Single Phase Transformer: Full Catalog of All Types & Specifications

In modern power systems, the single phase transformer remains one of the most widely deployed electrical assets worldwide. From rural electrification and residential supply to renewable energy and industrial auxiliary systems, its simplicity, reliability, and cost efficiency make it indispensable.

For international EPC contractors, utilities, and distributors, selecting the correct single phase power transformer requires not only understanding voltage and capacity ratings but also insulation systems, cooling methods, installation environments, and compliance with global standards.

1. What Is a Single Phase Transformer?

A single phase transformer is a static electrical device that transfers electrical energy between two circuits through electromagnetic induction using a single alternating current phase.

It consists of:

• Magnetic core (CRGO silicon steel)
• Primary winding
• Secondary winding
• Insulation system
• Cooling medium (oil or air)
• Tank or enclosure

It is primarily used in:

• Residential power supply
• Rural distribution networks
• Lighting systems
• Small commercial loads
• Control circuits

2. Main Types of Single Phase Transformer

Below is a structured classification of globally exported transformer types.

2.1 Classification by Installation Method

2.2 Classification by Insulation & Cooling Medium

The single phase oil filled transformer is the most widely exported due to its cost-performance ratio and high thermal capacity.

3. Technical Specifications Overview

International projects require compliance with IEC, ANSI, or IEEE standards.

3.1 Electrical Ratings

3.2 Core and Winding Materials

Modern low-loss core design reduces energy waste and improves lifecycle efficiency.

4. Special Transformer Types for Export Markets

4.1 Single Phase Pad Mounted Transformer

A Single Phase Pad Mounted Transformer (also known as a single-phase pad transformer or single-phase underground distribution transformer) is primarily used in underground power distribution systems for residential communities, commercial buildings, and small industrial loads. It is mounted on a concrete pad, with a fully enclosed, theft-proof, and weatherproof enclosure, replacing traditional pole-mounted transformers and providing a more aesthetically pleasing and secure power distribution solution. It is particularly popular in North America, Latin America, and parts of Asia/Europe.

Key Features and Advantages

Compact and Low-Profile Design: Aesthetically pleasing and low-profile, typically 30-50 inches in height, making it easy to install in green areas or residential areas.

Tamper-Resistant: Pry-resistant and shockproof design, compliant with ANSI C57.12.28 enclosure integrity standard.

Cooling Method: ONAN (natural oil and air cooling), using mineral oil or environmentally friendly FR3/natural ester oil.

Protection Configuration: Common CSP (Completely Self-Protected) design, with built-in fuses, surge arresters, and secondary circuit breakers, eliminating the need for additional external protection equipment.

Incoming line type: Radial Feed or Loop Feed, Dead-front or Live-front.

Efficiency: Meets or exceeds DOE 2016/202X energy efficiency standards; high-efficiency design reduces operating costs.

Common Model List (kVA Capacity Range and Typical Specifications) The mainstream capacity of single-phase pad transformers is concentrated in residential/small commercial applications. The most common ranges in the international market are as follows (based on IEEE/ANSI C57.12.38, Eaton, Prolec GE, ERMCO, Daelim, and other major manufacturers):

Typical voltage combinations (high voltage side / low voltage side):

Primary (HV): 12470GrdY/7200, 13200GrdY/7620, 14400/7200, 34500GrdY/19920, etc. (Common 2.4–34.5 kV range, BIL 60–150 kV)

Secondary (LV): 120/240V (most common, US residential standard), 240/480V, 347V, etc.

Tap Changer: ±2×2.5% or more, allowing voltage regulation

Main Series/Types (different manufacturers' names):

Mini-Pad / Shrubline: Compact, 10–167 kVA

Maxi-Pad / MaxiShrub: Slightly higher but with straighter cable routing, 10–167 kVA

Ranch Runner: Economical rural use, 10–50 kVA

Type 1 / Type 2: ANSI Standard front panel layout differences:

MicroTrim / Space-Saver: Ultra-compact, low-cost version

PEAK: Eaton high overload capacity series (supports temporary 109%+ load)

4.2 Single Phase Pole Mounted Transformer

Single-phase pole-mounted transformers (also known as single-phase pole-mounted transformers or single-phase overhead distribution transformers) are one of the most common types in power distribution systems. They are primarily installed on utility poles to step down medium-voltage distribution lines (typically 10-35kV) to the low-voltage user side (commonly 120/240V single-phase residential standards). They are widely used in overhead distribution networks in rural areas, suburbs, residential areas, and light commercial loads. Compared to pad-mounted transformers, they are less expensive, easier to install, and easier to maintain, making them a mainstream choice, especially in North America, Latin America, Southeast Asia, Africa, and Australia.

Key Features and Advantages

Installation Method: Pole-mounted, using slings or brackets to fix the transformer to a wooden/concrete pole, saving ground space.

