Application-Based Measures for Developing Cyber-Resilient Control and Protection Schemes in Power Networks

Electric power systems are a part of the most-crucial infrastructure on which societies depend. In order to operate efficiently and reliably, the physical layer in large electric power networks is coupled with a cyber system of information and communication technologies, which includes compound devices and schemes, such as SCADA systems and IEDs. These communication-base schemes and components are mainly a part of protection and control systems, which are known as the backbones of power networks, since the former detects abnormal conditions and returns the system to its normal state by initiating a quick corrective action, and the latter preserves the integrity of the system and stabilizes it following physical disturbances. This dissertation concentrates on the cyber-security of protection and control systems in power networks by unveiling a vulnerable protective relay, i.e., the LCDR, and a susceptible controller, i.e., the AGC system, and proposing application-based measures for making them resilient against cyber threats. LCDRs are a group of protective relays that are highly dependent on communication systems, since they require time-synchronized remote measurements from all terminals of the line they are protecting. In AC systems, this type of relay is widely used for protecting major transmission lines, particularly higher voltage ones carrying giga-watts of power. On the other hand, due to the limitations of other protection schemes, LCDRs has been identified as a reliable protection for medium-voltage lines in DC systems. Therefore, the cyber-security of LCDRs is of great importance. On this basis, this dissertation first shows the problem in both AC and DC systems and reveals the consequences and destructiveness of cyber-attacks against LCDRs through case studies. Then, it presents three solutions to address his problem, two for AC networks and one for DC grids. For AC systems, this dissertation presents two methods, one that can be used for SV-based LCDRs, and another one that works for both SV-based and phasor-based relays. Both methods are initiated after LCDRs pickup, to confirm the occurrence of faults and differentiate them from cyber-attacks. To detect attacks, the first method compares the estimated and locally-measured voltages at LCDR's local terminal during faults for both PS and NS. To estimate the local voltage for each sequence, the proposed technique uses an UIO, the state-space model of the faulty line, and remote and local measurements, all associated with that sequence. The difference between the measured and estimated local voltages for each sequence remains close to zero during real internal faults because, in this condition, the state-space model based on which the UIO operates correctly represents the line. Nevertheless, the state-space model mismatch during attacks leads to a large difference between measured and estimated values in both sequences. The second proposed method for an AC LCDR detects attacks by comparing the calculated and locally-measured superimposed voltages in each sequence after the relay picks up. A large difference between the calculated and measured superimposed voltages in any sequence reveals that the remote current measurements are not authentic. Given that local measurements cannot be manipulated by cyber-attacks, any difference between the calculated and measured superimposed voltages is due to the inauthenticity of remote current measurements. The proposed method for DC LCDRs is comprised of POCs installed in series with each converter. During faults, the resultant RLC circuit causes the POCs to resonate and generate a damped sinusoidal component with a specific frequency. However, this specific frequency is not generated during cyber-attacks or other events. Thus, LCDRs' pickup without detecting this specific frequency denotes a cyber-attack. Given that the frequency extraction process is carried out locally by each LCDR, the proposed approach cannot be targeted by cyber-attacks. On the other hand, an AGC system, which is the secondary controller of the LFC system, is a communication-dependent vulnerable controller that maintains tie-lines' power at their scheduled values and regulates grid frequency by adjusting the set-points of a power plant's governors. This dissertation proves the destructiveness of cyber-attacks against AGC systems by proposing a SHA that disrupts the normal operation of the AGC system quickly and undetectably. Afterwards, two methods are proposed for detecting and identifying intrusions against AGC systems and making them attack-resilient. Both methods work without requiring load data in the system, in contrast to other methods presented in the literature. To detect attacks, the first method estimates the LFC system's states using a UIO, and calculates the UIO's RF, defined as the difference between the estimated and measured states. In normal conditions, the estimated and measured values for LFC states are ideally the same. Therefore, an increase in the UIO's RF over a predefined threshold signifies an attack. This method also identifies attacks, i.e., determines which system parameter(s) is (are) targeted, by designing a number of identification UIOs. The general idea behind the second proposed method for detecting and identifying attacks against AGC systems is similar to the first one; yet, the second one takes into account the effect of noise as well. Therefore, instead of a UIO, the second method utilizes a SUIE for estimating the states of the LFC system and minimizing the effect of noise on the estimated states. Similarly, increasing the SUIE's RF over a predefined threshold indicates the occurrence of an attack

Extruded polycarbonate/Di-Allyl phthalate composites with ternary conductive filler system for bipolar plates of polymer electrolyte membrane fuel cells

