Mobile Stations (ETM)


Electric Energy Distribution and Transmission Companies compete in markets that require reliable and safe service according to very high quality standards. In order to avoid an interrupted service, many companies have adopted to duplicate their installed power capacity in each transformer station. This solution may represent unacceptable high financial costs, therefore the main challenges for Management of the Electrical Energy Companies in the XXI century are the Quality of the Investment Decisions and the optimization of Capital Costs.

As energy distribution business means strong capital investments, the electric transformer stocks must be particularly optimized without straying from the growth and avoiding unexpected events that might lead to economic penalization from the Regulatory Authorities, or even worse, customers moral penalization. Within this context, Tadeo Czerweny S.A. has developed an Engineering Department dedicated to propose concrete project solutions to Clients, in order to minimize capital costs: the Mobile Transformer Stations (ETM).

The incorporation of Mobile Transformer Stations (ETM) strategically located in the client electric energy supply region, considerably reduces capital investments and maintenance costs. A customized ETM design also allows this compact equipment to be on location within three or four hours after the unexpected event is reported.

In Tadeo Czerweny S.A. we concentrate our efforts to address each specific need of our customers.


Mobile Transformer Stations (ETM) can be provided mounted on lowboy trailers or universal skids. For primary voltages up to 138 KV and 20 MVA they can be built on trailers approved to travel along national roads and carrying conventional transformers with ONAN / ONAF refrigeration system, however, local regulations must be investigated before final specifications are issued to our Engineering Department.

As a general rule, ETM provisions above 20 MVA and 138 kV are only possible via very special designs because the main transportability limitations are weight, width and length, all of them regulated by Local/National laws. The final performance of an ETM is always a compromise between the physical features (weight and dimensions) and the required electrical power provision, in this matter Tadeo Czerweny has a highly trained professional team to achieve the best solution.

Provision Examples:

Basic guide to specify an ETM


Type I: (three skids or lowboy trailers)

  • High Voltage Module
  • Transformer Module
  • Medium-Low Voltage Module

Type II: (two skids or lowboy trailers)

  • Compact Mobile Station Module
  • Medium-Low Voltage Module

Type III: (one lowboy trailer)

  • Compact Mobile Station

This modular concept allows power provisions in 138 kV up to 40 MVA.


For power ratings above 15 MVA it is not recommended to require either a tertiary winding or transformer losses based on capitalization formulas applied to conventional stations. ETMs are designed to withstand emergencies, therefore the equivalent hours either for eddy or load losses quantification are totally different. It is also recommended to settle in 65º C the maximum copper over-temperature and in 60º C the oil over-temperature. These facts lead to reductions of up to 30% the transformer weight and consequently significant size reduction.


Toroidal/bushing-types, are preferable to conventional ones. Conventionals are heavier and need significant additional space. It is advisable to leave the final choice to our Design Department, since extra safety rates are not necessary due to the closeness of the protective elements they are connected to. Higher performance and protection levels lead to bigger dimensions and weight of the power transformer.


It is always recommended to consider the lowest levels specified by Standards for each type of voltage, this will finally yield smaller dimensions and weights. On top of that the protection level obtained using the latest OZn surge arresters is highly reliable even with the lowest accepted insulation levels.


It is not advisable to specify ceramic cover to insulate columns. Current silicon SBR polymers have shown very good performance under the most severe atmospheric conditions and represent an excellent solution when the aim is to reduce weight and to increase safety in transportation and possible vandalism.


Our Engineering Department will advise about the selection of the most convenient cooling system to get the best economical solution for a given power specified to the ETM.


Reconnectors with built-in overcurrent protection are available. They are very convenient as an economical option and an excellent solution to handle medium voltage fields constituted by cells with Switches and line Switch-disconnectors.


When direct current (DC) auxiliary services are required, it is recommended to select command voltages and load capacity as low as possible, a selection that might eventually be left to the manufacturer. Direct current auxiliary services must be supplied, under normal operating conditions, by the battery charger connected to the alternate current auxiliary services. It is preferred to avoid specifying auxiliary service capacity to feed external loads to the ETM, such as lighting premises, external battery chargers and others. These considerations lead to smaller dimensions and weights for the auxiliary service components.


It is necessary to select those with the lowest power consumption, this will minimize the rated power for auxiliary services.


Aluminum type are preferred when they are requested for the medium voltage outlet connection. They are lighter and offer excellent conductivity performance.


They should be avoided whenever is possible. Their incorporation considerably increases the ETM physical dimensions and weight.


ETM technical requirements corresponding to a Conventional Type Transformer Station are not recommended, such specifications often lead to the unfeasibility of the ETM project or at least drastically reduce transportation conditions.

Dimensions and Maximum Weight of Vehicles:
Each country has its own regulations and laws to control circulation of special vehicles/trucks, this must be strictly studied by the customer prior to set the Purchase or the Design order. At least the following data should be considered during internal research:

A/ Maximum Width
B/ Maximum Length
C/ Maximum Height
D/ Maximum weight with two axles and single wheels
E/ Maximum weight with two axles and dual wheels
F/ Maximum weight with three axles and dual wheels
G/ Special permits/requests for vehicles exceeding standards
H/ Sea-Port unloading/storing capacities
I/ Foreign Vehicles registration normatives


  • Low cost response to seasonal power charge demands.
  • Lower maintenance cost compared to traditional Transformer Stations.
  • Temporary power supply through ETM allows to reduce power cuts due to maintenance, with the additional advantage of performing off-load maintenance tasks on transformers and associate equipment.
  • Faster response, in case of emergencies, catastrophes, floods.
  • Temporary and cheaper power supply, in due course, for large building sites.