YBW Series Prefabricated Compact Substation

• Voltage: 10 / 35 kV
• Transformer: up to 2500 kVA
• Structure: HV + transformer + LV in one bay
• Standard: IEC 62271

The YBW Series Prefabricated Compact Substation is a fully integrated, factory-assembled power distribution solution that consolidates medium-voltage switchgear, a distribution transformer, and low-voltage distribution panelboards into a single weatherproof enclosure. Designed for outdoor installation, the YBW Series eliminates the need for conventional substation buildings, fencing, and extensive site construction.

Each unit is pre-tested and pre-commissioned at the factory before shipment, enabling rapid on-site energization with minimal field labor. The YBW Series is engineered to meet the demands of U.S. utilities, real estate developers, and EPC contractors seeking a compact, reliable, and code-compliant alternative to traditional pad-mounted or vault-style substation configurations.

Key Applications

Standards Compliance and Certifications

The YBW Series is designed and manufactured to comply with applicable North American standards. Compliance documentation and third-party listings are available for each configuration. Key standards include:

Technical Specifications

Electrical Ratings

Physical and Environmental

Design Features

Compartmentalized Construction

The YBW Series is divided into three primary functional compartments, each independently accessible and safety-interlocked:

High-Voltage Compartment — Houses the incoming primary terminations, load-break switches or vacuum fault interrupters, and high-voltage metering equipment. Dead-front elbow connections eliminate exposed live parts. Loop-feed configurations with six bushings and three-position (On/Off/Ground) switches are available for sectionalizing capability.

Transformer Compartment — Contains the core and coil assembly in a sealed tank (liquid-immersed) or dry-type encapsulated windings. Oil-immersed units utilize high-fire-point dielectric fluid. Ventilation louvers with thermostatically controlled fans ensure adequate cooling under full load.

Low-Voltage Compartment — Accommodates the main distribution switchboard, feeder breakers, branch panelboards, metering, and control wiring. UL 891-listed switchboard construction ensures compliance with NEC requirements for service-entrance and main-distribution applications.

Factory Pre-Testing and Pre-Commissioning

Every YBW Series unit undergoes a comprehensive factory acceptance test (FAT) protocol before shipment:

• Routine Electrical Tests — Applied voltage withstand, induced voltage, insulation resistance, power factor (for liquid-filled transformers), and winding resistance.

• Functional Verification — Switchgear operation, interlock function, ground continuity, relay calibration, and control circuit operation.

• Leak and Pressure Testing — For liquid-immersed transformer tanks.

• Witness Testing — Available upon request for utility-grade procurement; ISO/IEC 17025-certified test reports provided.

This pre-testing regime minimizes field start-up time, reduces the risk of commissioning delays, and ensures that the unit arrives ready for energization.

Safety and Security

• Tamper-Resistant Enclosure — Meets or exceeds ANSI/IEEE C57.12.28 security requirements, permitting installation in unsecured public areas without additional fencing-19.

• Dead-Front Design — All high-voltage connections utilize insulated elbows and bushings; no exposed live parts accessible during normal operation.

• Interlocked Compartments — Mechanical interlocks prevent opening the high-voltage compartment while energized and prevent operation of switches with doors open.

• Grounding Provisions — Copper ground bus with provisions for connection to station ground grid; ground rods and bonding per NEC Article 250.

Installation and Site Requirements

Pad and Clearance Requirements

The YBW Series requires a level, reinforced concrete pad (or engineered composite pad) with adequate load-bearing capacity for the unit’s weight. Typical utility clearance requirements for pad-mounted equipment:

• Front Working Clearance: 6 feet minimum (for safe operation and maintenance access)

• Side and Rear Clearance: 3 feet minimum

• Above-Grade Working Space: Per NEC Article 110.26 for low-voltage compartment access

Note: Local utility requirements may exceed these minimums. Always verify with the authority having jurisdiction (AHJ) and the serving utility before finalizing site layout-5-16.

Conduit and Cable Terminations

The YBW Series accommodates both radial and loop-feed primary configurations. Primary terminations are typically dead-front separable connector interfaces compatible with industry-standard elbows (200 A or 600 A). A spare conduit stub-up extending 5 feet from the pad is recommended for future high-voltage access-9.

Secondary conductors exit through the low-voltage compartment via bottom entry. Conduit burial depth, fill percentages, and ampacity derating must comply with NEC Sections 300.5, Chapter 9 Tables, and 310.15-11.

