Availability of Discharge class 3 surge arresters 3

[Rwelagedara]

Dear All,
We are looking to purchase some metal oxide surge arresters of rating 33kV, 10kA to be mounted on distribution transformers.

However, our consultant wants to use surge arresters of line discharge class 3 for this purpose. We tried to find this item with many surge arrester manufacturers , but all manufactures are having line discharge class 1 only .Required line discharge class 3 is not available.
I shall be much obliged of you could advice us,

[li]Whether line discharge class 3 is applicable to our requirement?
[li]What is the importance of line discharge class?
[li]Do you think this product with line discharge class 3 is available in market or can be manufactured?

 

[FacEngrPE]

Without more information, it is unclear if you are class per IEC 60099-4 or IEEE/ANSI C 62.11. These two standards are partly harmonized, the term class is used differently in the two standards. See

https://www.inmr.com/harmonizing-iec-ieee-arrester-standards/.

No way to know what is available in your area, but the data sheet for GE TRANQUELL
Surge Arresters shows class 2 to 5 available, and the "class" as used here to be related to both construction and energy capability. Energy capability increases considerably with "class number" so if class 3 is recommended, class 1 may have insufficient energy capability (I did not find a table including class 1 surge arresters, so there is some guessing here).

I suggest you ask your consultant to explain his calculations. That is one way to learn important things about selecting these devices.

Fred

 

[Kiribanda]

Line Dischage class was a parameter used in previous IEC 60099 whereas the equivalent parameter(s) used in IEEE C62.11 were
station class & distribution class. After harmonization both the IEC 60099 & IEEE C62.11 are using "CURRENT CHARGE/ENERGY
CLASSIFICATION". Based on that, IEC 60099 is now using station class (Heavy,Medium & Light) & distribution class (Heavy,Medium & Light).
Therefore, line discharge Class 3 is equivelant to Heavy or Medium STATION CLASS arresters (SH & SM) or Heavy Distributionn
Class (DH) arresters.
Based on above you will find that Class 3 is suitable for heavy energy handling networks mainly above 52kV voltage. In fact, since
your transformer is connected to a 33kV distribution system, honestly you donot need Class 3. They are suitable for 132 & 220kV subs.
But if your consultant still insists on Class 3 (wish to know the real reason), you can use ABB/POLIM-S Class 3 surge arresters
which will be pricier than Class 1 or 2.
Another point.
What is your supply authority using for their dis transformers connected to the same 33kV system?
I am sure it is Class 1 or 2. Cannot be Class 3.