In the era of digitizing electrical power networks to smarter systems, there arises an increased demand of security solutions in various components of the Smart Grid networks. The traditional and general security solutions applicable to hardware devices, network elements and software applications are no longer able to provide comprehensive readymade alternatives to secure the systems. As the scalability of the system increases, component-wise security solutions are essential for end-toend security. Considering this current scenario, in this paper, the key management techniques, particularly the lightweight Key Management Systems (KMS) methodologies that have been proposed in the past are reviewed in the context of Advanced Metering Infrastructure (AMI) of the Smart Grid Systems.