Direct Answer
To select the right package substation for a Saudi industrial project, determine the maximum demand load (kVA) with a future growth contingency, confirm the SEC or project MV supply voltage (13.8 kV or 33 kV), establish the available fault level, define the site's environmental IP rating requirement, and select the substation type compact, skid, or containerised based on site access, outdoor exposure, and mobility needs. Every selection decision should be validated against SEC Technical Standards.
Key Specification Parameters
Seven parameters must be established before a package substation can be correctly specified. Each is a dependency an error in any one will propagate through the entire design.
1. Load Requirements (kVA)
Calculate the maximum demand load for all connected equipment using load schedules. Apply a diversity factor (typically 0.65–0.85 for mixed industrial loads) and add a minimum 20–25% future growth contingency.
For Saudi facilities, account for peak summer HVAC demand which can be 30–40% higher than off-peak figures. Transformer ratings are standardised: 250, 315, 400, 500, 630, 800, 1,000, 1,250, 1,600, 2,000, 2,500 kVA.
2. Voltage Levels
Confirm the SEC or project MV supply voltage at the point of connection: 13.8 kV (most common), 33 kV (Jubail, Yanbu, high-density zones), or 11 kV (legacy systems).
The LV output is fixed at 380/400 V at 50 Hz for standard distribution. Facilities with large motors above 200 kW may require a separate 6.6 kV or 11 kV distribution tier confirm with the mechanical engineering team before finalising the substation SLD.
3. Short Circuit Rating (kA)
Obtain the declared fault level from SEC at the MV connection point. SEC 13.8 kV networks typically have fault levels of 25 kA to 31.5 kA; 33 kV networks may be higher.
All MV switchgear, the transformer, and the LV panel busbar must be rated at or above this figure. LV busbars are typically specified at 50 kA or 65 kA for 1 second to cover the prospective LV fault current from the transformer.
4. Cooling Requirements
All transformers are rated at a reference ambient of 40°C per IEC 60076. Saudi outdoor ambient temperatures reach 45–55°C. At 50°C ambient, an ONAN oil transformer operating at rated current will exceed its thermal limit.
Options: Specify a transformer with higher rated kVA to operate at reduced load percentage; specify ONAF cooling (fans) for derating recovery; or specify a transformer with Class H insulation rated for higher ambient. Always state the maximum site ambient temperature in the substation data sheet.
5. Environmental Protection (IP Rating)
IP rating is determined by the installation environment:
- • Indoor, controlled environment: IP31 or IP33
- • Indoor, dusty environment: IP42 or IP54
- • Outdoor, sheltered: IP44 or IP54
- • Outdoor, exposed to sand and rain: IP54 minimum, IP65 preferred
- • Coastal sites (salt spray): IP65 + marine-grade coating
6. Space Constraints
Measure the available footprint including access clearances required for operation and maintenance: minimum 1 m front access for LV panel, minimum 1 m side access for transformer oil sampling and cable entry.
If the available footprint is too small for a compact kiosk, consider a unitised substation with external MV switchgear. For very tight spaces basement electrical rooms confirm ceiling height for transformer lifting and RMU door swing clearance.
7. Future Expansion
Specify the LV panel with spare outgoing feeder ways (minimum 20% of initial populated ways as spare). Confirm the transformer can be paralleled with a future second unit if load growth requires it specify compatible vector groups (Dyn11) and tap positions.
For the RMU, specify a spare loop position even if not currently required adding a loop switch after installation requires a full MV outage on the ring. The incremental cost at manufacture is minimal.
Step-by-Step Selection Process
Obtain the Electrical Load Schedule
Compile the complete list of connected loads from the mechanical, process, and architectural teams. Calculate connected kVA for all equipment. Apply diversity and demand factors to obtain maximum demand kVA. This is the single most important input to substation selection errors here propagate through every subsequent decision.
Rule of thumb: If the maximum demand calculation gives a result very close to a standard transformer rating, round up to the next standard size. The cost difference between adjacent transformer ratings is small relative to the cost of a second substation when the first proves undersized.
