Heating panel, process gas heater comprising said panel and method for monitoring status of said panel
By using a star-shaped connected ternary resistor and current monitoring technology, the problem of low reliability caused by resistor aging is solved, enabling real-time status monitoring and fault prediction of the heating panel, thus improving equipment reliability and maintenance efficiency.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-06-28
- Publication Date
- 2026-03-31
AI Technical Summary
In existing technologies, resistors are prone to aging in process gas heating systems, resulting in low reliability of monitoring systems, difficulty in quickly identifying faults, and increased production risks and the possibility of downtime.
A star-shaped pattern is used to connect the ternary resistors. The fault of the resistor is identified by monitoring the current change at the center of the star. The current measuring device and control unit are used to realize real-time monitoring of the heating panel status and fault prediction.
It improves the reliability and maintenance efficiency of the heating panel, enables rapid identification of resistor faults, and reduces production risks and downtime.
Smart Images
Figure CN121773705A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of electric heaters. Specifically, it relates to a heating panel, a process gas heater including at least one heating panel, and a method for monitoring the state of said heating panel, preferably applied to steelmaking equipment. However, it can be applied to any panel used for electrically heating any industrial process. Background Technology
[0002] In the prior art, such as in equipment for heating steel products (e.g., tunnel furnaces), or in ladle and tundish preheating units, or in process gas heaters (PGHs) used in direct reduction, it is known to use gas heating systems to achieve the thermal targets required by the process and to heat the elements that need to be heated to the desired temperature.
[0003] Many such gas heating systems use burners, which result in the emission of carbon dioxide and other pollutants due to gas combustion. Furthermore, these known solutions also suffer from low performance.
[0004] Solutions have been proposed in the prior art that introduce the concept of electrically heating steel products, steel equipment components, or process gases. However, the reliability of such known solutions is low.
[0005] In reality, the resistors used will age over time, depending on the highest temperature they withstand and the number, magnitude, and gradient of temperature cycles.
[0006] The most common configuration for electrical connections of resistors is a three-phase AC power supply, where each resistor (here, "resistor" can also refer to a group of resistors connected in series or parallel) is connected to one phase of the three-phase system. If the three phases and the resistors that compose them are identical, then the electrical load is defined as "balanced," and the current through the three phases is the same, resulting in the same heat output due to the Joule effect.
[0007] This three-phase resistor system can be connected in parallel to a single three-phase power line, where the current is controlled by a switch, such as a solid-state switch called a thyristor.
[0008] The line current associated with the thermal power required by the process can easily reach several thousand amperes.
[0009] When more than one such system is connected in this manner, monitoring the state of one phase of the system becomes difficult (almost impossible) in the event of a failure in one of the resistors, because the final degree of imbalance in the three-phase currents may not be detectable by the instrumentation system. This is especially true as the line current and the number of parallel-connected three-phase groups increase.
[0010] In other words, the condition of the resistors is not being adequately monitored, so predicting and / or identifying a potential failure of one of the resistors is difficult (almost impossible) within a timeframe that would help reduce the risk of low-quality production or production downtime itself.
[0011] Therefore, a solution is needed that allows for highly reliable and low-emission equipment. Summary of the Invention
[0012] The purpose of this invention is to provide a heating panel that allows easy monitoring of the status of each heating element in order to quickly identify faults and take action by replacing the panel within the heating module.
[0013] Another object of the present invention is to provide a heating panel that is highly reliable and easy to maintain.
[0014] Another object of the present invention is to provide an effective method for monitoring the state of the heating panel.
[0015] The objective of this invention has been achieved by the heating panel as defined in claim 1.
[0016] For this purpose, one of the two most commonly used schemes is to connect the resistors in a "star pattern" because, in this configuration, the line current is lower than the corresponding current in a "delta" configuration, assuming the same output power. A second advantage is that the star center where the three phases (i.e., the three resistors) converge is accessible, allowing monitoring of its potential state. If the three phases (i.e., the three resistors constituting the three phases) are not identical, or if their resistivity and / or size changes over time, or even if one phase is interrupted, the load becomes "unbalanced," thus increasing the potential at the star center and generating current through the neutral line, which connects to the ground potential from the star center of the three-phase system.
