SE1651596A1 - Time synchronization of intelligent electronic devices - Google Patents

Abstract

There is provided mechanisms for time synchronization among a first set of IEDs within a first power system substation. A method comprises obtaining, by one IED in the first set of IEDs, time synchronization information between said one IED and an IED of a second set of IEDs within a second power system substation using an echo based time synchronization method. The method comprises performing time synchronization of the remaining IEDs within the first set of IEDs using the obtained time synchronization information.(Fig.)

Description

10 In general terms, atomic clocks (such as Cesium / Rubidium clocks) can provide very accurate and absolute time. But atomic clocks still needs some communications links and could be too expensive for wide area applications at each node in the power system. Atomic clocks may therefore be used only at some very important nodes in the power system.

In general terms, time synchronization based on the use of radio clocks is limited by uncertainties and variability in radio propagation.

In general terms, GPS information is widely used in power system and other industries for time synchronization. It can be regarded as being of low cost and has a comparatively good accuracy when it works well. Unfortunately, GPS is not reliable and secure enough for some applications, especially for protection applications.

Further, severe weather can interrupt GPS services for days, no matter how robust the device being configured to receive the GPS information is. GPS signals could be disturbed seriously by geography or meteorological conditions. Further, GPS information may be subject to jamming or spoo fi ng. Especially low-received-power, unencrypted civilian GPS signals have proven to be vulnerable to jamming and spoo attacks ng attacks.

PTP is a popular and mainstream time synchronization technology for the time synchronization among distributed clocks. It has a comparatively good accuracy and can be used inside substations / terminals or among substations / terminals. A combined use of GPS and atomic clocks can cooperate with PTP in the same time synchronization networks. For wide area applications, PTP can be implemented or transmitted by IP. However, PTP over Wide Area Networks (WANs) needs additional dedicated communication channels, which can be costly.

Hence, there is still a need for an improved time synchronization of power system applications.

SUMMARY An object of embodiments herein is to provide efficient time synchronization of power system applications.

According to a first aspect there is presented a method for time synchronization among a first set of IEDs within a first power system substation. The method comprises obtaining, by one IED in the first set of IEDs, time synchronization information between said one IED and an IED of a second set of IEDs within a second power system substation using an echo based time synchronization method. The method comprises performing time synchronization of the remaining IEDs within the first set of IEDs using the obtained time synchronization information.

Advantageously this method provides efficient time synchronization of power system applications.

Advantageously this method provides a low-cost, high-reliable, high-secure, easily-implemented time synchronization system for wide area applications, including protection relays and other IEDs, and which are independent of GPS.

Advantageously this method can cooperate with other synchronization methods (such as GPS, PTP, etc.) to enhance the reliability of the time synchronization.

Advantageously this method can act as redundancy to enhance reliability and security of existing mechanism for time synchronization.

Advantageously, for a scenario where the method is used as redundancy of PTP over WAN, it can enhance the reliability of the whole time synchronization system.

Advantageously, for a scenario where there is no PTP over WAN, the method can work well with GPS as a low-cost solution.

According to a second aspect there is presented a power system substation for time synchronization among a first set of IEDs within the power system substation. The power system substation comprises processing circuitry. The processing circuitry is configured to cause the power system substation to obtain, by one IED in the first set of IEDs, time synchronization information between said one IED and an IED of a second set of IEDs within a further power system substation using an echo based time synchronization method.

The processing circuitry is configured to cause the power system substation to perform time synchronization of the remaining IEDs within the first set of IEDs using the obtained time synchronization information.

According to a third aspect there is presented a computer program for time synchronization among a first set of IEDs within a power system substation, the computer program comprising computer program code which, when run on the power system substation, causes the power system substation to perform a method according to the first aspect.

According to a fourth aspect there is presented a computer program product comprising a computer program according to the fifth aspect and a computer readable storage medium on which the computer program is stored. The computer readable storage medium could be a non-transitory computer readable storage medium.

It is to be noted that any feature of the fi rst, second, third, and fourth aspects may be applied to any other aspect, wherever appropriate. Likewise, any advantage of the first aspect may equally apply to the second, third, and / or fourth aspect, respectively, and vice versa. Other objectives, features and advantages of the enclosed embodiments will be apparent from the following detailed disclosure, from the attached dependent claims as well as from the drawings.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a / an / the element, apparatus, component, means, 1O step, etc. "are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

LETTER DESCRIPTION OF THE DRAWINGS The inventive concept is now described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a schematic diagram illustrating a power system according to embodiments; Fig. 2 is a ch owchart of methods according to embodiments; Fig. 3 is a schematic diagram showing functional units of a power system substation according to an embodiment; and Fig. 4 shows one example of a computer program product comprising computer readable storage medium according to an embodiment.

