What Is a Control Transformer?

The control transformer is mainly suitable for circuits with AC 50Hz (or 60Hz), voltage 1000V and below, and can work continuously for a long time under rated load. Usually used in machine tools, mechanical equipment as electrical control lighting and indicator power.

In low-voltage power distribution systems, control transformers are named for their use in control systems. It is actually a step-down transformer with a variety of output voltages, and can also be used as a power source for low-voltage lighting and signal lights and indicators. ^[1]

The control transformer is used

Scope of application

BK series

Ambient air temperature -5 ° C to + 40 ° C, the average value within 24 hours does not exceed + 35 ° C;

The altitude of the installation site does not exceed 2000M;

The relative humidity of the atmosphere does not exceed 50% when the ambient air temperature is + 40 ° C, and there can be higher relative humidity at lower temperatures. The monthly average maximum humidity of the wettest month is 90%, and the average minimum temperature of the month is + 25 , and take into account the condensation on the product surface due to temperature changes. ^[2]

Rated power: 50/60 (KVA)

Efficiency (): 97%

Voltage ratio: 380/220 (V)

Shape structure: vertical

Cooling method: natural cooling

Moisture-proof method: open

Number of windings: double winding

Core structure: shell type

Cooling form: dry type

Core shape: E type

Power phase: single phase

Insulation resistance

The insulation resistance of the control transformer in the cold state should not be less than 10 M; the insulation resistance of the control transformer in the hot state and tide state should not be less than 2 M.

2. Insulation strength

The electrical insulation strength of the control transformer should be able to withstand the voltage withstand test of AC 50 Hz and 2 000 V sinusoidal AC voltage, without breakdown or flashover for 1 min.

3. Leakage current

The leakage current of the control transformer must not exceed 3 mA. ^[3]

A device that transforms voltage, current, or impedance. Made according to the principle of electromagnetic induction. The first transformer of practical value was invented by the British Gollard and Gibbs in 1883. It is mainly composed of two parts: iron core and coil (also called wire package). The iron core is generally made of silicon steel sheets, and can also be made of ferrite. The coil has two or more windings. The winding connected to the power supply is called the primary and the rest are called secondary. When an alternating voltage U ₁ is added to the primary winding, an alternating current I ₁ is generated in the primary winding, and an alternating magnetic flux is generated in the iron core, thereby generating an induced voltage U ₂ in the secondary winding. Under ideal conditions, the voltages U ₁ and U ₂ of the primary stage are proportional to the number of coil turns W ₁ and W ₂ of the primary stage, that is, U ₁ / U ₂ = W ₁ / W ₂ . The current I ₁ and I ₂ of the primary stage are inversely proportional to the number of coil turns W ₁ and W _{2 of the} primary stage, that is, I ₁ / I ₂ = W ₂ / W ₁ . The impedance of the primary stage is proportional to the square of the number of turns of the primary coil, that is, Z ₁ / Z ₂ = W ₁ / W ₂ . In general, there is no electrical connection between the primary and secondary (with the exception of autotransformers), so that the two circuits can be better divided. The type of transformer can be divided into single-phase, three-phase and multi-phase according to the number of power phases; it can be divided into core, shell, ring and metal foil transformers according to the core or coil structure.

The main parameters of the transformer are voltage ratio, voltage regulation, copper resistance, efficiency, temperature rise and electrical strength. Different types of transformers each have some special requirements. The transformer should have a sufficiently long life. The main factor that determines the life of a low-voltage transformer is thermal aging. Because its insulation system works at high temperatures for a long time, the paint film volatilizes and embrittles and cracks the insulation material, causing electrical breakdown. Every time the working temperature is increased by 8 to 10 ° C, the life will be shortened by half. For high-voltage transformers, corona discharge is the main factor affecting life. The impact is related to the operating frequency, the intensity of the corona discharge, the corona resistance of the insulating material, and the intensity of the working electric field. Corona discharge should therefore be avoided. Under various environmental conditions, the greatest impact on the reliable operation of the transformer is humidity. Transformers with poor moisture resistance are exposed to hot and humid environments for a long time, and the insulation resistance will be severely reduced or even the insulation layer will break down and burn out. For more important radio products and transformers used in electronic equipment, effective measures must be taken to prevent moisture. In the rainy season, it is necessary to periodically turn on the heat to dispel moisture to increase the service life of the transformer. ^[4]