In a utility-scale solar power plant, electricity does not move directly from photovoltaic modules into the transmission or distribution grid. Power from multiple inverter blocks must first be converted, collected, transformed to the required voltage level, controlled through the solar substation, and delivered to the grid connection point.
The oil-immersed power transformer installed in the collection or grid-connection substation is therefore a critical part of the complete photovoltaic power system. Its rated capacity, voltage ratio, impedance, vector group, insulation level, cooling arrangement, tap-changing method, protection accessories, terminal configuration, and monitoring signals must match the electrical design of the solar plant.
Saudi Arabia adds demanding environmental conditions to this process. Outdoor transformers may operate under high ambient temperatures, intense solar radiation, dust, sand, large daily temperature changes, and limited maintenance access. These conditions influence temperature rise, insulation life, radiator performance, oil sealing, bushing selection, external coating, control cabinet protection, and long-term operating stability.
HONLE manufactures oil-immersed transformers for power distribution, power generation, industrial systems, and substation applications. For Saudi Arabia solar substation projects, transformer configuration is confirmed according to the single-line diagram, project data sheet, required voltage class, plant capacity, site conditions, applicable standards, testing schedule, and documentation requirements.
Oil-Immersed Power Transformers Connect Solar Generation with the Grid
Different transformers perform different functions inside a solar plant
A large photovoltaic power plant normally contains several electrical stages. Solar modules produce DC power, inverters convert DC power into AC power, and transformers raise the voltage so that electricity can be collected and transmitted efficiently.
Depending on the plant architecture, transformers may be installed:
- Beside individual inverter blocks;
- Inside prefabricated inverter-transformer stations;
- Along the medium-voltage collection network;
- At the main collection substation;
- At the grid-connection substation;
- In the station auxiliary power system.
The transformer connected directly to an inverter block and the main power transformer installed at a grid-connection substation do not have the same duty.
An inverter block transformer usually handles the output of one inverter group and raises it to the medium-voltage collection level. A main substation transformer receives the combined output from multiple collection feeders and raises it to the voltage required by the grid.
Their capacities, winding arrangements, cooling systems, insulation structures, tap changers, protection devices, monitoring systems, and test requirements may therefore be different.
Main substation transformers carry the combined plant output
The main oil-immersed power transformer is commonly located between the medium-voltage collection system and the grid connection system.
It may carry the combined output of many inverter blocks. Its design must coordinate with:
- The rated output of the solar power plant;
- The number and capacity of inverter blocks;
- The medium-voltage collection system;
- The grid connection voltage;
- Reactive power requirements;
- The plant power controller;
- Short-circuit levels;
- Protection relay settings;
- Earthing and neutral arrangements;
- Parallel transformer operation;
- Future plant expansion.
A power transformer selected only according to a nominal capacity may not provide suitable voltage regulation, fault-current control, cooling performance, or operating margin.
The transformer data must therefore be reviewed together with the complete solar plant electrical design.
Transformer position determines the main design priorities
Table 1. Typical Power Transformer Positions in a Solar Power Plant
| Transformer position | Main function | Main design priorities |
| Inverter block power transformer | Raises inverter output to the collection voltage | Inverter compatibility, harmonics, cyclic loading, compact installation and outdoor protection |
| Medium-voltage collection power transformer | Connects generation blocks or collection sections | Collection voltage, cable interface, impedance and feeder protection |
| Main substation power transformer | Raises collection voltage to the grid connection level | MVA rating, insulation level, cooling, tap changer, short-circuit strength and monitoring |
| Auxiliary distribution transformer | Supplies control rooms, lighting, HVAC and communication equipment | Local load capacity, reliability, enclosure and auxiliary voltage |
| Station service transformer | Supports continuous substation operation | Redundancy, starting current, protection and emergency supply arrangement |
For a main solar substation transformer, electrical system coordination and long-term thermal performance normally receive greater attention than compact dimensions alone.
Transformer Capacity Must Follow the Actual Solar Plant Operating Conditions
Solar plant MW and transformer MVA are not directly interchangeable
Solar plant output is commonly stated in megawatts, while transformer capacity is stated in megavolt-amperes.