DETAILED DESCRIPTION The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the inventive concept are shown. This inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art.

Like numbers refer to like elements throughout the description. Any step or feature illustrated by dashed lines should be regarded as optional.

Fig. 1 is a schematic diagram illustrating a power system 1oo where embodiments presented herein can be applied. The power system 100 comprises a first power system substation 11oa (“Substation A”), a second power system substation 11ob (“Substation B”), and a third power system substation 110c (“Substation C”). Each power system substation 110a, 110b, 110c comprises IEDs 120a, 120b, 120c, 12od, 12oe, 12of. In the illustrative example of Fig. 1 the IEDs of Substation A are denoted IED A1, IED A2, IED A3, IED A4; the IEDs of Substation B are denoted IED B1, IED B2, B3, B4; and the IEDs of Substation C are denoted IED C1, IED C2, IED C3, IED C4.

Hence, IED A1, IED A2, IED A3, IED A4 form first set of IEDs, IED B1, IED B2, IED B3, IED B4 form a second set of IEDs, and IED C1, IED C2, IED C3, IED C4 form a third set of IEDs. In general terms, each IED 120a, 120b, 120c, 12od, 120e, 120f is a microprocessor-based controller of power system equipment, such as circuit breakers, transformers and capacitor banks. Each IED could be a protection relay, phasor measurement unit (PMU), meter, and / or merging unit.

The power system substations 110a, 110b, 110c are interconnected via communications links 130a, 13ob used e.g., for line differential protection.

The embodiments disclosed herein relate to mechanisms for time synchronization among a first set of IEDs 120a, 120b within a first power system substation 110a. In order to obtain such mechanisms there is provided a power system substation 110a, a method performed by the power system substation 110a, a computer program product comprising code, for example in the form of a computer program, that when run on a power system substation 110a, causes the power system substation 110a to perform the method.

The embodiments disclosed herein mainly focuses on wide area time synchronization which is becoming a blocking issue for wide area protection and control system applications.

Fig. 2 is an eye chart illustrating embodiments of methods for time synchronization among a first set of IEDs 120a, 120b within a f1rst power system substation 110a. The methods are performed by the power system substation 110a. The methods are advantageously provided as computer programs 420.

With reference to Fig.1, line differential protection devices located in different substations (IED 12oa and IED 12oc) are assumed to already be time synchronized by means of the line differential protection. Hence, step S102 is performed: S102: One IED 12oa in the first set of IEDs obtains time synchronization information between this one IED 12oa and an IED 12oc of a second set of IEDs 12oc, 120d within a second power system substation 110b using an echo based time synchronization method.

But this synchronization service is, according to prior art, only used by the IED 12oa and IED 12oc. The herein disclosed embodiments are based on re- using the existing time synchronization obtained by using the echo based time synchronization method. That is, according to embodiments disclosed herein, the time synchronization information of IED 12oa (and IED 12oc) will be shared to other IEDs 120b (120d) within the same substation 11oa (and 110b). Hence, step S104 is performed: S104: Time synchronization is performed of the remaining IEDs 120b within the first set of IEDs using the obtained time synchronization information.

This means that all IEDs in substations 11oa (and 110b) will be time synchronized.

The line differential protections between the power system substations 11oa, 110b could thus be time synchronized using an echo method. Time synchronization using an echo method is as such known in the art. Further, the echo based time synchronization method could be for a first line differential protection between this one IED 12oa and this IED 12oc of the second set of IEDs 12oc, 120d within the further power system substation 11ob.

The first set of IEDs 12oa, 120b could comprise those IEDs of the first power system substation 11oa that need time synchronization Further, the first set of IEDs 12oa, 120b could comprise all IEDs of the first power system substation 11oa.

Embodiments relating to further details of time synchronization among a first set of IEDs 12oa, 120b within a first power system substation 11oa as performed by the power system substation 11oa will now be disclosed.

There may be different ways for the time synchronization of the remaining IEDs within the first substation 11oa to be performed. According to an embodiment, performing the time synchronization in step S104 comprises a sub-step S104a to be performed: S104a: IED 120a shares the time synchronization information to the remaining IEDs 120b.

