Parallel operating conditions of power transformers

Categories:Industry information
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Time of issue:2021-06-09
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(Summary description)The ideal operation situation of parallel operation of transformers is: when the transformers are already in parallel, but there is no load, there should be no circulating system current in each transformer; after carrying the load together, each transformer can effectively distribute the load, which is approximately According to their respective volume market shares to focus on the load. Therefore, in order to achieve the desired operating conditions, the following conditions must be met when the transformers are operated in parallel:

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Parallel operating conditions of power transformers

(Summary description)The ideal operation situation of parallel operation of transformers is: when the transformers are already in parallel, but there is no load, there should be no circulating system current in each transformer; after carrying the load together, each transformer can effectively distribute the load, which is approximately According to their respective volume market shares to focus on the load. Therefore, in order to achieve the desired operating conditions, the following conditions must be met when the transformers are operated in parallel:

Categories:Industry information
Author:
Origin:
Time of issue:2021-06-09
Views:0

The ideal operation situation of parallel operation of transformers is: when the transformers are already in parallel, but there is no load, there should be no circulating system current in each transformer; after carrying the load together, each transformer can effectively distribute the load, which is approximately According to their respective volume market shares to focus on the load. Therefore, in order to achieve the desired operating conditions, the following conditions must be met when the transformers are operated in parallel:

(1) The working voltage ratio (transformation ratio) of each transformer should be the same;

(2) The characteristic impedance working voltage of each transformer should be similar;

(3) The wiring level of each transformer should be the same.

The following analyzes the adverse effects produced when a certain condition in the parallel operation of the transformer is not met:

(1) Transformers with different voltage ratios (transformation ratios) run side by side:

Since the principles of a three-phase transformer and a single-phase transformer are the same, in order to facilitate analysis, take two single-phase transformers running side by side as an example. Since the primary voltages of the two transformers are flat and the voltage ratio is not flat, the induced potential in the secondary windings is not flat, and a potential difference △e is present. Under the effect of Δe, circulating current ic appears in the secondary winding. When the extra capacity of the two transformers is equal, that is, sni=snii. The circulating current is:

ic=△e/(zdi＋zdii)

Where zdi-indicates the internal impedance of the first transformer

zdii-indicates the internal impedance of the second transformer

If zd is indicated by impedance voltage uzk, then

zd=uzk*un/100in

Where un indicates the extra voltage (v), in indicates the extra current (a)

When the extra capacity of the two transformers is not equal, that is, sni≠snii, the circulating current ic is:

ic=α＊ii/[uzki＋(uzkii/β)]

Where: uzki-indicates the impedance voltage of the first transformer

uzkii-indicates the impedance voltage of the second transformer

ini＜inii

α——The secondary voltage difference expressed as a percentage

ii——The secondary load current of transformer i

Based on the above analysis, it can be seen that under load conditions, the existence of circulating current ic increases the current of the transformer winding with a small transformation ratio and reduces the current of the transformer winding with a large transformation ratio. In this way, transformers running side by side cannot be in charge of the load in proportion to the capacity.

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Parallel operating conditions of power transformers

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