  As a national critical infrastructure, the smart grid has attracted
widespread attention for its cybersecurity issues. The development towards an
intelligent, digital, and Internetconnected smart grid has attracted external
adversaries for malicious activities. It is necessary to enhance its
cybersecurity by either improving the existing defense approaches or
introducing novel developed technologies to the smart grid context. As an
emerging technology, digital twin (DT) is considered as an enabler for enhanced
security. However, the practical implementation is quite challenging. This is
due to the knowledge barriers among smart grid designers, security experts, and
DT developers. Each single domain is a complicated system covering various
components and technologies. As a result, works are needed to sort out relevant
contents so that DT can be better embedded in the security architecture design
of smart grid. In order to meet this demand, our paper covers the above three
domains, i.e., smart grid, cybersecurity, and DT. Specifically, the paper i)
introduces the background of the smart grid; ii) reviews external cyber attacks
from attack incidents and attack methods; iii) introduces critical defense
approaches in industrial cyber systems, which include device identification,
vulnerability discovery, intrusion detection systems (IDSs), honeypots,
attribution, and threat intelligence (TI); iv) reviews the relevant content of
DT, including its basic concepts, applications in the smart grid, and how DT
enhances the security. In the end, the paper puts forward our security
considerations on the future development of DT-based smart grid. The survey is
expected to help developers break knowledge barriers among smart grid,
cybersecurity, and DT, and provide guidelines for future security design of
DT-based smart grid.
