Current Transformers
(72.5 kV and 170 kV)
CPSI assembles type CT and Type IOSK, CTs are of live tank type with rated voltage of 72.5 and 170 kV. All our Current Transformers adhere to the requirements of the international quality standards and our quality system, environment management system, safety management systems are certified to ISO 9001–2008, ISO 14001 and ISO 18001respectively.
Design
The primary winding consists of aluminum sections accommodated in the top housing. The primary winding is rigid, concentric and distributed uniformly around the insulated secondary winding in order to have optimum mechanical endurance against short circuit forces.
The primary windings are terminated on the sides of the top housing with provisions for convenient primary ratio change over. The cores and secondary windings are enclosed in a well-contoured, rigid aluminum shell, which is fully insulated from the top housing.
The secondary leads are taken to the base of the CT through an oil impregnated paper (OIP) insulated condenser bushing. The insulation structure is specially designed to have a uniform drop of electric field radially as well as longitudinally across the bushing. This is achieved by specially-contoured electrodes, uniform insulation around the electrodes and fine potential grading along the bushing. High quality insulating Kraft paper is used for insulation. The paper insulation is dried under heat and vacuum and impregnated with oil to achieve excellent insulation as well as ageing properties. The fully assembled CTs are dried and oil filled under vacuum in evacuated heating chambers.
Construction
Brown glazed porcelain Insulator with shed profile as per IEC 815 is used. Gray porcelains or variant shed profiles can also be supplied on request. The porcelains are cemented to aluminum alloy flanges on both sides with port land cement for providing optimum mechanical strength.
The top housing is made of corrosion resistant aluminum alloy, form fitted to the internal active body. The insulated primary and secondary windings are assembled in the top housing. Primary terminals, with ratio changeover arrangements are accessible on the sides.
Stainless steel bellow mounted at the top compensates for expansion/contraction of oil due to ambient temperature variations. Thus the CT is hermetically sealed. The bellow position viewed through the window on the Hood indicates the operational status and the oil level in the CT. An oil-filling plug is provided at the top of the bellow.
The fully encapsulated CT is impervious to rain, snow and ice and can sustain considerable temperature variations. High quality CRGO grade silicon steel, Mu-metal cores of wound ring type are used. Up to 6 cores of various accuracy classes, burdens and Rated Normal Current can be accommodated in one CT to meet different metering and protection requirements. The secondary winding is uniformly distributed over the circumference of the core. This minimizes the reactance of the winding and helps in obtaining accurate transformation ratio.
The CT base structure is made of Aluminum Alloy. The secondary terminal box, oil sampling valve and earthing pads are provided on the base. Main lifting lugs and mounting holes are also provided on the base.
To provide stability during lifting and for erecting up from prone position, two additional lugs are provided on the top housing.
Tests And Performance
The performance and reliability of these Current Transformers has been verified at renowned international testing laboratories like KEMA(Netherlands) and CPRI (India). The CTs are type tested for short circuit performance, Thermal Stability Test, Multiple Chopped wave Impulse test, wet Lightning Impulse Test, partial discharge etc. as per IEC 44-1 - 1996, IEC: 61869-1 (2007) & IEC: 61869-2(2012)
Transport
All CTs are to be transported in horizontal position only. For further details please refer to the instruction manual.
Maintenance
The product is self-contained, maintenance free and does not require spares. For regular and periodic checks on the equipment, please refer the instruction manual supplied with the CTs.