[0017] The heating panel according to the invention includes at least one heating element formed by a group of resistors interconnected in a star pattern, wherein each free end of each resistor in the group receives electrical energy from a different phase of a three-phase system and is connected to a first busbar via at least one controlled switch. The heating element also includes a first control switch positioned between the output of the controlled switch and the first busbar, and the first busbar is connected to at least one transformer via at least one second control switch. Furthermore, the star center of the group is connected to a second busbar, and a current measuring device is provided, located between the star center of the group and the second busbar or arranged along the second busbar, to detect the intensity of any current passing through the star center of the group. Finally, a control unit is provided, adapted to receive measurement data from the current measuring device to monitor the state of the heating panel.
[0018] Another aspect of the present invention is to provide a heating module, including at least one heating wall, wherein the heating wall is provided with at least one of the aforementioned heating panels.
[0019] Another aspect of the present invention is to provide a process gas heater suitable for heating process gas before its use in an industrial process, wherein the heater is passed through at least one pipe to deliver the process gas, and includes at least one of the aforementioned heating modules.
[0020] As described above, another aspect of the present invention is to provide a method for monitoring the state of a heating panel, the method comprising the following steps: - The current change at the star center of the ternary resistor of the at least one heating element is detected by means of a current measuring device, and - The status of the heating panel is monitored by a control unit, which receives measurement data from a current measuring device and processes the measurement data to detect possible malfunctions of the at least one heating element.
[0021] More specifically, the present invention can be used in direct reduction equipment, particularly process gas heaters.
[0022] Advantageously, the panel of this solution can also be used in other equipment, such as furnaces for heating steel products, preheating units for ladles and tundishes, and annealing furnaces for galvanized strip. Attached Figure Description
[0023] The following descriptions will refer to the accompanying drawings, in which: Figure 1 An example of a heating panel with details of at least one heating element is shown. Figure 2 An example of a heating panel with multiple heating elements is shown. Figure 3 An example of a heated wall including two heating panels is shown. Figure 4 An example of a heating module including multiple heating walls is schematically shown, and Figure 5 An example of a heating module is shown schematically.
[0024] The components involved in this specification are appropriately represented by conventional symbols in the accompanying drawings, and only specific details relevant to understanding the embodiments of the invention are shown, in order to avoid highlighting details that are obvious to those skilled in the art. Specific reference is made to the description provided below. Detailed Implementation
[0025] The solution of the present invention will now be described with reference to the accompanying drawings.
[0026] The purpose of this invention is to provide a heating panel, a process gas heater including the panel, and a method for monitoring the state of the panel.
[0027] To further reduce emissions, a concept has been proposed for electrically heating process gases (e.g., CH4, H2, and combinations thereof) in process gas heaters, which achieves high reliability through monitoring the heating element.
[0028] To preventively diagnose open circuits in resistors, the solution involves a ternary resistor array connected in a star pattern and monitoring the star center to identify errors or faults in one or more resistors that result in non-zero (or more precisely, non-negligible) current at the star center through continuous monitoring.
[0029] When three resistors are connected in a star pattern, each phase is connected (individually) to the three ends of the three resistors, and the other three ends are connected to each other to form the star center. The sum of the three currents flows on the neutral line, but since the three currents are equal in magnitude and 120° out of phase with each other, their sum is zero.
[0030] If the star configuration is balanced, meaning the three resistors have the same value, the potential at the center of the star is zero, therefore there is no neutral current at the center of the star.
[0031] Reference Figure 1 The heating panel P includes at least one heating element T formed by a ternary resistor R1, R2, R3.
[0032] Three resistors R1, R2, and R3 are interconnected in a star pattern, and each free end of each resistor R1, R2, and R3 in the ternary group receives power from a different phase of the three-phase system.
[0033] Each free end of each resistor R1, R2, R3 is also connected to the first bus 3 via its respective controlled switch 4 (e.g., a silicon controlled rectifier SCR).
