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11 KV 33 KV
Technical Specification As Per IS : 2705
General Particulars 11KV 33 KV
Highest System Voltage( H.S.V.) 12 KV ( r.m.s.) 36 KV (r.m.s.)
Power frequency dry/ wet withstand voltage on primary winding for one minute 28 KV ( r.m.s.) 70 KV ( r.m.s.)
Lightning Impulse withstand Voltage ( 1.2 x 50 μs ) 75 KV ( r.m.s.) 170 KV ( r.m.s.)
PD measuring Voltage / Permissible Voltage 7.6/50 23.0/50
Specific Particulars
Rated Transformation Ratio As per customer requirement (in Amp.)
Rated Primary Current Upto 2000 Amp.
Rated Secondary Current 1 Amp /  5 Amp / 0.577 Amp.
Short Time Thermal Current (Ith) As per customer requirement.
In general CT is to be specified with STF of 100 for 1 Sec. or STC (lth) equal to the system fault level whichever is lower. KA ( r.m.s. )
Ith duration 0.5 to 3.0 Second
Short Time Dynamic Current 2.5 X Ith KA (Peak)
Number of Cores Upto 3 cores
Output Burden Upto 60VA, 0.8 pf Lagging
Accuracy Class For Metering :
0.2S, 0.2, 0.5S, 0.5, 1.0 & 3.0. For Protection:                                                  
5P, 10P, 15P & PS
IAF, ALF, Knee Point Voltage, Exciting Current & Resistance As per customer requirement / Design Constraints
Type of construction Epoxy Resin cast suitable for differnt panels.
Constructional / Salient Features
1. CRGO M-4 or M-3 grade toroidal cores are wound with secondary enameled copper wire, which is distributed uniformally on the periphery of the core to achieve minimum leakage reactance. Inter-layer insulation is provided to avoid secondary windiang short-circuiting in times of fault in the system.
2. Primary winding consists of flexible rope of copper and has the required number of turns in one or more sections. Their ends are crimped and taken out through copper rectangular strips or rods as per customer requirement.
3. Insulation consists of high quality epoxy resin. Initially, the secondary wound cores are mounted & cast in the required mould ensuring minimum clearance as per the voltage requirements. Then the primary winding is cast along with the above in the required mould. Casting is done under vacuum in the epoxy resin cast plant specifically dedicated for the purpose. It has mixing & pouring chambers with controlled temperature and vacuum conditions. Procedure of casting is followed strictly by the resin manufacturer for the particular resin-mix.
4. Curing is done at 1000 C or at room temperature for the specified time depending upon the type of resin used.
5. Each transformer undergoes all the routine tests before dispatch and is delivered safe at site duly packed. However, following precautions must be observed for its intended performance:
Transformer is to be unpacked fully before carrying out site tests.
Before energizing, all the secondary terminals not in use are to be short circuited and grounded. Primary connection is to be tightened sufficiently to avoid hot connection.
6. As the transformer is fully encapsulated, routine maintenance is limited to clean the outer surface only.
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