We know that when two huge black holes collide they produces gravitational waves in space time curvature. So if I am not wrong another object in space if goes in that direction during production of waves then that huge black holes can push that object like star, sun, planet into opposite direction. So, indirectly, two objects in space can repel each other in a very few cases.
Is it also the case that two planets can repel each other in a few cases?
No, gravity always pulls things together.
Gravitational waves can cause a stretching of an object as they pass, but not much "push". After the waves pass, the object will return to its unstretched shape and it will not have moved. There is an effect in which an object can gain momentum (ie be pulled) when it enters the region around a rotating black hole. However it is dragged sideways, it isn't pushed away.
This "frame dragging effect" also happens around other rotating bodies, and has been measured around the Earth. It is a very subtle effect that required some very sensitive measurements.
There are no situations in which two planets could actually "repel" each other. The dominant term in the gravity between two planets will always pull them together.
Gravitational waves mostly just shake things, there's not much push-- especially in comparison to the gravity of the object that created the waves. It seems unlikely there could ever be a net push. Still, it is thought that empty space already has a tendency to "push" objects apart, based on the idea of "dark energy." So two objects in an otherwise empty universe, if they are far enough apart, would be seen to push each other apart based on a gravitational effect-- but it would not be viewed as the gravity of the objects, but rather the antigravity, in effect, of all the empty space between them.
