Shore Power (Cold Ironing) Transformer: How to Size a 6.6/11 kV Port Connection, Why 50 Hz and 60 Hz Ships Change the Design, and What IEC/IEEE 80005-1 Requires

The answer first: a port shore connection needs a purpose-built shore power (cold ironing) transformer, not a spare distribution unit — because the berth load is harmonic-rich and cyclic, and it has to be delivered at 6.6 kV or 11 kV across a 50 Hz or 60 Hz interface

A shore power transformer steps the port's medium-voltage grid — typically 33 kV, 22 kV, 20 kV or 11 kV — down to the voltage the ship's shore connection point actually expects: normally 6.6 kV or 11 kV for high-voltage shore connection (HVSC), and 440 V or 690 V for smaller craft supplied under low-voltage shore connection. It is sized on the ship's berth load — hotel load, reefer plugs, cargo and ballast pumps — and not on the ship's installed generator capacity, because a berthed ship draws only a fraction of its sea-going load. It must be a harmonic-rated unit, because the current it delivers is distorted by reefer compressor inverters, thyristor frequency converters and switch-mode power supplies on board. And it has to respect two hard rules that decide the whole installation: a transformer changes voltage, not frequency (50 Hz shore into a 60 Hz ship is a converter problem, never a transformer problem), and its secondary must satisfy the IEC/IEEE 80005-1 shore-to-ship interface, including the equipotential bonding conductor and insulation monitoring. Specify the unit for that duty and it runs quietly for twenty years; order an ordinary distribution transformer and the port inherits hot windings, nuisance trips and a failed power-quality acceptance at handover.

Key takeaways

• Size on berth load, not on the ship's generators. Hotel load plus reefer plugs plus pumps, converted to kVA at a realistic power factor and then derated — the same load-first logic as any transformer sizing and budget calculation.
• A transformer cannot turn 50 Hz into 60 Hz. Flux is proportional to voltage over frequency, so the same unit cannot simply be re-rated across frequencies; if shore and ship frequency differ, a frequency converter must be in someone's scope. See 50 Hz vs 60 Hz transformer design.
• Reefer plugs and thyristor loads set the harmonic rating. Eddy loss rises with the square of harmonic order, so a standard unit on cold-ironing duty overheats. Specify a K-factor or a documented derate and read the mechanism in why harmonic current overheats transformers.
• IEC/IEEE 80005-1 governs the interface, not just the voltage. Equipotential bonding before energization, insulation monitoring, sequenced connection and cable management all belong to the shore installation the transformer sits inside.
• Shore supplies run mostly at light load, so efficiency is an economics question. A port transformer spends most hours at a small fraction of rating, so no-load loss dominates its energy cost — efficiency grade and total cost of ownership matter more than first price.

What is shore power (cold ironing), and why are ports installing it now?

Shore power — also called cold ironing, alternative maritime power (AMP) or on-shore power supply (OPS) — means feeding a berthed ship from the port's electrical grid so that its auxiliary diesel engines can be shut down. A ship at the quay still needs electricity for lighting, HVAC, galley, fresh water and sewage systems, pumps, cargo systems and reefer containers: a few hundred kW for a small coaster, several MVA for a container ship or a cruise vessel. Running auxiliary engines at the quay burns marine fuel in the middle of a city and emits nitrogen oxides, sulphur oxides, particulate matter and CO₂ metres from the terminal gate, which is why regulators now require the connection instead of merely encouraging it.

Three regulatory drivers shape cold-ironing projects in 2026:

• EU — Regulation (EU) 2023/1804 (AFIR): shore-side electricity supply must be deployed at TEN-T core maritime ports by the end of 2029 and at comprehensive ports by the end of 2030, which is driving tenders for shore installations across European terminals.
• EU — Directive (EU) 2023/959 (revised EU ETS): from 1 January 2030, container and passenger ships at berth in an EU port must use on-shore power supply for all of their electricity demand while moored, with a defined exemption route — an obligation on the ship that creates guaranteed demand for shore-side capacity.
• USA — CARB At-Berth Regulation (California, 2007 and amended 2020): ocean-going vessels calling at California ports must control at-berth emissions, in practice by connecting to shore power or an approved equivalent, with the vessel categories and phase-in dates expanded over time.