Here, we report multifunctional polycarbonate (PC)-based conductive polymer composites (CPCs) with outstanding performance manufactured by a simple extrusion process and intended for use in bipolar plate (BPP) applications in polymer electrolyte membrane (PEM) fuel cells. CPCs were developed using a ternary conductive filler system containing carbon nanotube (CNT), carbon fiber (CF), and graphite (G) and by introducing di-allyl phthalate (DAP) as a plasticizer to PC matrix. The samples were fabricated using twin-screw extrusion followed by compression molding and the microstructure, electrical conductivity, thermal conductivity, and mechanical properties were investigated. The results showed a good dispersion of the fillers with some degree of interconnection between dissimilar fillers. The addition of DAP enhanced the electrical conductivity and tensile strength of the CPCs. Due to its plasticizing effect, DAP reduced the processing temperature by 75 °C and facilitated the extrusion of CPCs with filler loads as high as 63 wt% (3 wt% CNT, 30 wt% CF, 30 wt% G). Consequently, CPCs with the through-plane electrical, in-plane electrical and thermal conductivities and tensile strength of 4.2 S cm-1, 34.3 S cm-1, 2.9 W m-1 K-1, and 75.4 MPa, respectively, were achieved. This combination of properties indicates the potential of PC-based composites enriched with hybrid fillers and plasticizers as an alternative material for BPP application

Bidirectional and Stretchable Piezoresistive Sensors Enabled by Multimaterial 3D Printing of Carbon Nanotube/Thermoplastic Polyurethane Nanocomposites

Fabricating complex sensor platforms is still a challenge because conventional sensors are discrete, directional, and often not integrated within the system at the material level. Here, we report a facile method to fabricate bidirectional strain sensors through the integration of multiwalled carbon nanotubes (MWCNT) and multimaterial additive manufacturing. Thermoplastic polyurethane (TPU)/MWCNT filaments were first made using a two-step extrusion process. TPU as the platform and TPU/MWCNT as the conducting traces were then 3D printed in tandem using multimaterial fused filament fabrication to generate uniaxial and biaxial sensors with several conductive pattern designs. The sensors were subjected to a series of cyclic strain loads. The results revealed excellent piezoresistive responses with cyclic repeatability in both the axial and transverse directions and in response to strains as high as 50%. It was shown that the directional sensitivity could be tailored by the type of pattern design. A wearable glove, with built-in sensors, capable of measuring finger flexure was also successfully demonstrated where the sensors are an integral part of the system. These sensors have potential applications in wearable electronics, soft robotics, and prosthetics, where complex design, multi-directionality, embedding, and customizability are demanded

Finite-element modeling and optimization of 3D-printed auxetic reentrant structures with stiffness gradient under low-velocity impact

Additive manufacturing technologies such as fused filament fabrication (FFF) allow the production of metastructures with global properties that can be tailored to their specific application. This study simulated and optimized an auxetic re-entrant structure with a stiffness gradient for enhanced energy absorption with low acceleration peaks under different low-velocity impact conditions. The finite-element method (FEM) was used, and appropriate constitutive models were fitted to static and dynamic tensile and compressive data of acrylonitrile butadiene styrene (ABS) tested under various strain rates. A Johnson–Cook plasticity model demonstrated the best compromise between accuracy and computational efficiency. A simulation strategy using explicit FEM was developed to simulate additively manufactured auxetic metastructures under impact conditions. There was good agreement between the model prediction and the experimentally observed structural response. A parametric optimization was implemented to enhance the energy absorption capability with low acceleration peaks of a graded auxetic re-entrant structure for different impact velocities

Early Risk stratification for Arrhythmic death in Patients with ST-Elevation Myocardial Infarction

BACKGROUND: Sudden cardiac death is a leading cause of death in patients with ST-elevation myocardial infarction (MI). According to high cost of modern therapeutic modalities it is of paramount importance to define protocols for risk stratification of post-MI patients before considering expensive devices such as implantable cardioverter-defibrillator. METHODS: One hundred and thirty seven patients with acute ST-elevation MI were selected and underwent echocardiographic study, holter monitoring and signal-averaged electrocardiography (SAECG). Then, the patients were followed for 12 ±3 months. RESULTS: During follow-up, 13 deaths (9.5%) occurred; nine cases happened as sudden cardiac death (6.6%). The effect of ejection fraction (EF) less than 40% on occurrence of arrhythmic events was significant (P<0.001). Sensitivity and positive predictive value of EF<40% was 100% and 76.95% respectively. Although with lesser sensitivity and predictive power than EF<40%, abnormal heart rate variability (HRV) and SAECG had also significant effects on occurrence of sudden death (P=0.02 and P=0.003 respectively). Nonsustained ventricular tachycardia was not significantly related to risk of sudden death in this study (P=0.20). CONCLUSION: This study indicated that EF less than 40% is the most powerful predictor of sudden cardiac death in post MI patients. Abnormal HRV and SAECG are also important predictors and can be added to EF for better risk stratification

Early septal activation, successful lateral ablation

The coronary sinus activation pattern is an important clue for the detection of arrhythmia mechanisms and/or localization of accessory pathways. Any change in this pattern during radiofrequency ablation should be evaluated carefully to recognize the presence of another accessory pathway or innocence of the accessory pathway during arrhythmia. Intra-atrial conduction block can change the coronary sinus activation pattern. Negligence regarding this phenomenon can cause irreversible complications. Here we describe a case with left lateral accessory pathway conduction in which intra-atrial conduction block completely reversed the coronary sinus activation pattern. (Cardiol J 2008; 15: 181-185

A patient with sick sinus syndrome, atrial flutter and bidirectional ventricular tachycardia: Coincident or concomitant presentations?

