Surge Arrester in HT Side of the Transformer

Sir: you said "According to my understanding in step down transformer HT side surge arresters for the protection of the transformer primary winding."

Your right. Consider a 250 KVA transformer with 15 KV primary/ 400v secondary. Disregarding efficiency, its primary is rated for 17A, its secondary for 600 amps, and those windings will be sized accordingly. Lets say for ex., the primary windings are 12 AWG = 2.5mm^2. Wouldn't u wanna protect those windings with a surge protector, and isnt such a protection required by code?

Thanks you sir. I also same in your boat. Any country code of practise got stated need to protected the HT side of the transformer? If is it stated is it for protection of the transformer? Anyway surge can flow to LV side equipments connected?

<...no way the equipment connected to DB cab be damage because of surge...>

No-one can make any installation totally lightning-strike-free.

Yet, the most common mistake is to install such surge protection devices incorrectly. Lightning represents a severe over-voltage event which requires a shunt type surge protector. It must be installed as close as reasonably possible to the point where a load takes its power. This device, of course, is a MOV (metal oxide varistor) rated for the line voltage at the load.

Another common type of surge protection is the line reactor which will help with limiting inrush from over-voltages caused by other (non-lightning) events. Both type of surge protection is the best approach. After that, you can use over-voltage, under-voltage, phase loss, and rotation relays to protect equipment for events that the other surge protection devices don't cover. Of course, you could always use a UPS to protect vital equipment. They have surge protection built in.

Dear All,

We have an 18 MW Diesel Engine Generator of 11kV Gen. Voltage, connected to a 11/132 kV Transformer. Between the Generator and the Transformer we have a 11kV Vacuum Circuit Breaker acting as a Generator Circuit Breaker. Adjacent to Generator Terminals in Parallel to it, a Surge Arrester (Rated Voltage - 12kV, 10kA and 12.6 kV MCOV ) and Surge Capacitor of rating (15kV and .25 mfd) respectively is connected in parallel in all 3 phases to protect against any switching surges. (Between Generator and GCB)

We have also proposed to provide a Surge Arrester of Similar rating as mentioned above Between GCB and Transformer 11kV Terminals.

Could you please clarify whether a Surge Capacitor is also required to be provided between GCB and Transformer 11kV terminals in parallel with SA in all 3 phases.???

Besides, we have a 120kV and 10kA Lightning arrester connected at the transformer HT end.

Regards,

Raghavendran.R

Please start a new thread if you want everyone to see it.

If HT supply to transformer is via overhead line - You must install LA as close as possible to the transformer. This is to protect it against direct or indirect lightning.

If HT supply is through underground cable LA is not required as there is no question of direct or indirect lightning surge.

If HT supply is mixture of overhead line and cable, cable being at Transformer end AND the length of cable is long (say more than a kilometer) - LA is not required. Reason being the capacitance of cable to ground acts as a surge absorber. Hence energy of any lightning surge of O/H line, as it travels through the cable, is divert to earth, thus its wave shape modified to safe value by the time it reaches the Transformer terminals.

I do not know how big is your transformer but in case of large Transmission Line transformers, besides LA, the first turn of transformer winding has very thick insulation (say approx 25 mm in thickness compared to normal thickness of 0.5mm) and is gradually tapered of in first one or two turns to normal size. This is called surge coil and protects transformer against surge. This design is only followed in Transformers of few MVA and above and not in small Distribution Transformers.