Beyond these, China, Korea, Japan, Singapore and several Gulf ports operate their own shore-power programmes and tariff incentives. The commercial consequence for a transformer factory is straightforward: OPS is now procured as a complete shore-side package — MV switchgear, transformer, optional frequency converter, cable management system and controls — and the transformer is the component that has to match both ends: the port grid upstream and the ship interface at the quay. That is also why cold ironing belongs to the same family of purpose-built project transformers as EV charging infrastructure, battery storage and data centre power: the load profile, not the voltage alone, defines the unit.

Where does the transformer sit in a shore power installation?

A cold-ironing installation is a chain, and every link constrains the transformer:

Two configuration choices are made at design stage. First, where the frequency conversion happens: on shore (one converter serves every ship that calls) or on board (each ship brings its own). Second, whether the shore transformer is needed at all: some ships carry their own shore-connection transformer, in which case the port delivers HV directly and only cable management and switchgear are required. Confirm which case applies before quoting — the difference is an entire unit.

The isolating function is worth stating explicitly. A transformer with a delta primary and a star secondary, neutral brought out — a Dyn11 vector group — does three useful things at a quay: it matches voltage, it decouples the port's earthed (TN) system from the ship's insulated (IT) system so that a single earth fault does not circulate through the hull and the bonding conductor, and its delta winding traps triplen harmonics (3rd, 9th, 15th) so they do not reach the port grid. Those are engineering reasons to specify a vector group, not conventions to be copied.

How do you size a shore power transformer? Six steps from berth load to nameplate

1. Collect the berth load schedule. Ask the operator or terminal for the ship's shore-consumption figure (hotel load: HVAC, lighting, galley, fresh water, sewage, pumps) plus any cargo-system and reefer load. Where no figure exists, estimate from the auxiliary generator rating at roughly 60–80% for a large vessel in a hot climate — an industry-experience rule, not a standard.
2. Count the reefer plugs. At container terminals, reefers often dominate the shore load: each reefer container draws roughly 4.5–6.5 kW (industry experience, ambient and duty dependent), so 500 plugs represent 2.25–3.25 MW of connected load before diversity. Apply the terminal's own diversity factor (commonly 0.7–0.9) rather than 1.0.
3. Convert to kVA at a realistic power factor. S = P / PF with PF around 0.85–0.90 for a mixed hotel and pump load. Transformers are rated in kVA, so an under-estimated PF is an under-sized unit.
4. Apply the berth duty, not the sea-going peak. Bow thrusters and main propulsion are off at the quay, which is why the berth load is far below the ship's generator rating. But the shore supply must still ride through the worst berth condition — full HVAC plus all reefers plus simultaneous pump starts — so check the load factor rather than averaging it: load factor and overload capacity decide how much margin is legitimate.
5. Derate for environment and harmonics. A quay is a hot, humid, salt-laden place: correct for 40–45 °C ambient, solar gain and the harmonic content discussed below. Cooling class and temperature rise are chosen here — see cooling methods and temperature rise.
6. Select the next standard rating and check it against the port's fault level. A 3 MVA berth load typically lands on a 3.15–4 MVA unit (industry practice), but the upstream short-circuit level and protection settings must agree: a low-impedance shore transformer contributes more fault current to the port MV bus. Run the short-circuit current calculation before freezing the impedance.

The working formula is simply:

S_required (kVA) = ( P_hotel + P_reefer x k_reefer + P_cargo ) / ( PF x k_harm )

where k_reefer is the terminal diversity factor, PF the displacement power factor of the berth load and k_harm the harmonic derating factor (below 1.0) taken from IEEE C57.110 for the expected current spectrum. The same load-first logic — and the same refusal to size from connected capacity — is what the transformer selection guide applies to industrial projects, and the engineer's calculator for the rest of the system sits in the power system engineering toolbox.

Typical orders of magnitude, given as industry experience to help you sanity-check a bid rather than as standard values:

50 Hz or 60 Hz? The frequency trap that ruins shore power projects

This is the single most expensive misunderstanding in the cold-ironing market. A transformer changes voltage, not frequency. If the port grid supplies 50 Hz and the ship's electrical system is 60 Hz — the common case in Europe, Asia and Africa, because most ocean-going ships are built around 60 Hz — then no transformer ratio, tap position or vector group can bridge the gap. A frequency converter (static, IGBT or thyristor based, or in older installations a rotary machine) must be in the scope, either on shore or on board.

