Description:FIELD
The present disclosure relates to the field of power distribution systems. More particularly, the present disclosure relates to a system for selectively performing auto-reclosing operations in a hybrid transmission line and a method thereof.
DEFINITIONS
As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicates otherwise.
Auto-reclosing operation – "auto-reclosing operation" hereinafter refers to an automated operation performed by a circuit breaker, wherein the circuit breaker, after opening in response to a detected fault, is automatically reclosed following a short delay without requiring manual intervention.
Hybrid transmission line – "hybrid transmission line" hereinafter refers to a power transmission line composed of two distinct conductor sections, viz., an overhead line section (typically installed aboveground) and a cable section (typically installed in a subterranean environment).
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
Generally, auto-reclosing is employed in overhead transmission lines to restore power rapidly after a temporary or transient fault is detected. The auto-reclosing operation is executed by a circuit breaker in the overhead transmission line, which first interrupts the power flow in the event of a fault, and then recloses after a predefined time delay if system conditions allow. The auto-reclosing operation is typically managed by relays, which monitor overhead transmission line parameters and accordingly control the reclosing logic of the circuit breaker. Auto-reclosing significantly improves power reliability by reducing power restoration time caused by transient faults in overhead transmission lines.
However, in transmission lines that include underground cable sections, auto-reclosing is generally blocked. This is due to the higher likelihood of permanent faults in cable sections, where reclosing the circuit breaker could result in equipment i.e. cable damage or operational hazards. In metropolitan city with dense population like Mumbai, transmission lines are being converted into hybrid configurations, where an overhead line section transitions into an underground cable section. In such hybrid transmission lines, auto-reclosing has been disabled entirely, meaning that even temporary faults in the overhead section would lead to full line tripping, requiring manual intervention for restoration.
There is, therefore, felt a need for a system and a method for selectively performing auto-reclosing operations in a hybrid transmission line, that alleviates the aforementioned drawbacks.
OBJECT
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
An object of the present disclosure is to provide a system and a method for selectively performing auto-reclosing operations in a hybrid transmission line.
Another object of the present disclosure is to provide a system and a method for selectively performing auto-reclosing operations in a hybrid transmission line, that permits auto-reclosing only for faults located within an overhead line section of the hybrid transmission line.
Yet another object of the present disclosure is to provide a system and a method for selectively performing auto-reclosing operations in a hybrid transmission line, that inhibits auto-reclosing when a fault is detected in the cable section of the hybrid transmission line.
Still another object of the present disclosure is to provide a system and a method for selectively performing auto-reclosing operations in a hybrid transmission line, that reduces power restoration time durations caused by transient faults in the overhead line section of the hybrid transmission line.
Another object of the present disclosure is to provide a system and a method for selectively performing auto-reclosing operations in a hybrid transmission line, that reduces manual intervention in restoring power following transient faults in the hybrid transmission line.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure envisages a system for selectively performing auto-reclosing operations in a hybrid transmission line. The hybrid transmission line includes an overhead line section and a cable section, and is configured to electrically couple a first power station and a second power station. A first circuit breaker and a second circuit breaker are connected at the overhead line section and the cable section, respectively, and are configured to interrupt power flow in response to a detected fault by relays.
The system comprises a first relay and a second relay. The first relay is connected to the overhead line section of the hybrid transmission line and to the first circuit breaker. The first relay is configured to measure electrical parameters of the transmission line at the overhead line section, compute a fault impedance from the measured electrical parameters, compare the computed fault impedance with a first impedance threshold for the overhead line section, determine whether a fault is located in the overhead line section, and generate a control signal to permit auto-reclosing of the first circuit breaker when the fault is located within the overhead line section. The second relay is connected to the cable section of the hybrid transmission line and to the second circuit breaker. The second relay is configured to measure electrical parameters of the transmission line at the cable section, compute a fault impedance from the measured electrical parameters, compare the computed fault impedance with a second impedance threshold for the cable section, determine whether a fault is located in the cable section, and generate a control signal to inhibit auto-reclosing of the second circuit breaker when the fault is located within the cable section.
In an embodiment, the first impedance threshold for the overhead line section corresponds to 80% of the total impedance of the overhead line section of the hybrid transmission line. The first impedance threshold for the overhead line section is computed as ZOH = (ROH+jXOH)×LOH×k1, where, ROH represents resistance value of the overhead line section per Kilometer (Km), XOH represents reactance value of the overhead line section per Km, LOH represents length of the overhead line section in Km, and k1 represents a safety margin factor for the overhead line section and is set to 0.8 value, to ensure faults within the overhead line section are reliably detected and to prevent overreach.
In an embodiment, the second impedance threshold for the cable section corresponds to 120% of the total impedance of the cable portion of the hybrid transmission line. The second impedance threshold for the cable section is computed as ZCABLE = (RCABLE+jXCABLE)×LCABLE×k2, where, RCABLE represents resistance value of the cable section per Km, XCABLE represents reactance value of the cable section per Km, LCABLE represents physical length of the cable section in Km, and k2 represents a safety margin factor for the cable section and is set to 1.2, to ensure faults within the cable section are reliably detected and auto-reclosing of the second circuit breaker is inhibited by the second relay.
In an embodiment, the first relay includes a first potential transformer and a first current transformer, and is configured to measure electrical parameters including a voltage and a current at the overhead line section of the hybrid transmission line, and compute the fault impedance as ZA = V_A/I_A , where, ZA represents fault impedance measured by the first relay, VA represents the voltage measured during a fault condition at the overhead line section of the hybrid transmission line through the first potential transformer, and IA represents the current measured during the fault condition at the overhead line section of the hybrid transmission line through the first current transformer.
In an embodiment, the first relay is further configured to scale the computed fault impedance ZA based on the ratio of the first current transformer turns to the first potential transformer turns.
In an embodiment, the second relay includes a second potential transformer and a second current transformer, and is configured to measure electrical parameters including a voltage and a current at the cable section of the hybrid transmission line, and compute the fault impedance as ZB = V_B/I_B , where ZB represents fault impedance measured by the second relay, VB represents the voltage measured during the fault condition at the cable section of the hybrid transmission line through the second potential transformer, and IB represents the current measured during the fault condition at the cable section of the hybrid transmission line through the second current transformer.
In an embodiment, the second relay is further configured to scale the computed fault impedance ZB based on the ratio of the second current transformer turns to the second potential transformer turns.
In an embodiment, each of the first and second relays comprises a drop-off timer configured to maintain the respective generated control signal for a time period that exceeds a dead time associated with the corresponding circuit breaker, such that the generated control signal to permit or inhibit auto-reclosing remains valid throughout the dead time, even after the circuit breaker is opened.
In an embodiment, the first relay and the second relay are communicatively coupled via a data communication channel.
In an embodiment, the first relay and the second relay includes a memory configured to store a count of prior auto-reclose operations, and the first relay and the second relay are further configured to inhibit further auto-reclosing of the first circuit breaker and the second circuit breaker respectively, when the number of reclose attempts exceed a predefined attempt threshold count.
The present disclosure further envisages a method for selectively performing auto-reclosing operations in a hybrid transmission line, wherein the hybrid transmission line includes an overhead line section and a cable section, and is configured to electrically couple a first power station (A) and a second power station (B), wherein a first circuit breaker and a second circuit breaker are connected at the overhead line section and the cable section, respectively, and are configured to interrupt power flow in response to a detected fault.
The method comprises the steps of:
measuring, by a first relay connected to the overhead line section of the hybrid transmission line and to the first circuit breaker, electrical parameters of the transmission line at the overhead line section;
computing, by the first relay, a fault impedance from the measured electrical parameters;
comparing, by the first relay, the computed fault impedance with a first impedance threshold for the overhead line section;
determining, by the first relay, whether a fault is located in the overhead line section;
generating, by the first relay, a control signal to permit auto-reclosing of the first circuit breaker when the fault is located within the overhead line section;
measuring, by a second relay connected to the cable section of the hybrid transmission line and to the second circuit breaker, electrical parameters of the transmission line at the cable section;
computing, by the second relay, a fault impedance from the measured electrical parameters;
comparing, by the second relay, the computed fault impedance with a second impedance threshold for the cable section;
determining, by the second relay, whether a fault is located in the cable section; and
generating, by the second relay, a control signal to inhibit auto-reclosing of the second circuit breaker when the fault is located within the cable section.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
A system and a method for selectively performing auto-reclosing operations in a hybrid transmission line, will now be described with the help of the accompanying drawings, in which:
Figure 1 illustrates a system for selectively performing auto-reclosing operations in a hybrid transmission line, in accordance with an embodiment of the present disclosure; and
Figures 2A- 2B illustrate a flow chart of the method for selectively performing auto-reclosing operations in a hybrid transmission line, in accordance with an embodiment of the present disclosure.
LIST OF REFERENCE NUMERALS USED IN DETAILED DESCRIPTION AND DRAWING
10 – Hybrid transmission line
12 – Overhead line section
14 – Cable section
100 – System
102 – First relay
104 – Second relay
106 – Data communication channel
200 – Method
A – First power station
B – Second power station
DETAILED DESCRIPTION
Embodiments, of the present disclosure, will now be described with reference to the accompanying drawing.
Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.
The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," “including,” and “having,” are open-ended transitional phrases and therefore specify the presence of stated features, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, operations, elements, components, and/or groups thereof.
When an element is referred to as being "connected to" or "coupled to" another element, it may be directly on, connected, or coupled to the other element. As used herein, the term "and/or" includes any and all combinations of one or more
The present disclosure envisages a system 100 for selectively performing auto-reclosing operations in a hybrid transmission line 10 and is explained with respect to Figure 1. Figure 1 illustrates the system 100 for selectively performing auto-reclosing operations in the hybrid transmission line 10.
The hybrid transmission line 10 includes an overhead line section 12 and a cable section 14. The overhead line section 12 typically consists of conductors suspended on transmission towers or poles and is exposed to environmental conditions. The overhead line section 12 is more susceptible to transient faults caused by lightning strikes, vegetation contact, bird interactions, or temporary conductor galloping. The cable section 14, on the other hand, comprises insulated underground power cables configured for subterranean installation. The cable section 14 provides improved protection from external disturbances but is relatively expensive to install and maintain, and faults in cable sections are more likely to be permanent due to insulation damage or moisture ingress.
The hybrid transmission line 10 is configured to electrically couple a first power station A and a second power station B, for transmission of electrical power from the first power station A to the second power station B. A first circuit breaker and a second circuit breaker are connected at the overhead line section 12 and the cable section 14, respectively. The first and second circuit breakers are configured to interrupt power flow in response to a detected fault in the hybrid transmission line 10, thereby isolating faulted hybrid transmission line 10 and preventing the propagation of fault currents in other lines, receiving power stations and power system.
The system includes a first relay 102 and a second relay 104.
The first relay 102 is connected to the overhead line section 12 of the hybrid transmission line 10 and to the first circuit breaker. The first relay 102 is configured to measure electrical parameters of the hybrid transmission line 10 at the overhead line section 12. The first relay 102 is connected to the first circuit breaker at the first power station A, from which the overhead line section 12 of the hybrid line (10) originates. Further, the first relay 102 is configured to compute a fault impedance from the measured electrical parameters. The first relay 102 is further configured to compare the computed fault impedance with a first impedance threshold for the overhead line section 12 in order to determine whether a fault is located in the overhead line section 12. Accordingly, the first relay 102 is configured to generate a control signal to permit auto-reclosing of the first circuit breaker when the fault is located within the overhead line section 12. In an embodiment, if the computed fault impedance by the first relay 102 is more than the first impedance threshold then the control signal to permit auto-reclosing of the first circuit breaker is not generated and the first circuit breaker will not go for auto-reclosing.
The second relay 104 is connected to the cable section 14 of the hybrid transmission line 10 and to the second circuit breaker. The second relay 104 is configured to measure electrical parameters of the transmission line at the cable section 14. The second relay 104 is connected to the second circuit breaker at the second power station B, where the cable section 14 of the hybrid line 10 is terminated. Further, the second relay 104 is configured to compute a fault impedance from the measured electrical parameters. The second relay 104 is further configured to compare the computed fault impedance with a second impedance threshold for the cable section 14 in order to determine whether a fault is located in the cable section 14. Accordingly, the second relay 104 is configured to generate a control signal to inhibit auto-reclosing of the second circuit breaker when the fault is located within the cable section 14. In an embodiment, if the computed fault impedance by the second relay is more than the second impedance threshold then the control signal to inhibit auto-reclosing of the second circuit breaker is not generated (i.e., control signal to permit auto-reclosing of the second circuit breaker is generated) and the second circuit breaker will go for auto-reclosing.
In an embodiment, at any point of time of the fault, the sum of the fault impedance computed by the first relay 102 at the first power station A and the fault impedance computed by the second relay 104 at the second power station B is equal to total impedance of hybrid line. In an embodiment, the first impedance threshold for the overhead line section 12 corresponds to 80% of the total impedance of the overhead line section of the hybrid transmission line 10, such that when the fault impedance computed by the first relay 102 is less than or equal to the first impedance threshold, the fault is determined to be located within the overhead line section 12, and the first relay 102 generates a control signal to permit auto-reclosing of the first circuit breaker. Additionally, the first impedance threshold is set to 80% of the total impedance of the overhead portion to prevent overreach, a situation where the first relay 102 falsely detects a fault beyond its intended zone (i.e., into the cable section 14). Thus, the system 100 ensures that only faults within the overhead line section 12 are identified for auto-reclosing. This margin of safety, i.e., 20% accounts for inaccuracies in impedance calculation.
The first impedance threshold for the overhead line section 12 is computed as:
ZOH = (ROH+jXOH)×LOH×k1,
where:
ROH represents resistance value of the overhead line section 12 per Kilometer (Km),
XOH represents reactance value of the overhead line section 12 per Km,
LOH represents length of the overhead line section 12 in Km, and
k1 represents a safety margin factor for the overhead line section 12 and is set to 0.8 value, to ensure faults within the overhead line section 12 are reliably detected and to prevent overreach.
In an embodiment, the second impedance threshold for the cable section 14 corresponds to 120% of the total impedance of the cable portion of the hybrid transmission line 10, such that when the fault impedance computed by the second relay 104 is less than or equal to the second impedance threshold, the fault is determined to be located within the cable section 14, and the second relay 104 generates a control signal to inhibit auto-reclosing of the second circuit breaker. Additionally, the second impedance threshold is set to 120% of the cable impedance to prevent underreach, a condition where the second relay 104 may fail to detect a fault within the cable section if the measured impedance is slightly lower than actual fault impedance due to error (for instance error due to CT and PT error). Thus, the system 100 ensures that all faults occurring within the cable section 14 are reliably detected, thereby ensuring accurate blocking of auto-reclosing for the second circuit breaker.
The second impedance threshold for the cable section 14 is computed as:
ZCABLE = (RCABLE+jXCABLE)×LCABLE×k2,
where:
RCABLE represents resistance value of the cable section 14 per Km,
XCABLE represents reactance value of the cable section 14 per Km,
LCABLE represents physical length of the cable section 14 in Km, and
k2 represents a safety margin factor for the cable section 14 and is set to 1.2, to ensure faults within the cable section 14 are reliably detected and auto-reclosing of the second circuit breaker is inhibited by the second relay 104.
In an embodiment, the values corresponding to ROH, XOH, LOH, k1, RCABLE, XCABLE, LCABLE, and k2 are obtained from an operator, based on the specific configuration of the hybrid transmission line 10.
In an embodiment, the first relay 102 includes a first potential transformer and a first current transformer. The first potential transformer and the first current transformer are configured to measure electrical parameters, including a voltage and a current at the overhead line section 12 of the hybrid transmission line 10. Accordingly. the first relay 102 is configured to compute a fault impedance as:
ZA = V_A/I_A ,
where:
ZA represents fault impedance measured by the first relay 102,
VA represents the voltage measured during the fault condition at the overhead line section 12 of the hybrid transmission line 10 through the first potential transformer, and
IA represents the current measured during the fault condition at the overhead line section 12 of the hybrid transmission line 10 through the first current transformer.
In an embodiment, the first relay 102 is further configured to scale the computed fault impedance ZA based on the ratio of the first current transformer turns to the first potential transformer turns.
In an embodiment, the second relay 104 includes a second potential transformer and a second current transformer. The second potential transformer and the second current transformer are configured to measure electrical parameters including a voltage and a current at the cable section 14 of the hybrid transmission line 10. Accordingly, the second relay 104 is configured to compute a fault impedance as:
ZB = V_B/I_B ,
where:
ZB represents fault impedance measured by the second relay 104,
VB represents the voltage measured during the fault condition at the cable section 14 of the hybrid transmission line 10 through the second potential transformer, and
IB represents the current measured during the fault condition at the cable section 14 of the hybrid transmission line 10 through the second current transformer.
In an embodiment, the second relay 104 is further configured to scale the computed fault impedance ZB based on the ratio of the second current transformer turns to the second potential transformer turns.
In an embodiment, each of the first and second relays (102, 104) comprises a drop-off timer configured to maintain the respective generated control signal for a time period that exceeds a dead time associated with the corresponding circuit breaker, such that the generated control signal to permit or inhibit auto-reclosing remains valid throughout the dead time, even after the circuit breaker is opened.
When the the first and second relays (102, 104) generates the respective control signals to the circuit breaker upon detecting a fault condition, the circuit breaker opens and initiates the dead time timer. During this period, the the first and second relays (102, 104) calculates the fault impedance and compares it with the first impedance threshold and the second impedance threshold, respectively. Based on this comparison, the the first and second relays (102, 104) either permits or inhibit the auto-reclosing of the first and second circuit breakers, as described in the foregoing embodiments. If the the first and/or second relay (102, 104) permits auto-reclosing, then, upon expiry of the dead time, the circuit breaker closes in response to the auto-reclose control signal, respectively.
At any given time during a fault condition, the sum of the fault impedance measured by the first relay 102 from the first power station A and the fault impedance measured by the second relay 104 from the second power station B, equals the total impedance of the hybrid line 10.
Accordingly, during fault conditions, there are two possible scenarios:
First scenario: If the first relay 102 measures a fault impedance within its first impedance zone (i.e., computed fault impedance is less than the first impedance threshold), then at the same time, the second relay 104 measures a fault impedance above its respective second impedance threshold. In this case, the first relay 102 generates the control signal to permit auto-reclosing at the first circuit breaker of the first power station A, while the second relay 104 does not generate a control signal to inhibit auto-reclosing of the second circuit breaker. Consequently, auto-reclosing occurs at both the first circuit breaker and the second circuit breaker at their respective power stations.
Second scenario: If the first relay 102 measures a fault impedance above its first impedance zone (i.e., computed fault impedance is greater than the first impedance threshold), then at the same time, the second relay 104 measures a fault impedance within its respective second impedance threshold. In this case, the first relay 102 does not generate the control signal to permit auto-reclosing at the first circuit breaker of the first power station A, while the second relay 104 does generates a control signal to inhibit auto-reclosing of the second circuit breaker. Consequently, auto-reclosing does not occur at either the first circuit breaker or the second circuit breaker.
In an embodiment, the first relay 102 and the second relay 104 are communicatively coupled via a data communication channel 106.
In an embodiment, the first relay 102 and second relay 104 includes a memory. The memory is configured to store a count of prior auto-reclose operations. The first relay 102 and the second relay 104 are further configured to inhibit further auto-reclosing of the first circuit breaker and the second circuit braker respectively, when the number of reclose attempts exceed a predefined attempt threshold count. This indicates that the fault in the overhead line section 12 is likely a permanent fault and requires manual intervention for fault recovery. Inhibiting further auto-reclosing of the circuit breakers helps prevent potential damage to the overall system.
In an embodiment, the count of prior auto-reclose operations is set to one. This means that after detection of a fault, if the first relay 102 detects the fault in the overhead line section 12, it will allow an auto-reclose operation to occur at the first power station (A). At the same time, the second relay 104 will detect that the fault lies outside the cable section 14 and will not generate a block signal for auto-reclosing, thereby allowing auto-reclosing at the second power station (B). Thus, after tripping in such a case and upon elapsing of the dead time at both power stations (A, B), the auto-reclosing operation occurs only once. In an embodiment, the count of prior auto-reclose operations is set to a count more than one.
A related concept is the reclaim time of the relay, which is a drop-off timer that starts as soon as the actual auto-reclose operation is completed and the circuit breakers are closed. If another fault occurs before the elapsing of the reclaim timer on the hybrid line 10, the relay will always block auto-reclosing for the hybrid line 10, regardless of whether the fault is in the overhead line section 12 or the cable section 14. The first relay 102 and the second relay 104 treats such a fault as a permanent fault. However, if the fault occurs after the reclaim time has elapsed, the relays (102, 104) treat it as a new, fresh transient fault. Since the hybrid line 10 had remained stable after the first fault until the reclaim time elapsed, the relays (102, 104) will initiate a fresh auto-reclose cycle, allowing auto-reclosing if the fault is in the overhead line section 12, or blocking auto-reclosing if the fault is in the cable section 14.
In an embodiment, the first relay 102 and the second relay 104 include one or more processors configured to compute fault impedance based on measured voltage and current values, compare the computed fault impedance with a respective predefined impedance threshold, determine the location of the fault within the hybrid transmission line 10, and generate a corresponding control signal to either permit or inhibit auto-reclosing of the associated circuit breaker.
In an embodiment, the system 100 further comprises a human-machine interface operatively connected to the first relay 102 and the second relay 104. The human-machine interface is configured to provide a visual display of operational parameters, circuit breaker status (open/closed/auto-reclosed), relay status (for example: active/inactive/fault detected), and computed fault impedance values. The human-machine interface enables an operator to monitor real-time measurements from the overhead line section 12 and the cable section 14 of the hybrid transmission line 10, including the measured voltage and current values, fault detection determinations, and the permit or inhibit status of the first and second circuit breakers. In an embodiment, the values corresponding to ROH, XOH, LOH, k1, RCABLE, XCABLE, LCABLE, and k2 are obtained from an operator through the human-machine interface. In an embodiment, the human-machine interface can be a standalone embedded hardware unit with a display device (such as a monitor, touchscreen, mobile display, or like devices) and input devices (such as a keyboard, touch panel, physical buttons, or like devices). In another embodiment, the human-machine interface can be integrated into a supervisory control and data acquisition (SCADA) system, wherein the human-machine interface functions are accessible through a graphical user interface (GUI) on a remote workstation.
The present disclosure further envisages a method for selectively performing auto-reclosing operations in a hybrid transmission line 10 and is explained with respect to Figures 2A-2B. Figures 2A—2B illustrate a flow chart of the method 200.
The hybrid transmission line 10 includes an overhead line section 12 and a cable section 14, and is configured to electrically couple a first power station A and a second power station B. A first circuit breaker and a second circuit breaker are connected at the overhead line section 12 and the cable section 14, respectively, and are configured to interrupt power flow in response to a detected fault.
The method 200 includes to following steps:
At step 202: measuring, by a first relay 102 connected to the overhead line section 12 of the hybrid transmission line 10 and to the first circuit breaker, the electrical parameters of the transmission line at the overhead line section 12.
At step 204: computing, by the first relay 102, a fault impedance from the measured electrical parameters.
At step 206: comparing, by the first relay 102, the computed fault impedance with a first impedance threshold for the overhead line section (12).
At step 208: determining, by the first relay 102, whether a fault is located in the overhead line section 12.
At step 210: generating, by the first relay 102, a control signal to permit auto-reclosing of the first circuit breaker when the fault is located within the overhead line section 12.
At step 212: measuring, by a second relay 104 connected to the cable section 14 of the hybrid transmission line 10 and to the second circuit breaker, the electrical parameters of the transmission line at the cable section 14.
At step 214: computing, by the second relay 104, a fault impedance from the measured electrical parameters.
At step 216: comparing, by the second relay 104, the computed fault impedance with a second impedance threshold for the cable section 14.
At step 218: determining, by the second relay 104, whether a fault is located in the cable section 14.
At step 220: generating, by the second relay 104, a control signal to inhibit auto-reclosing of the second circuit breaker when the fault is located within the cable section 14.
The processor mentioned in the foregoing embodiments may be an integrated circuit chip, and has a signal processing capability. In an implementation process, steps in the foregoing method embodiments can be implemented by using a hardware-integrated logical circuit in the processor, or by using instructions in the form of software. The processor may be a general-purpose processor, a digital signal processor (digital signal processor, DSP), an application-specific integrated circuit (application-specific integrated circuit, ASIC), a field programmable gate array (field programmable gate array, FPGA), or another programmable logic device, a discrete gate or transistor logic device, or a discrete hardware component. The general-purpose processor may be a microprocessor, or the processor may be any conventional processor or the like. Steps of the methods disclosed in the embodiments of this disclosure may be directly performed and completed by a hardware processor, or may be performed and completed by a combination of hardware and software modules in the processor. The software module may be located in a mature storage medium in the art, such as a random-access memory, a flash memory, a read-only memory, a programmable read-only memory, an electrically erasable programmable memory, or a register. The storage medium is located in the memory, and a processor reads the information in the memory and completes the steps in the foregoing methods in combination with the hardware of the processor.
The memory in the foregoing embodiments may be a volatile memory or a non-volatile memory, or may include both a volatile memory and a non-volatile memory. The non-volatile memory may be a read-only memory (read-only memory, ROM), a programmable read-only memory (programmable ROM, PROM), an erasable programmable read-only memory (erasable PROM, EPROM), an electrically erasable programmable read-only memory (electrically EPROM, EEPROM), or a flash memory. The volatile memory may be a random-access memory (random access memory, RAM), used as an external cache. Through example but not limitative description, many forms of RAMs may be used, for example, a static random access memory (static RAM, SRAM), a dynamic random access memory (dynamic RAM, DRAM), a synchronous dynamic random access memory (synchronous DRAM, SDRAM), a double data rate synchronous dynamic random access memory (double data rate SDRAM, DDR SDRAM), an enhanced synchronous dynamic random access memory (enhanced SDRAM, ESDRAM), a synchlink dynamic random access memory (synchlink DRAM, SLDRAM), and a direct rambus random access memory (direct rambus RAM, DR RAM). It should be noted that the memory described in this specification includes but is not limited to these and any memory of another proper type.
In an embodiment, the data communication channel 106 refers to a medium or interface that facilitates the exchange of data between the first relay 102 and the second relay 104. The data communication channel 106 may include wired technologies, such as Ethernet, serial communication (e.g., RS-485 – Recommended Standard 485), or fiber optic communication, as well as wireless technologies, such as Wi-Fi (Wireless Fidelity) or radio frequency (RF) communication. The data communication channel 106 may also support industry-standard communication protocols such as IEC 61850 (International Electrotechnical Commission standard for communication networks and systems for power utility automation), DNP3 (Distributed Network Protocol version 3), or other standard or proprietary protocols designed for protection, control, and automation systems.
A person of ordinary skill in the art may be aware that, in combination with the examples described in the embodiments disclosed in this specification, units and algorithm steps may be implemented by electronic hardware or a combination of computer software and electronic hardware. Whether the functions are performed by hardware or software depends on particular applications and design constraint conditions of the technical solutions.A person skilled in the art may use different methods to implement the described functions for each particular application, but it should not be considered that the implementation goes beyond the scope of this application.

Working example:
Consider a hybrid transmission line 10 electrically coupling a first power station A and a second power station B. The hybrid transmission line 10 comprises an overhead line section 12, approximately 10 km in length and a cable section 14, approximately 3 km in length. The electrical characteristics of the overhead line section 12 include a resistance ROH = 0.02 Ω/km and a reactance XOH = 0.3 Ω/km. The overhead line section 12 is exposed to environmental factors such as lightning and vegetation. The cable section 14 consists of underground insulated cables routed through urban infrastructure to minimize external disturbances. The electrical characteristics of the cable section 14 include a resistance RCABLE= 0.02Ω/km and a reactance XCABLE = 0.1 Ω/km.
To enable selective auto-reclosing in the hybrid transmission line 10, the system 100 includes a first relay 102 and a second relay 104.
The first relay 102 is connected with first circuit breaker at first power station (A) from where the overhead portion of hybrid line is getting start, and is configured to compute a fault impedance ZA based on measured electrical parameters. To avoid overreach, the first relay 102 is configured to calculate the first impedance threshold of the overhead line section 12. The first impedance threshold is calculated as:
ZOH = (ROH+jXOH)×LOH×k1
= (0.02 + j0.3)×10×0.8 =(0.16+j2.4) Ω
|ZOH| = 2.405 Ω
Thus, the first relay 102 will permit auto-reclosing of the first circuit breaker only if the computed fault impedance ZA ≤ ZOH, ensuring faults within the overhead line section 12 are accurately detected.
The second relay 104 is operatively connected to second circuit breaker at second power station (B) to which the cable portion of hybrid line is getting terminated, and is configured to compute a fault impedance ZB based on measured electrical parameters. To avoid underreach, the second relay 104 is configured to calculate the second impedance threshold of the cable section 14. The second impedance threshold is calculated as:
ZCABLE = (RCABLE+jXCABLE)×LCABLE×k2
= (0.02 +j 0.1)× 3×1.2 =(0.072+j 0.36) Ω
| ZCABLE | = 0.3671 Ω
Thus, the second relay 104 will inhibit auto-reclosing of the second circuit breaker only if the computed fault impedance ZB ≤ ZCABLE, ensuring faults within the cable section 14 are accurately detected.
For example, suppose a fault occurs, the first relay 102 computes ZA =2.1 Ω and the second relay 104 computes ZCABLE = 0.95 Ω, i.e., ZA < ZOH and ZB > ZCABLE, therefore, both the relays detect the fault on overhead section of hybrid line, and therefore, auto-reclosing happens in both the first circuit breaker and the second circuit breaker.
Alternatively, suppose a fault occurs, the first relay 102 computes ZA=2.6 Ω and the second relay 104 computes ZCABLE = 0.33 Ω. Then ZA > ZOH and ZB < ZCABLE, therefore, both the relays detect the fault on cable section of hybrid line, and therefore, auto-reclosing does not happen in both the first circuit breaker and the second circuit breaker.
Advantageously, the system 100 ensures that auto-reclosing is only permitted in the case of transient faults within the overhead line section, while auto-reclosing is inhibited for faults in the cable section, which are more likely to be permanent. Thus, the system improves power system reliability, minimizes manual interventions, and prevents equipment damage.
It may be clearly understood by a person skilled in the art that, for the purpose of a convenient and brief description, for a detailed working process of the foregoing apparatus and method, refer to a corresponding process in the foregoing method embodiments, and details are not described herein again.
The foregoing description of the embodiments has been provided for purposes of illustration and is not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.
TECHNICAL ADVANCEMENTS AND ECONOMIC SIGNIFICANCE
The present disclosure described herein above has several technical advantages including, but not limited to, a system and a method for selectively performing auto-reclosing operations in a hybrid transmission line, that:
permits auto-reclosing only for faults located within an overhead line section of the hybrid transmission line;
inhibits auto-reclosing when a fault is detected in the cable section of the hybrid transmission line;
reduces power restoration time caused by transient faults in the overhead line section of the hybrid transmission line; and
reduces manual intervention in restoring power following transient faults in the hybrid transmission line.
The foregoing disclosure has been described with reference to the accompanying embodiments, which do not limit the scope and ambit of the disclosure. The description provided is purely by way of example and illustration.
The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The foregoing description of the specific embodiments so fully reveals the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation. , Claims:WE CLAIM:
A system (100) for selectively performing auto-reclosing operations in a hybrid transmission line (10), wherein the hybrid transmission line (10) including an overhead line section (12) and a cable section (14), and configured to electrically couple a first power station (A) and a second power station (B), wherein a first circuit breaker and a second circuit breaker are connected at the overhead line section (12) and the cable section (14), respectively, and are configured to interrupt power flow in response to a detected fault, said system (100) comprising:
a first relay (102) connected to the overhead line section (12) of the hybrid transmission line (10) and to the first circuit breaker, said first relay (102) being configured to measure electrical parameters of the hybrid transmission line (10) at the overhead line section (12), compute a fault impedance from the measured electrical parameters, compare the computed fault impedance with a first impedance threshold for the overhead line section (12), determine whether a fault is located in the overhead line section (12), and generate a control signal to permit auto-reclosing of the first circuit breaker when the fault is located within the overhead line section (12); and
a second relay (104) connected to the cable section (14) of the hybrid transmission line (10) and to the second circuit breaker, said second relay (104) being configured to measure electrical parameters of the transmission line at the cable section (14), compute a fault impedance from the measured electrical parameters, compare the computed fault impedance with a second impedance threshold for the cable section (14), determine whether a fault is located in the cable section (14), and generate a control signal to inhibit auto-reclosing of the second circuit breaker when the fault is located within the cable section (14).
The system (100) as claimed in claim 1, wherein the first impedance threshold for the overhead line section (12) corresponds to 80% of the total impedance of the overhead line section of the hybrid transmission line (10).
The system (100) as claimed in claim 2, wherein the first impedance threshold for the overhead line section (12) is computed as:
ZOH = (ROH+jXOH)×LOH×k1,
where:
ROH represents resistance value of the overhead line section (12) per Kilometer (Km),
XOH represents reactance value of the overhead line section (12) per Km,
LOH represents length of the overhead line section (12) in Km, and
k1 represents a safety margin factor for the overhead line section (12) and is set to 0.8 value, to ensure faults within the overhead line section (12) are reliably detected and to prevent overreach.