Cooling and Insulation: The mainstream type is oil-immersed, using ONAN cooling, and mineral oil or environmentally friendly ester oil (FR3/natural ester); a few dry-type types are used in special environments.

Protection Type:

Conventional: Requires an external fuse/surge arrester.

CSP (Completely Self-Protected): Built-in fuse, surge arrester, and secondary circuit breaker; the most popular export configuration.

MagneX or other self-protection types: With a resettable interruptor.

Efficiency Standards: Meets or exceeds DOE 2016/202X energy efficiency requirements (mandatory in the US market); high efficiency, low loss design.

Standards Compliance: ANSI C57.12.00, C57.12.20, IEEE, NEMA, RUS, IEC; UL/cUL, CSA certifications are common for North American exports.

Other Advantages: Corrosion-resistant coating (ANSI 70 gray), anti-theft design, with pressure relief device, adjustable taps (±2 × 2.5% taps).

Common Model List (kVA Capacity Range and Typical Specifications) Single-phase pole-mounted transformers typically cover residential to medium-sized loads. The most common ranges in the international market are as follows (based on data from major manufacturers such as Prolec GE, ERMCO, Eaton, Daelim, and Weisho):

Typical Voltage Combinations (Primary HV / Secondary) LV):

Primary: 2400/4160Y, 7200/12470Y, 7620/13200Y, 13200/22860Y, 34500GrdY/19920, etc. (2.4–34.5 kV range, BIL 60–150 kV)

Secondary: 120/240V (North American residential standard), 240/480V, 347V, etc.

Tap Changer: Typically 5 stops (±2×2.5%), externally operated, no-load tap changer.

4.3 Single Phase Oil Filled Transformer

Single Phase Oil Filled Transformer (also known as Single Phase Oil Immersed Transformer or Single Phase Oil-Filled Distribution Transformer) is a reliable, cost-effective solution for stepping down medium voltage to low voltage in overhead or underground distribution systems. These transformers use mineral oil (or eco-friendly alternatives like FR3 natural ester fluid) for superior insulation, cooling, and heat dissipation, making them ideal for outdoor applications in residential, rural, commercial, and light industrial settings.

Key Features & Benefits

Oil-Immersed Design (ONAN Cooling): Natural oil natural air cooling provides excellent thermal performance, high overload capacity (up to 150-200% temporary), and long service life (typically 25-40+ years).

High Efficiency: Meets or exceeds DOE 2016/202X efficiency standards (U.S.), IEC 60076, ANSI/IEEE C57.12.00, and energy regulations in Europe, Latin America, and Asia—reducing no-load and load losses for lower operational costs.

Robust Construction: Sealed tank with pressure relief device, corrosion-resistant coating (ANSI 70 gray), lifting lugs, and bushings for easy installation and maintenance.

Protection Options:

CSP (Completely Self-Protected): Built-in primary fuses, secondary circuit breakers, and lightning arresters—no external protection needed (most popular for export).

Conventional: Requires external fuses/arresters.

Fluid Options: Standard mineral oil or fire-resistant/biodegradable FR3 fluid for enhanced safety in urban/residential areas.

Certifications: UL/cUL, CSA, IEEE, ANSI, IEC compliant; RUS-approved models common for North America/Latin America.

Dual Voltage & Taps: Often dual primary voltage designs with ±2×2.5% off-load tap changer for voltage adjustment.

Common Models & Specifications

Single phase oil filled transformers are available in pole-mounted (overhead) and pad-mounted configurations, with mainstream kVA ratings for global markets:

Typical Voltage Ratings:

Primary (HV): 2400/4160Y, 7200/12470Y, 7620/13200Y, 13200/22860Y, 34500GrdY/19920 (2.4–34.5 kV class, BIL 60–150 kV)

Secondary (LV): 120/240V (split-phase, North American standard), 240/480V, or 347V

Frequency: 50/60 Hz

Mounting Types:

Pole-Mounted Transformer: Overhead installation on utility poles—compact, economical for rural/suburban grids.

Pad-Mounted Transformer: Ground-level enclosure for underground feeds—tamper-resistant, aesthetic for residential/commercial areas.

4.4 Single Phase to Three Phase Transformer

Single Phase to Three Phase Transformer (also known as Single-to-Three Phase Converter Transformer, Phase Conversion Transformer, or Single Phase Input to Three Phase Output Transformer) refers to specialized transformers or transformer-based systems designed to enable three-phase power output from a single-phase input source. This is essential in locations where only single-phase utility power is available (e.g., rural areas, residential zones, or small workshops), but three-phase equipment like motors, CNC machines, pumps, compressors, welders, or industrial machinery is required.

Important Clarification: A standard transformer alone cannot create true balanced three-phase power from single-phase input because it lacks the inherent 120° phase shift of three-phase systems. Pure transformers step voltage up/down or provide isolation but do not generate additional phases. Instead, "single phase to three phase transformers" in practice often combine:

A phase converter (rotary, static, or digital) to create artificial three-phase from single-phase.

