THREE PHASE PADMOUNTED
TRANSFORMER TRAINING
www.lipower.org
What We Will Cover
•What is a Three-Phase Pad Mounted Transformer?
•What are its Applications?
•How is it Installed?
•How is it Wired?
•The Specification Package
•The Specification Letter
•Miscellaneous
What is a Three-Phase Pad Mounted Transformer?

Outside
 Metal Encased, Tank, Fins, Cabinet
– Sits on a Three Piece Vault
– Fragile Enclosure, Not for Storage

Inside Contains
 Oil Tank, Windings, Terminals
 Primary and Secondary Compartments
 Grounding Loop
 Cables and Terminations
What is a Three-Phase Pad Mounted Transformer?
 Steps Down Primary Voltage to Secondary
 Primary Side (4kV, 13kV, or both)
 Secondary Side (120/208v, 277/480v)
 Three Phase Wye Configuration Only
 Pad Mounted, or Submersible
 Di-Electric Fluid (insulates and cools)
 LIPA Sizes Range From:
 75KVA to 1000KVA for 120/208
 75KVA to 1500KVA for 277/480
 Special Order 2500KVA’s
The outside of a Three-Phase Pad Mounted Transformer
Side View of a 150KVA Pad Mounted Transformer
The Outside of a Three-Phase Pad Mounted Transformer
 Orientation Away From Building
 Clearances
 5’ From Transformer to Building Wall
 10’ to Vent Openings, Doors, Windows
 25’ to Non-Fire-Rated Openings
 Auditorium Exits
 Truck Accessible (delivery & removal purposes)
 NEC Class 1, Division 1, and 2 Locations Shall Require a
Minimum 25 ft. Clearance (oil, gas, etc)
 Set Vault Level, Grade to Slope Away
 Traffic Protection
The Inside of a Three-Phase Pad Mounted Transformer
Inside a Three-Phase Pad Mounted Transformer
Primary Compartment
(left side)
 Primary Connections
(radial, or loop)
 Incoming - H1C, H1A,
H1B
 Outgoing - H2B, H2A,
H2C
 No Load Tap Changer
 A Through E (2.5%
increments, middle
is zero boost)
 Bayonet Fuses, Protect
Primary Side of
Transformer
Inside a Three-Phase Pad Mounted Transformer
Primary Compartment
 Load Break Elbows
 Sizes: #2, 1/0, 3/0
 Lightning Arrestor
Elbows (radials, and
open points)
 Static Drain Wires
(#14, and #10 Cu.)
 Grounding Loop
#2BTN, One HLC
 Primary Bushings
 Standoff Bushing
Slots (open point)
Inside a Three-Phase Pad Mounted Transformer
Primary L/B Elbow
 Load Break Elbow, Bushing,
Static Drain Wire, and Primary
Cable
 Detail in Spec. Package
 Follow Mfg. Instructions
 Pulling Eye
 Test Point, & Cap
 5’ of Taped Neutral
 #2 EPR Insulated May be
Hylinked
 Sealing Strip, 36” Below Hose
Clamp
Inside a Three-Phase Pad Mounted Transformer
Primary Bushing
 Supplied by LIPA with
L/B, L/A Elbow
 Screws in
 Must be Kept Clean,
Contamination Will
Cause Electrical
Failure
 #14 Static Drain Wire
From Eyelet to
Grounding Split Bolt
 L/B Elbow Should
Cover Yellow (now
RED) Band
Inside a Three-Phase Pad Mounted Transformer
Secondary Compartment
(right side)
 Secondary Spades;
X0, X1, X2, X3
 Nema 2 Hole Lugs
(tinned alum. Or Cu.)
 Al Lug - Extra
Belleville Washer Req
 Oxide Inhibitor on Al
 Cu to be Tinned, or
Alloy plated
 750 Cu now Accepted
 Buss Supports
Inside a Three-Phase Pad Mounted Transformer
Secondary
Compartment
 Color Coding
 120/208v or
277/480v
 Integrated/Isolat
ed
 8 Sets Max
 Grounding Pads,
Loop, Split Bolts,
Ground Rods
 Oil Drain Valve
Inside a Three-Phase Pad Mounted Transformer
Secondary
Compartment
•Pressure
Relief Valve
•Do Not Pull
•Oil Fill Level
•Oil
Temperature
Gauge
•Oil Level
Gauge
Inside a Three-Phase Pad Mounted Transformer
Nameplate
 Identifies Primary and
Secondary Voltage
 Indicates Voltage on
Different Tap Settings
 Shows Internal Coil
Configuration
 Indicates Transformer
Weight
 Indicates Transformer
Impedance
Inside a Three-Phase Pad Mounted Transformer
Common equipment
 Primary Cable
 Sizes: 3-2/c#2, 1/0, 3/0
 Secondary Cable


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 Sizes: Minimum #2, Maximum 750
Maintain 5’ min. Slack in Vault
Maintain as Much Physical Separation as Possible
Grounding Pads, Lugs, and Split Bolts
Bare #6 Cu to Ground Rods
Bare Tinned Copper #2 for Ground Loop
What are its Applications?