[0034] The opposite ends of the three resistors R1, R2, and R3 are connected to form a so-called star center CS.
[0035] The first control switch 2A is located between the output of the controlled switch SCR 4 and the first bus 3.
[0036] The first busbar 3 is connected to the transformer 1 via the second control switch 2B. For example, conventionally, the transformer MV / LV is a 33 / 0.69 kV ONAN (oil-immersed self-cooled) transformer.
[0037] In the heating element T, the star-shaped center CS of the ternary group R1, R2, R3 is connected to the second busbar 8.
[0038] Advantageously, a current measuring device 6 is provided, which is located between the star center CS of the ternary group R1, R2, R3 and the second busbar 8.
[0039] Alternatively, the current measuring device 6 can be positioned along the second busbar 8.
[0040] The purpose of the current measuring device 6 is to detect the intensity of the possible current passing through the star center CS of the ternary resistor.
[0041] In addition, a control unit PLC is provided, which is adapted to receive measurement data from the current measuring device 6 to monitor the status of the heating panel p.
[0042] Component 7 is a remote input / output unit used to collect analog or digital inputs and transmit them over a network.
[0043] The system provides access to the neutral line of the ternary resistor via a measuring instrument, allowing the reading of any current flowing through the star's center CS. If the star is perfectly balanced, the potential at the star's center CS is zero, therefore there is no current flowing through the neutral line.
[0044] Conversely, assuming the phase current is likely to be quite large, around 300 A, even a small imbalance in the three resistors of the star configuration will produce an easily measurable effective current value, as they are approximately a few A.
[0045] If the current at the star center CS is continuously monitored by a measurement system, it is possible to quickly identify changes in the current at the star center CS, predict changes in the resistivity of the heating element T, and provide maintenance procedures, including replacing the heating element T or the heating panel P containing the heating element T.
[0046] Since the resistors used in the heating element T are made of a metal alloy, their resistivity will change over time due to the expansion they undergo.
[0047] Therefore, by monitoring the current at the star center CS, which is the current circulating in the neutral wire that connects the star center of the three-phase system of resistors to the neutral line, the change in the resistivity of the heating element can be analyzed, and a replacement can be provided during the first production stoppage if it exceeds the alarm threshold, or if necessary, during the production shutdown period.
[0048] Preferably, the controlled switch SCR 4 is a thyristor, and more preferably, it is a 3P zero-crossing thyristor.
[0049] In some embodiments, the heating panel P includes a plurality of heating elements T, each heating element T being formed by a set of resistors R1, R2, R3 connected in a star pattern, and the controlled switch SCR 4 simultaneously controls the plurality of heating elements T1-Tn.
[0050] As an explanation, Figure 1 Two heating elements, T1 and T2, are shown.
[0051] In a preferred embodiment, the first busbar 3 is a three-phase (busbar trunking or cable) line, and the second busbar 8 is a neutral (busbar trunking or cable) line.
[0052] Preferably, the current measuring device 6 is a current sensor 6.
[0053] By installing current sensor 6, an early diagnosis of the remaining lifespan of the heating element can be obtained.
[0054] At the beginning of their lifespan, resistors are all “approximately” equal, but over time, their resistivity changes, and some may be damaged by different heating-cooling cycles, thus changing their nominal resistance value and causing star imbalance.
[0055] The fact that resistors are not strictly "identical" at the start of their lifespan is irrelevant to the effectiveness of this invention. In fact, the absolute value of the current circulating from the star center to the neutral line at the start of a resistor's lifespan is not critical; what matters is the change in this current over time, which indicates the degradation of one or more resistors and defines predictive maintenance intervention logic through condition monitoring techniques.
[0056] The resistors R1, R2, and R3 that form the ternary group that makes up the heating element T are selected from different types: • Metal resistors are made of iron-chromium-aluminum or nickel-chromium alloys in the form of wires, panels or other geometries, and are produced by drawing or rolling sintered powder; • Resistors made of ceramic materials, such as silicon carbide (SiC); • Resistors made of ceramic metals (e.g., molybdenum disilicide MoSi2).
[0057] Each resistor and each resistor triplet has a power range from tens of kW to hundreds of kW. In terms of maximum interruptible and / or manageable current, the power limitation is entirely due to the maximum capacity of switches and thyristors available on the market.
[0058] The power and number of parallel triplet arrays are given by the following: •Required thermal power, • Furnace / heater geometry, • Volume uniformity within the required temperature range • Temperature control precision and accuracy, and • Heating gradient.
[0059] The selection of resistors is based on optimization of operating temperature and current management.
[0060] Metal resistors are commonly used as the basis for producing heating elements T.
[0061] Preferably, the resistor is selected from resistors made of an iron, chromium and aluminum alloy (Fe-Cr-Al).
[0062] In various embodiments, the resistor is wavy.
[0063] The selected diameter of the wires that make up the resistor is typically 3 to 10 millimeters.
[0064] Typically, for example, a line voltage of 690V is selected.
[0065] Each resistor triplet is fixed to a refractory component to allow for free thermal expansion of the resistor.
[0066] Preferably, the heating panel P further includes a remote input / output unit RIO, which receives measurement data detected by the current measuring device 6. The remote input / output unit RIO sends data to the network NET for remote monitoring of the status of the heating panel P. Specifically, the remote input / output unit RIO receives measurement data in analog or digital format and sends it to the network for processing.
[0067] The control unit PLC is adapted to continuously control the measurement data detected by the current measuring device 6, and if the measurement data exceeds the alarm threshold, the control unit PLC is adapted to generate a request to replace the panel P.
[0068] Figure 2 An example of a panel P including multiple heating elements T1, T2, T3, ... Tn is shown.
[0069] In a preferred application of the present invention, a process gas heater can be panelized using multiple panels P1...Pn, each panel including multiple heating elements T1...Tn.
[0070] The present invention also aims at a heating wall, indicated by reference numeral W, comprising at least one heating panel P as described above.
[0071] Figure 3 The wall W is shown, which includes two heating panels, P1 and P2.
[0072] Finally, as Figure 4 As shown, the heating module M includes multiple heating walls W1...Wn.
[0073] The modularity provided by the panel P, consisting of the smallest components or basic blocks, allows for the creation of different wall W and heating modules M with high flexibility and availability.
[0074] The present invention also relates to a process gas heater, such as a CH4 and / or H2 heater, which is adapted to heat the process gas before it is used in an industrial process, wherein the heater is passed through at least one conduit to deliver the process gas, and includes at least one heating module (M) as described above.
[0075] Finally, the present invention also relates to a method for monitoring the state of a heating panel P, comprising the following steps: - The current change in the star-shaped center CS of the three-element resistor group R1, R2, R3 of the heating element T is detected by means of the current measuring device 6, and The status of the heating panel P is monitored by the control unit PLC, which receives measurement data from the current measuring device 6 and processes them to detect possible faults in the heating element T.
[0076] Specifically, the control unit PLC identifies the current change trend between or along the second busbar 8 and the star center CS of the triplet R1, R2, R3, and generates a request to replace the heating panel P if the current exceeds the alarm threshold.
[0077] An embodiment will be described below for illustrative purposes only.
[0078] Preferably, the process gas heater includes at least two heating modules, such as four modules M1, M2, M3 and M4.
[0079] Reference Figure 5 Each module M preferably includes two hot zones A and B.
[0080] In each hot zone A and B, there are two walls. For example... Figure 5 As shown, two walls W1 and W2 will be provided for region A and two walls W3 and W4 will be provided for region B.
[0081] Each wall W consists of two heating panels, P1 and P2, in sequence. Each heating panel P includes several heating elements T1, T2, and Tn.
[0082] For illustrative purposes only, each module M includes 216 resistors, and each hot zone A and B includes 108 resistors.
[0083] Specifically, hot zone A includes two walls W1 and W2, and each wall W includes fifty-four resistors distributed to the two panels P1 and P2. Therefore, each panel P consists of 27 resistors. Each triplet includes three resistors, so for each panel P, there will be nine triplets, i.e., nine heating elements T.
[0084] Now refer to Figure 6-10 Another embodiment is described.
[0085] A phasor is a mathematical tool used to represent variables in the frequency domain or harmonic time domain. It is widely used in circuit analysis and the analysis of sinusoidal frequency systems.
[0086] A phasor represents a complex sinusoidal quantity as a vector in the complex plane. A phasor is described by its length (magnitude) and its angle relative to a reference axis. The magnitude of a phasor is the peak or effective value of the sinusoidal quantity, while the angle represents the phase of the quantity relative to a reference time point.
[0087] In summary, phasors are vector representations of sinusoidal quantities, simplifying the analysis of sinusoidal frequency systems and allowing mathematical calculations using complex algebra.
[0088] In the case of a three-phase AC voltage system, the choice of phase reference depends on the conventions or applicable specifications and standards used in the specific system. There are two common conventions for connecting loads: star connection and delta connection.
[0089] In a star connection, one phase is selected as the zero-phase voltage reference or reference phase. Traditionally, the other two phases are 120 degrees (2π / 3 radians) out of phase with each other. The star center is the connection point for all loads. This point may or may not be connected (i.e., connected to a relevant point in the power supply).
[0090] The distinction between connecting or not connecting the neutral point or the star center in a star connection is useful in unbalanced situations.
[0091] Specifically, in balanced operation, i.e., when all loads are equal, it makes no difference whether the star center is connected or not. This is because if the three loads are the same, the voltage at the star center is zero, and there is no current flowing in the neutral line (because the vector sum of the three phase currents is equal to zero).
[0092] Conversely, if the three loads are unbalanced, the voltage at the center of the star configuration is zero. Therefore, without a neutral line, the voltage across each load would vary. Thus, the neutral line is used to "force" the center voltage to be zero, maintaining the voltage at its nominal value even under unbalanced load conditions. Finally, if connected, the current in the neutral line is equal to the vector sum of the currents in each phase.
[0093] Using the star connection as a reference, where one of the four lines is neutral, such as... Figure 1 The configuration is such that the phase shift is calculated with one of these phases as a reference. It is known that the other two phases are 120° and 240° out of phase with respect to the reference phase. Considering the definition of phasors as described above, it is possible to understand which phases (i.e., the resistive elements of the ternary) will deteriorate over time, thus causing a fault.
[0094] Treating the load as resistive means that the phase current has no phase shift relative to the supply voltage that generates it. This allows for the measurement of the phase of the supply voltage and assumes that it is, to some extent, equal to the phase of the corresponding current. Furthermore, it should be remembered that the neutral current is equal to the vector sum of the three-phase currents.
[0095] In ideal operation, the phasors of the three-phase currents should be essentially equal, so the fourth neutral phasor should be almost zero (considering tolerance) or zero.
[0096] By measuring the voltage of the reference phase with a suitable voltmeter and using it as a phase reference, the phase shift of the current generated in the neutral line under unbalanced load conditions relative to the reference phase can be verified (voltage measurement is recommended because it is easier and less invasive; in fact, direct measurement of current requires the use of an inline probe, which presents potential accessibility and space issues).
[0097] The power supply voltage is applied by the network and the load is connected in a star pattern using a four-wire method, so that the power supply voltage remains constant even when the load is unbalanced.
[0098] When resistor degradation leads to an increase in value, the relative current flowing through it will decrease because the four-wire configuration keeps the voltage constant. This means that the sum of the three-phase currents (i.e., the current flowing on the neutral wire) will be non-zero, and the phase shift of this neutral current will provide information about which current(s) have decreased (due to the increase in relative resistance).
[0099] The following three examples illustrate some possible combinations of heating element performance degradation (reduced current) resulting from the use of the methods described above.
[0100] a) If the load associated with 0° deteriorates (see...) Figure 6 The three arrows, represented by cF0, cF120, and cF240, represent the phase currents (and thus, the currents flowing through the load, i.e., the resistor), while the arrow representing cN represents the neutral current. It can be noted that the phase current cF0 decreases to a certain degree, which is a sign of load deterioration associated with 0° phase. The resulting neutral current cN will have the same phase as the decreased current and will be negative (in phase terms, this means a further +180° phase shift). Therefore, the resulting phase cN is 0° + 180° = 180°.
[0101] b) If the load associated with 0° and the load associated with 120° have the same degradation, i.e., the increase in load resistance leads to a decrease in current (see...) Figure 7 The three arrows cF0, cF120, and cF240 represent phase currents (thus flowing across the load or resistor), while the arrow representing cN represents the neutral current. Notice how the two phase currents cF0 and cF120 decrease in degree, a sign of deteriorating load on the 0° and 120° phases. In this example, it should be noted that the decrease in both phases is the same. The resulting neutral current cN will have an intermediate phase between these two decreasing phase currents and will be negative (in phase terms, this means a further phase shift of +180°). Therefore, the resulting phase is [(0° + 120°) / 2] + 180° = 240°. Thus, the resulting neutral current cN is superimposed on cF240.
[0102] c) If the load associated with 0° and the load associated with 120° deteriorate at different rates, i.e., an increase in load resistance leads to a decrease in current (see...). Figure 8 The arrows cF0, cF120, and cF240 represent the phase currents (thus flowing across the load on the resistor), while the arrow representing cN is the neutral current. Notice how the two phase currents, cF0 and cF120, have decreasing degrees, a sign of deteriorating loads on the 0° and 120° phases. In this example, it should be noted that the decreases in these two phases are different. Therefore, the resulting neutral current cN will have an intermediate phase, although weighted relative to the decreases in the two currents, and with a negative sign (meaning a further phase shift of +180° at the phase level). Notice how the resulting phase is close to the previous case (hence 240°), but with a slight shift, making it closer to the case where only the 0° phase is decreased (in fact, the 0° phase has the largest decrease). Therefore, it can be seen from the diagram that in this case, two phases are also problematic, just to different degrees.
[0103] refer to Figure 9 Component 6, or current measuring device 6, is a current transformer that has integrated phase measurement functionality. Therefore, relative to... Figure 1 The circuit, Figure 9 The circuit provides a connection 9 between the current measuring device 6 and one of the controlled switches 4, since it is known that the phase meter must have a reference phase to understand the imbalance relative to the other two.
[0104] Alternatively, if the current measuring device 6 does not have the function of measuring phase, see [reference needed]. Figure 10It is necessary to add another phase measuring device 10, which will be connected to at least one controlled switch 4 via connection 9. The controlled switch 4 will actually be used as a reference and through device 11, which is adapted to calculate the phase difference (including the current on the branch of the current measuring device 6) between the controlled switch 4 and the star center CS, in order to understand which of the three is the unbalanced phase according to the described concept.
[0105] The above description of specific embodiments is able to illustrate the invention from a conceptual point of view, enabling others using the prior art to modify and / or adapt such specific embodiments in various applications without further study and without departing from the concept of the invention, and thus it can be understood that such adaptations and modifications as equivalents of the specific embodiments are quite considerable.
[0106] Without departing from the scope of the invention, the apparatus and materials used to perform the various functions described may have various properties.
[0107] It is worth noting that the terms or expressions used are descriptive only and therefore non-restrictive.
[0108] Obviously, structural details and embodiments may be varied extensively with respect to what has been described and shown above by way of example without prejudice to the principles of the invention, but without departing from the scope of the invention.
[0109] Where a structural feature or technique mentioned in any consecutive claims is followed by a reference numeral or figure, the sole purpose of introducing such reference numeral is to increase the comprehensibility of the same claims. Therefore, such reference numeral does not limit the interpretation of each element identified by such reference numeral, but is merely an example.
