Design Guide for Time ion of Electrical System 21-07-2009

8/7/2019 Design Guide for Time ion of Electrical System 21-07-2009

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DESIGN GUIDEfor Time Synchronisation of Electrical systems

CORE ENGG.ELECTRICAL

Document No REL-CORE-NEE-E10-P-003 Sh 2/20

TABLE OF CONTENTS

1.0 PREAMBLE ....................................................................................................................................................................... 3

1.1 OBJECTIVE........................................................................................................................................................................ 31.2 PURPOSE OF TIME SYNCHRONISATION......................................................................................................................... 3

2.0 EQUIPMENTS TO BE SYN CHRONIZED ...............................................................................................................3

2.1 NEED FOR SYNCHRONISAT ION....................................................................................................................................... 3

3.0 GENERAL CONCEPTS..................................................................................................................................................4

3.1 TIME DEFINITIONS........................................................................................................................................................... 43.2 SYNCHRONISATION PRINCIPLE....................................................................................................................................... 43.3 NECESSARY FEATURES OF IED CLOCK......................................................................................................................... 4

4.0 TIME REFERENCE ........................................................................................................................................................55.0 TIME SYNCHRONISATION CODES / PROTOCOLS ........................................................................................7

5.1 POTENTIAL FREE CONTACT ............................................................................................................................................ 75.2 IRIGB .............................................................................................................................................................................. 75.3 NETWORK TIME PROTOCOL (NTP)............................................................................................................................... 85.4 SIMPLE NETWORK TIME PROTOCOL (SNTP) .............................................................................................................. 85.5 TIME SYNCHRONISATION OPTIONS IN RELAYS............................................................................................................ 9

6.0 SIGNAL CABLING..........................................................................................................................................................9

7.0 INFORMATION TO BE PROVIDED TO C&I FOR MASTER CLOCK SPECIFICATION .................10

ANNEXURE A : LEAP YEAR / LEAP SECOND..................................................................................................................12

ANNEXURE B : IRIG-B ...............................................................................................................................................................13

ANNEXURE C : NETWORK TIME PROTOCOL (NTP) ..................................................................................................16

ANNEXURE D : FORMAT OF DATA TO BE PROVIDED TO C&I..............................................................................17

ANNEXURE E : TIME SYNCHRONISATION PROTOCOLS AVAILABLE IN RELAYS .....................................18


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1.0 Preamble

1.1 Objective

This guide is intended to assist the designer in the implementation of TimeSynchronisation for Electrical systems.

1.2 Purpose of Time synchronisation

1.2.1 Numerical relays have the facility to store fault records in the form of oscillo-graphicwaveforms and event logs showing the sequence of protection device operation. Theyprovide essential information that can lead to an understanding of just how the protectiondevice behaved under fault conditions. The fault record has become a tool that allows the

protection engineer to perform a cross check of the operation of the device against theapplied settings.

1.2.2 In most cases, the electrical fault creates fault records in more than one relay. Timesynchronisation of relays and fault-recorders simplifies the task of fault analysis.

1.2.3 Time synchronisation also increases the accuracy of control decisions by automaticcontrol and protection equipment. This is relevant in the switchyard, where numericalBay control units are used.

1.2.4 It is necessary to synchronise the clocks of Energy meters, especially those used forABT (availability based tariff) applications involving tariff switching.

2.0 Equipments to be synchronized

The following equipments are all eligible for time synchronisation. The decision to

synchronise all or some of them will rest with the designer. The chief considerationsare Customer specification if any, Economic consideration and Need for

synchronisation. The last is elaborated below.

2.1 Need for synchronisation

2.1.1 Switchyard SCADA, relays and Bay control units: The switchyard and the transmissionnetwork are highly interconnected. Fault analysis will invariably depend on data frommany devices. The devices shall therefore be synchronised without exception.

2.1.2 Switchyard energy meters: If an Availability Based Tariff is implemented, the energymeters need to be synchronised. Synchronisation is also necessary if the tariff meters arepart of an energy balance calculation based on data stored in the meters at pre-designatedtimes.