Typical for Large Load, NonResidential Customers; Long
Distance From Existing
Facilities; and Looped
Commercial Industrial Parks

Pad Mounted Transformers are
LIPA’s Standard Installation,
Non-Standard is Submersible, or
Network

Transformer is Delivered,
Owned, and Maintained by LIPA
for Secondary Metered Service
How is the Three-Phase Pad Mounted Transformer
Installed?
 Set on a Three Piece Vault, Always Provided
by Contractor (see approved vendor list)
 Pad Orientation
 Primary Side, Secondary Side
 Doors to Face Away From Building
 10’ Clear in Front of Pad for Switching
 Grade Away 1% Slope
 Old Way – Poured Foundation (slab) –
Primary and Secondary Cables Have no
Slack
 Boom Truck Delivers Transformer, Lifts it
onto Vault
How is the Three-Phase Pad Mounted Transformer
Installed?
Boom Truck
 Can Deliver All
Transformers
Line Truck
 Delivers up to
500 kVA
Who Wires the Three-Phase Pad Mounted
Transformer?
LIPA Provides
 Three Load Break Elbows (rated for 200
ampere)
 Three Lightning Arrestor Elbows
 With Three NEMA 2-Hole Lugs
 One Hot Line Clamp
 Bushings Come as a Pair With L/B Elbow and
L/A Arrestor Elbow
Who Wires the Three-Phase Pad Mounted
Transformer?
Radial Installation
 Contractor Installs Primary and Secondary Cable
 Contractor Wires L/B and L/A Elbows
 Contractor Makes Secondary Connections
 Contractor Wires All Grounding
 Contractor Supplies Secondary Lugs, Static Drain
Wires, Ground Rods, Ground Wire, and Grounding
Split Bolts
CIPUD Installation
 Contractor Supplies and Wires Secondary
 LIPA Wires Primary & Grounding
Specification Package Details
 Provides Information Common to All Jobs
 Pad Specifications, Vault Details
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Primary Side, Secondary Side
Contractor to Discuss Location Before Pad is Set
Knock Outs: 4” PVC Sleeve Flush With Wall, Concreted in Place
Duct Seal or Cap Unused Conduits
Galvanized Conduits Require Bonding

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Bollard 3.5” Heavy Steel Wall (minimum)
Concrete Filled
Must be Painted Yellow
Doors Must be Able to Open
Required on All Sides Subject to Vehicular Traffic
 Protection From Traffic
Specification Package Details
Primary Cables
 Phases Must be Identified (1, 2, 3 rings), on Both
Extremities
 15kV Tree-Retardant Cross-Linked Polyethylene for
Aluminum (TR-XLPE)
 Ethylene Propylene Rubber (EPR) for Copper
 Semi-Con 12 Mil
 Insulation 220 Mil, Insulation Shield 30 Mil Semi-Con
 Jacket 50 Mil Semi-Con
Specification Package Details
Secondary Services
 480v - One Service
 Exception: Fire Pumps
 208v - Multiple Services
 Services Must be Labeled
Cables
 480v (must be installed in conduit)
 USE-2, XHHW-2, or RHW-2
 8 Sets Max
 208v
 USE-2, THW-2, THWN-2, XHHW-2, or RHW-2*
 *With neoprene or hypalon jacket only
Three-Phase Specification Letter
 Gives Project Specific Details, Such as:
 Reiterates Customer Load Letter
 Designated Riser Pole, or Point of Termination
 Describes Cable Ownership
 Provides Costs, if Any
 Inrush Information, Motor Starting Limitations
 Restates Basic Installation Rules,

Call Before You Dig
 Repeats Primary and Secondary Cable
Specifications
Miscellaneous
 Provide Advance Notification of Projects
 Access to an Energized Vault is Forbidden
 Industrial Code Rules 753, and 57
 These Requirements Conform to the NEC
 Contractor to Comply With:
 Applicable Codes
 Three Phase Transformer Spec. Package
 Redbook
 Lists Distribution Design Representatives
 www.lipower.org
QUESTIONS
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