Coordination of Varistors With Transient Voltage Suppression Diodes in Automotive DC Systems

The coordination of metal-oxide varistors with transient voltage suppression diodes commonly employed for the protection of sensitive electronic equipment in DC automotive systems is experimentally investigated. Double-exponential impulse currents adopted in relevant standards, concave and rectangular impulse currents resembling field records on lightning-related surge events, as well as temporary overvoltages, are employed to stress the surge protective components and evaluate their coordination. Experimental results and the subsequent analysis reveal that effective coordination of varistors with bidirectional diodes can be a challenging task, especially under long-duration and high-energy electromagnetic pulses. Under such conditions, the safety and uninterrupted operation of vehicles containing low-voltage electrical circuits with embedded sensitive electronic equipment is threatened.

proper coordination is of paramount importance [10], especially in automotive electrical systems, where constant, reliable, and uninterrupted operation is crucial.
Research is being conducted in both industry and academia, aiming to understand how surge protective devices perform in actual conditions in the field and how efficiently they can protect sensitive electronic equipment [10], [11], [12], [13].The fast response, zero follow current, and enhanced surge-withstand capability of varistors makes them ideal for protecting electrical and electronic systems in DC applications [14], [15], [16], [17].However, when enhanced voltage protection levels are required, transient voltage suppression diodes are commonly employed thanks to their lower clamping voltage and ultra-fast response [18], [19], [20], [21].Thus, it is common to employ cascade protection schemes utilizing metal-oxide varistors (MOVs) and transient voltage suppression diodes (TVSs) as shown in Fig. 1.Actually, one-port surge protective devices (Fig. 1(a)) or two-port surge protective devices with protective components coordinated via series impedance (Fig. 1(b)) are employed to ensure the safety of the equipment of electrical systems against incoming surges and electromagnetic pulses [10], [19].The common practice of using gas discharge tubes coordinated with transient voltage suppression diodes in telecom systems cannot be applied in DC power systems; this is because of the limited ability of gas discharge tubes to interrupt the follow current of DC power systems, where there is no zero-crossing of voltage and current.Thus, the coordination of metal-oxide varistors (MOVs) with transient voltage suppression diodes (TVSs) in automotive DC systems is necessary and it is investigated to determine the energy sharing and protection level [19], [22] of such combination (MOV-TVS), although it is not commonly found in conventional surge protection applications [10].It is important to note that the dynamic response of surge protective components under electromagnetic pulses of wide frequency and energy content [23], [24], [25], [26], [27] makes the design of coordination circuits a formidable task and a continuous challenge of decisive importance [28], [29], [30], [31].
The novelty of this work lies in the evaluation of the voltage coordination, apart from the energy coordination, of MOVs with bidirectional TVSs commonly employed in automotive DC systems that utilize sensitive equipment; for that purpose, custommade and commercially available current generators are used to represent in laboratory environment high-and low-frequency surge events.The efficiency of coordination arrangements is evaluated against a wide frequency range (DC up to ∼250 kHz).Actually, (i) double-exponential impulse currents of 8/20 µs and 10/350 µs standard waveforms commonly employed in the surge protection industry, (ii) concave exponential impulse currents and long-duration rectangular impulse currents resembling field records on lightning-related surge events and electromagnetic pulses, and (iii) DC overvoltages are employed representing temporary overvoltages foreseen by forthcoming international standards.The experimental results and their subsequent analysis show that MOV-TVS coordination through air or magnetic core coils provides an improved protection level that is crucial for sensitive equipment, but it is not always efficient, particularly in low-frequency long-duration events, which jeopardize the safety of equipment with integrated protective diodes.This is important when considering that several research and development projects are ongoing in the automotive industry associated with electric functions of vehicles and surge protection against overvoltages.

II. EXPERIMENTAL SETUPS AND MEASUREMENT PROCEDURES
The transient response and coordination of surge protective devices are investigated for currents with a wide range of peak value (10 A-5000 A) and total duration (30 µs-5 sec) covering a variety of electromagnetic pulses and temporary overvoltages that may occur in DC systems [7], [32], [33], [34].