The physics behind it is the voltage-per-hertz rule. Core flux is proportional to V/f, so a transformer designed for 6.6 kV at 60 Hz applied at 6.6 kV and 50 Hz would run at about 120% of its design flux: the core saturates, magnetising current and no-load loss climb, noise rises and the winding overheats. The only way to keep the same unit healthy at 50 Hz is to reduce the voltage to roughly 0.833 of design — 6.6 kV becomes about 5.5 kV — which no longer matches the ship. Conversely, a 50 Hz-designed transformer operated at 60 Hz has lower flux and is thermally safe, so a 50/60 Hz dual-rated unit is a legitimate specification; a "60 Hz only" unit is not. The full mechanism, including what changes in loss, noise and impedance, is set out in 50 Hz vs 60 Hz transformer design.

One more specification consequence: if the transformer is fed from a converter rather than directly from the port grid, its primary sees a switched, harmonic-rich waveform and it becomes a converter-duty unit in the sense of IEC 61378-1, with a harmonic loss factor designed in rather than assumed away — the same discipline that green hydrogen rectifier transformers and solar PV and inverter step-up units demand. Say clearly on the datasheet whether the unit is grid-fed or converter-fed; the two designs are not interchangeable.

Why harmonics, not kVA alone, decide the shore power transformer specification

The current drawn through a shore connection is far from sinusoidal. Reefer containers run inverter-driven compressors; the ship's own conversion equipment may use a thyristor bridge; the galley, lighting and electronics present switch-mode power supplies. The result is a current spectrum with meaningful 5th, 7th, 11th and 13th harmonic components, plus triplens from single-phase loads. Two consequences follow for the transformer:

• Winding eddy-current loss rises with the square of harmonic order. Fifth-harmonic current at 30% of fundamental produces roughly 0.3² x 5² = 225% of the fundamental eddy loss it would cause — the transformer's hottest spot moves from the winding surface inward and insulation life is consumed at a rate the nameplate temperature rise never reflected. This is exactly the mechanism described in why harmonic currents overheat transformers.
• Power quality at the port's point of common coupling is the port authority's problem, and the transformer is where it is usually solved. Harmonic limits are commonly applied per IEEE 519 at the interface with the public grid; the transformer's delta winding blocks triplens, and a K-rated or documented-derate design keeps the unit alive while the filter or converter strategy handles the rest.

Practically, the specification should state one of three things: a K-factor rating (K-4, K-9 or K-13 are the usual cold-ironing choices), a documented derating calculation to IEEE C57.110 for the expected spectrum, or a converter-duty design to IEC 61378-1 when the unit sits behind a converter. Add low flux density, a foil or multi-parallel low-voltage winding and adequate cooling, and the unit will carry the duty; omit them and the first summer of reefer traffic will show it. For oil-immersed candidates, the general requirements of IEEE C57.12.00 sit alongside the IEC 60076 series. Energy performance deserves a separate line in the evaluation: because a port transformer idles for most of the day and only loads up when a ship calls, no-load loss dominates its lifetime energy cost — an argument for a better loss grade or an amorphous core, and definitely an argument for a total cost of ownership comparison rather than a lowest-price tender.

Impedance, taps and the cable run: three numbers that interact at the quay

Shore connections are long. The cable management system typically runs 100–400 m from the shore substation to the ship, and in large terminals it can approach a kilometre. That changes the design conversation:

• Voltage drop. A long, heavily loaded 6.6 kV cable run loses voltage; the port installation is normally engineered to keep total drop in the low single digits (3–5% is typical industry practice). A low-impedance transformer helps voltage regulation but raises fault current at the quay.
• Short-circuit impedance (uk%). Common cold-ironing practice sits in the 5–8% band. Raising uk% limits the fault current the shore supply contributes to the port bus and to the ship's switchboard, at the cost of worse voltage regulation and higher load loss. Lowering it does the reverse. That trade-off is quantified in the short-circuit current calculation and in voltage regulation — decide it, do not inherit it.
• Taps. Off-circuit taps of plus or minus 2 x 2.5% cover the ordinary variation in port grid voltage, and they must be reconciled with the ship's own transformer tap position. Unless the port asks for dynamic voltage control, an off-load tap changer is enough — and cheaper to maintain. If two shore supplies feed one terminal bus, revisit the conditions for parallel operation so circulating current does not eat the harmonic margin.

One further check is often forgotten: the shore transformer's duties are rated at one frequency and one voltage, but its customer is whoever calls next. Where a terminal serves a mixed fleet, either standardise the connection voltage and put frequency conversion on shore, or accept a lower utilisation of the installed unit and say so in the tender documents.

What changes in a salt-air coastal environment?