Channelopathies are among the major causes of syncope or sudden cardiac death in patients with structurally normal hearts. In these patients, the atrium, ventricle or both could be affected and reveal different presentations. In this case, we present a patient with an apparently structurally normal heart and recurrent syncope, presented as sick sinus syndrome with atrial flutter and bidirectional ventricular tachycardia. (Cardiol J 2007; 14: 585-588)

Relationship between QRS complex notch and ventricular dyssynchrony in patients with heart failure and prolonged QRS duration

Background: Cardiac resynchronization therapy (CRT) has been accepted as an established therapy for advanced systolic heart failure. Electrical and mechanical dyssynchrony are usually evaluated to increase the percentage of CRT responders. We postulated that QRS notch can increase mechanical LV dyssynchrony independently of other known predictors such as left ventricular ejection fraction and QRS duration. Methods: A total of 87 consecutive patients with advanced systolic heart failure and QRS duration more than 120 ms with an LBBB-like pattern in V1 were prospectively evaluated. Twelve-lead electrocardiogram was used for detection of QRS notch. Complete echocardiographic examination including tissue Doppler imaging, pulse wave Doppler and M-mode echocardiography were done for all patients. Results: Eighty-seven patients, 65 male (75%) and 22 female (25%), with mean (SD) age of 56.7 (12.3) years were enrolled the study. Ischemic cardiomyopathy was the underlying heart disease in 58% of the subjects, and in the others it was idiopathic. Patients had a mean (SD) QRS duration of 155.13 (23.34) ms. QRS notch was seen in 49.4% of the patients in any of two precordial or limb leads. Interventricular mechanical delay was the only mechanical dyssynchrony index that was significantly longer in the group of patients with QRS notch. Multivariate analysis revealed that the observed association was actually caused by the effect of QRS duration, rather than the presence of notch per se. Conclusions: QRS notch was not an independent predictor of higher mechanical dyssynchrony indices in patients with wide QRS complex and symptomatic systolic heart failure; however, there was a borderline association between QRS notch and interventricular delay

Predictors of ventricular tachycardia induction in syncopal patients with mild to moderate left ventricular dysfunction

Background: In patients with mild to moderate left ventricular dysfunction (LVD) (35% &#163; LVEF &#163; 50%) who present with syncope, demonstration of tachy and/or brady-arrhythmia has prognostic value. In this group of patients electrophysiological study (EPS) is often necessary. Methods: A total of 53 consecutive patients with mild to moderate LVD and history of undetermined syncope underwent EPS. Sinus node function, His-Purkinje system conduction and ventricular electrical stability were evaluated. Results: Twenty eight patients (52.8%) had induction of sustained monomorphic ventricular tachycardia (VT) and five (9.4%) patients had a sustained ventricular arrhythmia other than monomorphic VT (ventricular flutter, ventricular fibrillation, and polymorphic VT) induced during EPS. Abnormal sinus node function and/or His-Purkinje system conduction was found in five (9.4%) patients. Age, gender, history of myocardial infarction, type of underlying heart disease and history of revascularization were not predictors of VT induction. Wide QRS morphology independently, and lower left ventricular ejection fraction and presence of pathologic q wave in precordial leads dependently, could increase risk of VT induction. Conclusions: The EPS can determine which patient with syncope and mild to moderate LVD is likely to benefit from placing an ICD for prevention of sudden cardiac death. Pathologic precordial q wave, wide QRS morphology and lower left ventricular ejection fraction could be predictors of VT induction during EPS. Wide QRS morphology has an independent effect in this category

Can prodromal symptoms predict recurrence of vasovagal syncope?

Background: Vasovagal syncope (VVS) is a common symptom with empirical therapy and high recurrence rate. Our goal was to determine whether the pattern of presyncopal prodromal symptoms can predict the recurrence probability of vasovagal syncope. Methods: Seventy-nine consecutive patients (male/female: 53/26) with history of VVS and positive tilt table test (TTT) were enrolled in the study and completed the follow-up time for one year. They all had normal electrocardiograms and cardiac echocardiography without underlying disease. All of them were evaluated meticulously for prodromal symptoms (diaphoresis, nausea, palpitation and blurred vision) and frequency of syncopal spells in their past medical history. They received metoprolol at maximum tolerated dose and were taught tilt training as an empirical therapy after TTT. Results: Fifty-four patients (68.4%) reported at least one of the four main prodromal symptoms. Median syncopal &#177; presyncopal spells were 4 episodes. Forty-two patients (53.2%) experienced recurrence of syncope or presyncope during the follow-up period. In recurrent symptomatic patients, diaphoresis had been more significantly reported in their past medical history (p = 0.018) and they had more syncopal spells before TTT (p = 0.001). Age, gender and type of TTT response did not have any effect on the recurrence of VVS. Conclusions: Patients with a history of diaphoresis as a prodromal symptom and more pretilt syncopal attacks experience more syncopal or presyncopal spells during follow-up