A. Devices Under Test
Metal-oxide varistors (MOVs) and bidirectional transient voltage suppression diodes (TVSs), typically utilized for protecting automotive electrical circuits integrating sensitive electronic equipment, were employed as devices under test (DUTs); devices of the same batch were selected with the same breakdown voltage (V 1mADC ).Table I presents the basic electrical characteristics of the DUTs.For each DC system, TVSs of peak pulse power (PPP) of 1500 W with a maximum continuous operating voltage practically equal to the nominal voltage were chosen to represent challenging cases of energy and voltage coordination with MOVs; it is noted that MOVs for the same DC system voltage typically utilize higher maximum continuous operating voltage.The ambient temperature during experiments was maintained constant at 22 °C, and after each stress, DUTs were allowed to cool down to avoid temperature effects on their transient response [16].

B. Voltage-Current Characteristics of MOVs and TVSs
The voltage-current characteristics of the DUTs were determined by employing the experimental setups presented in Fig. and using a 600 MHz oscilloscope (Tektronix TDS 3064B).The voltage-current curves of the DUTs up to about 1 A were measured by employing a 1750 VA programmable AC/DC power supply (Agilent 6813B).The current was recorded using high-power, low intrinsic inductance resistors, R I via a 100 MHz differential probe (Tektronix P5205A), and a LeCroy PP008 MHz probe was utilized to record the voltage at the DUT terminals (Fig. 2(a)).Typical MOVs responses under DC voltages are shown in Fig. 3(a); voltage and current records (V R , I R ) were obtained for various stress levels.
The voltage-current curves of the DUTs for currents higher than ∼1 A were acquired by using impulse current generators (Fig. 2(b)).Double-exponential impulse currents with three distinct waveforms were considered.8/20 µs [35] and 10/350 µs waveforms per IEC and UL relevant standards [35], [36], and a non-standard waveform, ∼6/13 µs, with time to half in agreement with that of currents monitored stressing surge protective devices in the field [12], were used.Current transformers  (Pearson 3100, 310 and 301X) were employed to monitor the impulse currents, and a LeCroy PP008 500 MHz probe was used to record the residual voltage at DUTs terminals.Typical MOVs responses, when stressed with double-exponential impulse currents, are shown in Fig. 3(b).For the determination of the voltage-current characteristic, the voltage V R was recorded at the peak current I R (Fig. 3(b)) [36].

C. Coordination of MOVs With TVSs
Energy and voltage coordination of metal-oxide varistors (MOVs) with bidirectional transient voltage suppression diodes (TVSs) was investigated by employing standard (Fig. 4(a)), concave (Fig. 4(b)), and rectangular (Fig. 4(c)) impulse current generators and a programmable DC power supply (Fig. 4(d)).After each surge current (Figs.5-7) or overvoltage application (Fig. 8), the TVS functionality is examined by imposing the nominal system voltage; leakage current higher than 1mA was interpreted as an energy coordination failure.Attempting to effectively coordinate the surge protective components (MOVs and TVSs), inductors were inserted between them (Figs.inductance on the current flow towards the TVS, I TVS : The impact of the coordination coil on the energy and voltage coordination is assessed by recording (i) the maximum current Authorized licensed use limited to the terms of the applicable license agreement with IEEE.Restrictions apply.flowing through the TVSs, (ii) the voltage at the TVS terminals and their peak pulse power dissipation and time to failure.
Exponential impulse currents (8/20 µs and 10/350 µs) employed in relevant standards [36] were recorded with the aid of 10 MHz current transformers (Pearson 310 and 301X), and the voltage at the TVSs terminals was measured with a 500 MHz probe (LeCroy PP008) as shown in Fig. 5.In addition, ∼1/5 µs exponential impulse currents with concave front that resemble lightning current waveforms recorded in the field [12], [37], were applied by a 10-stage Marx Generator to assess coordination and measured via Pearson 301X (Fig. 6).
Long-duration impulse currents, representing low-frequency electromagnetic events associated with lightning strokes of very long duration or continuing currents proceeding or/and following the lightning return stroke [38], were produced by a 7-stage rectangular impulse current generator (Fig. 7(a)).
Current sharing was measured by recording the voltage drops along the high-power, low-inductance disk resistors (R IT , R ID ) via differential probes Tektronix P5205A (Fig. 7(b)) because the available Pearson current transformers (3100, 310 and 301X) saturated for low-frequency long-duration currents; electrical characteristics of disk resistors are given in Fig. 7(c).DC temporary overvoltages were also imposed to assess MOV and TVS coordination (Fig. 8(a)), following the experimental procedure described in the forthcoming international standard [39]; in an analogous way to long-duration impulse current experiments, DC current sharing between the components was measured by voltage drop at low-inductance power wirewound resistors (Fig. 8(c)) via differential probes Tektronix P5205A, and TVS voltage was monitored with LeCroy PP008 500 MHz probes (Fig. 8(b)).