A quay is one of the harsher places to install a transformer: salt aerosol, humidity that cycles daily, high ambient temperature, solar gain on a steel enclosure and occasional wave splash or washdown water. Four specification responses are normal in shore-power packages:

• Corrosion category. Outdoor coastal equipment is specified to corrosion category C5-M in the ISO 12944 system of classification, with a defined paint system and dry-film thickness rather than "marine paint". Stainless or hot-dip-galvanised fasteners, and corrosion-protected tanks and radiators, follow from it.
• Enclosure and ingress protection. Verify the ingress protection class to IEC 60529 that the location really needs — outdoor units commonly IP54 or IP55, and IP66 where hosing or deck washdown is possible. An indoor-rated unit in an outdoor enclosure is a common cost-cutting mistake.
• Condensation control. Daily temperature cycling inside an unheated enclosure drives moisture into the insulation. Anti-condensation heaters, breathing/expansion control and, for oil-immersed units, a sealed or conservator arrangement chosen deliberately, all belong in the datasheet: compare the alternatives in oil-immersed vs dry-type selection and check insulation limits in insulation class and temperature rise.
• Ambient, noise and fire. Design ambient of 40–45 degrees Celsius with solar gain should be stated, since it directly cuts the usable rating. Berths are also close to housing, so night-time noise limits and the fire-separation rules that apply to the enclosure should be fixed at design stage, not after the first complaint.

Physical logistics deserve a line too: the unit must survive its journey to a port and be lifted onto a quay within the load limits and access routes of the terminal — covered in transportation and installation and, before shipment, in the pre-shipment inspection checklist.

What does IEC/IEEE 80005-1 require on the shore side?

IEC/IEEE 80005-1 is the standard for high-voltage shore connection systems and defines the 6.6 kV and 11 kV shore-to-ship interface at both 50 Hz and 60 Hz. Its requirements shape the shore installation the transformer belongs to:

• Equipotential bonding before energization. The ship's hull must be bonded to shore earth and that bond verified before the power conductors are energized, which is why the cable management system carries a dedicated bonding conductor and why the connection is an interlocked sequence rather than a plug-and-play cable.
• Insulation monitoring and residual-current protection. The shore connection is monitored for insulation faults, and the protection scheme is coordinated with the ship's own protection so that an earth fault on board does not circulate through the shore supply.
• Data communication for monitoring and control. The safety interlock between shore and ship is carried as a communication sequence with defined signals — the subject of IEC/IEEE 80005-2 — so the transformer's control and monitoring interfaces must be compatible with the shore control cabinet.
• Low-voltage shore connection for smaller craft. Supplies up to 1 kV, typically for ferries, fishing vessels and small craft, are covered by the low-voltage part of the same standard family (IEC/IEEE 80005-3), where a voltage-matching transformer may not be required at all.

The transformer itself follows IEC 60076-1 (general), IEC 60076-2 (temperature rise), IEC 60076-3 (insulation levels and dielectric tests) and IEC 60076-5 (ability to withstand short circuit), or IEC 60076-11 for dry-type construction. Shipboard electrical installations, if the unit ever sits on the vessel side of the interface, follow IEC 60092. Classification society rules (for example DNV, ABS, Lloyd's Register or ClassNK) can add requirements when the transformer is part of a shipboard system, and port authorities frequently impose their own protection and metering standards. The practical output for a manufacturer is a datasheet that states the applicable standard list explicitly, provides an earthing/bonding terminal at both ends, and offers the monitoring interfaces the shore control system needs.

What must the shore power transformer datasheet specify?

Reading the nameplate that results is itself a skill: the fields above appear as rated voltage, rated current, impedance, vector group and cooling class, and their meanings are unpacked in how to read a transformer nameplate.

Which tests and commissioning checks apply?

Factory testing follows the standard power-transformer pattern plus the harmonic-specific extras the duty justifies. Routine tests per IEC 60076-1 include winding resistance, ratio and phase relation, short-circuit impedance and load loss, no-load loss and current, insulation resistance and dielectric tests; oil-immersed units additionally need oil breakdown voltage, moisture and a dissolved-gas baseline, plus tap-changer operation checks. Type tests — temperature rise, lightning impulse and sound level where specified — are the ones to confirm in the contract if the design is being pushed. Where the unit is harmonic-rated or converter-fed, a harmonic loss measurement or a documented harmonic-loss calculation belongs in the test schedule, and zero-sequence impedance is worth having where the delta winding is relied upon to block triplens.

