Will normal overload relays trip on single phasing?

Yes.

Say we have 5.5 KW motor & it takes 10/11 Amps in Each Phase( Say 10.4,10.2,108 Amps in R,Y,B. We set the Over-load rleay at 10/11 Ampere.

3 Phase total current (10.4+10.2+10.8)= 31.4 Amps ----- Eq-1

If it become Single phase ( Or 2 Wire ), R-Phase got disconnected by any reason say loose Connection or Pro-long Heating. Then Y & B Phase will share 31.4 Amps ( Eq-1), So Each Phase take approx.15.7 Amps. But Overload relay set at 10-11 Amps. It will Trip the Motor in Overload.

If correctly set normal overload relays will trip when motor is fully loaded due to rise in current passing through the closed supply lines but with delta connected motors patially overloaded,the rise in line current may not b sufficient to operate the overload relay and eventually one phase may become overheated

It should as motor will continue to run on two phases and drawing greater load which ultimately will result in tripping of motor by the overload relay.

What do you means by normal overload relays mean not numerical relay ? 

Yes every relay will trip on overload if your current is more in one phase.

Yes it will trip, but takes time to trip. Because it has to produce a current which will be more than of  the setting of the overload. Thus of course will damage your motor in the long run. A delay of a second is vital in the life of a motor economically, specially on large motors.

Dear sir

Over load relay can't detect the single phasing, it can detect only overload.

But during the single phasing automatically the load will increase hence indirectly it will trip.

Single phase preventer is the exact protection for single phasing issues.

yes.it will trip.single phasing protection is an important feature for motor protection, they very purpose of putting a relayin circuit.

Yes. A 3-phase overload relay can be installed into a single phase system making sure that all 3 sensing bi-metal elements of the relay carry the current of the load