# Transactive Energy to Thwart Load Altering Attacks on Power Distribution Systems
The attack-thwarting system forestalls the progress of the attack in harming stability and reliability of the power grid, without triggering the emergency load curtailment. To the best of our knowledge, this paper is the first that proposes an attack-thwarting system for guarding against load altering attacks. Two points are noteworthy about the attack-thwarting systems. First, there is a clear difference between attack thwarting systems and intrusion-detection systems (IDSs). The later systems are preventative security measures that are set up in a power grid to detect cyber attacks by monitoring communication traffic and power consumption data [25]. In contrast, the former systems are set up in a power grid to invoke a response to cyber attacks, so as to halt an attack's progress in damaging the grid [25]. The latter systems are studied well in the literature of load altering attacks [6; 7; 10; 20; 21], but the former systems are not. Second, the attack-thwarting systems are an essential part of the new _defense-in-depth_ strategy for the protection of cyber-physical systems [25; 26]. In this new defense strategy, the physical system in a cyber-physical system should be protected even if the cyber system is intruded. This new strategy ensures that the physical system can continue performing correctly, even if the cyber system is disrupted by the cyber attackers [26]. The proposed attack-thwarting system in this paper is based on provoking real-time adjustment of a flexible loads' power consumption in response to the load altering attack. In fact, the proposed system enables energy exchanges between the power distribution systems and the flexible loads to counter the power imbalances caused by the load altering attack. Such energy exchanges should be carried out in real-time operation of the power grid in accordance with the fast timing of the load altering attack. Also, the energy exchanges should be in-proportion to the power imbalances caused by the load altering attack, so as to preclude exacerbation of frequency disturbances. To fulfill the above requirements, the energy exchanges in the proposed attack-thwarting system are framed in a _transactive energy_ framework [27]. The emerging transactive energy framework enables real-time energy exchanges between power consumers and the power distribution systems. The contributions of this paper to the field can be summarized as follows:  
* An attack-thwarting system is proposed that can successfully counter load altering attacks on power distribution systems. The proposed attack-thwarting system uses energy exchanges between the power distribution systems and the flexible loads to counterbalance the harmful impact of the load altering attacks. * The energy exchanges in the proposed attack-thwarting system are framed in a transactive energy framework, so as to fulfill the essential requirements in thwarting the load altering attacks. * The performance of the proposed attack-thwarting system is assessed by conducting numerical simulations on IEEE standard 33-bus power distribution system. It is shown that the proposed attack-thwarting system can successfully forestall progress of a load altering attack without triggering emergency load curtailment. The rest of this paper is organized as follows: Power balancing in power grids is discussed in Section 2. The automatic generation control mechanism in power generators is explained in Section 3. The load altering attacks are reviewed in Section 4. The proposed attack-thwarting system is introduced in Section 5. Numerical simulations are provided in Section 6. Finally, the paper is concluded in Section 7.