grammar

[Omprakash_Prajapat]

State electricity boards are estimated to have accumulated losses of a massive Rs. 70,000 crore.

In my opinion it should be like this

State electricity boards estimated to have accumulated losses of a massive Rs. 70,000 crore.

[Mister Micawber]

It is spelt 'grammar'.

No, the first sentence is correct: it should be in passive voice. (What you have constructed is just a sentence fragment.)
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Native English teacher at Mister Micawber's

[Omprakash_Prajapat]

Mr. Mister

why second sentence is wrong?

[Beeesneees]

There is no main verb.
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Cheers m' dears!

[Alan]

Hi,

Why is the second sentence wrong?

It's not a question of being or not being a 'main verb'. In the second sentence you have omitted 'are' but this is a passive construction and should be 'are estimated'. In other words it's not the electricity boards doing the estimating but the boards are estimated (considered) by people to have accumulated losses ..

Alan
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English as a Second Language
You can read my ESL story Present Simple

[Omprakash_Prajapat]

But sir,

Electricity Boards are the group of peoples.

[Mister Micawber]

Then you will need to change another part of your sentence:

State electricity boards estimated that they have accumulated losses of a massive Rs. 70,000 crore.
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Native English teacher at Mister Micawber's

[Omprakash_Prajapat]

Mr. Mister

It means we can use 'to have' only in passive voice sentences.

[Mister Micawber]

It means we can use 'to have' only in passive voice sentences.-- Huh? No, I didn't suggest that.

I wanted to have a sandwich.

Or do you see a more specific restriction of that kind?
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Native English teacher at Mister Micawber's

[Omprakash_Prajapat]

hmm

But, how can I distinguish the use of ' to have'?