Is custom duty on repair & return of electronic equipment

Hi All, recently, I've purchased an electronic kit(4Kgs) from spain and paid duty charges (INR 20,000). Now i need to send the particular spare to Spain for repair & return. How should i do this? Should i pay duty again?. What are the documents to produce to avert duty charges. I'm an individual purchased this kit for my project. 

 

Looking forward your answers & valuable help.

 

Thanks & regards

Peter Manoj