III. RESULTS AND DISCUSSION
The experimental investigation presented in this work covers a frequency bandwidth from DC up to ∼250 kHz representing a wide range of lightning-related surges with dominant frequency 25-250 kHz for positive and negative lightning first strokes [40]; thus, the presented experimental investigation practically covers the vast majority of fast-front transients that are associated with a frequency range of 10 kHz-1 MHz [41] as well as electromagnetic pulses having similar frequency bandwidth.

A. Voltage-Current Characteristics of MOVs and TVSs
Fig. 9 shows the voltage-current (V-I) characteristics of varistors (MOVs), and transient voltage suppression diodes (TVSs) determined as presented in Section II-B (Fig. 3); the V-I curves are drawn up to the maximum 8/20 µs current that each component can withstand as denoted by the vertical dotted lines in Fig. 9.It can be deduced from the V-I curves that the TVSs conduct current at lower voltages than the MOVs and thus provide a better protection level for the equipment under protection; this behavior makes the low-high coordination strategy [42] through matching the V-I curves of MOV-TVS practically impossible.On the other hand, TVSs have a significantly lower surge-withstand capability.

B. Coordination of MOVs With TVSs for Standard Exponential Impulse Currents
The experimental setup (Fig. 5(a)) presented in Section II-C was employed to evaluate the energy and voltage coordination between MOVs and TVSs under standard double-exponential impulse currents of 8/20 µs and 10/350 µs waveform.
In 8/20 µs experiments, different coordination coils representing lump circuit elements or/and wires were considered between the surge protective components.The surge protection schemes, Authorized licensed use limited to the terms of the applicable license agreement with IEEE.Restrictions apply.which are MOVs coordinated with TVSs through coils up to 20 µH, were stressed in each case with surge current up to TVS or MOV failure.For 10/350 µs experiments, the coordination coil inductance was increased to extreme values to achieve effective energy coordination that prevents TVSs failures; this was practically impossible to achieve for peak currents higher than 300 A. 1) Energy Coordination: Typical results on the current sharing between MOVs and TVSs for standard double-exponential impulse currents of 8/20 µs waveform are shown in Fig. 10 for the 12V DC system and Table II for all systems at 2 kA.Increasing the coordination coil inductance decreases the current flow towards the TVSs as well as the absorbed charge (Q TVS ), and a bigger portion of the current flows through the MOVs (Fig. 10), that consequently absorb a bigger portion of the impulse charge (Q MOV /Q TVS ) for all automotive systems under study (Fig. 11).
The steep rise of the current (high current derivative) at the beginning of the waveform forces the current to flow predominately through the MOV due to the high impedance of the coil (Fig. 5).Thus, efficient coordination with the aid of passive elements such as coils is possible (Fig. 11), and a 20 µH inductance resulted in MOV-TVS protection schemes with surge withstand capability in the order of the standalone MOVs denoted with vertical lines in Fig. 9.
A summary of the performed 10/350 µs experiments and the results in terms of energy coordination is presented in Table III.Similar current sharing behavior has been observed for 10/350  µs experiments (Fig. 12); as the coordination inductance increases, the current flow towards the TVSs decreases, and the MOVs absorb a larger portion of the impulse charge as shown in Fig. 13.However, the efficiency of the coil on Q MOV /Q TVS seems less pronounced in case of 10/350 µs with respect to 8/20 µs experiments (Figs.11 and 13).Thus, in long wavetail surge events such as 10/350 µs waveforms, energy coordination by employing coils is challenging (Fig. 12); coordination inductances up to 40 µH (double of that proved efficient for 8/20 µs experiments) resulted in ineffective coordination when MOV-TVS were stressed with currents slightly higher than the maximum current that standalone TVSs could handle, as written in the footnote of Table III.Even at 80 µH effective coordination could be achieved only for relatively low current amplitudes, about 1.25 times the maximum current that standalone TVSs could handle (Table III and Fig. 12).Thus, the surge-withstand capability of the surge protection schemes Authorized licensed use limited to the terms of the applicable license agreement with IEEE.Restrictions apply.