A transformer for voltage matching (e.g., 230V single to 400V/460V three-phase) or isolation.

Common setups include rotary phase converter + transformer packages, autotransformer-based converters (e.g., Scott connection approximations), or specialized isolating converter transformers with capacitors/inductors for phase shifting in lighter loads

Key Features & Benefits

Phase Conversion Capability: Converts single-phase (e.g., 220-240V or 120V) to balanced or near-balanced three-phase output.

Voltage Flexibility: Step-up/step-down options (e.g., 230V 1Φ to 400V/460V 3Φ) for global compatibility.

High Efficiency & Reliability: Low losses, overload protection, long life (20+ years); often with overload capacity.

Types:

Rotary Phase Converter + Transformer: Uses an idler motor to generate third phase; most robust for heavy/inductive loads.

Static Phase Converter + Transformer: Capacitor-based; economical for light/start loads but limited to ~2/3 rated power.

Digital/Static Phase Converter: Solid-state (VFD-like); clean sine wave, precise control, UL-listed options.

Autotransformer Converter (e.g., TMT Series): Isolating type, single-phase 230V to three-phase 400V without neutral.

Standards & Certifications: UL/cUL, CSA, IEC, CE; DOE/IEEE compliant for efficiency.

Advantages: Cost-effective alternative to utility three-phase upgrade; easy installation; supports motor starting torque.

Common Models & Specifications

Mainstream capacities suit workshops to small industrial use (HP/kVA ratings based on motor loads; 1 HP ≈ 0.746 kVA):

Typical Voltage Configurations:

Input (Single-Phase): 220-240V, 120V, or 480V.

Output (Three-Phase): 220-240V, 400V, 415V, 460V/480V.

Frequency: 50/60 Hz.

Efficiency: ≥95-98% in digital models.

Popular Types & Examples (from Phoenix, DPS, Ronk, ATO, etc.):

Rotary Packages: 3-100 HP, often bundled with step-up transformers.

Digital: 5-20 HP, pure sine wave, precise for CNC/VFD loads.

Static: 1-10 HP, capacitor-start models.

5. Transformer Wiring and Electrical Diagrams

Understanding wiring is essential for field engineers.

5.1 Single Phase Transformer Wiring Diagram (Basic Concept)

Primary winding connects to high voltage input.
Secondary winding supplies stepped-down voltage.

Common configurations:

• Two-bushing primary
• Three-bushing (with neutral)
• Center-tapped secondary

5.2 Single Phase Transformer Diagram (Structural View)

A simplified structural layout includes:

Proper insulation clearance and creepage distance are critical for export compliance.

6. Engineering Design Considerations

From a working engineering perspective, transformer selection involves more than voltage matching.

6.1 Load Calculation

Transformer capacity should be selected at 70–80% normal loading to allow:

• Future expansion
• Voltage stability
• Reduced thermal stress

6.2 Temperature Rise

Standard limits:

Oil-filled transformers typically operate with Class A insulation.

6.3 Efficiency and Losses

Two key losses:

• No-load loss (core loss)
• Load loss (copper loss)

High-efficiency export models comply with DOE or EU EcoDesign regulations.

7. International Standards & Certifications

For global exports, compliance may include:

• IEC 60076
• IEEE C57
• ANSI standards
• CE certification
• UL certification (for specific markets)

Factory testing includes:

• Ratio test
• Winding resistance test
• Insulation resistance test
• Induced voltage test
• Temperature rise test

8. Packaging & Export Considerations

For overseas shipment:

• Vacuum oil filling
• Nitrogen sealing (optional)
• Anti-corrosion coating
• Wooden or steel pallet packing
• Shock-proof bracing

Humidity and salt-spray protection are critical for coastal regions.

9. Maintenance & Service Life

Typical service life: 20–30 years.

Maintenance checklist:

• Oil level inspection
• Insulation resistance test
• Load monitoring
• Bushings condition check

Dry type transformers require periodic dust cleaning.

10. Future Trends in Single Phase Transformers

Emerging developments include:

• Amorphous core technology
• Smart monitoring sensors
• IoT-enabled load diagnostics
• Environment-friendly ester oil

These innovations reduce energy loss and improve operational transparency.

The single phase transformer remains a cornerstone of global power distribution systems. Whether selecting a single phase oil filled transformer, single phase dry type transformer, single phase pad mounted transformer, or single phase pole mounted transformer, proper engineering evaluation ensures long-term reliability.

For utilities, EPC contractors, and distributors, understanding specifications, wiring principles, and compliance requirements is essential when sourcing from an international transformer manufacturer.

Choosing the right single phase distribution transformer is not simply a purchase decision—it is an infrastructure investment that directly impacts grid stability, safety, and operational efficiency.