion
resistance.
2.0
CONSTRUCTION Insulators, High-Voltage Bus, Ground-Connection Pads, and

Low-Voltage Components
2.01
Insulators

The interrupter-switch and fuse-mounting insulators shall be of a cycloaliphatic epoxy resin
system with characteristics and restrictions as follows:

(a)
Operating experience of at least 25 years under similar conditions.

(b)
Adequate leakage distance established by test per IEC Publication 507, Artificial
Pollution Test on High Voltage Insulators to be Used on AC Systems.

(c)
Adequate strength for short-circuit stress established by test.

(d)
Conformance with applicable ANSI standards.

(e)
Homogeneity of the cycloaliphatic epoxy resin throughout each insulator to provide
maximum resistance to power arcs. Ablation due to high temperatures from power
arcs shall continuously expose more material of the same composition and properties
so that no change in mechanical or electrical characteristics takes place because of
arc-induced ablation. Furthermore, any surface damage to insulators during installa-
tion or maintenance of the pad-mounted gear shall expose material of the same
composition and properties so that insulators with minor surface damage need not be
replaced.
2.02
High-Voltage Bus

(a)
Bus and interconnections shall consist of aluminum bar of 56% IACS conductivity.

(b)
Bus and interconnections shall withstand the stresses associated with short-circuit
currents up through the maximum rating of the pad-mounted gear.

(c)
Bolted aluminum-to-aluminum connections shall be made with a suitable number of
1/213 galvanized steel bolts, with two Belleville spring washers per bolt, one under
the bolt head and one under the nut. Bolts shall be tightened to 50 foot-pounds torque.

(d)
Before installation of the bus, all electrical contact surfaces shall first be prepared by
machine-abrading to remove any aluminum-oxide film. Immediately after this opera-
tion, the electrical contact surfaces shall be coated with a uniform coating of an oxide
inhibitor and sealant. 4

S&C Information Sheet 663A-451
S&C Source-Transfer PMH Pad-Mounted Gear
2.03
Ground-Connection Pads

(a)
A ground-connection pad shall be provided in each compartment of the pad-mounted
gear.

(b)
The ground-connection pad shall be constructed of 3/8 in. thick steel. It shall be nickel
plated and welded to the enclosure, and shall have a short-circuit rating equal to that
of the pad-mounted gear.

(c)
Ground-connection pads shall be coated with a uniform coating of an oxide inhibitor
and sealant prior to shipment.
2.04
Low-Voltage Components

(a)
All low-voltage components, including stored-energy operators and source-transfer
control, shall be located in a grounded, steel-enclosed compartment separated from
high voltage to provide isolation and shall be arranged to allow complete accessibility
for test and/or maintenance without exposure to high voltage.

(b)
Low-voltage wiring, except for short lengths such as at terminal blocks and the
secondaries of sensing devices, shall be in grounded conduit or raceways where
necessary for isolation from high voltage.
3.0
CONSTRUCTIONEnclosure, Doors, Ventilation Openings, and Finish
3.01
Enclosure

(a)
The pad-mounted gear enclosure shall be of unitized monocoque (not structural-
frame-and bolted- sheet) construction to maximize strength, minimize weight, and
inhibit corrosion.

(b)
A separate grounded, steel-enclosed low-voltage control compartment shall be
provided for the source-transfer control and stored-energy operators.

(c)
The basic material shall be 11-gauge hot-rolled, pickled and oiled steel sheet.

(d)
All structural joints and butt joints shall be welded, and the external seams shall be
ground flush and smooth. The gas-metal-arc welding process shall be employed to
eli