Medium Voltage Control Power Transformers

Medium Voltage Control Transformers are single phase transformers used to supply low voltage control power in medium voltage switchgear. These reliably, step-down medium voltage inputs which range from 2.4kV to 15kV to low voltages of 120/240 VAC. These low voltages are used to supply power to a control circuit in electrical panels, where a large variety loads are necessary or there is a need to connect to a primary distribution circuit. CPT Details

• Primary taps 3 +/-2.5%
• For indoor use only
• Self-cooled cast coil
• Available as unfused only

Medium Voltage Control Power Transformers (CPTs) are single-phase dry-type transformers used to supply control power in medium voltage switchgear and transformers. They have open construction with an epoxy resin encapsulated coil. Power ratings of 5, 10 and 15kVA with nominal primary voltages range from 2.4kV to 15kV and secondary voltages typically are configured for 120/240V (series parallel) operation. It is supplied with three +/-2.5% taps above and below nominal voltage on the primary winding. For low power losses, the magnetic core is wound with grain-oriented electrical steel, and the high-voltage coil is vacuum encapsulated in epoxy resin. In addition to protecting the coil from moisture and foreign particulate matter, the resin epoxy provides a higher ability to withstand mechanical forces during short-circuits, than standard varnished Vacuum Pressure Impregnation (VPI) or “dip in varnish and then bake” process.

Medium voltage current transformers from 5kV to 35.5kV Class system voltages are available in Bar Type, Window Type, and Wound Primary Type, with a primary current rating up to 1000 Amps. CTs are encapsulated with epoxy or polyurethane resin cast construction, and are able to withstand heavy fault conditions, but are not made for exposure to sunlight. The core and coil assemblies are vacuum molded to ensure a homogenous, bubble-free construction. The medium voltage CT construction provides high di-electric and BIL 4.5 to 125 full wave crest kV.

The MV CTs can be supplied with round or rectangular windows in the center. This provides easy installation for customers as they can use their primary cable or bus bar through the CT ID. Usually, these CTs come with an equal-potential shield around the ID surface. This equal-potential screen is attached with a pigtail (lead with connector) which comes out of the ID surface. This arrangement allows uniform distribution of charge (non-concentrated) around the surface, which further ensures that the CTs withstand high current and high voltage environments in long-term use.

We also provide wound primary medium voltage CTs where primary and secondary terminals are usually taken out from the top surface of the CTs. Customers can make the primary connections using these terminals. The bus bar type MV CT construction usually has resin-cast CTs with bus bars built into the construction. Various primary bar arrangements can be supplied to suit most applications. Medium voltage CTs come with or without mounting brackets.

MV CTs are designed to meet IEEE C57.13 or IEC 60044 standards. A partial discharge test is carried out as per Canadian CAN3-C13-M83 or as per IEC 60044. Standard burdens are used to measure accuracies (ratio and phase angle error) on calibrated accuracy test bridges. Hi-pot tests are carried out as per the required standards.