A package substation is a factory-assembled unit that combines medium voltage switchgear, a distribution transformer and low voltage switchgear in a single enclosure, so a site can step utility power down to usable voltage without building a conventional substation room. Industrial sites choose it when they have a large power demand, a tight programmed, limited space or a utility requirement for their own step-down point. This guide from Paklink LLC explains how package substations work, what they contain, how to choose and size one, and what to plan on site. If your project involves electrical works for substations in Dubai, use it as a decision checklist before you request quotes. For the full scope of an industrial electrical project, read our complete guide to industrial electrical contractors in Dubai.
In short:
- A package substation packs medium voltage switchgear, a transformer and a low voltage board into one tested unit, built in a factory.
- It saves site time and space, but it still needs a foundation, cable routes, earthing and utility coordination.
- The transformer rating, cooling and enclosure material must suit Dubai’s heat, dust and humidity.
- Most problems come from late utility coordination, poor site preparation and underestimated heat, not from the unit itself.
What is a package substation?
A package substation, also called a compact or prefabricated substation, is a complete power distribution point delivered as one assembled and tested unit. Power enters at medium voltage, passes through the transformer, and leaves at low voltage for the site’s loads.
In Dubai’s distribution network, medium voltage is commonly 11 kV, and the low voltage side is 415 V three-phase. Confirm the exact supply voltages for your site with the utility, since they set the whole design. If you want a deeper look at the two voltage levels, see LV vs MV switchgear.
Package substations are covered by IEC 62271-202, the standard for high-voltage and low-voltage prefabricated substations. The parts inside follow their own standards: IEC 62271-200 for medium voltage switchgear, IEC 60076 for the transformer and IEC 61439 for the low voltage assembly. You can browse these on the IEC website.
What does a package substation contain?
A package substation has three main compartments plus supporting systems. Looking from the incoming cable to the outgoing feeders, you will find:
| Section | What it contains | What it does |
|---|---|---|
| Medium voltage compartment | A ring main unit or switchgear with switches, circuit breakers or fused switches, and protection relays | Receives the utility supply, protects the transformer and allows safe isolation |
| Transformer compartment | An oil-immersed or dry-type distribution transformer | Steps medium voltage down to low voltage |
| Low voltage compartment | Main breaker, outgoing feeders, metering and often capacitor banks | Distributes power to the site and protects the outgoing circuits |
| Supporting systems | Earthing, ventilation, lighting, fire detection, oil containment where needed | Keep the unit safe, cool and maintainable |
The ring main unit, or RMU, is common on the medium voltage side. It combines switches and protection in a compact arrangement that suits loops in the distribution network. On the low voltage side, the outgoing feeders usually supply distribution boards and motor control centers around the site.
What types of package substation are there?
Package substations differ in how they are enclosed and how people can access them. The two basic access types are walk-in units, where an operator enters the enclosure, and compact units, where operation is done from outside.
| Type | Description | Best for | Watch out for |
|---|---|---|---|
| Compact (non-walk-in) | Sealed enclosure operated from outside | Small footprints, standard loads | Limited internal space for modifications |
| Walk-in | Enclosure with room to enter and work inside | Larger installations with more equipment | Needs more space and good ventilation |
| Containerized | Equipment built into a steel container, often walk-in | Fast delivery, relocation, temporary or modular sites | Heat build-up in sun, so insulation and cooling matter |
| Skid-mounted | Equipment on a steel base frame | Industrial sites and process areas | Needs protection from the weather where not enclosed |
The enclosure material is a separate choice:
| Enclosure material | Strengths | Limitations |
|---|---|---|
| Galvanized or painted steel | Strong, widely used, good for containers | Needs a good finish in coastal or harsh air |
| Stainless steel | High corrosion resistance | Higher cost |
| GRP (fiberglass) | Corrosion-free, non-conductive | Lower impact strength, check fire and UV performance |
| Concrete | Durable, good thermal mass | Heavy, so it needs strong lifting and foundations |
Which transformer should a package substation use?
