Ports and container terminals are becoming increasingly electrified.
Ship-to-shore cranes, yard cranes, reefer container racks, pumps, lighting, workshops, gate systems, office buildings, charging equipment, and shore power facilities can all depend on the terminal electrical network. Unlike a conventional commercial building, these loads do not operate with the same pattern.
Some loads remain relatively stable for hours. Others rise and fall within seconds as cranes accelerate, lift, lower, and move containers. New reefer racks or electrified handling equipment can also increase demand significantly after the terminal has already entered operation.
For this reason, selecting a power transformer for a port or container terminal requires more than adding the rated power of every connected device.
The transformer needs to match the terminal’s actual load profile, incoming network voltage, peak demand, harmonic conditions, short-circuit requirements, installation environment, redundancy strategy, and future expansion plan.
Start With the Terminal Load Structure
The first step is to divide the terminal into major electrical load groups.
A typical container terminal may contain:
- Ship-to-shore cranes
- Rail-mounted or rubber-tyred gantry cranes
- Reefer container racks
- Pumps and drainage systems
- Workshops and maintenance facilities
- Terminal lighting
- Administration and gate buildings
- Conveyors or cargo-handling equipment
- Electric vehicle and equipment charging
- Shore-to-ship power systems
These loads behave differently.
A power transformer supplying several cranes faces a different operating pattern from a transformer mainly supplying refrigerated containers. A transformer serving office buildings and lighting may also have a very different load profile from the main industrial distribution transformer.
This is why large terminals often benefit from dividing the electrical system into several distribution zones instead of supplying every load from one very large transformer.
For example, the terminal electrical design may separate:
| Distribution Area | Main Load Characteristic |
| Quay area | Large cranes, highly variable demand |
| Container yard | Gantry cranes and handling equipment |
| Reefer area | Long-duration, relatively continuous load |
| Buildings | Lighting, HVAC, offices and control systems |
| Maintenance area | Motors, tools, compressors and workshops |
| Shore power area | Large berth-specific electrical demand |
The power transformer should therefore be selected according to the load connected to its particular distribution section rather than only the total installed capacity of the entire port.
Why Do Crane Loads Matter So Much?
Container cranes can create some of the most demanding electrical conditions in a terminal.
A ship-to-shore crane repeatedly performs operations such as:
- Hoisting containers
- Lowering containers
- Trolley travel
- Gantry travel
- Acceleration
- Deceleration
- Braking
This means electrical demand can change rapidly.
Unlike a pump or ventilation fan operating near a stable point, crane equipment can produce short periods of high power demand followed by much lower demand.
Modern crane drives commonly use variable-frequency control, so the transformer and upstream distribution system must also account for power-electronic loads.
Do not size the transformer from crane nameplates alone
Suppose a terminal has several cranes.
Adding the rated power of every crane together assumes all drives reach their maximum electrical demand at exactly the same time. In many terminals, that may substantially overstate continuous demand.
However, using only the average terminal load can create the opposite problem.
The transformer still needs to tolerate realistic simultaneous crane operations and repeated load fluctuations without excessive voltage variation or thermal stress.
Transformer sizing should therefore consider:
- Number of cranes
- Maximum crane power
- Expected simultaneous operation
- Operating cycle
- Peak duration
- VFD characteristics
- Regenerative operation
- Other loads on the same bus
The load curve is usually more useful than a single total kW figure.
For an existing terminal expansion project, measured operating data can provide valuable information about actual peak demand and load variation.
Calculate Transformer Capacity From Simultaneous Demand
After identifying the major loads, the next step is estimating the maximum credible simultaneous demand.
Consider a simplified example for one terminal distribution zone:
| Load Group | Expected Peak Demand |
| Crane operations | 3,000kW |
| Reefer racks | 1,200kW |
| Yard equipment | 600kW |
| Pumps and auxiliary systems | 250kW |
| Lighting and buildings | 300kW |
| Total active demand | 5,350kW |
If the overall operating power factor at this condition is approximately 0.90:
Apparent power = 5,350kW ÷ 0.90 ≈ 5,944kVA
The design requirement is therefore approximately 5.94MVA before considering factors such as:
- Future terminal expansion
- Transformer loading target
- Redundancy
- Ambient conditions
- Harmonic heating
- Abnormal operating scenarios
This example does not mean that every port with these loads should simply purchase a 6MVA power transformer.
