What is the? K factor? in transformers


"K" transformatori za nelinearna opterećenja

(transformatori dizajnirani s K-factorom)

U distributivnim mrežama normalna opterećenja se smatraju kada ukupni factor harmonica u struji tereta ne prelazi 5%, a factor parnih harmonica 1%. Nelinearna opterećenja uzrokuju izobličenje struje i napona. Negativni učinci viših harmonica struja i napona te promjene opterećenja uzrokuju dodatne gubitke u jezgri i u namotina transformatora, što može uzrokvati kvar istog. Promjene opterećenja mogu biti frekvencijski pretvarači, kondenzatorske baterije, lučne peći, aparati za zavarivanje, elektronička trošila i klime. Jedna od metoda koja omogućuje opterećenje višim harmonicima je dizajniranje transformatora tzv. K-factorom.

K-factor je mjera za utjecaj viših harmoničkih članova u struji na transformer, a definiran je rema ANSI / IEEE preporuci C57.110-1986. K-factor transformatora definira kako isti podnosi dodatno zagrijavanje (povećani gubici) izazvano višim harmoničkim članovima u struji.

Na temelju K-faktora se računa smanjenje raspoložive snage transformatora zbog dodatnih gubitaka, a pri dizajniranju novog transformera za povećanje snage istog da bi transformer zadovoljio 100% opterećenje. Znači transformer s većim K-factorom može podnijeti veći nelinearni teret, tj. povećano opterećenje višim harmonicima, a da mu se zbog toga ne smanji opteretivost snagom na nazivnoj frekvenciji. Ovisnost smanjenja opteretivosti transformatora o porastu K -faktora tereta, tj harmoničkog izobličenja tereta, prikazana je na slici 7. K-factor npr. 4, 9, 13, 20, 30 označavaju da su takvi transformatori ispitani i certificirani za nelinearna opterećenja.


"K" transformer for non-linear loads

(transformers designed with K-factor)

When total harmonics factor in load current does not exceed 5% and even harmonics factor 1%, these are considered to be normal loads in distribution networks. Non-linear loads cause current and voltage distortions. Negative effects of higher harmonics of currents and voltage, as well as changes in load cause additional losses in the core and transformer windings, which may result in the fault of the same. Changes in load may be caused by frequency converters, condenser batteries, arc furnaces, welding units, electronic units and air-conditioning devices. One of the methods allowing for loading with higher harmonics is designing of transformers by applying so-called K-factor. K-factor is a measure for influence of higher harmonics members in the current on the transformer and it is defined pursuant to ANSI / IEEE recommendation C57.110-1986. Trasformer's K-factor defines how the transformer is acting under additional warm-up (increased losses) caused by higher harmonics members in the current.

Decrease of available transformer power is calculated pursuant to K-factor due to additional losses and it is used for the power increase of the same during design phase in order for the transformer to fulfill a 100% load. This means that a transformer with a higher K-factor may bear higher non-linear load, i.e. increased load of higher harmonics, whereas this does not reduce its load capacity by power on nominal frequency. Dependence of transformer load capacity on burden K-factor increase, i.e. harmonic distortion of burden is represented in Fig. - 07 K-factors e.g. 4, 9, 13, 20, 30 mean that such transformers had been tested and certified for non-linear loads.



"K" transformers for the non-linear loading

(Transformers designed with the K factor)

In the case of power networks, normal Loads if the total harmonic factor in the load current does not exceed 5% and the pair harmonic factor 1%. Non-linear loads cause distortion of current and voltage. The negative influences of the harmonic currents and voltages as well as changes in load cause additional losses in the core and in the windings of the transformer, which can lead to damage. Changes in load can be frequency converters, capacity batteries, arc melting furnaces, welding equipment, electronic consumers and air conditioning systems. One of the methods that enables harmonic loading is to construct a transformer using the so-called K-factor.

The K-factor is a measure for the influence on the harmonic components in the transformer current and is defined in accordance with ANSI / IEEE recommendation C57.110-1986. The transformer's K-factor is defined as it can withstand additional heating (increased losses) caused by harmonic components in the current.

The K-factor is used to calculate the reduced available power of the transformer due to additional losses, and when designing a new transformer for a higher power of the same, so that the transformer can cope with a 100% load. This means that a transformer with a higher K-factor can withstand a larger non-linear load, i.e. an increased load on the harmonic, without losing the load capacity of the nominal frequency. The dependence on the load reduction of the transformer via the increased K-factor load or the deformed harmonic load is shown in Picture 7 K-factors shown, e.g. B. 4, 9, 13, 20, 30 indicate that such transformers have been checked and certified for non-linear loads.