The required transformer MVA should not be selected by simply copying the solar plant MW rating. The final capacity depends on active power, reactive power duty, required power factor, inverter operating characteristics, cooling stages, design margin, ambient temperature, overload conditions, and redundancy requirements.
For example, the power transformer may need to carry additional apparent power when the plant supplies or absorbs reactive power for grid voltage control. The apparent power passing through the power transformer can therefore be higher than the active MW output alone indicates.
Capacity selection should confirm:
- Maximum plant active power;
- Required reactive power range;
- Minimum and maximum operating power factor;
- Inverter output characteristics;
- Continuous and temporary loading;
- Expected daily loading cycle;
- ONAN and ONAF ratings;
- Required operating margin;
- Transformer redundancy;
- Future expansion plans;
- Battery energy storage integration, where applicable.
When two power transformers share the plant output, the project must also define whether each transformer carries half of the normal load or whether either unit must support additional load when the other unit is unavailable.
The daily solar generation cycle affects thermal loading
Solar power output normally increases after sunrise, reaches a higher level around the middle of the day, and decreases toward sunset. Cloud movement, plant controller commands, inverter availability, and grid instructions can also cause shorter-term changes in transformer loading.
This operating pattern differs from a continuously stable industrial load.
The thermal review should consider:
- The duration of peak loading;
- Repeated daily heating and cooling;
- Ambient temperature during peak generation;
- Reactive power demand during high output;
- Temporary overload expectations;
- Cooling fan operating periods;
- Reduced nighttime loading;
- Seasonal differences in solar generation.
IEC 60076-7 provides guidance for mineral-oil-immersed transformer loading, operating temperature, and thermal aging. The final loading assessment must still use the project’s actual ambient conditions and operating profile.
Transformer losses influence long-term plant performance
A solar substation transformer remains in service for many years, and electrical losses continue throughout its operating life.
No-load losses occur whenever the transformer is energized, even when solar generation is low or unavailable. Load losses increase as current passes through the windings.
For solar plant applications, guaranteed loss values may affect:
- Annual energy delivery;
- Plant performance calculations;
- Operating revenue;
- Thermal performance;
- Cooling requirements;
- Total lifecycle cost.
The project data sheet should clearly identify the required maximum no-load loss, load loss, auxiliary cooling power, and permitted tolerances.
HONLE reviews the required loss limits together with power transformer capacity, core design, winding conductor, impedance, temperature rise, and cooling arrangement before finalizing the technical proposal.
Voltage Ratio, Impedance and Winding Connections Must Match the Grid Design
Voltage ratio starts with the approved single-line diagram
A solar power plant may use a collection voltage such as 33kV, 35kV, or another project-specific level. The main transformer then raises this voltage to the required grid connection voltage.
Before transformer design begins, the project team should confirm:
- Rated high-voltage winding voltage;
- Rated low-voltage winding voltage;
- Tertiary winding voltage, where required;
- Highest voltage for equipment;
- System frequency;
- Permitted system voltage variation;
- Required tap range;
- Number and size of tap steps;
- Neutral insulation level;
- Grid-side earthing method;
- Collection-side earthing method.
The rated voltage ratio alone does not define the complete insulation design.
Bushing ratings, lightning impulse withstand level, power-frequency withstand level, winding insulation, internal clearances, external clearances, neutral insulation, surge protection, and terminal arrangement must correspond to the approved system voltage and insulation coordination study.
Vector group must coordinate with grounding and protection
The power transformer vector group defines the winding connection and phase displacement between the high-voltage and low-voltage sides.
It also affects:
- Zero-sequence current;
- Earth-fault current paths;
- Neutral grounding;
- Protection relay operation;
- Harmonic circulation;
- Parallel operation;
- Compatibility with upstream and downstream equipment.
The final vector group should be provided in the transformer data sheet or approved single-line diagram.
A commonly used vector group from another project should not be copied automatically. The correct arrangement depends on the inverter transformer connections, collection system grounding, utility requirements, protection philosophy, and grid interface design.
HONLE reviews the requested vector group together with winding insulation, neutral arrangement, terminal layout, and protection requirements before production.
Percentage impedance affects both fault current and voltage regulation
Transformer impedance is an important system parameter.
A lower percentage impedance can reduce voltage drop during normal operation but may allow a higher short-circuit current. A higher percentage impedance can help limit fault current but may increase voltage variation and reactive power consumption.