Confirm the SEC or Project MV Supply Voltage
Contact the local SEC district office or project MV engineer to confirm the available supply voltage and the maximum demand allowed at the connection point (kVA allocation). For private industrial projects, confirm the project MV distribution voltage from the site single-line diagram. Transformer primary voltage must exactly match the declared supply voltage specifying the wrong primary voltage is a costly error to rectify after manufacture.
Obtain the Available Fault Level
Request the short circuit level (kA) at the MV connection point from SEC or the project electrical engineer. This value determines the minimum rated short circuit current (Isc) of the MV switchgear and the minimum rated peak withstand current (Ipk) of the LV busbar. A substation with undersized fault current ratings will fail destructively on first fault this is a safety-critical specification parameter.
Define the Site Environmental Class
Visit the site and document: maximum and minimum ambient temperatures, proximity to coast or industrial emission sources, prevailing wind direction and sand/dust exposure, whether the substation will be indoor or outdoor, and whether flooding or standing water is possible. Map these conditions to an IEC 62271-202 environmental class and specify the corresponding IP rating, ventilation type, enclosure material, and coating system.
Select the Substation Type
| If your site has... | Specify this type |
|---|---|
| Fixed outdoor pad, SEC ring connection, ≤ 1,600 kVA | Compact kiosk package substation |
| Process plant, existing shelter or building, > 1,600 kVA | Skid-mounted substation |
| Remote location, no permanent shelter, or potential relocation | Containerised substation |
| Building with existing MV room and multiple floor zones | Unitised substation (transformer + LV panel only) |
Select Transformer Cooling Type
For indoor applications in commercial buildings, hospitals, or data centres: specify dry-type (AN/AF) or cast resin transformers to eliminate oil containment. For all other Saudi applications, oil-immersed (ONAN at cooler sites, ONAF at sites with high ambient temperature or heavy loading) transformers are standard. Always state the maximum site ambient in the order: "Transformer to be rated for continuous operation at rated kVA at 50°C ambient."
Specify the LV Panel Configuration
Define the required outgoing feeders number, rating (A), and cable entry direction (top or bottom). Specify metering: SEC typically requires a check meter on the transformer secondary in addition to any SEC billing meter. Specify CT ratios compatible with the protection relay settings. Include spare ways, APFC panel provision, and any telemetry or SCADA output requirements in the LV panel specification.
Issue the Data Sheet and Request for Quotation
Document all decisions in a formal substation data sheet: rated kVA, primary voltage, secondary voltage, vector group, impedance, cooling type, maximum ambient, RMU configuration, LV panel feeder schedule, IP rating, standards compliance (IEC 62271-202, IEC 60076, IEC 61439), factory test requirements (FAT), and required certifications (SASO, SEC approval). Issue this document with the RFQ to ensure all suppliers price against identical specifications.
Common Mistakes Engineers Make When Specifying Package Substations in Saudi Arabia
Mistake 1: Specifying for 40°C Ambient
The Error
Ordering a standard ONAN oil transformer with IEC-standard 40°C ambient rating, then installing it in an outdoor Saudi site where summer ambient reaches 50–55°C. The transformer runs above its thermal limit continuously, accelerating insulation ageing and reducing service life from 30+ years to under 10 years.
The Correct Approach
Always state the maximum site ambient temperature in the data sheet. For Saudi outdoor sites: specify ONAF (with fans) or a transformer with a higher kVA rating to create a thermal margin. Confirm with the manufacturer that the stated kVA output is achievable at the actual site ambient.
Mistake 2: Ignoring the Available Fault Level
The Error
Specifying MV switchgear and LV busbars rated at 25 kA when the SEC supply fault level at the connection point is 31.5 kA. On first MV fault, the switchgear interrupting rating is exceeded catastrophic failure, personnel risk, and lengthy replacement lead time.