The system (100) as claimed in claim 1, wherein the second impedance threshold for the cable section (14) corresponds to 120% of the total impedance of the cable portion of the hybrid transmission line (10).
The system (100) as claimed in claim 4, wherein the second impedance threshold for the cable section (14) is computed as:
ZCABLE = (RCABLE+jXCABLE)×LCABLE×k2,
where:
RCABLE represents resistance value of the cable section (14) per Km,
XCABLE represents reactance value of the cable section (14) per Km,
LCABLE represents physical length of the cable section (14) in Km, and
k2 represents a safety margin factor for the cable section (14) and is set to 1.2, to ensure faults within the cable section (14) are reliably detected and auto-reclosing of the second circuit breaker is inhibited by said second relay (104).
The system (100) as claimed in claim 1, wherein said first relay (102) includes a first potential transformer and a first current transformer, and is configured to measure electrical parameters including a voltage and a current at the overhead line section (12) of the hybrid transmission line (10), and compute a fault impedance as:
ZA = V_A/I_A ,
where:
ZA represents fault impedance measured by said first relay (102),
VA represents the voltage measured during the fault condition at the overhead line section (12) of the hybrid transmission line (10) through said first potential transformer, and
IA represents the current measured during the fault condition at the overhead line section (12) of the hybrid transmission line (10) through said first current transformer.
The system (100) as claimed in claim 6, wherein said first relay (102) is further configured to scale the computed fault impedance ZA based on the ratio of said first current transformer turns to said first potential transformer turns.
The system (100) as claimed in claim 1, wherein said second relay (104) includes a second potential transformer and a second current transformer, and is configured to measure electrical parameters including a voltage and a current at the cable section (14) of the hybrid transmission line (10), and compute a fault impedance as:
ZB = V_B/I_B ,
where:
ZB represents fault impedance measured by said second relay (104),
VB represents the voltage measured during the fault condition at the cable section (14) of the hybrid transmission line (10) through said second potential transformer, and
IB represents the current measured during the fault condition at the cable section (14) of the hybrid transmission line (10) through said second current transformer.
The system (100) as claimed in claim 8, wherein said second relay (104) is further configured to scale the computed fault impedance ZB based on the ratio of said second current transformer turns to said second potential transformer turns.
The system (100) as claimed in claim 1, wherein each of the first and second relays (102, 104) comprises a drop-off timer configured to maintain the respective generated control signal for a time period that exceeds a dead time associated with the corresponding circuit breaker, such that the generated control signal to permit or inhibit auto-reclosing remains valid throughout the dead time, even after the circuit breaker is opened..
The system (100) as claimed in claim 1, wherein said first relay (102) and said second relay (104) are communicatively coupled via a data communication channel (106).
The system (100) as claimed in claim 1, wherein said first relay (102) and the second relay (104) includes a memory configured to store a count of prior auto-reclose operations, and said first relay (102) and the second relay (104) are further configured to inhibit further auto-reclosing of the first circuit breaker and the second circuit breaker respectively, when the number of reclose attempts exceeds a predefined attempt threshold count.
A method (200) for selectively performing auto-reclosing operations in a hybrid transmission line (10), wherein the hybrid transmission line (10) includes an overhead line section (12) and a cable section (14), and is configured to electrically couple a first power station (A) and a second power station (B), wherein a first circuit breaker and a second circuit breaker are connected at the overhead line section (12) and the cable section (14), respectively, and are configured to interrupt power flow in response to a detected fault, the method (200) comprising the steps of:
measuring (202), by a first relay (102) connected to the overhead line section (12) of the hybrid transmission line (10) and to the first circuit breaker, electrical parameters of the transmission line at the overhead line section (12);
computing (204), by said first relay (102), a fault impedance from the measured electrical parameters;
comparing (206), by said first relay (102), the computed fault impedance with a first impedance threshold for the overhead line section (12);
determining (208), by said first relay (102), whether a fault is located in the overhead line section (12);
generating (210), by said first relay (102), a control signal to permit auto-reclosing of the first circuit breaker when the fault is located within the overhead line section (12);
measuring (212), by a second relay (104) connected to the cable section (14) of the hybrid transmission line (10) and to the second circuit breaker, electrical parameters of the transmission line at the cable section (14);
computing (214), by said second relay (104), a fault impedance from the measured electrical parameters;
comparing (216), by said second relay (104), the computed fault impedance with a second impedance threshold for the cable section (14);
determining (218), by said second relay (104), whether a fault is located in the cable section (14); and
generating (220), by said second relay (104), a control signal to inhibit auto-reclosing of the second circuit breaker when the fault is located within the cable section (14).

Dated this 01st day of September, 2025

_______________________________
MOHAN RAJKUMAR DEWAN, IN/PA – 25
OF R. K. DEWAN & CO.
AUTHORIZED AGENT TO THE APPLICANT

TO,
THE CONTROLLER OF PATENTS
THE PATENT OFFICE, MUMBAI