The choice is mainly between oil-immersed and cast resin dry-type transformers, and it depends on where the substation sits and what the fire rules allow.
| Transformer type | How it is cooled and insulated | Typical use | Trade-off |
|---|---|---|---|
| Oil-immersed | Insulating oil circulates and cools the windings | Outdoor and ground-level units, high efficiency | Needs oil containment, and fire safety measures near buildings |
| Cast resin (dry type) | Windings are cast in resin and cooled by air | Indoor areas, near occupied buildings, where oil is not welcome | Typically higher cost, and more sensitive to dust and moisture if not protected |
Cooling matters more than people expect. Transformers are rated for a temperature rise above ambient, so a hot site reduces the usable capacity unless the design allows for it. Ask the supplier to confirm the rating at your ambient temperature.
When does a site need a package substation?
A site needs a package substation when it requires its own step-down point and wants the speed, compactness and factory-tested quality of a prefabricated unit. The common triggers are:
- Large power demand: the load is high enough that the utility supplies the site at medium voltage.
- A utility requirement: the utility asks for an on-site substation as a condition of connection.
- A tight programmed: factory assembly and testing move work off the critical path.
- Limited space: there is no room for a traditional substation building.
- Modular or remote sites: a unit that is built and tested elsewhere, then installed in a short time, suits remote or phased projects.
A conventional substation built on site still has its place. The comparison looks like this:
| Factor | Package substation | Conventional substation |
|---|---|---|
| Construction time | Shorter, because most work is done in the factory | Longer, because of civil works and on-site assembly |
| Footprint | Compact | Larger |
| Testing | Much of it done in the factory | More testing on site |
| Flexibility to customize | Limited to the manufacturer’s design range | High |
| Expansion | Add another unit or extend the lineup where the design allows | Easier to build in extra space from the start |
| Civil works | Foundation, trench and cable routes | Full building |
How do you size the transformer?
Size the transformer from the design load in kVA, then add margin for growth and for the ambient conditions. The steps are:
- Calculate the load in kVA. Divide the active power in kW by the power factor.
- Apply diversity, where the design standard allows it.
- Add a growth margin based on the expansion plan.
- Check the ambient temperature and cooling to confirm the transformer can deliver the capacity.
- Choose the next standard rating above the result.
An illustrative example: a plant has a design load of 900 kW at a power factor of 0.9.
| Step | Calculation | Result |
|---|---|---|
| Load in kVA | 900 kW divided by 0.9 | 1,000 kVA |
| With a 20% growth margin | 1,000 kVA multiplied by 1.2 | 1,200 kVA |
| Standard rating | Next standard size above 1,200 kVA | 1,250 kVA |
The growth margin here is only an illustration. Use the figure from your own expansion plan and the consultant’s specification. Improving the power factor, for example with power factor correction using capacitor banks, can reduce the kVA the transformer has to supply.
What protection and metering does a package substation need?
Protection must clear faults quickly and coordinate with the utility’s network. On the medium voltage side, the transformer is usually protected by fuses or a circuit breaker with relays, and the low voltage side has its own main breaker and outgoing protection.
Metering arrangements depend on the utility’s rules. Some projects need utility metering at medium voltage, others at low voltage, so agree the arrangement with the utility early. The same applies to relay settings and any requirements for communication or monitoring.
What does a utility coordination process involve?
A package substation that connects to the public network must follow the utility’s procedures for design review, equipment approval, inspection and energization. The details are set by the utility and change over time, so check the current requirements directly with DEWA for projects in Dubai.
In practice, coordination affects the programme more than any other factor. Late agreement on the supply arrangement, metering or relay settings can delay energization of an otherwise finished unit. An experienced contractor starts the conversation with the utility at design stage.
What site preparation does a package substation need?
The unit arrives ready to connect, but the site must be ready for it. Our comparison of cable trays vs conduits helps when you plan the cable routes. Plan for these items before delivery:
- Foundation: a concrete base or plinth designed for the unit’s weight, with cable entry provisions.
- Cable routes: trenches or ducts for medium voltage incoming cables and low voltage outgoing cables.
- Access and lifting: a route and crane position for delivery, with space for maintenance access afterwards.
- Clearances: safe distances from buildings, fences and other equipment, as the standards and the fire authority require.
- Earthing: an earthing system designed for the site’s fault levels, with soil resistivity measured, not assumed.
