What is power zerk (transients)? Why does it happen?

That sounds like a total new thing to me. Could you explain a bit please?

sometime suddenly all machine stop..at same time
so i want to know its reason..

Is it transient/spike that you are talking about?
Could you please link some document or source which describes "power zerk"?

yes its spike or transient...
i dont know about its reason but on my experience i know only that sometime due to voltage variation in short time, its power zerk.

why this happen and what is its solution..?
i have problem that at this time all machine stop.

Well, mostly the sources for transients are load fluctuations. Sometimes faults which are not directly in the immediate network of the power system can cause it too. Not so well designed power electronic circuits are other sources.

Operations as simple as throwing a switch to either power ON or power OFF substantial loads can cause transients in power system. Although most electric components like motors, lightings and other power loads will not mostly have issues when dealing with such transients, the story is different when power electronic components having sophisticated control has to deal with transients. Servo Drive units used in many industrial environments for precision control of machines could possibly be one good example which are easily affected by transients. Manufacturers require proper filters and isolation transformers to be used with them to ensure reliable working.

There once was a case at the place I work when the automatic switching of a power factor correcting capacitor was triggering a transient making one of the Servo Drive driven machines to stop regularly. Using an isolation transformer solved the issue by the way.

thank u