The time synchronization of IEDs 120a, 120b within the substation 11oa may be based on the Precision Time Protocol, PTP, the Inter-Range Instrumentation Group code B, IRIG-B, the Network Time Protocol, NTP, or the Simple Network Time Protocol, SNTP. Hence, according to an embodiment the time synchronization information is shared using PTP, IRIG-B, NTP, or SNTP.

According to an embodiment at least IED 120a comprises a PMU, and the time synchronization of the remaining IEDs 120b is performed using the PMU. Existing time synchronization mechanisms used in the line differential protection can be used to time synchronize the PMUs in a wide area. In general terms, a PMU is a device configured to measures electrical signals on an electricity grid using a common time source for synchronization. Time synchronization allows synchronized real-time measurements of multiple remote measurement points on the grid. The resulting measurement is known as a synchro-phasor. In further aspects, PMUs could be co-located (in the same substations) with line differential protection IEDs 120a, 120b 12oc, 12oe. PMUs could cooperate both with existing GPS synchronization as well as PTP / IEEE 1588. PMUs could serve as a reliable synchronization to guard the GPS synchronization system for the wide area protection system applications. If the GPS error shifts from a given time limit band, a GPS error alarm could be provided and the wide area protection system might be switched into the time synchronization as performed in steps S102, S104 disclosed above.

The line differential protection is a typical two-terminal system (where each terminal is operatively connected to a respective IED). However, some line differential protection mechanisms can support more than two terminal lines. For example RED 670 from ABB can support up to 5 terminal lines.

This means that 5 substations can be time synchronized using one differential protection system. That is, the single IED 12ob could have a line differential protection with respective IEDs of four other substations. If one of those substations can be further time synchronized with another substation by using the herein disclosed methods, then all those five substations can be time synchronized with this substation 11oa.

The embodiments herein disclosed may be extended to the configuration of multi-line differential protection systems. For example, Fig. 1 shows a power system comprising three substations 11oa, 11ob, 11oc which are synchronized by two line differential protection systems (each represented by its communications line 13oa, 13ob). Hence according to an embodiment there is a second differential protection between IED 12ob and an IED 12oe of a third set of IEDs 120e, 12of within a third power system substation 11oc.

S106: IEDs 12ob provides the time synchronization information to IED 120e of the third set of IEDs 12oe. 12of.

Although Fig. 1 only shows three substations 11oa, 11ob, 11oc, the skilled person understands that the herein disclosed embodiments could be extended to any number of substations 11oa, 11ob, 11oc.

In some aspects the line differential protections have respective communications links 13oa, 13ob having symmetric delay. In case of communication channel asymmetry, known mechanisms which can detect, and compensate for, the channel asymmetry can be used.

The embodiments herein disclosed are primarily not intended to replace existing mechanism for time synchronization, e.g. based on PTP or GPS information. On the contrary, the embodiments herein disclosed could cooperate with existing mechanism for time synchronization as a low-cost redundancy. However, for power systems for which PTP information is not to be moved over WAN, the herein disclosed embodiments can be used as the main time synchronization mechanism.

Fig. 3 schematically illustrates, in terms of a number of functional units, the components of a power system substation 110a, 110b, 110c according to an embodiment. Processing circuitry 210 is provided using any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), etc., capable of executing software instructions stored in a computer program product 410 (as in Fig. 4), e.g. in the form of a storage medium 230. The processing circuitry 210 may further be provided as at least one application specific integrated circuit (ASIC), or field programmable gate array (FPGA).

Particularly, the processing circuitry 210 is con fi gured to cause the power system substation 110a, 110b, 110c to perform a set of operations, or steps, S102-S106, as disclosed above. For example, the storage medium 230 may store the set of operations, and the processing circuitry 210 may be con fi gured to retrieve the set of operations from the storage medium 230 to cause the power system substation 110a, 110b, 110c to perform the set of operations. The set of operations may be provided as a set of executable instructions.

Thus the processing circuitry 210 is thereby arranged to execute methods as herein disclosed. The storage medium 230 may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory. The power system substation 110a, 110b, 110c may further comprise a communications interface 220 at least configured for communications with another power system substation 110a, 110b, 110c. As 11 such the communications interface 220 may comprise one or more transmitters and receivers, comprising analogue and digital components. The processing circuitry 210 controls the general operation of the power system substation 110a, 110b, 110c e.g. by sending data and control signals to the communications interface 220 and the storage medium 230, by receiving data and reports from the communications interface 220, and by retrieving data and instructions from the storage medium 230. Other components (such as IEDs), as well as the related functionality, of the power system substation 110a, 110b, 110c are omitted in order not to obscure the concepts presented in Fig. 3.