At site, the checks that actually prevent trouble are: insulation resistance on cables before and after pulling; phase rotation and polarity; continuity of the equipotential bonding conductor through the cable management system; a full test of the connection interlock sequence (ideally with the ship or a simulator) so the safety chain is proven before the first real call; protection relay settings agreed with the port; and a load and harmonic measurement on the first connection, which is the only way to confirm that the specified harmonic duty was the real one. The full sequence is listed in the commissioning tests checklist, and the protection hardware that supports it in transformer protection devices.

Five specification mistakes that ruin shore power transformers

1. Sizing from the ship's installed generator capacity. It looks conservative and is actually wrong in both directions: an oversized unit burns no-load loss every idle hour, while a unit sized on an average instead of the worst berth condition saturates in the reefer season. Size on load, then check.
2. Assuming the transformer will match shore frequency to ship frequency. It will not, and the converter is the largest single line item someone has to pay for. Put it in the scope discussion on day one.
3. Ordering a standard distribution transformer for harmonic duty. Reefer inverters and thyristor converters can push a design past its hot-spot limit within a season. Specify the harmonic rating explicitly.
4. Ignoring the interaction between impedance, taps and the cable run. A terminal that loses several percent of voltage along 400 m of cable, on a transformer at the wrong tap, hands the ship less than 6.6 kV and the interlock does not care whose fault that is.
5. Treating the quay as an ordinary switch room. Indoor enclosure, standard paint, no anti-condensation heater and mild-steel hardware will be visibly corroding within two years and will fail insulation tests within ten.

A final commercial point: in cold ironing, as in most civic infrastructure, the transformer is bought once and paid for continuously through losses, maintenance and replacement risk. Comparing a K-13 unit with a documented harmonic derate against the cheapest compliant offer on first price alone is the mistake that the total cost of ownership calculation exists to prevent, and the terms that will decide the argument after delivery — warranty, spares, service — are the ones covered in transformer warranty terms. For EU terminal projects, the CE marking evidence chain is the CE certification guide.

Sources / 资料来源

• Source: IEC/IEEE 80005-1 — Utility connections in port, Part 1: High voltage shore connection (HVSC) systems — General requirements
• Source: IEC/IEEE 80005-2 — Utility connections in port, Part 2: High and low voltage shore connection systems — Data communication for monitoring and control
• Source: IEC/IEEE 80005-3 — Utility connections in port, Part 3: Low voltage shore connection (LVSC) systems — General requirements
• Source: IEC 60076-1 / -2 / -3 / -5 — Power transformers (general, temperature rise, insulation levels and dielectric tests, ability to withstand short circuit)
• Source: IEC 60076-11 — Power transformers, Part 11: Dry-type transformers
• Source: IEC 61378-1 — Converter transformers, Part 1: Transformers for industrial applications
• Source: IEC 60092 series — Electrical installations in ships
• Source: IEEE C57.110 — Recommended practice for establishing liquid-filled and dry-type transformer capability when supplying nonsinusoidal load currents
• Source: IEEE C57.12.00 — General requirements for liquid-immersed distribution, power and regulating transformers
• Source: IEEE 519-2022 — Recommended practice and requirements for harmonic control in electric power systems
• Source: IEC 60529 — Degrees of protection provided by enclosures (IP code)
• Source: ISO 12944 — Corrosion protection of steel structures by protective paint systems
• Source: Regulation (EU) 2023/1804 — Alternative Fuels Infrastructure Regulation (shore-side electricity supply at TEN-T ports)
• Source: Directive (EU) 2023/959 amending Directive 2003/87/EC — EU Emissions Trading System, on-shore power supply obligation for container and passenger ships at berth in EU ports from 2030
• Source: California Air Resources Board (CARB) — At-Berth Regulation, 2007 and 2020 amendments (control of emissions from ocean-going vessels while at berth)
• Source: IMO MARPOL Annex VI — Regulations for the prevention of air pollution from ships (shore-side electricity as an emission-reduction measure)
• Source: Classification society shore connection and shipboard electrical rules (DNV, ABS, Lloyd's Register, ClassNK) — 行业经验值
• Source: 中国交通运输部 — 港口岸电 (port shore power) promotion policy — 行业经验值
• Source: QDTB Engineering Team — industry experience / 行业经验值 for typical berth-load bands by vessel type, reefer plug loading, shore supply rating bands, cable run lengths, impedance and tap practice, harmonic derating assumptions and design ambient values