OIP Insulated Transformers

Current Transformer


Gemini’s range of OIP Insulated Instrument Transformers use Oil Impregnated Paper  Insulation and are designed for serving in Outdoor applications,  with several unique features with one aim – TOTAL RELIABILITY. Our present range of OIP Current Transformers  include CTs from 12 kV to 145 kV as per International Standards (IEC).


Design


Gemini’s OIP insulated outdoor products are subjected to extreme climatic conditions at Customer Sites and hence Quality and Reliability have been built into the Product, right from the design stage and are followed up through established manufacturing processes, rigorous In-process Quality checks and the designs validated by exhaustive type testing and satisfactory field performance.

 

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.
  • Thin Mild Steel Tank - Resilience effect - Absorbs mechanical shocks on primary terminals.
  • 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.


Technical Data

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.