Industries
Transformers and switchgear for solar, wind and battery storage connections
Step up transformers, medium voltage switchgear and substations for solar, wind and battery storage sites. The transformer is sized on apparent power, so the plant can supply the reactive power your grid code requires.
The equipment chain
- 01InvertersConvert the direct current of panels or batteries to alternating current at low voltage. Their output voltage sets the transformer's low voltage winding.
- 02TransformerSteps the inverter output up to the network voltage, sized on apparent power so the plant can deliver the reactive power the grid code asks for.
- 03MV switchgearCollects the transformer feeders and connects the site. The protection here is often the interface protection the network operator requires.
- 04GridThe connection point the operator offers. Its voltage and capacity, and on a battery site the import as well as the export, are fixed in the connection agreement.
A generation or storage connection runs the transformer the other way round: it steps the inverter voltage up to the network. The transformer is exposed to the inverters' harmonics, and on a battery site it carries power in both directions.
Grid codes commonly require the plant to provide reactive power, so the connection and the transformer are sized on apparent power. A transformer chosen from the kilowatt rating of the inverters can fall short of what the code requires.
What decides the ratings
The reactive power capability your grid code requires sets the apparent power the transformer must carry. German medium voltage connection rules, for example, require generating units to provide reactive power between cos φ 0.95 under excited and 0.95 over excited. The apparent power is then at least the active power divided by 0.95.
The EU transformer loss regulation exempts transformers that supply DC loads, and expressly leaves photovoltaic and wind applications out of that exemption.
What to settle early
| Consideration | Why it matters here |
|---|---|
| Reactive power requirement | Sets the apparent power rating |
| Inverter harmonics | Affect transformer specification and losses |
| Bidirectional duty on storage | The transformer imports and exports |
| Connection point and voltage | Set by the network operator |
| Grid code certification | Plant certificates may be required above a size threshold |
| Insulating gas | EU rules restrict fluorinated gas in new distribution switchgear |
The German example
German connection rules set specific thresholds for certification, for simplified procedures and for the minimum agreed connection power.
Equipment for this application
What we need to quote
- Active power of the plant and the reactive power requirement
- Inverter or converter voltage and number of units
- Connection voltage and the network operator
- Whether the site stores energy, and the import and export duty
- Grid code and certification requirements that apply
- Programme date for equipment on site
Building or expanding a facility?
Send the whole equipment schedule as one project, each item with its own requirements.