(MOV-TVS) is not significantly higher than the surge withstand capability of the standalone TVSs.It is important to note that even extreme coordination inductances of 380 µH do not guarantee energy coordination for currents higher than 100 A, 10/350 µs (Table III).Nevertheless, high inductance values are impractical to implement by employing air core coils, especially in automotive systems, where the available space is limited.On the other hand, magnetic core coils may be considered due to limited size but exhibit drawbacks on energy coordination; Fig. 14 shows the transient response of TVSs when 380 µH air core and toroid magnetic core coils are employed for coordination.In such long duration events, the magnetic core coils saturate, their inductance drops, and as a result, a bigger portion of the current flows towards the TVSs that are led to failure.It is important to note that the air core coil, in contrast to magnetic core coil of the same inductance, provide an effective energy coordination for 12V DC systems at 450 A, 10/350 µs (Table III, Fig. 14).It is not hence always possible to employ magnetic core coils for effective coordination in such long wavetail surges and effective coordination with passive elements is generally tricky; advanced materials and design may be employed in magnetic core coils for coordination purposes [43].
2) Voltage Coordination: Fig. 15 shows a typical response of a standalone MOV, a standalone TVS, and a surge protection scheme (MOV coordinated with TVS), for a 12V DC system, when stressed with a 500 A, 8/20 µs impulse current.The protection level (maximum voltage of 17 V) offered to the equipment  under protection by the surge protection scheme (MOV-TVS) is better than the protection level offered by the standalone TVS (21 V) in case of the same incoming surge current (500 A, 8/20 µs).
In addition, the superior protection level offered by the surge protection scheme is ensured for an extended current range with respect to the standalone TVS.For example, for a 12V DC system (Fig. 16(a)), the protection level at 700 A, 8/20 µs, is 17 V for the protection scheme (MOV-TVS via 20 µH coil), 24 V for the standalone TVS, and 88 V for the standalone MOV and the surge withstand capability of the surge protection scheme (MOV-TVS) is 3 kA, 8/20 µs practically equal to the standalone MOV whereas that of the standalone TVS is 0.7 kA, 8/20 µs.The voltage-current curves of surge protective components (standalone MOVs or TVSs) and surge protection schemes (MOV-TVS) are presented for all DC systems for 8/20 µs experiments in Fig. 16; an inductance of ∼20 µH was proved successful in energy coordination for all systems under study increasing the surge withstand capability of MOV-TVS up to the surge withstand capability of the MOV under 8/20 µs.As a rule, larger coordination coil inductances enhance voltage protection level and result in generally wider surge withstand capability of the surge protection schemes.It is noteworthy that the effect of the superimposed system voltage is negligible, as shown in Fig. 17.
Concerning the voltage coordination between the surge components, for standard impulse currents of 10/350 µs waveform, similar behavior has been observed as described above but to a lesser extent; the surge protection scheme (MOV-TVS) provides an improved protection level compared to the standalone MOV and TVS (Fig. 18).However, since no significant improvement on the surge-withstand capability of the surge protection schemes can be achieved compared to the surge-withstand capability of the standalone TVSs due to the inefficiency of the coordination coil (Fig. 18 and Table III), the employment of MOVs does not yield any major advantages over the placement of standalone TVSs.

C. Coordination of MOVs With TVSs for High-Frequency Surges
The experimental arrangement given in Section II-C (Fig. 6(a)) was employed to assess the energy coordination Authorized licensed use limited to the terms of the applicable license agreement with IEEE.Restrictions apply.between MOVs, and TVSs under concave impulse currents 2 kA, 1/5 µs.
While this current amplitude can lead TVSs to fail in short circuit, it does not damage varistors.The coordination inductance that represents lump circuit elements or/and wires connecting the surge protective components was increased until effective coordination was achieved, that is TVS failures were prevented.A summary of all the experimental results in terms of effective or ineffective coordination is presented in Table IV.
Fig. 19 shows typical current sharing experimental results for the 24V DC system; increasing the coordination coil inductance decreases the current flow towards the TVS, and a larger portion of the current flows through the MOV.It is important to note that unlike the case of standard exponential impulse currents, the current begins to flow through the TVS during the concave part of the waveform when the current derivative is relatively low (inset graph in Fig. 19); when the current derivative rises so does the impedance of the coordination coil and thus part of the current flows via the MOV.This indicates that the current sharing between surge components may be more accurately investigated using exponential impulse currents with varying concave front durations, which can be achieved by altering the Marx generator impulse voltage and the air gap length (Fig. 6).
Fig. 20 depicts the peak current via the TVS as a function of the coordination coil inductance, L, and the impulse charge ratio (Q MOV /Q TVS ) for all system voltages.As L increases, so does the charge absorbed by MOVs, while the peak current that flows through the TVSs diminishes until effective coordination is achieved.For each system, effective coordination was achieved with different coordination coils (Table IV) since the electrical characteristics of the surge protective components coordinated in each case varied.Because the protective components selected for the 42V system (Table I) exhibit the lowest surge current withstand capability, their coordination was the most challenging one but was achieved at ∼10 µH for 2 kA, 1/5 µs.
The high-frequency content of the concave exponential impulse currents makes feasible the effective energy coordination via coils between the surge protective components.Thus, effective coordination is possible against high-frequency surge events such as induced surges due to negative lightning first and subsequent strokes.

D. Coordination of MOVs With TVSs for Low-Frequency Surges and Temporary Overvoltages
The rectangular impulse current generator experimental arrangement (Fig. 7(a)) given in Section II-C was employed to assess the energy and voltage coordination between MOVs and TVSs under long-duration impulse currents.A summary of the performed experiments is presented in Table V.
For all DC systems and coordination coils up to 380 µH, TVSs were led to failure mode (short circuit), and effective energy coordination with MOVs could not be achieved.Fig. 21 depicts typical current and voltage records for surge protective components employed in 42V DC automotive electrical systems.For low inductance values (Fig. 21(a)), practically the whole current flows through the TVSs.Even when extreme inductances (380 µH) are considered, and a significant part of the current flows towards the MOVs during the high current derivative part of the waveform, effective energy coordination still cannot be achieved, and TVSs fail (Fig. 21(b)).It is noteworthy that the TVSs exhibit a transient behavior before failing, with their impedance rising before plummeting to a very low value at the time instant of failure, t f , when the short-circuited TVSs cause Authorized licensed use limited to the terms of the applicable license agreement with IEEE.Restrictions apply.

TABLE V TIME TO FAILURE AND PEAK PULSE POWER OF TRANSIENT VOLTAGE SUPPRESSION DIODES
a sharp increase in the output current of the generator (Fig. 21).
The peak pulse power (PPP) dissipation before failure and the time to failure of the TVSs is given in Table V.As expected by TVS datasheets, when the peak pulse power dissipated by the diodes rises the time to failure diminishes.Since energy coordination could not be effective (Fig. 21 and Table V), voltage coordination does not enhance the protection level (Fig. 22); thus, the employment of MOVs does not improve the surge-withstand capability and the protection offered by standalone TVSs.
The surge protection schemes (MOV-TVS) were also evaluated against temporary overvoltages (Fig. 8(a)).Based on the experimental procedure described in the forthcoming international standard [39], two times the nominal system voltage, V N , was applied to the components (Fig. 8(b)) with a prospective short circuit current of 10 A that resembles limited current test per UL standard [35].In all cases, the TVSs conducted all the current and failed in less than 5s; thus, no effective energy coordination was achieved for any coordination coil.Typical experimental results are presented in Fig. 23 for all DC systems.The peak pulse power (PPP) dissipation versus the time to failure of the TVSs for all low-frequency surges and temporary overvoltages is given in Fig. 24; recorded time to failure values correspond to PPP values beyond the guaranteed PPP withstand capability of TVS so performance is in line with the datasheet of the TVS manufacturer.
Electric circuits of vehicles exposed to low-frequency electromagnetic pulses associated with (i) lightning strokes (LEMP) and continuing currents [38], (ii) electrostatic quasi-DC charging of their non-conductive parts [44], (iii) solar storms [45], and (iv) high-altitude nuclear explosions (late-time NEMP)  [46], may experience failure since effective coordination is not always feasible.To achieve effective coordination in such events, advanced passive or active coordination approaches are required conceptually described in [31].
Authorized licensed use limited to the terms of the applicable license agreement with IEEE.Restrictions apply.

