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Difference between no-load and load of transformer
Release time: 2017-08-28 Clicks: 1237 times

For power supply novices who are new to transformer knowledge, there are always some confusing knowledge points in a large number of basic concepts. No-load transformer operation is one of them. Although there is a lot of information explaining these two concepts separately, there are few materials explaining the difference between the two.

This article will introduce the transformer no-load and transformer load operation, and explain the difference between the two. Let ’s take a look at the editor.

No-load operation of transformer

The no-load operation of a transformer refers to the working state when the primary winding of the transformer is connected to the power supply and the secondary winding is open. At this time, the current in the primary winding is called the no-load current of the transformer. No-load current generates a no-load magnetic field. Under the action of the main magnetic field (that is, the magnetic field that cross-links the first and second windings at the same time), the electromotive force is induced in the first and second windings.

When the transformer is running at no load, although there is no power output on the secondary side, the primary side still draws a part of the active power from the power grid to compensate for hysteresis loss and eddy current loss in the iron core due to magnetic flux saturation. The amount of hysteresis loss depends on the frequency of the power supply and the area of the hysteresis loop of the core material; the eddy current loss is proportional to the maximum magnetic flux density and the square of the frequency. There is also copper loss due to no-load current. For transformers with different capacities, the magnitudes of no-load current and no-load loss are different.

Transformer load operation

The load operation of the transformer refers to the working condition when the primary winding is connected to the power supply voltage and the secondary winding is leased to the load. At this time, the secondary side of the transformer also has current flowing, and the access circuit of the original transformer is correspondingly increased compared to no-load. The voltage on the secondary side will be affected by the load and change.

Normal periodic load operation:

1. The transformer can be operated at rated current throughout the year under rated conditions of use. 2. Transformer is allowed to periodically run at over rated current when the average relative aging rate is less than or equal to 1.

3. When the transformer has more serious defects (such as abnormal cooling system, severe oil leakage, local overheating, abnormal analysis results of dissolved gas in oil, etc.) or weak insulation, it is not suitable to run at over rated current.

4. Under normal cyclic load operation mode, the allowable load factor K2 and time can be determined according to one of the load guide methods when the rated current is exceeded.

The difference between the two

The main difference between transformer no-load operation and load operation is mainly reflected in the secondary coil. The transformer load runs the secondary coil connected to the load and generates large power. The no-load operation of the secondary coil is open-circuited and generates micropower.

A transformer uses the principle of electromagnetic induction to change the AC voltage. The main components are a primary coil, a secondary coil, and an iron core (magnetic core). It is often used in electrical equipment and wireless circuits for step-down voltage, matching impedance, safety isolation, etc. When the transformer is running at no load, it only consumes no-load loss, that is, iron loss and stray, which is 6% of the total capacity. When the load is running, it is no-load loss + load loss, that is, copper loss, which is the total transformer consumption.

This article introduces the transformer's no-load operation and load operation respectively. After completing the basic knowledge, the differences between the two are explained in detail, which is an article suitable for novices to read. I hope that friends who have questions about no-load and load can solve their confusion after reading this article.

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