Phase Indication Lamp Flickering in HT Panel

Some where in the indicating lamp circuit, neutral point is open.

you have to isolate it by regrouping .check removing lamp circuit alone connected to grid PT, similarly lamp circuit connected to BUS PT.

There is no open circuit in indication lamp. If I remove the lamp circuit, flickering stops. Even I remove the star point of all the three neutral points of PT.

Maybe a shielded cable if it's just noise.....but I would first check the voltage feed to the bulb with a power analyser to determine if it's harmonics, noise, transient etc....it may be indicative of a larger problem....

https://en.wikipedia.org/wiki/Electric_power_quality

I would guess it is a power issue, but there is something confusing with the description.

What do you mean by "lamps being connected to earth"? Since they are connecter in Star, they need to be connected to the neutral point, and according to the North American electrical regulation, there can be only one connection from Neutral to ground, and that would be at the transformer.

If you please, can you provide more information about the plant? Maybe a schematic?

what is the frequency of the flickering? Maybe you are seeing 3rd harmonics, 150Hz or 180Hz, from having multiple grounds on a 'power system'...

All 3 lamps flickering?

each phase in time with the others, phase 1 flickering on-off same time everywhere?

Most definitely, some one there in the control room has a screw loose.

Pl go thro the above SLD of PT. If I remove the "PT sec Star Point earth" or "Indication Lamp Star Point earth," flickering stops.

Also, the voltage between both of the star point w.r.t earth is 30 V (instead of 0).

Sounds to me like there is still a screw loose. Although, with the data presented, there could still be a phasor problem, such that the three phases are not locked into grid frequency (you did not state the flicker frequency, which I hope is way less than 1 Hz or you really are going to have a problem).

You think you have earth ground, but I now submit you should must investigate earthing potentials throughout your facility, stop ignoring any ground fault alarms (if you did), and get proper bonding to earth ground as established by grounding network near the generator.

Part of the problem falls to the choice of using LEDs vs. Incandescent bulbs. LEDs are by their very nature on-off devices that inherently lack any electrical/thermal inertia. The design of the electronics in the base of the LED determines its response to the AC waveform; i.e., the larger the capacitor (if any) the longer the LED stays lit as the AC voltage falls below its extinguishing voltage.

Incandescent bulbs operating at 50/60Hz have enough thermal inertia which, when coupled with the persistence of the human eye, create the "picture" of a constantly lit bulb, plus they provide a constant path for draining off any phantom/capacitive voltage that in reality doesn't provide enough current to heat the filament.