distribution transformer comparison between above and below 800 kva

Conso Electrical Science and Technology Co., Ltd has produced 10 kv to 35 kv distribution transformer since 2006. Conso Electrical has accumulated extensive and rich experience on designing and manufacturing. The engineers of Conso Electrical believe the 10 kv distribution transformers have significant difference on technical specification and product structure between above and below 800 kva.

1.The difference of the distribution transformer on technical specification:

The larger capacity of a distribution transformer could support a larger rated current. Moreover, the distribution transformer above 800 kva need more serious protection on internal pressure and current stability.

A.internal pressure: When a serious fault occurs inside the transformer, a large amount of gas will be generated. It would accelerate insulation aging and reduce heat dissipation capacity. It may even cause an explosion, When the internal pressure of the transformer exceeds the critical value. A larger capacity distribution transformer would create more gas in one operational failure. Since the amount of gas generated at this time is sufficient to cause serious consequences, distribution and power transformers with a capacity of 800kva and above need to be installed with gas relays according to IEC 60076.

B.current stability: A larger capacity of distribution and power transformer would have more circuit from both side of primary and secondary. A more sensitive circuit breaker and CT will be needed to protect a distribution transformer from both near-end and far-end distribution lines. the two main current protection of distribution transformer is differential protection and current quick-break protection.

2.The difference of the distribution transformer on product structure:

Since a operational failure will create a more serious consequence from a larger capacity distribution transformer. It is necessary to a larger capacity distribution transformer to have a more solid internal structure and sensitive components.

To protect a distribution transformer from a short circuit, a more solid internal structure shall be designed, because a more serious electric energy will be released. Furthermore, a distribution transformer above 800 kva would adopt continuous or spiral winding, such as foil wrap. Meanwhile, a larger capacity distribution transformer need a more powerful cooling system. It is necessary to adopt OFAF cooling method to some distribution transformers above 800 kva, especially when the transformer is overloaded.  

Since a larger distribution and power transformer would generate more gas in a operational failure. A gas relay shall be equipped on a distribution transformer. It will sound the alarm when minor gas gathered the top of a distribution transformer, and shut-off the main circuit breaker when the inside pressure had a terrible increase. Furthermore, to arrange the inside pressure, a transformer breather also will be adopted to protect distribution transformers survived from insulation aging. Meanwhile, to reduce the loss from power failure, some distribution transformer above 800 kva might equips on-Load tap changer (OLTC) rather than no-load tap changer (NLTC).

A distribution transformer has an obvious difference from both technical specification and product structure between above and below 800 kva. It is because the larger capacity distribution transformers need more serious protection to survive from operational failure.