Gemini’s design philosophy aims at the following aspects :

• True Hermetic Sealing ensures that the OIP Insulation retains the original properties even after several years of field operations;

• Our products are well engineered, our processes are well established. These factors ensure high reliability of our products whilst in service.

• Our products are truly maintenance-free; hence, only periodical cleaning of the products is required.

• Our products are designed to be user-friendly - right from unpacking, handling, erection, testing, commissioning and day to day operations in the field.

• Safety has been built into our products. Even in the unlikely event of an internal failure, the Instrument Transformer DOES NOT SHATTER or explode. A corrugated Stainless Steel Diaphragm has been provided, which, besides lending compensating volume for oil expansions during normal operations, acts as a proven pressure relief device, by peeling off from the tank from the weld and thus averts any explosion of the porcelain insulator.

Design Highlights:

• Thin Mild Steel Tank - leads to low Eddy Current in the CT tank and hence low heating even at higher currents.

• Lumped Primary Winding with rectangular copper strips - Highest mechanical strength during Short Circuit conditions, thus gives high Dynamic Current withstand-ability.

• Specially designed rectangular copper lugs for CT primary winding terminations provide strong and reliable joints and no hot spots.

• Capacitive graded Insulation is provided in the secondary lead out bushing. This ensures uniform voltage distribution and partial discharge free performance ensuring longer life of the product.

• Crimped joints are provided on secondary leads. This averts loose connections possible in fastened joints.

• Cemented flanges are used on Porcelain Insulator. This results in uniform mechanical stress distribution on the elastomer gasket - joints and hence minimizes the prospects of any oil leakage.

Process Highlights

• Major Paper insulation is dried in autoclaves, as per proven cycles under controlled vacuum and temperature.

• The EHV grade transformer oil is degassed and filtered until the desired properties are achieved.

• Each Instrument Transformer is pneumatically pressure tested at 1 kg/cm2 (gauge) at various assembly stages in order to assure the effectiveness of sealings provided.

• After oil flooding, each unit is hydraulically pressurized at 1 kg/cm2 (gauge) and maintained under pressure for 6 hours to ensure complete and homogeneous soaking of paper with oil and also checks effectiveness of sealings.

• Our products are adequately treated for corrosion resistance.

• Uniform Insulation thickness with capacitive graded Condenser Bushing is used in all Current and Voltage transformers from 12 kV up to 145 kV Class.

Tests And Performance

• All Product designs have been validated by type-tests as per applicable IEC Standards.

Highest System Voltage	Unit	12 kV	36 kV	72.5 kV	145 kV
Applicable Standards	IEC 60044-1 (2003); IS 2705 (1992)
Rated System Voltage	kV	11	33	66	132
Type Designation CT		GCT 12	GCT 36	GCT 72.5	GCT 145
One Min, Power Frequency. DRY/WET With stand Voltage on Primary Winding	kV	28/38	70/80	140/160	275
One Min. Power Frequency. Withstand Voltage On Secondary Windings	kV	3 kV or as per relevant standard.
Lightning Impulse	kVp	95	170	325	650
Total Creepage Distance	mm	400	1040	2250	3625
Arcing Distance	mm	208	425	816	1208
Rated Primary Current	A	Up to 1600 A.
Rated Secondary Current	A	1A or 5A.
Short Time Thermal Withstand Current/Duration	kA/s	40/1
Short Time Dynamic Withstand Current	kAp	100
Number of Cores	3/4 or as per requirement.
Output/Accuracy	As per requirement.