The required impedance should coordinate with:
- Grid short-circuit capacity;
- Collection system fault level;
- Switchgear ratings;
- Cable ratings;
- Protection relay settings;
- Voltage regulation requirements;
- Reactive power calculations;
- Parallel transformer operation.
For transformers operating in parallel, voltage ratio, vector group, percentage impedance, impedance tolerance, phase sequence, tap position, and rated capacity must be coordinated.
HONLE manufactures the power transformer according to the approved impedance value and tolerance rather than replacing the system-study requirement with a general catalog value.
Tap-changing arrangement supports voltage control
Solar plant voltage changes with grid conditions, generation level, reactive power operation, and the impedance of the collection and transmission systems.
The transformer may therefore require either:
- An off-circuit tap changer; or
- An on-load tap changer.
An off-circuit tap changer is adjusted only after the transformer has been de-energized. It is suitable when voltage adjustment is infrequent and operating conditions are relatively stable.
An on-load tap changer allows the power transformer ratio to be adjusted while energized. It may be required when the substation must provide continuous voltage regulation or coordinate with the plant power controller.
For an OLTC application, the project should confirm:
- Tap range;
- Number of tap positions;
- Step voltage;
- Normal tap position;
- Maximum operating current;
- Motor-drive voltage;
- Local and remote control;
- Automatic voltage regulation;
- Tap-position indication;
- SCADA communication;
- Alarm and maintenance requirements.
The tap changer, winding arrangement, control cabinet, protection system, and remote signals are reviewed as one complete operating system.
Saudi Arabia Site Conditions Must Be Included in the Transformer Design
High ambient temperature reduces cooling margin
Heat generated by the core and windings is transferred to the transformer oil and then released through the tank and radiators.
When the surrounding air temperature is high, the temperature difference between the radiator surface and the ambient air becomes smaller. Heat dissipation becomes more difficult, and the available thermal margin is reduced.
A Saudi solar substation specification should provide:
- Maximum ambient temperature;
- Minimum ambient temperature;
- Daily average temperature;
- Monthly or seasonal temperature profile;
- Required top-oil temperature rise;
- Required winding temperature rise;
- Installation altitude;
- Maximum solar radiation;
- Expected loading cycle;
- Permitted overload conditions.
IEC 60076-2 covers temperature-rise requirements and cooling methods for liquid-immersed power transformers. The transformer temperature-rise design must also follow any stricter project or utility limits.
Cooling calculations should be completed using the specified ambient temperature rather than assuming that every installation follows standard reference conditions.
Direct solar radiation affects more than the transformer tank
Solar substations are commonly installed in open areas with little natural shade.
Direct sunlight can heat:
- The transformer tank;
- Radiators;
- Conservator;
- Marshalling kiosk;
- Tap changer control cabinet;
- Cable boxes;
- Terminal enclosures;
- Temperature instruments;
- Oil-level indicators;
- External wiring;
- Gaskets and sealing materials.
Saudi Electricity Company material specifications provide a useful indication of local outdoor design conditions. Some SEC transformer specifications require surfaces exposed to direct solar radiation to be considered at 75°C plus the effect of internal heating. The exact temperature requirement for each solar substation must be taken from the approved project specification.
The external design may therefore need to address:
- UV-resistant components;
- Suitable external coating;
- Outdoor-rated instruments;
- Control cabinet insulation or ventilation;
- Cable entry sealing;
- Gasket temperature resistance;
- Fan motor protection;
- Instrument visibility in strong sunlight;
- Adequate spacing around radiators.
Adding radiator surface area alone is not enough if the radiator layout restricts airflow or makes cleaning difficult.
Dust and sand influence cooling and external insulation
A properly sealed power transformer tank prevents dust from entering the oil and active parts. However, dust and sand can still accumulate on external equipment.
Potentially affected parts include:
- Radiator fins;
- Cooling fans;
- Bushings;
- Surge arresters;
- Terminal boxes;
- Marshalling kiosks;
- Temperature indicators;
- Oil-level indicators;
- Tap changer drives;
- Cable entries.
Dust deposits on radiators can reduce heat-transfer efficiency. Contamination on bushings may affect external insulation performance, especially when dust is combined with moisture, industrial pollution, or coastal salt.