The Correct Approach
Always obtain the declared fault level from SEC before issuing the substation specification. Specify MV switchgear rated ≥ the declared fault level. For LV busbars, calculate the prospective short circuit current at the transformer secondary for the selected transformer impedance and specify accordingly.
Mistake 3: Undersizing for Future Load Growth
The Error
Specifying the transformer kVA for the current connected load with no growth margin. Within 3–5 years, load additions from new equipment, expanded production, or additional HVAC fill the substation to capacity. A second substation must be purchased and installed at 3–5× the cost of simply specifying the next standard rating at the outset.
The Correct Approach
Apply a minimum 20–25% contingency to the maximum demand kVA and round up to the next standard transformer rating. Specify the LV panel with 20% spare feeder ways. Confirm the RMU has an additional loop position for a future substation extension.
Mistake 4: Specifying the Wrong RMU Configuration
The Error
Ordering a 2L+T RMU (two loop switches plus one transformer feeder) for a site that SEC will eventually require to serve as a pass-through for two separate ring circuits. On commissioning, the RMU has insufficient switch positions a new RMU must be ordered or the ring cannot be completed.
The Correct Approach
Confirm the final RMU configuration with the SEC district office before ordering. If the final network configuration is uncertain, specify one additional spare loop switch position the cost is marginal at manufacture and avoids a complete RMU replacement later.
Mistake 5: Omitting Factory Acceptance Testing
The Error
Accepting a package substation without a Factory Acceptance Test (FAT) to reduce cost and delivery time. Faults in MV switchgear interlock settings, incorrect CT ratios, or misconfigured protection relays are discovered on site where correction is far more expensive and time-consuming than at the factory.
The Correct Approach
Require a FAT as a contractual deliverable for all package substations. The FAT should include: high-voltage dielectric testing of MV switchgear, functional testing of all protection relays and interlocks, continuity and insulation resistance testing of LV wiring, and verification of metering CT accuracy. The FAT report forms part of the O&M documentation handed over to the client.
Frequently Asked Questions
Q: What transformer kVA rating should I specify for my package substation?
A: Base the rating on the maximum demand load (kVA) from the load schedule, with a diversity factor applied. Add a minimum 20–25% contingency for future growth. For Saudi industrial facilities, account for peak summer HVAC demand which may be 30–40% higher than off-peak consumption. A transformer running continuously above 80% of rated kVA at Saudi ambient temperatures will have a significantly reduced service life.
Q: What short circuit rating should I specify for a package substation in Saudi Arabia?
A: The short circuit rating depends on the fault level available from the SEC or project MV network at the connection point. SEC 13.8 kV networks typically have fault levels of 25 kA to 31.5 kA. All MV switchgear, the transformer, and LV busbar must be rated at or above the declared fault level. LV busbars are typically rated 50 kA or 65 kA for 1 second to cover the prospective short circuit current from the transformer.
Q: Should I specify an oil-immersed or dry-type transformer for my package substation?
A: For outdoor package substations and industrial applications, oil-immersed (ONAN/ONAF) transformers are standard lower cost, easier to maintain, and widely available with SEC-approved specs. For indoor commercial buildings, hospitals, and data centres where fire risk is a concern, dry-type or cast resin transformers are preferred. For all types, confirm thermal performance at 50°C ambient, not the IEC standard 40°C.
Q: Do I need an APFC panel with my package substation?
A: If the facility's loads include significant inductive equipment motors, HVAC compressors, welding and the substation is SEC-connected on a kVA billing tariff, power factor correction is almost always justified. The LV panel should include provision for a future APFC connection. Where PF correction is required from day one, an integrated APFC panel can be specified as part of the package substation assembly.
EAMFCO - Package Substation Engineering and Manufacturing for Saudi Projects
EAMFCO's engineering team provides substation data sheet preparation, load calculations, and full specification support for Saudi industrial and infrastructure project tenders. Our factory-assembled package and unit substations integrate SF₆ RMUs, oil and dry-type transformers, and IEC 61439-compliant LV panels all factory tested and documented before delivery. Continue reading: