Numerical Transformer Differential Relay

Features

• Biased current differential protection
• Fast differential Hi-set
• Dual slope characteristics
• Inbuilt CT Ratio correction factor
• Adjustable 2nd harmonic restraint
• Adjustable 5th harmonic blocking
• Inbuilt Vector group compensation
• Two groups of settings
• History of 5 latest faults

JND 040 provides differential protection for power transformer. The relay measures the line current of each phase from each of the windings of the transformer. Relay calculates the differential current (Id) and restraining current (Ir) per phase. The differential characteristics define the operating and the restraining regions. The shape of the characteristics defined by Initial pickup (ik), SLOPE1 (DF1), SLOPE2 (DF2) and break point (kp) are programmable. If ‘Ir’ is less than ‘kp’, then characteristics is defined by ‘DF1’ and is applicable for small differential currents. If ‘Ir’ is greater than or equal to ‘kp’, then characteristics is defined by ‘DF2’ and is applicable for large differential currents. If the operating point i.e. (Id, Ir) is within the operating region, then the relay trips. The relay provides programmable 2nd and 5th harmonic current restraint, which, exist when transformer is energized and over excitation condition exists respectively. The relay provides stability on external “line to line” and “line to ground” faults. The relay has in-built vector group compensation selection and CT ratio correction, hence the usage of external interposing CT can be avoided.