The project should confirm whether the site is:
- Inland desert;
- Near the coast;
- Exposed to industrial pollution;
- Subject to frequent sandstorms;
- Located at high altitude;
- Difficult to access for maintenance.
These conditions may influence creepage distance, bushing type, enclosure protection, coating system, radiator arrangement, sealing method, corrosion protection, and maintenance recommendations.
Coastal locations require additional corrosion review
Not every Saudi solar plant is located in the same environment.
A project near the coast may experience salt contamination and higher corrosion risk, while an inland desert project may face heavier dust and greater day-to-night temperature changes.
For coastal or corrosive locations, the transformer specification may need to define:
- Paint system;
- Surface preparation;
- Coating thickness;
- Corrosion category;
- Galvanized external parts;
- Stainless-steel hardware;
- Terminal material;
- Control cabinet material;
- Salt-mist requirements;
- Bushing creepage distance.
These requirements should be confirmed before the general arrangement drawing and material selection are finalized.
Cooling and Accessories Must Follow the Transformer Operating Duty
ONAN and ONAF ratings should be defined separately
Under ONAN cooling, transformer oil circulates naturally inside the tank and radiators, while surrounding air removes heat without powered fans.
Under ONAF cooling, fans increase airflow across the radiators and allow the transformer to carry a higher approved load.
When both cooling stages are specified, the data sheet should clearly state:
- ONAN rated capacity;
- ONAF rated capacity;
- Number of cooling stages;
- Number of fan groups;
- Fan redundancy;
- Fan motor voltage;
- Automatic start temperature;
- Automatic stop temperature;
- Manual and automatic control;
- Local and remote status signals;
- Alarm conditions.
Fans should not be used to compensate for an insufficient basic radiator design. The transformer should maintain the approved ONAN rating when the forced-air cooling system is unavailable.
HONLE confirms the radiator quantity, radiator arrangement, fan configuration, temperature controls, and cooling-stage ratings according to the required MVA and temperature-rise limits.
Tank and oil preservation systems depend on transformer size
HONLE’s oil-immersed range includes hermetically sealed distribution transformers as well as larger 35kV and 110kV oil-immersed power transformers. The S11 distribution transformer, for example, uses a sealed corrugated tank without a separate oil conservator.
Larger power transformers may require:
- Main tank;
- Detachable radiators;
- Oil conservator;
- Air-cell or breather arrangement;
- Buchholz relay;
- Oil-level indicator;
- Pressure relief device;
- Oil temperature indicator;
- Winding temperature indicator;
- Cooling control cabinet;
- Marshalling kiosk;
- Oil sampling valves;
- Drain and filter valves.
The final oil preservation and tank structure depend on transformer capacity, voltage class, oil volume, transportation limits, cooling arrangement, maintenance plan, and project specification.
Protection accessories should match the substation protection philosophy
A main solar substation transformer may require several mechanical and electrical protection devices.
The final accessory list may include:
- Buchholz relay;
- Pressure relief device;
- Sudden pressure relay;
- Oil temperature indicator;
- Winding temperature indicator;
- Magnetic oil-level gauge;
- Low oil-level alarm;
- Cooling fan alarms;
- OLTC protection;
- Neutral current transformers;
- Bushing current transformers;
- Online dissolved gas monitoring;
- Moisture monitoring;
- Fiber-optic winding temperature monitoring;
- Remote alarm and trip contacts.
Not every transformer needs every accessory.
The required configuration should follow transformer size, voltage class, utility practice, protection relay design, maintenance strategy, and project data sheet.
SCADA requirements should be confirmed before control wiring is completed
Solar substations normally use centralized monitoring and control.
Power Transformer signals may need to be connected to the substation SCADA or plant control system. These can include:
- Oil temperature;
- Winding temperature;
- Oil level;
- Pressure alarm;
- Buchholz alarm and trip;
- Fan group status;
- Fan failure alarm;
- OLTC position;
- OLTC motor status;
- Local or remote control mode;
- Circuit trip signals;
- Control power supply alarm.
Before finalizing the marshalling kiosk and terminal blocks, the project should provide:
- Complete signal list;
- Alarm and trip matrix;
- Required analog outputs;
- Communication protocol;
- Terminal numbering rules;
- Control voltage;
- Cable entry direction;
- Spare terminal requirements;
- Space-heater requirements;
- Cabinet lighting requirements.
