Time delay for 50Ns.

[beyond86]

Gents,
I have some problems with choose of time delay for 50N sensitive (core balance CT). I have 10 kV network, where neutral grounded through resistor (150A).
Which minimal time delay 50Ns recommended for this type of network?
I chose time delay 0.05 sec for feeder which supply transformer 10\0.4 kV. Pickup current 20A primary.
Is it possible spurious trip of 50Ns during start-up transformer (inrush current)?

 

[RRaghunath]

When you have CBCT, the delay can ideally be zero.
Make sure the 10kV power cable is centered well in CBCT window and that the armour, if taken through the window, is brought out the same way following the cable termination.
If the above rules are met, the delay of 0.05s will not create any problem of 51Ns maloperation due to transformer energising inrush currents.

 

[beyond86]

RRaghunath, thanks!