Three Winding Transformer - TCC Tab

Select this check box to plot transformer damage curve for 100% withstand. This is without taking into consideration the derating factor for winding connection type and the type of fault.

Select this check box to plot transformer damage curve taking into consideration the derating factor for winding connection type and the type of fault. The transformer curve shifts left by 58% or 87% depending on the connection type.

Select this check box to plot the transformer damage curves as Category II to IV (thermal and mechanical withstand) for frequently occurring faults. The curve shifts towards the left depending upon the transformer impedance.

When this check box is selected, the program automatically scales the TCC curves based on the phase connection type. Traditionally, for 3PH curves in a TCC, scaling the curves based on the reference voltage is adequate. If a line-to-neutral connected 1PH device is to be plotted with an upstream 3PH device, then the LN connected 1PH curve needs to be shifted by a factor of the SQRT(3) in addition to the voltage-based scaling. Similarly, if a line-to-neutral connected 1PH device is to be plotted with an upstream 1PH-3W device, then the LN connected 1PH curve needs to be shifted by a factor of the 2 in addition to the voltage-based scaling.

When the check box is not selected, scaling based on the phase connection type is not applied.

The check box status for individually stored TCC plots can be different. The default for new TCC plots is obtained from the database for the device.

The standard according to which the curve is plotted.

The maximum time in seconds for which the transformer damage curve is plotted.

When the IEC 76-5.4 standard is selected, the thermal ability of the transformer to withstand short circuit is plotted for the time specified here. The default is 2 seconds.

Magnetizing inrush current as multiples of full load amps for the primary winding.

Time taken by magnetizing inrush current in terms of number of cycles.

Calculation basis for full load amps. “MVA O/L” is the MVA capacity for overload and “Rated MVA” is the self-cooled capacity.

(Three-winding transformer only) The side of transformer for which the short circuit withstand is plotted. Short circuit is applied on Secondary or Tertiary side. The primary line current is shown in the plot.

Specify whether the protective device is accessible only to qualified personnel (supervised) or unsupervised. This affects the protective device settings based on NEC rules.