E. General Discussion
Transient voltage suppression diodes are commonly employed to protect sensitive electronic equipment in automotive DC systems due to their enhanced voltage protection level with respect to varistors (Fig. 9).Their limited surge-withstand capability, though, makes them vulnerable to surges.Metal-oxide varistors with enhanced surge-withstand capability, on the other hand, if properly coordinated with transient voltage suppression diodes, can lead to a surge protection scheme that utilizes a higher surge withstand capability and a better protection level (Fig. 16).Effective coordination of the components through coils is, however, particularly challenging and strongly depends on the energy content and the waveform of the incoming surge current.
More specifically, in high-frequency & short-duration events, the high impedance of the coordination coil forces part of the surge current to flow through the MOVs (Figs. 19 and 20).Thus, the surge-withstand capability of the surge protection scheme (MOVs coordinated with TVSs) improves as the coordination coil inductance rises (Fig. 16(c)) reaching a maximum, which is practically the surge-withstand capability of the MOVs.At the same time, as the coordination coil inductance rises, the voltage protection level improves with respect to standalone components.This is because the voltage at the TVSs terminals, that is, the voltage seen by the equipment under protection, is reduced due to lower current conduction through the TVS.However, the use of coils in surge protection schemes for coordination purposes should consider cost and space limitations and account for possible failures associated with excessive load or surge current flow.In low-frequency & long-duration surges, the low impedance of the coordination coil makes effective energy coordination challenging, and thus, the surge-withstand capability of the surge protection schemes does not significantly improve (Table III, Fig. 21) and voltage coordination fails (Fig. 22).Consequently, the coordination of MOVs with TVSs does not yield any major advantages over the placement of standalone TVSs, and advanced coordination schemes are needed that may involve the use of active coordination techniques or special varistors with very low residual voltage with respect to the V 1mADC ; effective coordination and surge protection should be confirmed through experiments employing the connected equipment [47], [48].
Based on the whole experimental investigation and subsequent analysis, Table VI shows the surge withstand capability and voltage protection level of standalone components and surge protection schemes against electromagnetic pulses of different dominant frequencies and energy content that may stress the electrical circuit of vehicles.These qualitative results apply also on the surge protection of emerging DC systems [49].
Considering the limited energy absorption capability of conventional TVSs at a reasonable cost, apart from inductance-based coordination techniques, advanced solutions and patented technologies may be used to provide efficient energy coordination in a wide frequency spectrum employing power electronics and/or advanced materials [19], [22], [31], [50], [51], [52].Efficient surge protection and coordination will be even more challenging in the near future since the upper limit of operating voltage level will increase to the kV range where high power surge protection components are required, and the sensitivity of electronic devices integrated into electric vehicles will necessitate enhanced electromagnetic shielding.

IV. CONCLUSION
The energy and voltage coordination of varistors (MOVs) with transient voltage suppression diodes (TVSs) employed in automotive DC systems has been experimentally investigated.The current sharing between the surge protective components has been monitored, and the surge-withstand capability and voltage protection level of the surge protection schemes (MOVs coordinated with TVSs) has been evaluated.Experimental results and their subsequent analysis have revealed that: r Effective coordination employing coils that limit the peak current flowing towards the transient voltage suppression diodes is possible at high-frequency & short-duration surge events.Surge protection schemes employing MOV and TVS, combining the desirable surge protection characteristics of each protective component, can be effectively used to protect electrical circuits integrated into vehicles against lighting-related stress.
r Conventional toroidal magnetic core coils with a current rating of several decade Amperes, commonly employed in the automotive industry due to their smaller size compared to air core coils of the same inductance, saturate at surge current levels of several hundred Amperes.Thus, they have limited coordination against long-duration electromagnetic pulses with high energy and low dominant frequency.Special-purpose magnetic core coils may be used for coordination objectives.
r The coordination of MOVs with TVS via coils yields no significant improvement in the surge-withstand capability and protection level of standalone TVS in case of lowfrequency & long-duration surge events.Thus, such surge protection schemes employing MOV and TVS cannot effectively protect electrical circuits integrated into vehicles against high-energy events such as nuclear electromagnetic pulses and solar storms.Based on the above, advanced passive or active coordination approaches based on new non-linear materials and control circuits are needed to increase the resilience of vehicles' DC systems against low-frequency and long-duration electromagnetic pulses.Authorized licensed use limited to the terms of the applicable license agreement with IEEE.Restrictions apply.