A project may instead use two transformers supplying different sections, or two parallel units where redundancy and maintenance requirements justify that arrangement.
Installed capacity is not the same as simultaneous demand
A terminal could have 10MW of connected equipment without ever drawing 10MW simultaneously.
Conversely, a terminal with an average load of only 4MW may still experience recurring peaks well above that level.
The transformer needs to be designed around the actual operating scenario.
This is particularly important for container terminals because equipment utilization changes with:
- Vessel schedules
- Cargo volume
- Reefer occupancy
- Number of active cranes
- Day and night shifts
- Seasonal demand
- Terminal expansion
A realistic operating model reduces the risk of both undersizing and unnecessary oversizing.
Check Harmonics and Fast Load Changes From Power Electronics
Terminal electrification increasingly depends on power electronics.
Crane drives, VFD-controlled motors, charging systems, UPS equipment, frequency converters, and other electronic loads can introduce harmonic currents into the electrical system.
These harmonics may increase losses and heating in transformers and cables.
For the power transformer, the engineering review should consider:
- Percentage of nonlinear load
- Harmonic spectrum where available
- Expected RMS current
- Transformer temperature rise
- Neutral loading where relevant
- Cable and switchgear capability
- Power-factor correction equipment
- Harmonic filters if required
The objective is not simply to specify a larger transformer whenever VFDs are present.
The manufacturer and electrical designer should understand how much of the connected load is power-electronic and whether the harmonic conditions are significant enough to affect transformer design.
Crane regeneration also affects the electrical system
When a crane lowers a heavy container or decelerates, some drive systems can regenerate electrical energy.
Depending on the system design, this energy may be:
- Returned to the terminal electrical network
- Shared with other crane drives
- Stored
- Dissipated through braking equipment
This makes the crane load more dynamic than a conventional motor load.
The power transformer should therefore be considered as part of the complete electrical distribution system rather than as an isolated piece of equipment.
Treat Reefer Container Loads Differently From Crane Loads
Refrigerated containers create another major electrical demand in modern container terminals.
A reefer container needs electricity to maintain the required cargo temperature while stored in the terminal.
A large terminal may have hundreds or thousands of reefer connection points.
The electrical behavior of this area differs significantly from crane operations.
Crane demand tends to fluctuate rapidly. Reefer loads are generally more continuous, although individual refrigeration compressors cycle according to container temperature and ambient conditions.
When selecting the power transformer supplying reefer racks, engineers should consider:
- Number of reefer outlets
- Expected occupancy
- Maximum simultaneous reefer demand
- Seasonal temperature
- Expansion of reefer capacity
- Cable length
- Distribution voltage
- Backup strategy
For example, a terminal may currently operate 400 reefer positions but plan to expand to 600 positions.
If the transformer is selected only around current occupancy, the future rack expansion may require premature transformer replacement or another substation.
However, sizing the transformer for every future reefer outlet operating at maximum power simultaneously may also create unnecessary spare capacity.
The transformer capacity should follow a realistic development plan.
Reefer areas can justify separate transformer capacity
Separating reefer distribution from crane distribution can provide several advantages in appropriate projects.
It may simplify:
- Load forecasting
- Protection coordination
- Expansion
- Energy monitoring
- Maintenance
- Fault isolation
It also prevents large crane load changes from unnecessarily affecting sensitive refrigeration distribution.
Whether this separation is required depends on terminal size and electrical architecture.
How Should Shore Power Affect Transformer Selection?
Ports that provide shore-to-ship electricity introduce another large load into the power system.
When a vessel connects to shore power, onboard auxiliary generators can be shut down and the vessel receives electricity from the land-based electrical network.
This can significantly increase the terminal’s electrical demand.
A shore power system may require:
- Medium-voltage incoming power
- Transformer equipment
- Switchgear
- Protection
- Frequency conversion
- Cable management
- Berth connection equipment
The electrical characteristics of the vessel may not be identical to the local utility network.
Voltage and frequency requirements therefore need to be matched by the complete shore power system.