Claims
1. A heating panel (P) comprising at least one heating element (T) formed by a triplet of resistors (R1, R2, R3) interconnected in a star pattern, wherein each free end of each resistor (R1, R2, R3) of the triplet receives electrical energy from a different phase of a three-phase system and is connected to a first busbar (3) through at least one controlled switch (SCR, 4), and wherein at least one first control switch (2A) is interposed between the output of the controlled switch (SCR, 4) and the first busbar (3), wherein the first busbar (3) is connected to at least one transformer (1) through at least one second control switch (2B), wherein the star center (CS) of the triplet (R1, R2, R3) is in turn connected to a second busbar (8), wherein a current measuring device (6) is provided, which is arranged between the star center (CS) of the triplet (R1, R2, R3) and the second busbar (8) or along the second busbar (8), so as to detect the intensity of the possible current passing through the star center (CS) of the triplet, and wherein a control unit (PLC) is provided, which is adapted to receive the measurement data from the current measuring device (6) to monitor the status of the heating panel (P).
2. The heating panel according to claim 1, wherein, The at least one controlled switch (SCR, 4) is a thyristor, in particular a 3P zero-crossing thyristor.
3. The heating panel according to claim 1 or 2, wherein, The heating panel comprises a plurality of heating elements (T), each formed by a triplet of resistors (R1, R2, R3) interconnected in a star pattern, and wherein the at least one controlled switch (SCR, 4) simultaneously controls the plurality of heating elements (T).
4. The heating panel according to any of the preceding claims, wherein, The first busbar (3) is a three-phase busbar trunk or cable line, and the second busbar (8) is a neutral busbar trunk or cable line.
5. The heating panel according to any of the preceding claims, wherein, The current measuring device (6) is a current sensor (6).
6. The heating panel according to any of the preceding claims, wherein, The resistors (R1, R2, R3) are selected from the following types: - metallic resistors made in wire or panel or other geometric shapes made with sintered powders stretched or rolled in iron-chromium-aluminum or nickel-chromium alloys; - resistors made of ceramic materials, for example silicon carbide SiC; or - resistors made of cermet, for example molybdenum disilicide MoSi2.
7. The heating panel according to any of the preceding claims, wherein, The heating panel (P) comprises a remote input / output unit (RIO) for receiving the measurement data detected by the current measuring device (6) and sending them to a network (NET) for remote monitoring of the status of the heating panel (P).
8. The heating panel according to any of the preceding claims, wherein, The control unit (PLC) is adapted to control the measurement data detected by the current measuring device (6) and, in the event that the measurement data exceed an alarm threshold, the control unit (PLC) is adapted to generate a request for replacement of the panel (P).
9. The heating panel according to any of the preceding claims, wherein, The current measuring device (6) connected to the star center (CS) is a current transformer integrated with a phase measurement function, and wherein a connection (9) of the current measuring device (6) with one of the controlled switches (4) serving as a reference phase is provided.
10. The heating panel according to any one of claims 1 to 8, wherein, For current measuring devices (6) connected to the star center (CS) without phase measurement, a phase measuring device (10) connected to the star center (CS) is added, as well as a device (11) adapted to calculate the phase difference between the controlled switch (4) and the star center (CS), said device being connected to said phase measuring device (10) through a connection (9).
11. A heating wall (W) comprising at least one heating panel (P) according to any one of the preceding claims 1 to 7.
12. A heating module (M) comprising at least one heating wall (W) according to claim 11.
13. A process gas heater adapted to heat a process gas before its use in an industrial process, wherein said heater is crossed by at least one duct to deliver the process gas, and comprises at least one heating module (M) according to claim 12.
14. A method for monitoring the status of a heating panel according to any one of claims 1 to 10, said method comprising the steps of: - detecting, by means of said current measuring devices (6), a current variation in the star center (CS) of the triad of resistors (R1, R2, R3) of said at least one heating element (T), and - monitoring, by a control unit (PLC), the status of said heating panel (P), said control unit receiving measurement data from said current measuring devices (6) and processing said measurement data to detect possible malfunctions of said at least one heating element (T).
15. The method of claim 14, wherein, Said control unit (PLC) identifies a current variation trend between or along said second busbar (8) and the star center (CS) of the triad (R1, R2, R3), and in case said current exceeds an alarm threshold, said control unit (PLC) generates a request for replacement of the heating panel (P).