Fig. 4 shows one example of a computer program product 410 comprising computer readable storage medium 430. On this computer readable storage medium 430, a computer program 420 can be stored, which computer program 420 can cause the processing circuitry 210 and thereto operatively coupled entities and devices, such as the communications interface 220 and the storage medium 230, to execute methods according to embodiments described herein. The computer program 420 and / or computer program product 410 may thus provide means for performing any steps as herein disclosed.

In the example of Fig. 4, the computer program product 410 is illustrated as an optical disc, such as a CD (compact disc) or a DVD (digital versatile disc) or a Blu-Ray disc. The computer program product 410 could also be embodied as a memory, such as a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM), or an electrically erasable programmable read-only memory (EEPROM) and more particularly as a non-volatile storage medium of a device in an external memory such as a USB (Universal Serial Bus) memory or a Flash memory, such as a compact Flash memory. Thus, while the computer program 420 is here schematically shown as a track on the depicted optical disk, the computer program 420 can be stored in any way which is suitable for the computer program product 410. 12 The inventive concept has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended patent claims.

Claims (10)

10 15 20 25 13 CLAIMS 1. A method for time synchronization among a first set of intelligent electronic devices, IEDs, (120a, 12ob) within a first power system substation (11oa), the method comprising: obtaining (S102), by one IED (12oa) in the first set of IEDs, time synchronization information between said one IED (12oa) and an IED (12oc) of a second set of IEDs (12oc, 12od) within a second power system substation (11ob) using an echo based time synchronization method; and performing (S104) time synchronization of the remaining IEDs (120b) within the first set of IEDs using the obtained time synchronization information. The method according to claim 1, wherein performing the time synchronization comprises: sharing (S1o4a), by said one IED (12oa) and to said remaining IEDs (120b), the time synchronization information. The method according to claim 2, wherein the time synchronization information is shared using the Precision Time Protocol, PTP, the Inter- Range Instrumentation Group code B, IRIG-B, the Network Time Protocol, NTP, or the Simple Network Time Protocol , SNTP. The method according to claim 1, wherein there is a second differential protection between one of said remaining IEDs (120b) and an IED (12oe) of a third set of IEDs (12oe, 12of) within a third power system substation (110c ), the method further comprising: providing (S106), by said at least one of said remaining IEDs (120b), the time synchronization information to said IED (12oe) of the third set of IEDs (12oe, 12of). 5. The method according to claim 1, wherein said IEDs (12oa, 12ob) are protection relays, phasor measurement units (PMUs), meters, and / or merging units. 10 15 20 25 14 The method according to claim 1, wherein the first set of IEDs (12oa, 12ob) comprises those IEDs of the first power system substation (11oa) that need time synchronization. The method according to claim 1, wherein the echo based time synchronization method is for a first line differential protection between said one IED (12oa) and said IED (120c) of said second set of IEDs (120c, 120d) within said further power system substation (110b). 8. A power system substation (11oa) for time synchronization among a first set of intelligent electronic devices, IEDs, (12oa, 12ob) within the power system substation (11oa), the power system substation (11oa) comprising processing circuitry (210) , the processing circuitry being configured to cause the power system substation (11oa) to: obtain, by one IED (12oa) in the first set of IEDs, time synchronization information between said one IED (12oa) and an IED (120c) of a second set of IEDs (120c, 120d) within a further power system substation (110b) using an echo based time synchronization method; and perform time synchronization of the remaining IEDs (12ob) within the first set of IEDs using the obtained time synchronization information. 9. A computer program (420) for time synchronization among a first set of intelligent electronic devices, IEDs, (120a, 12ob) within a power system substation (11oa), the computer program comprising computer code which, when run on processing circuitry ( 210) of the power system substation (11oa), causes the power system substation (11oa) to: obtain, by one IED (12oa) in the first set of IEDs, time synchronization information between said one IED (12oa) and an IED ( 120c) of a second set of IEDs (120c, 120d) within a further power system substation (110b) using an echo based time synchronization method; and perform time synchronization of the remaining IEDs (12ob) within the first set of IEDs using the obtained time synchronization information. 15 A computer program product (410) comprising a computer program (420) according to claim 9, and a computer readable storage medium (430) on which the computer program is stored.