Confirming these details before production reduces wiring changes during factory acceptance testing and site commissioning.
Transformer Construction Must Withstand Electrical and Mechanical Stress
Short-circuit forces influence winding and clamping design
During an external short circuit, the transformer windings may experience high current and strong electromagnetic forces.
The winding structure, conductors, spacers, axial clamping, radial support, leads, core frame, and mechanical connections must be designed to withstand these forces.
IEC 60076-5 covers the ability of power transformers to withstand the thermal and dynamic effects of external short circuits.
The project should provide:
- System short-circuit level;
- Fault duration;
- Grid impedance;
- Transformer impedance;
- Earthing arrangement;
- Any special short-circuit requirements.
HONLE uses the approved electrical parameters as the basis for winding calculation, conductor selection, insulation structure, and mechanical support.
Insulation coordination must include switching and lightning conditions
Outdoor solar substations may be connected through overhead lines, underground cables, switchgear, or a combination of these systems.
Transformer insulation levels should coordinate with:
- Highest voltage for equipment;
- Lightning impulse withstand level;
- Power-frequency withstand level;
- Switching impulse requirement, where applicable;
- Surge arrester ratings;
- Bushing insulation level;
- Neutral insulation;
- Pollution level;
- Installation altitude;
- External clearances.
The project’s insulation coordination study and technical specification remain the basis for final transformer design.
Terminal arrangement should match the substation layout
Power Transformer terminals may connect to:
- Overhead conductors;
- Cable boxes;
- Bus ducts;
- Gas-insulated switchgear;
- Air-insulated switchgear;
- Neutral grounding equipment;
- Surge arresters;
- Current transformers.
The general arrangement drawing should confirm:
- HV and LV terminal position;
- Bushing orientation;
- Phase-to-phase spacing;
- Phase-to-earth clearance;
- Cable box direction;
- Bus duct interface;
- Neutral terminal position;
- Surge arrester mounting;
- CT location;
- Maintenance access.
Terminal arrangement should be reviewed before the transformer foundation, cable trench, bus structure, and substation layout are finalized.
Factory Testing Confirms the Approved Power Transformer Parameters
IEC 60076 provides the main technical basis
IEC 60076-1 applies to three-phase and single-phase power transformers and defines general requirements for ratings, connections, testing, and related transformer data.
Depending on the project scope, additional parts of IEC 60076 may be applied for:
- Temperature rise;
- Insulation levels and dielectric tests;
- Short-circuit withstand;
- Loading;
- Sound levels;
- Protective devices;
- Other special transformer requirements.
The project specification may also include:
- Saudi utility requirements;
- EPC specifications;
- Grid-code requirements;
- Guaranteed loss limits;
- Special material requirements;
- Inspection procedures;
- Approved test forms;
- Drawing formats;
- Third-party inspection.
The applicable standard editions, project deviations, guaranteed values, and additional tests should be confirmed during the technical review.
Routine tests are included in the factory test schedule
Depending on power transformer type, voltage class, and applicable standard, routine testing may include:
- Measurement of winding resistance;
- Measurement of voltage ratio;
- Verification of vector group;
- Verification of phase displacement;
- Measurement of no-load loss;
- Measurement of no-load current;
- Measurement of load loss;
- Measurement of short-circuit impedance;
- Separate-source AC withstand test;
- Induced AC voltage test;
- Insulation resistance measurement;
- Tap changer functional checks;
- Alarm and trip contact checks;
- Control wiring checks;
- Cooling fan functional checks;
- Oil testing;
- Tank leak testing;
- Verification of nameplate information;
- Verification of terminal markings.
Test values are recorded in the factory test report and checked against the approved transformer data.
Type and special tests should be agreed before production
Some projects require tests beyond the routine test program.
These may include:
- Temperature-rise test;
- Lightning impulse test;
- Switching impulse test;
- Sound-level measurement;
- Zero-sequence impedance measurement;
- Partial discharge measurement;
- Frequency response analysis;
- Capacitance and dielectric dissipation factor measurement;
- Short-circuit withstand verification;
- Oil dissolved gas analysis;
- Tank vacuum or pressure test;
- Special dimensional inspection.
