2 Questions - floating neutral and separate grounding system

[a10jp]

I have 2 questions:

Q1: Recently as I was working on a radar site and discovered that the 5KV distribution system operating the radar is running on a floating neutral system. The site has very good ground grid (less than 3 ohms) with lightning protection and is running entirely on generator power. The system from the radar is kept separate from the other site facilities. The maintenance electrician told me that the power flux always stay within a certain operating range, although he did not tell me what that is. Why is a floating neutral being used here? COuld anyone figure out the reason? I thought floating neutral on HV can be an unsafe practice.

Q2: The same old arguemnt again, that the grounding system for sensitive data system should be kept ENTIRELY separate from the power system grounding. The arguemnt was to avoid noice and interference from the power side travelin g back to the data side. I heard that many times before. Is this a common practice for separate grouning system vs a common grounding system because the whole site is feeding off from the same source?
I was taught to think the a common grouding system is preferred provided the grounding on the power distribution side is done correctly.

 

[davidbeach]

Separate grounding systems are a good way to kill things, both people and equipment. To eliminate noise from the sensitive equipment, that grounding system should be bonded to the power ground system at exactly one location, no more, no less.

Ungrounded 5kV system means that the first ground fault doesn't trip anything; high resistance grounded would be far better, but ungrounded is not uncommon.

 

[waross]

You don't give much information on the 5KV system.
If you have a wye-delta transformer bank the primary wyepoint/neutral must be floated even though the system may be grounded and a neutral conductor is present at the transformer bank.
respectfully

 

[slavag]

Hi.
Agree with David.
Please pay attention for ungrounded system you also need
protections like to SEF or 59N (residual overvoltage).
Regards.
Slava