TECHNICAL NOTES
Protection Class
Class I transformers
A transformer in which the protection against electric shock relies on the basic insulation but includes additional precautions, such as an earthing terminal for the connection of accessible conductive parts to the protective earthing conductor.
Class II transformers
A transformer in which the protection against electric shock relies on a double or reinforced insulation, there being no provision for protective earthing or reliance upon installation conditions.
Class III transformers
A transformer in which the protection against electric shock relies on supply at SELV, and in which voltages higher than those of SELV (50Vac) are not generated. There are no earthing terminals for the connection of accessible conductive parts to the protective earthing conductor.
Protection degree
Our transformers are built by default with a protection degree that can vary from IP00 to IP20, depending upon the construction.
Cooling
By default, our transformers are designed to be installed in environments cooled by natural air. Upon request it is possible to build transformers for environments with no airflow or with forced ventilation.
Nominal power
Power in transformers is usually expressed in VA (apparent power). If the needed power value is expressed in Watt, it must be considered that the relation between the two numbers is based upon the cosφ (W = VA x cosφ). It is also important to consider the efficiency of the load, as it will affect the power output of the transformer.
Nominal frequency
Our transformers are designed by default to work with the nominal frequency of 50 Hz, however they can work correctly at 60Hz. Upon request they can be built specifically for the 60Hz frequency. We can also provide special constructions that can work with custom frequency values based on specific requests from the Client.
Insulation Thermal Class
The insulation Thermal Class determines the maximum temperature to which the insulating materials can be exposed without compromising their mechanical and electric characteristics. It is usually expressed in combination with the maximum ambient temperature for which the transformer is designed. In the table below are reported the typical thermal classes used in transformer production:
| Thermal class | B (120° C) | F (140° C) | H (165° C) |
|---|
Nominal power / ambient temperature ratio
| Ambient temperature | 40° C | 45° C | 50° C | 55° C | 60° C | 65° C |
|---|---|---|---|---|---|---|
| Nominal power | 100% | 90% | 80% | 72% | 66% | 62% |
Nominal power / altitude ratio
| Altitude | 1.000 mt | 1.500 mt | 2.000 mt | 2.500 mt | 3.000 mt | 3.500 mt |
|---|---|---|---|---|---|---|
| Nominal power | 100% | 90% | 80% | 72% | 66% | 62% |
Standards reference
| Standard | Description | Notes |
|---|---|---|
| IEC 61558-1 | Safety of power transformers, power supply units and similar | General common parts. |
| IEC 61558-2-1 | Separation transformers designed for general purpose | Rated supply voltage and rated output voltage not exceeding 1.000 Vac. Double or reinforced insulation not required. Rated output not exceeding 1KVA for monophase and 5KVA for three-phase transformers. |
| IEC 61558-2-2 | Control transformers | Rated supply voltage and rated output voltage not exceeding 1.000 Vac. Double or reinforced insulation not required. |
| IEC 61558-2-4 | Isolation transformers | Rated supply voltage not exceeding 1.000 Vac and rated output voltage not exceeding 500 Vac. Double or reinforced insulation required. Rated output not exceeding 25KVA for monophase and 40KVA for three-phase transformers. |
| IEC 61558-2-6 | Safety isolating transformers | Rated supply voltage not exceeding 1.000Vac and rated output voltage not exceeding 50Vac. Double or reinforced insulation required. Rated output not exceeding 10KVA for monophase and 16KVA for three-phase transformers. |
| IEC 61558-2-13 | Autotransformers designed for general purpose | Rated supply voltage and rated output voltage not exceeding 1.000 Vac. Rated output not exceeding 20KVA for monophase and 100KVA for three-phase autotransformers. |
| IEC 61558-2-15 | Transformer for medical locations | Rated supply voltage not exceeding 1.000Vac and rated output voltage not exceeding 250Vac. Double or reinforced insulation required; shield between primary and secondary required. Rated output within the 500 VA - 10KVA range. |
| IEC 60601 | Transformers for the supply of electro-medical appliances | Isolation transformers. |
| IEC 61558-2-20 | Small reactors | Inductors, reactors, starting reactors. |
| IEC 60289 | Reactors | |
| IEC 60076-11 / IEC 726 | Power transformers | Power transformers and autotransformers. |