- Oil containment: a bund or sump where oil-filled transformers are used.
- Drainage and flood level: the base height should keep the unit clear of water.
- Lightning protection and surge protection, where the risk assessment calls for them.
How does Dubai’s climate affect a package substation?
Heat is the biggest factor, followed by dust, humidity and coastal air. Sun on a metal enclosure raises the internal temperature, which reduces transformer and switchgear capacity and shortens the life of components.
| Condition | Effect | Design response |
|---|---|---|
| High ambient temperature and solar gain | Equipment runs hotter, capacity is derated | Rating confirmed at site temperature, sun shields or double roofs, adequate ventilation or cooling |
| Dust and sand | Clogged filters, contamination, tracking risk | Suitable IP rating, filtered ventilation, regular cleaning |
| Humidity and condensation | Corrosion and insulation problems | Anti-condensation heaters, sealed cable entries |
| Coastal or industrial air | Corrosion of enclosure and fittings | Stainless steel, GRP or a high-grade protective finish |
Ask the supplier to state the ambient temperature they used for the ratings, and to show how the design copes with solar gain.
How is a package substation tested and commissioned?
A sound process tests the unit in the factory first, then proves it again on site. The usual stages are:
- Factory acceptance tests: visual and mechanical checks, insulation and dielectric tests, transformer tests, protection and control checks.
- Delivery and positioning: inspection for transport damage, careful lifting and correct placement on the foundation.
- Cable installation and termination: medium and low voltage cables are installed, tested and terminated.
- Site acceptance tests: insulation resistance, earthing resistance, protection relay tests and functional checks.
- Utility inspection and energization: inspections are completed and the unit is switched on in the agreed sequence.
- Handover: test reports, as-built drawings, relay settings records, manuals and operator training.
Ask to attend or witness the factory tests where possible. Problems found in the factory are cheap to fix. The same problems found on site are not.
How do you maintain a package substation?
A planned maintenance routine keeps the unit safe and extends its life. Typical activities are:
- Thermal imaging of connections and switchgear
- Checking and tightening terminations
- Oil sampling and analysis for oil-immersed transformers
- Cleaning and replacing ventilation filters
- Testing protection relays and their batteries
- Earthing resistance tests
- Inspecting seals, heaters and the enclosure finish
Maintenance of medium voltage equipment must be done by qualified people following lockout procedures and the safety rules that apply.
What mistakes do package substation projects commonly make?
Most problems come from planning, not from the unit. Six mistakes appear again and again:
- Late utility coordination, which delays energization
- A transformer rated without allowing for ambient temperature
- A foundation or cable route that is not ready on delivery day
- No room for crane access or maintenance
- Choosing an enclosure material that does not suit the environment
- Skipping factory witness tests, and finding faults on site
Planning a substation for your industrial site?
If you are deciding between a package and a conventional substation, or preparing a site for one, talk to the team at Paklink LLC about your load, supply voltage and programmed. You can also explore what Paklink LLC delivers on industrial electrical projects.
Frequently asked questions
What is a package substation?
A package substation is a factory-assembled unit that combines medium voltage switchgear, a transformer and low voltage switchgear in one enclosure, tested before delivery.
What is the difference between a package substation and a conventional substation?
A package substation is prefabricated and delivered as a unit, so it is faster and more compact. A conventional substation is built on site, which allows more customization but takes longer.
What voltage does a package substation use in Dubai?
Distribution in Dubai commonly steps medium voltage, often 11 kV, down to 415 V three-phase. Confirm the exact voltages for your site with the utility.
What standard covers package substations?
IEC 62271-202 covers prefabricated high-voltage and low-voltage substations. The equipment inside follows its own standards, such as IEC 62271-200, IEC 60076 and IEC 61439.
Should I choose an oil-immersed or a dry-type transformer?
Oil-immersed units suit outdoor installations and offer high efficiency, but they need oil containment. Dry-type units suit indoor areas near occupied buildings. The fire rules and the location decide.
How long does a package substation take to deliver?
Delivery time depends on the manufacturer, the design and the current order book, so ask each supplier for a programme. Factory assembly usually shortens site work compared with a built substation.