Do not simply add shore power to an existing terminal transformer
A terminal transformer originally selected for cranes, reefers, lighting, and buildings may not have sufficient spare capacity for a major shore power installation.
The project should determine:
- Maximum vessel demand
- Number of simultaneous vessel connections
- Shore power voltage
- Local utility capacity
- Existing transformer loading
- Frequency conversion requirements
- Redundancy strategy
For large projects, shore power may be better treated as a dedicated electrical distribution section rather than simply another feeder from the existing transformer.
This also allows later expansion to additional berths to be planned more clearly.
A port that expects substantial future electrification should consider shore power requirements when defining the upstream substation even if not every berth is equipped during the first construction phase.
Select the Right Voltage, Impedance, and Distribution Architecture
Large container terminals can cover a substantial physical area.
Supplying high-power equipment over long distances at low voltage would require high current and large cable cross-sections.
For this reason, medium-voltage distribution is often important within larger industrial and infrastructure projects.
The exact voltage arrangement depends on the local utility supply and project design.
Possible incoming network voltages may include:
- 10kV
- 11kV
- 20kV
- 22kV
- 33kV
- 35kV
Larger projects may also connect to a higher-voltage utility network before stepping down to the terminal medium-voltage distribution system.
HONLE’s transformer portfolio includes distribution transformers as well as larger oil-immersed power transformer solutions for higher-voltage projects.
Transformer impedance needs coordination
Percentage impedance affects both short-circuit current and voltage performance.
Lower impedance can help reduce voltage drop under sudden load changes, but it also increases prospective short-circuit current.
Higher impedance can limit fault current but may increase voltage variation during large load changes.
The transformer impedance should therefore be coordinated with:
- Utility short-circuit level
- Switchgear rating
- Crane load changes
- Cable impedance
- Protection settings
- Parallel transformer operation
- Acceptable voltage variation
Selecting a transformer only by voltage ratio and MVA can overlook these system-level requirements.
Oil-Immersed or Dry-Type Power Transformer for a Port?
Both oil-immersed and dry-type transformers can be used in port infrastructure.
The choice mainly depends on installation location, voltage level, capacity, environmental conditions, fire requirements, cooling, and maintenance strategy.
Oil-immersed power transformers
Oil-immersed transformers are commonly considered for:
- Outdoor substations
- Main terminal substations
- High-capacity distribution points
- Utility interfaces
- Large infrastructure projects
Transformer oil provides electrical insulation and heat transfer, making oil-immersed construction suitable for many continuous-duty outdoor and industrial applications.
For a large port receiving medium- or high-voltage utility power, an oil-immersed power transformer may therefore form part of the main substation.
Dry-type transformers
Dry-type transformers can be suitable for:
- Indoor electrical rooms
- Terminal buildings
- Workshops
- Enclosed substations
- Locations where an oil-free installation is preferred
Because dry-type transformers depend primarily on air for cooling, the electrical room must provide sufficient ventilation.
A small enclosed room near the quay should not be selected without checking transformer heat dissipation.
One port can use both transformer types
There is no reason every transformer across a large terminal must use the same construction.
For example:
| Location | Possible Transformer Direction |
| Main outdoor substation | Oil-immersed |
| Crane distribution substation | Project-dependent |
| Reefer substation | Project-dependent |
| Indoor terminal building | Dry-type |
| Maintenance workshop | Dry-type or oil-immersed |
| Utility interface | Often oil-immersed |
The final choice should follow the actual electrical and installation requirements.
Coastal Conditions Need Special Attention
Ports have another characteristic that ordinary inland industrial plants may not face to the same degree: the marine environment.
Transformer equipment may be exposed to:
- High humidity
- Salt-laden air
- Wind
- Rain
- High solar radiation
- Large temperature changes
- Industrial dust and pollution
Salt contamination and moisture can affect external insulation, metal surfaces, terminals, and auxiliary equipment over time.
For outdoor transformers installed near the coastline, the project should therefore review:
- Corrosion protection
- Surface coating
- Enclosure materials
- Outdoor insulation
- Bushing configuration
- Cable boxes
- Sealing
- Terminal protection
- Drainage
- Foundation height
- Maintenance access
The transformer location also matters.
Equipment installed directly beside the quay may experience more severe salt exposure than equipment located further inland inside a protected substation.
