What are the specifications and model numbers of transformers, and how are they determined?
Release date:
2021-11-12 11:01
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What are the specifications and model numbers of a transformer? How are these specifications and model numbers determined?
I. Classification
Classification by cooling method: dry-type (self-cooled) transformers, oil-immersed (self-cooled) transformers, and fluorinated‑compound (evaporative‑cooled) transformers.
Classification by moisture-proofing method: open-type transformers, potting-type transformers, and sealed-type transformers.
Classification by core or winding structure: Core-type transformers (lamination‑core, C‑type core, ferrite core), Shell-type transformers (lamination‑core, C‑type core, ferrite core), Toroidal transformers, and Metal‑foil transformers.
Classification by number of power phases: single-phase transformers, three-phase transformers, and polyphase transformers.
Classification by application: power transformers, voltage-regulating transformers, audio transformers, intermediate-frequency transformers, high-frequency transformers, and pulse transformers.
II. Characteristic Parameters of Power Transformers
1. Operating frequency
Transformer core losses are highly dependent on frequency; therefore, transformers should be designed and operated at a specific frequency, known as the operating frequency.
2. Rated Power
The output power at which a transformer can operate continuously under specified frequency and voltage conditions without exceeding the prescribed temperature rise.
3. Rated Voltage
Refers to the voltage that may be applied to the transformer windings, which must not exceed the specified value during operation.
4. Voltage Ratio
It refers to the ratio of the primary voltage to the secondary voltage of a transformer, which can be distinguished as the no-load voltage ratio and the loaded voltage ratio.
5. No-load current
When the secondary winding of a transformer is open-circuited, a certain current still flows in the primary winding; this current is referred to as the no-load current. The no-load current consists of the magnetizing current (which generates magnetic flux) and the core-loss current (caused by core losses). For a 50-Hz power transformer, the no-load current is essentially equal to the magnetizing current.
6. No-load loss
It refers to the power loss measured on the primary side when the transformer’s secondary winding is open-circuited. The primary losses consist of core losses, with a smaller contribution from copper losses—i.e., the power dissipated in the primary winding due to the no-load current.
7. Efficiency
It refers to the percentage of the ratio of secondary power P2 to primary power P1. Generally, the larger a transformer’s rated power, the higher its efficiency.
8. Insulation Resistance
It indicates the insulation performance between the windings of a transformer and between each winding and the core. The magnitude of the insulation resistance is influenced by the properties of the insulating materials used, as well as by temperature and humidity levels.
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