A substation is not a transformer
A substation is a site. The transformer is one piece of equipment on it, alongside circuit breakers, disconnect switches, instrument transformers, surge arresters, buswork, relays and a control house. People searching for the difference between a substation and a transformer are usually looking at a fenced yard and calling the whole thing by the name of its largest object.
Substation transformer versus pad mounted
A substation transformer steps transmission voltage down to distribution voltage, often 69 kV or 138 kV down to 12.47 kV or 34.5 kV, and is measured in MVA. A pad mounted transformer takes that distribution voltage down to the building voltage and is measured in kVA. They are different classes of machine. The pad mount is the last step, the substation unit is the step before it.
Unit substations
A unit substation is a transformer bolted directly to switchgear on the primary side, the secondary side, or both, assembled and tested as one lineup. You see them in plants, hospitals and data centres where the transformer sits indoors and the connection must be enclosed rather than cabled. It is a packaging decision rather than a different transformer.
Dead front and live front switchgear
The same distinction that applies to pad mounted transformers. Dead front means the energised parts are behind an insulated barrier and connections are made with loadbreak elbows, so an operator faces no exposed conductor. Live front means the bushings and connections are exposed behind the door. Dead front is the modern standard for anything the public can reach, and it is what we supply unless a job specifically calls for live front.
Common questions
What is the difference between a substation and a transformer
A substation is a site holding many pieces of equipment. A transformer is one of them. A substation also contains breakers, switches, instrument transformers, surge arresters, buswork and protective relays.
What equipment is used in a substation
Power transformers, circuit breakers, disconnect switches, current and potential transformers for metering and protection, surge arresters, buswork, grounding, protective relays and a control house. Distribution substations add voltage regulators and capacitor banks.
What is the difference between dead front and live front switchgear
Dead front keeps all energised parts behind an insulated barrier, with connections made through loadbreak elbows so nothing live is exposed when the door is open. Live front leaves bushings and connections exposed behind the door. Dead front is standard anywhere the public has access.
Which transformer is used in a substation
A power transformer, usually above 5 MVA, stepping transmission voltage down to distribution voltage. It is a different class of machine from the pad mounted distribution transformers that feed individual buildings.
Free to cite with a link to this page. Work out current at any rating with the kVA to amps calculator.