Cooling still has to match the climate
Many international ports operate in hot and humid environments.
A transformer working close to rated load in high ambient temperature has less thermal margin than the same power transformer operating in a mild climate.
Cooling design should therefore be matched to:
- Rated capacity
- Expected loading
- Ambient temperature
- Transformer losses
- Installation arrangement
- Required temperature rise
For larger oil-immersed transformers, the required cooling arrangement should be established as part of the transformer design.
Plan the Transformer Around Terminal Expansion
Ports rarely remain electrically unchanged for their entire service life.
A terminal may later add:
- More ship-to-shore cranes
- Electrified yard cranes
- Additional reefer racks
- Electric terminal tractors
- Battery charging stations
- New warehouses
- Expanded rail facilities
- Additional shore power berths
The transformer strategy should therefore consider future phases from the beginning.
This does not mean installing all future transformer capacity immediately.
Several approaches are possible.
Reserve capacity in the first transformer
This works when future growth is moderate and reasonably predictable.
Install transformers in parallel
Parallel units may support capacity growth and redundancy, provided their electrical characteristics and protection systems are suitable for parallel operation.
Build multiple substations
For a large terminal, distributing transformer capacity across crane, reefer, building, charging, and shore power areas can make future expansion more flexible.
Reserve space for future transformers
Sometimes the most practical approach is installing only the required first-stage transformer while reserving foundations, switchgear positions, cable routes, and physical space for another unit.
This avoids operating an unnecessarily oversized transformer for many years while still protecting the terminal’s expansion path.
HONLE supplies both dry-type and oil-immersed power transformers for industrial and infrastructure projects. Transformer configuration can be matched to required capacity, voltage ratio, impedance, cooling, installation environment, terminal arrangement, and other project-specific electrical requirements.
For a port or container terminal, the correct power transformer should ultimately match the way the terminal actually operates—not just the sum of equipment nameplates.
A well-planned transformer system should support today’s crane and reefer loads while leaving a practical path for tomorrow’s electrified terminal.
FAQ
How large should a power transformer be for a container terminal?
There is no fixed transformer capacity for a container terminal. The required rating depends on crane demand, reefer loads, buildings, pumps, charging equipment, shore power, simultaneous operation, power factor, redundancy, and future expansion. Large terminals may use several transformers rather than one central unit.
Can cranes and reefer racks use the same transformer?
Yes, provided the transformer and distribution system are designed for the combined load. However, large terminals may separate crane and reefer distribution because their operating characteristics are different. Crane demand can change rapidly, while reefer loads are generally more continuous.
Do crane VFDs affect power transformer selection?
They can. A high proportion of VFD and power-electronic loads may introduce harmonics and additional transformer heating. The project should evaluate the nonlinear load percentage, harmonic conditions, transformer losses, and expected operating current.
Is an oil-immersed transformer suitable for a port?
Yes. Oil-immersed transformers are commonly suitable for outdoor substations and high-capacity infrastructure distribution. Port installations should additionally consider humidity, salt contamination, corrosion protection, cooling, foundation conditions, and maintenance access.
Can dry-type transformers be used in container terminals?
Yes. Dry-type transformers can be used in indoor electrical rooms, terminal buildings, workshops, and other locations where an oil-free design is preferred. Ventilation, ambient temperature, enclosure requirements, and maintenance space still need to be considered.
Does shore power require a separate transformer?
It depends on the shore power architecture and existing terminal distribution system. Large shore power loads may justify a dedicated transformer or substation, particularly where voltage transformation, electrical separation, frequency conversion, multiple berths, or future expansion are involved.
Should a port install one large transformer or several smaller transformers?
Both arrangements are possible. A single large transformer can simplify some parts of the system, while multiple transformers can divide crane, reefer, building, or shore power loads and may improve expansion flexibility and fault isolation. The decision should be based on terminal layout, redundancy requirements, load distribution, cable distances, maintenance strategy, and future development.
Can another power transformer be added when the terminal expands?
Yes. Many terminal electrical systems can be designed for staged expansion. Reserving substation space, switchgear positions, cable routes, and suitable protection arrangements during the initial project can make it easier to add another transformer when new cranes, reefer racks, charging equipment, or shore power facilities are commissioned.