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# Transformer riddle no.4 – Generator transformer of power plants

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• #73
Hamid

Regarding to physical size of national power systems, rate of power exchange and transmission lines capacity are increased by using of high voltage technology.
Regarding to physical size of national power systems, rate of power exchange and transmission lines capacity are increased by using of high voltage technology.
Step up or generator transformers increase the produced voltage of power generators in great power plants. Therefore it seems the unique function of these transformers is the increasing of generator voltage equal to voltage of national grid.
But as you know, in small and individual power systems (e.g. industrial power plant and related power distribution system) the generator transformers are used as the electromagnetic interface stage between generator and power distribution system. In this mentioned system the transmission and distribution voltage is medium voltage, therefore output of generator may be used directly in distribution system.

How can you explain the essential function of generator transformer in small power systems?

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• #1277
OSPREY

Economics. The cost of a generator increases as you increase the output voltage, to the point that it is more ecnomical to furnish one with a lower output voltage and a transformer to meet the higher voltage requirement. And of course there is a limit on how high a voltage you can wind on a generator. Economics.

#1278
Robert_cameron_jr

As I understood in the courses I took for Power, the use of these were exactly just that: economics. Their essential function is to step up voltage for the transmission losses to be mitigated (step voltage up, current steps down, and since transmission losses are proportional to the magnitude of the current, losses are minimized). Their voltage step down is more efficient (arguably) when not dropping voltage to the low specs. households use, so in turn they are more efficient from the generator to the equipment here (also because of the distance transmitted, but that is a seperate issue). I only remember this from school. Anyone from industry is welcome to take me back to school here! I am sure I need some more of it every so often.

#1279
GUEST

The function of generator transformer is to shield generator from distribution system.

#1280
Biswanath.das

In some cases shielding of harmonics generated in system is done by GT. Voltage regulation is also required by using OLTC of GT. I have seen Industrial system useing 415V as generator output voltage and directly connected to load through LV switchgear.For example, DG set used in Jute industry. But the criteria is again harmonics which is also mitigated by using filtering circuts. Also one poing if load center is near to generating station LV generator can also be selected. In a nutshell its Techno-economic consideration for selecting GT.

#1281
N.Suresh

Dear friend, The Generator Transformer is designed based on the genartaing voltage. For ex. if the generating voltage is 11 kV and the national grid being 400 kV the GT will be 11/400 kV, 154 MVA Transformer. In case of 6.6 kV Voltage generation to step up to 220 kV, a 400 MVA Transformer is used since normally the state grid being 220 kV. The 11 kV side will be having a switchgear. For the exctiation an Unit Auxilary transformer normaly reffered as UAT will be used to give the exciatation. In some 220/6.6 kV station transformer will be used. Again it depends on the system design. A separate DC system will be there for the power house and a separate DC system for the 400 kV Switchyard protection system will be there. The GT will be having have separate protection system for the Generator and the transformer. The LV side will be having busduct and the HV side will be through ACSR conductor of suitable size depending upon the voltage. More precisely these concepts will be understood upon prcatial expereince. Regards N.Suresh

#1289
Hamid

One of important roles of transformers in power systems is matching of two different grounding systems. Because of prevention of high earth faults current, the generators grounding system is selected high impedance. But in medium voltage distribution system, the low impedance grounding system is preferred for control of over voltage phenomenon. Therefore application of matching transformer is necessary in most conditions. Of course reduction of short circuit level and voltage compatibility is important too.

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