According to the Search API documentation about rate limits:
"When using the Search API you are not restricted by a certain number of API requests per hour, but instead by the complexity and frequency."
But I receive in response headers parameter 'X-RateLimit-Limit'=150 So I am limited to 150 API calls per hour.
Why?

Replies
The Search API is at https://search.twitter.com/search.json -- you shouldn't be getting those headers when using that endpoint.