Fig. 3 .
Fig. 3. Indicative experimental records of voltage and current for the devices under test.(a) DC test, (b) impulse current test.

Fig. 4 .
Fig. 4. (a) Double-exponential impulse currents generator, (b) concave exponential impulse currents generation with the aid of 10-stage Marx generator, (c) long duration impulse current generator, (d) power supply employed for temporary overvoltage tests.

Fig. 5 .
Fig. 5. Coordination experiments: (a) Setup for standard double-exponential impulse currents, (b) experimental records of current sharing between MOV and TVS and voltage at TVS for 24V DC systems and L = 80 µH.

Fig. 6 .
Fig. 6.Coordination experiments: (a) Setup for concave exponential impulse currents, (b) experimental records of current sharing between MOV and TVS for 24V DC systems and L = 0.19 µH.

Fig. 7 .
Fig. 7. Coordination experiments: (a) Setup for long-duration impulse currents, (b) experimental records of current sharing between MOV and TVS and voltage at TVS for 24V DC systems and L = 380 µH, (c) disk resistors characteristics.

Fig. 8 .
Fig. 8. Coordination experiments: (a) Setup for DC temporary overvoltages, (b) experimental records of applied voltage and current sharing at MOV and TVS for 12V DC systems and L = 10 µH, (c) wirewound resistors characteristics.

Fig. 11 .
Fig. 11.Peak TVS current and impulse charge ratio (Q MOV /Q TVS ) versus coordination coil inductance; 450 A, 8/20 µs impulse current.Ineffective and effective coordination is represented by full and empty points, respectively.

Fig. 13 .
Fig. 13.Peak TVS current and impulse charge ratio (Q MOV /Q TVS ) versus coordination coil inductance; ∼250 A, 10/350 µs impulse current.Ineffective and effective coordination is represented by full and empty points, respectively.

Fig. 16 .
Fig. 16.Voltage-current characteristics of surge protective components and surge protection schemes for 8/20 µs surge currents: (a) 12V DC (b) 24V DC (c) 42V DC system; lines drawn up to the surge withstand capability.

Fig. 17 .Fig. 18 .
Fig. 17.Voltage-current characteristics of the surge protection schemes with and without the system voltage superimposed during the surge event; 42V DC system.

Fig. 20 .
Fig. 20.Peak TVS current and impulse charge ratio (Q MOV /Q TVS ) versus coordination coil inductance; 2 kA, 1/5 µs impulse current.Ineffective and effective coordination is represented by full and empty points respectively.

Fig. 22 .
Fig. 22. Response of MOV and surge protection scheme (MOV coordinated with TVS via 330 µH air core coil) in a ∼70 A rectangular impulse current; 12V DC.

Fig. 24 .
Fig.24.TVS peak pulse power as a function of time to failure; dotted line corresponds to guaranteed peak pulse power withstand capability obtained from the datasheet of the TVSs.
Evangelos T. Staikos (Student Member, IEEE) was born in Thessaloniki, Greece in 1994.He received the M.Eng.degree in electrical and computer engineering in 2018 from the Aristotle University of Thessaloniki, Thessaloniki, Greece, where he is currently working toward the Ph.D. degree with High Voltage Laboratory.His research interests include metal-oxide varistors characterization and modeling, surge protection of power, telecommunication, and automotive systems.

TABLE I ELECTRICAL
CHARACTERISTICS OF SURGE PROTECTIVE COMPONENTS USED AS DEVICES UNDER TEST

TABLE II ENERGY
COORDINATION OF SURGE PROTECTIVE COMPONENTS FOR DOUBLE-EXPONENTIAL IMPULSE CURRENTS 2 KA, 8/20 µS

TABLE IV ENERGY
COORDINATION OF SURGE PROTECTIVE COMPONENTS FOR EXPONENTIAL IMPULSE CURRENTS 2 KA, 1/5 µS WITH CONCAVE FRONT Fig. 19.Current sharing between MOV and TVS for concave exponential impulse current of 2 kA, 1/5 µs; 24V DC system.