Yes. You can have two secondary windings with equal percentage impedances. In India, we have several 315 and 400 kV transformers with 400/33-33 kV YNynyn units at Solar firms. Some of them have 5-limbed core construction without a stabilising delta winding,
In 2021, the Central Electricity...
1) Transformer overloading standards have changed significantly during the past 30 years. The relevant standards today are IEC 60076-7 ed2.0-2017 & IEEE C57.91-2011 for oil-filled transformers and IEC 60076-12-2008 & C57.96-2013 for dry-type transformers.
2) Manufacturers design transformers for...
Cucky, as someone who has designed large power transformers according to IEC and IEEE standards for more than half a century, let me confirm that I was making the same cooling circuit regardless of the standard. The temperature rises (oil/winding/ hotspot ) are the same in both standards...
cuky, as per my under standing, the temperature rise difference between IEC and IEEE is only 2C. The reference ambient temperatures are same. IEC 20 C is the yearly average and not stipulated in IEEE.
As per IEC60076-2, the maximum permissible winding hot spot temperature rise is 78 C, over a...
Let me disagree.
IEC specifies
Temperature rises based on max ambient air temp of 40C, monthly average of 30C and annual average of 20C. In case any one or more of the parameters differs from above, temperature rises can be modified as specified in IEC std clause 6.3.2 and table 2.
As per...
Yes, you can use FR-3 at that rating. In India, we have transformers with 315 MVA 420 kV rating and FR-3 filling. But what advantage are you expecting with such oils in such large ratings?
Oil's resistivity is less than that of air. The IR ratio in an air-to-oil-filled condition was 1:20. But with modern oils of high resistivity, this is now around 1:10.
If the tertiary is not loaded, one corner is kept earthed to avoid power frequency transferred overvoltages. An earthing transformer is used for extensive tertiary lines. Neutral earthing through the resistor is used to limit ground fault current, and the reactor is used to limit arc flash...
Most of the reported OLTC failures were in auto-transformers where the line end tap-changer is at a high voltage of 132 or 220 kV. OLTC is now being eliminated in India in 400 kV and 765 kV auto-transformers.
Theoretically, you can save material by going for an auto connection. However, the savings will decrease as the voltage ratio increases. It is almost 1:3 here(limit around 1:2), and you require both DETC and OLTC. Hence, I will suggest a two-winding transformer. We have already discussed...
Waross, thank you for the explanation. I have a question: Why is the primary neutral of T1 kept ungrounded? If it is grounded, is there no longer a need for a stabilizing delta winding?
Thank you, Scott. I was waiting for your response. What I meant was an oil-filled dead tank ( hairpin ) CT. When such CTs fail, there is normally an explosion with porcelain shattering. Many power engineers interpret that such failure can happen from open circuiting of the CT secondary. Post |...
It is well known that open-circuiting the secondary circuit of CT while carrying primary current will create overvoltage on secondary terminals. But will this lead to violent failure of CT with explosion? Has anyone noticed CTs in service with open-circuited secondary terminals?
The need for a tap changer depends on the voltage variations required on the secondary side, the voltage fluctuations expected on the primary side, and the characteristics of the grid. The purpose of a tap changer is to keep the voltage at the consumer (load) end constant.
The secondary...