The test schedule should define:
- Applicable standard;
- Acceptance criteria;
- Witness requirements;
- Hold points;
- Third-party inspection;
- Test report format;
- Required test certificates.
Early confirmation allows the design, production schedule, testing capacity, inspection arrangement, and delivery plan to follow the same approved scope.
HONLE Manufactures Transformers According to Confirmed Project Data
Our product range covers several oil-immersed transformer applications
HONLE Group was founded in 1998 and focuses on the research, development, manufacturing, and supply of electrical equipment. Our transformer range supports power distribution, industrial systems, power stations, and substation applications.
Our current oil-immersed transformer range includes:
- Three-phase oil-immersed distribution transformers;
- Voltage-regulating oil-immersed transformers;
- 35kV oil-immersed power transformers;
- 110kV oil-immersed power transformers.
HONLE’s 35kV oil-immersed power transformers are designed for power distribution, substations, industrial electrical systems, and related power applications. Our 110kV oil-immersed transformer range is intended for higher-voltage power plant and substation duties.
For a Saudi solar substation project, product selection is based on the required capacity, voltage class, cooling method, loss limits, insulation level, tap-changing arrangement, accessories, and test scope.
When the required voltage class or transformer configuration differs from the available standard range, the engineering, production, and testing requirements are reviewed separately before the technical and commercial proposal is finalized.
110kV Oil-Immersed Power Transformers
Manufacturing begins after the technical schedule is confirmed
The project process normally includes:
- Receiving the transformer data sheet and single-line diagram;
- Reviewing electrical ratings and operating conditions;
- Confirming missing or conflicting parameters;
- Preparing the technical proposal;
- Issuing a deviation list where necessary;
- Preparing general arrangement and technical drawings;
- Completing drawing review and approval;
- Releasing the approved design for production;
- Carrying out manufacturing and quality inspections;
- Completing factory testing;
- Issuing test reports and shipping documents;
- Preparing export packaging and delivery information.
This sequence keeps the electrical design, mechanical structure, accessory list, control wiring, tests, and project documentation aligned with the approved data sheet.
Quality documents are matched to the supplied transformer
HONLE’s quality and certification information includes ISO 9001 quality management, ISO 14001 environmental management, ISO 45001 occupational health and safety management, IEC standards compliance, and CE-marked products.
For each project, the document package is prepared according to the transformer type, applicable standards, contractual requirements, and approval process.
Documents may include:
- Company qualification documents;
- Product technical data;
- General arrangement drawing;
- Foundation drawing;
- Terminal arrangement drawing;
- Rating and diagram plate drawing;
- Accessory list;
- Control schematic;
- Marshalling kiosk wiring diagram;
- Quality plan;
- Inspection and test plan;
- Factory test report;
- Transformer oil report;
- Packing list;
- Installation instructions;
- Operation and maintenance manual;
- Recommended spare-parts list.
Project-specific certificates, test reports, and approval documents are confirmed during the quotation and document-submission stages.
Complete Inquiry Data Supports an Accurate Technical Proposal
The project data sheet should cover electrical and environmental requirements
An inquiry stating only the capacity and voltage ratio cannot define a complete solar substation transformer.
The following information allows HONLE to prepare a more accurate technical proposal.
