Can you guess what is fireball and what is its purpose? So let us understand what is Firewall. Firewall is basically barriers that are used to protect adjacent structures or item in case of any fire burst and to further stop spread of fire to adjacent structure or item. In our case it is oil filled transformer and the surrounding building or structure has to be protected. So what can be done? The Firewall requirement is clearly given in the tabulation as per IS1646 and IEC61936 based on the oil capacity and the minimum clear spacing between the transformer and the structure. If the distance between the building, structure, equipment or transformer installed nearby adjacent to the lick it failed, the transformer containing substantial amount of oil will be provided by Firewall if it is less than the stipulated clearance given. Otherwise no need of providing Firewall. To conclude the recommendation for providing Firewall are generally governed by volume of oil in transformer and clear separation space available between transformer and to nearby structure/building/equipment, etc. Now we can see the great line depicted in Indian standard, and IEC based on space and volume of oil. Requirement of Firewall based round transformer oil capacity as per IS:1646 is given here. If you see then oil capacity, the aggregate oil capacity, if it is greater than 2000 and the individual oil capacity is less than 5000, then the minimum clear spacing required to avoid Firewall is 6 metres. And the individual 5000 to 20,000 is 8 metres. And for individual about 20,000, the minimum clear spacing required to avoid Firewall is 15 metres. Requirement of Firewall based on transformer oil capacity, this is as per IEC:61936 if you see. Liquid volume in liters 1000 to 2000 litres where the minimum clearance from other transformer or building of non-combustible material is 3 metres. And for clearance from the building of combustible material is 7.5 metres. Similarly, if the oil is between 2000 to 20,000 liters, the minimum clearance from other transformer or building of non-combustible material is 5 metres. And the minimum clearance from the building of combustible material is 10 metres. In the case of liquid volume, which is 20,000 to 40,000 liters, the minimum clearance from other transformer or building of non-combustible material is 10 metres. And minimum clearance from the building of combustible material is 20 metres. When it is about 45,000, then the minimum clearance from other transformer or building of non-combustible material is 15 metres. And the minimum clearance from the building of combustible material is 30 metres. >> The elbow points are illustrated below with the two examples. Please note that as seen from the FIGURE-1, if the clearance is less than given the portion of the valve marked as A shall have a fire rating of REI in 90 REI 90. And B can be non-combustible material with no REI rating. Please refer FIGURE-2. And if clearance see less than G2 and the greater than G1, the portion of the Firewall indicated as B shall be non-combustible material with no REI rating. And C can be any material. Now you will see the significance of REI 90. R is the load bearing structure. E stand for Fire integrity. I for thermal Insulation. And 90 is the duration in minutes to withstand the fire. If the Firewall is stand alone and he's not having any load bearing capacity, then its fire rating is stated as REI90. For load bearing wall, which is part of a building, then its fire rating is stated as REI90. >> A typical example of transformer installed on a double pole structure with HP connection via bare conductor is shown on screen right now. Here, if you see carefully we can observe that, one, ground clearance that is live part ground is 4000 a month, that is more than 275. We should also understand that the ground clearance is the deciding factor to decide the mounting height of the transformer. Two, face to face and the face to the earth clearance are maintained as per guidelines depicted in IS:1180. For 0.433 kv, the minimum face to face clearance is 75mm, and face to earth clearances 40mm. Similarly for 11 kv, the minimum face to face clearance is 255m, and minimum Phase two Clearance is 140mm. Another typical example of transformer installed on plinth with accessories mounted on double pole structure is shown in the diagram. If the transformer capacity is high instead of mounting onto pole structure, it will be mounted on plinth. Again, the question raises on how to find the head of the plinth. Here the criteria for plinth height is to maintain the minimum ground clearances to the late part of the transformer, which is the terminal at the bushing. Nominal system voltage for 11 kv is minimum is, maintained as 2750. Now let us examine a transformer insulation in an outdoor substation for the requirement of Firewall. We have shown the layout arrangement of 33/11 kv outdoor situation with the two numbers of transformers installed side by side. If we closely observed, we can understand that two numbers, oil filled transformers of individual oil capacity of 2005 liters are installed with an edge edged distance between the two transformers as 6.5 m. Further as per IS:1646, which is spelled out, two conditions, separating walls shall not be necessary in case of transformers having an aggregate oil capacity exceeding 2000 liters. But individual oil capacity of less than 5000 liters, if the distance between transformers and other apparatus is more than 6 metres. Since in referred example, the aggregate oil capacity is more than 2000 liters, that is 2005 liters each. We need to check the separation distance to arrive on a conclusion whether to provide Firewall or not. Here the clear space availability is 6.5 metres, that is more than 6 metres as stipulated in IS. Hence we do not give Firewall because adequate clear separation space is available. We will see another example of 33/11kv outdoor substation shown in the layout arrangement of transformer again. On close observation, we can see that two numbers of the mv oil filled transformers of individual oil capacity, 2005 letres are installed, edge distance between two transformers be 5 metres. Hence referring to the requirement depicted in IS:1646 that we had just discussed in the previous slide. Since oil aggregate capacity is more than 2000 litre and clear space is also less than 6 metres, it is recommended to provide Firewall between the two transformers. So far we have discussed about technical data sheet of a transformer, different methods of transformer insulation, and recommendation for providing Firewall as explained in Indian standards as well IEC. Further, we have also gone through a few practical cases to understand how to implement these guidelines in action. >> Continued in next part.