Site Preparation Considerations

• Soil Conditions: For frost-susceptible areas, conduit penetration through the pad must accommodate frost heave using expansion fittings or flexible conduit sections.

• Drainage: Pad elevation should be set to prevent water accumulation at the compartment doors.

• Access: Knuckle-boom crane access required for transformer replacement; verify approach clearances during site planning.

Frequently Asked Questions

Q1: What is the difference between a YBW prefabricated compact substation and a conventional pad-mounted transformer?

A: A conventional three-phase pad-mounted transformer contains only the transformer and a limited primary switching provision (typically an internal load-break switch). It requires a separate low-voltage switchboard or panelboard installation, usually inside the building being served or in a separate enclosure.

The YBW Series integrates the high-voltage switchgear, transformer, and low-voltage distribution panelboard into a single enclosure. This consolidated approach offers:

• Single-Point Responsibility — One factory-tested assembly rather than multiple field-assembled components

• Reduced Footprint — Up to 75% less land area than a conventional substation-8

• Faster Commissioning — Factory pre-testing eliminates most field wiring and functional testing

• Simplified Specification — One purchase order covers the complete power delivery package

Q2: Is the YBW Series compliant with U.S. electrical codes and standards?

A: Yes. The YBW Series is designed and manufactured to comply with the standards listed in the Standards Compliance section above. Specific compliance documentation, including UL listings (UL 891 for low-voltage switchboards, UL 67 for panelboards, UL 506 for transformers where applicable), ANSI/IEEE C57 documentation, and DOE efficiency certifications, is provided with each quotation and shipment.

For utility procurement, witnessed factory acceptance testing with ISO/IEC 17025-certified reports is available to satisfy utility-grade verification requirements-3-14.

Q3: What primary voltage classes and transformer capacities are available?

A: The YBW Series is offered in the following common configurations:

Custom voltage and capacity combinations are available. Contact the factory for availability.

Q4: How long does installation take compared to a traditional substation?

A: The YBW Series dramatically compresses the construction schedule. Key time savings:

The YBW Series requires only a prepared pad, conduit terminations, and final connections. Because the unit is factory pre-tested, field commissioning is limited to verification of external connections and functional checks-2.

Q5: What maintenance requirements does the YBW Series have?

A: Maintenance requirements are comparable to a conventional pad-mounted transformer plus switchboard installation:

• Visual Inspection — Semi-annual inspection of enclosure integrity, ventilation openings, and security features

• Transformer Fluid Testing — Annual dissolved gas analysis (DGA) and dielectric strength testing for liquid-immersed units (per IEEE C57.106 guidelines)

• Switchgear Exercise — Annual operation of load-break switches or vacuum interrupters

• Low-Voltage Inspection — Periodic thermographic survey of bus connections and breaker terminations

• Ventilation System — Inspection and cleaning of thermostatically controlled fans and intake filters

Because the YBW Series is a sealed, tamper-resistant assembly, internal maintenance is performed by qualified utility or electrical service personnel only. Service access is available through the compartment doors with appropriate PPE and lockout/tagout procedures.

Q6: Can the YBW Series be configured for loop-feed distribution?

A: Yes. The YBW Series supports both radial and loop-feed primary configurations. Loop-feed units are equipped with:

• Six primary bushings (two per phase, plus ground provisions)

• Two-position or three-position load-break switches (On/Off, or On/Off/Ground)

• Bushing-mounted elbow-type surge arresters at radial ends and normally open loop points

Three-position switches permit closed-transition loop feed and sectionalizing, allowing the unit to be isolated without interrupting service to downstream loads-9.

Q7: What documentation is provided with the YBW Series?

A: Standard documentation package includes:

• Certified Test Reports — Routine electrical test results, functional verification records

• Compliance Certificates — UL listings, ANSI/IEEE compliance declarations, DOE efficiency documentation

• Outline Drawings — Dimensioned elevation, plan view, and pad details

• Electrical Schematics — Single-line diagram, control wiring diagrams, interconnection diagrams

• Installation Manual — Site preparation, setting instructions, connection procedures, torque specifications

• Operation and Maintenance Manual — Operating procedures, maintenance schedules, troubleshooting guide

• Recommended Spare Parts List — One-year operating spares with current pricing

Additional documentation (witness test reports, seismic certifications, arc-flash studies) available upon request.