Why PT and CT Terminals are Star Connected

Why PT and CT Terminals are Star Connected

In Alternating Current power system two most important instrument transformers are frequently used, one is current transformer and voltage transformer or potential transformer. One interest thing is, both the transformers are star connected. in this tutorial, we are going to see the advantage of star configuration.

Advantage of Star connection in Potential transformer:

• In potential transformer the primary and secondary windings are star connected, because in star configuration, the line voltage is root 3 times of phase voltage, hence the voltage distribution to each winding is reduced or divided by 1.732 times. Due to that the insulation cost on the primary winding comes lesser. But in delta configuration the line voltage is equal to phase voltage, therefore we have to insulate the transformer to withstand up to 11kV.
• PT’s primary winding one terminal is directly connected to the main supply another one is connected with the ground, refer the drawing, therefore any fault in the potential transformer the fault current directly goes to the ground, the fault current do not enter in to our power distribution.

Note: All PTs are connected through a 11kV fuse unit.

• Easy installation: in this, the PT primary terminal is connected with the line voltage and secondary terminal is connected to the ground, therefore the installation procedure is simple, easy replacement and maintenance free.

Why CT secondary terminals are star connected:

Star configuration is having an advantage of the line current is equal to phase current, therefore our protecting device measures the exact CT’s secondary current. It optimizes our system protection status.[wp_ad_camp_1]

Never forget to read:

• Why CT secondary Terminal should be in short condition.
• What is the Use of Transformer vector grouping
• Why Transformer rating in KVA
• What is the use of CT equipotential Ring of the transformer?
• What is Voltage Drop and How to calculate voltage drop?
• Electrical calculations

• Voltage Drop Calculations
• Wire calculations
• Electrical Why Question
• How to Read Potential Transformer nameplate details