Table 2. Information Required for a Saudi Solar Substation Transformer Inquiry
| Information category | Details to provide |
| Transformer application | Inverter block, collection substation, main grid substation or auxiliary supply |
| Single-line diagram | Transformer position and connected equipment |
| Rated capacity | Required ONAN and ONAF MVA ratings |
| Voltage data | HV, LV and tertiary voltage where applicable |
| Highest system voltage | Required equipment voltage class |
| System frequency | Project frequency |
| Vector group | Approved winding connection |
| Percentage impedance | Required value and tolerance |
| Tap changer | Off-circuit or OLTC, tap range, steps and control |
| Insulation level | Power-frequency, lightning impulse and switching impulse requirements |
| Neutral arrangement | Earthing method for each winding |
| Short-circuit data | Fault level and fault duration |
| Loss limits | Maximum no-load and load losses |
| Temperature rise | Top-oil and winding limits |
| Site conditions | Ambient temperature, altitude, dust, solar radiation and coastal exposure |
| Cooling arrangement | ONAN, ONAF and fan redundancy |
| Accessories | Protection, monitoring, CTs, indicators and valves |
| SCADA requirements | Signal list, communication and remote-control requirements |
| Terminal arrangement | Bushings, cable boxes, bus duct or overhead connection |
| Applicable standards | IEC, utility and project specifications |
| Factory tests | Routine, type, special and witnessed tests |
| Documentation | Drawings, reports, manuals and approval formats |
| Transportation limits | Maximum dimensions, weight, route and unloading conditions |
Transportation conditions should be reviewed during design
Large power transformers may be subject to transport limits relating to:
- Total shipping weight;
- Main tank dimensions;
- Transport height;
- Road clearance;
- Port handling;
- Crane capacity;
- Site access;
- Unloading method;
- Oil-filled or oil-drained shipment;
- Detachable radiators;
- Conservator removal;
- Bushing removal;
- Nitrogen filling;
- Shock and tilt monitoring.
Transportation requirements can affect tank dimensions, detachable components, oil handling, packaging method, and site assembly work.
For this reason, transport route and unloading conditions should be provided before the final mechanical design is approved.
Frequently Asked Questions
Are oil-immersed transformers suitable for Saudi solar substations?
Yes. Oil-immersed power transformers are suitable for many outdoor solar collection and grid-connection substations because transformer oil provides electrical insulation and transfers heat from the active parts to the tank and radiators.
The final design must still match the ambient temperature, solar radiation, dust level, voltage class, loading profile, cooling system, protection arrangement, and maintenance conditions of the project.
Should transformer MVA equal the solar plant MW capacity?
Not automatically.
Transformer MVA depends on active power, reactive power, power factor, inverter operation, cooling-stage rating, design margin, overload conditions, redundancy, and future expansion.
The final rating should follow the approved load-flow study and plant operating requirements.
Does every main solar transformer require an OLTC?
No.
The requirement for an OLTC depends on grid voltage variation, plant voltage-control strategy, reactive power operation, utility requirements, and the transformer’s position in the electrical system.
Some applications can use an off-circuit tap changer, while others require an OLTC with automatic voltage regulation and remote tap-position monitoring.
What cooling method is suitable for a Saudi solar substation?
The cooling method depends on transformer capacity, ambient temperature, loading profile, required redundancy, and permitted temperature rise.
ONAN may be sufficient for some transformers. Larger units may use ONAN/ONAF ratings so that fan-assisted cooling is available at higher loading levels.
The cooling arrangement must be confirmed through the transformer thermal design.
What tests can be witnessed before shipment?
Witnessed tests may include routine tests, selected type tests, or special tests according to the inspection and test plan.
The project should specify which tests require client witnessing, third-party inspection, hold points, and approved test reports before production begins.
What information should be provided first?
The most useful initial documents are:
- Single-line diagram;
- Transformer data sheet;
- Site condition data;
- Applicable standards;
- Required test schedule;
- Accessory list;
- SCADA signal list;
- Transportation limits;
- Required project documents.
These details allow the electrical, mechanical, cooling, testing, and delivery scope to be reviewed together.
Conclusion
An oil-immersed power transformer for a Saudi Arabia solar substation must be designed around the complete photovoltaic generation and grid-connection system.
Plant output, reactive power duty, collection voltage, grid voltage, vector group, impedance, neutral treatment, tap range, insulation level, cooling stages, temperature rise, short-circuit strength, harmonic data, protection accessories, SCADA signals, test requirements, and transportation conditions all influence the final transformer configuration.
Saudi Arabia’s outdoor environment also requires careful attention to high ambient temperature, direct solar radiation, dust, sand, possible coastal contamination, and maintenance access.
HONLE manufactures oil-immersed distribution transformers, 35kV oil-immersed power transformers, and 110kV oil-immersed power transformers for project-based electrical applications. For solar substation inquiries, our engineering and production work follows the confirmed transformer data sheet, approved drawings, factory test schedule, documentation requirements, and delivery conditions.
Providing the single-line diagram, technical data sheet, site conditions, applicable standards, required accessories, test scope, and transport information at the beginning of the project helps us prepare a transformer proposal that matches the actual solar substation.