Load and No-load Operation of Transformer
For newcomers who are new to transformer knowledge, there are always some confusing knowledge points in a large number of basic concepts. Transformer on load operation and transformer no-load operation are included. This article will introduce load and no-load operation of a transformer, and explain the difference between the two.
Load operation of the transformer
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. Compared with no-load, the access circuit of the original transformer is correspondingly increased, and the voltage at the secondary side will change due to the influence of the load.
Operation of normal periodic load
- The transformer can run at rated current throughout the year under rated conditions of use.
- Transformer is allowed to periodically run at over rated current when the average relative aging rate is less than or equal to 1.
- When the transformer has rather serious defects (such as abnormal cooling system, severe oil leakage, local overheating, abnormal analysis results of dissolved gas in oil and so on.) or weak insulation, it is not suitable to run at over rated current.
- 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.
No-load operation of the 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, and the no-load current generates an 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.
During no-load operation of the transformer, although there is no power output on the secondary side, the primary side still draws a portion of the active power from the grid to compensate for hysteresis loss and eddy current loss (referred to as iron 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. Eddy current loss is proportional to the magnetic flux density and the square of the frequency. In addition, there is copper loss caused by no-load current. For transformers with different capacities, the magnitudes of no-load current and no-load loss are different.
The difference between the two
The main difference between transformer no-load operation and load operation is mainly reflected in the secondary coil. When the transformer is running under load, its secondary coil is connected to the load and generates a large amount of power. During no-load operation, its secondary coil is open-circuited, generating micropower.
Transformer is a device that uses the principle of electromagnetic induction to change AC voltage. Its main components are primary coil, secondary coil and iron (magnetic core). It is often used in electrical equipment and wireless circuits for step-down voltage, matching impedance, safety isolation and so on. 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 transformer is running at load, it consumes no-load loss + load loss, that is, copper loss, i.e., the total consumption of the transformer.