2.1.3 Unit Protection: This includes the Generator protection panel, Generator Fault Recorderpanel and the GT-UAT-ST protection panels. The data in these devices need to becorrelated with the plant DCS and also the switchyard. The devices shall therefore besynchronised without exception.


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2.1.4 Automatic Bus transfer system: This system consists of intelligent devices which recordthe transient signals like bus/incomer voltages and also the commands to breakers andtheir statuses. Time synchronisation of the system assists in the analysis of transferfailures. It is useful, though not strictly necessary to time synchronise this system.

2.1.5 Relay Management System (RMS) and Energy Management System (EMS): Thesesystems need to be time synchronised. They pass on the time signal to all the connectedrelays and meters.

2.1.6 MV and LV switchgear relays (if not connected to RMS): It is recommended tosynchronise the relays at the following locations. They contain useful information whichneed to be correlated in the event of system disturbances and voltage dips which lead toUnit tripping. Incomers, Ties and Bus PTs of MV Station switchgear and Unit switchgear

Incomers and Bus couplers of 415V Station PMCC and Unit PMCC

Incomers of 415V Emergency PMCC

2.1.7 The SCADA, RMS and EMS consist of one or more interconnected Servers(Computers). The relays and meters listed above may be referred to as IEDs (IntelligentElectronic Devices).

3.0 General concepts

3.1 Time definitions

3.1.1 The error of a clock is the difference between the actual time of the clock, and the timethe clock is intended to have.

3.1.2 The rate accuracy of a clock is normally called the clock accuracy and means how muchthe error increases, i.e. how much the clock gains or loses time.

3.2 Synchronisation principle

3.2.1 From a general point of view synchronisation can be seen as a hierarchical structure. Adevice is synchronized from a higher level and provides synchronisation to lower levels,if any.

3.2.2 A device is said to be synchronized when it periodically receives synchronisationmessages (Time reference) from a higher level. As the level decreases, the accuracy of

the synchronisation decreases as well.

3.2.3 The maximum error of a clock is a function of: The maximum error of the last used synchronisation message

The time since the last used synchronisation message

The rate accuracy of the internal clock in the module

3.3 Necessary features of IED clock

3.3.1 It should operate independently of the external Time reference.


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3.3.2 Its time should be compared to the Time reference when available, and the time updatedonly after a fixed difference is established.

3.3.3 It should update its time in a predictable manner. For some IED applications, a sudden

jump in time is undesirable due to the error it causes in the recorded data. In suchdevices, the clock must slew its time at a controlled rate, thereby correcting the timeerror gradually.

4.0 Time Reference

4.1.1 The time reference is taken from the Global positioning System (GPS). It is an absolutesystem to continuously provide the following information to unlimited users. 3 dimensional Position Fixing (Latitude; Longitude & altitude)

Velocity (Speed/Course) measurement by detecting the Doppler shift in the radio

signals emitted by GPS Satellites

Time Reference generation, utilizing the fact that the system is operated on commonprecise time base

4.1.2 GPS is sponsored and operated by the US Department of defence. Civilian access to thesystem is subject to US government Selective Availability (SA) policy.

4.1.3 GPS provides continuous worldwide coverage, 24 hours a day under all weatherconditions. Satellites distributed in 6 orbital planes (4 in each plane) spaced around theequator, pass over the earth at an altitude of approximately 20,000 kilometres. Eachsatellite has an orbital period of 12 side real hours (11 Hrs and 58 Minutes of civil time).A single satellite will orbit the earth twice a day, tracing the exact foot print path; butpassing 4 minutes earlier than the day before. At least 4 satellites will be in view at any

time above any point on the earth. Each GPS satellite bears an ultimate precision clockutilizing Rubidium-Caesium oscillation whose accuracy is comparable to InternationalAtomic Time. The satellites transmit highly accurate, real time, worldwide navigationinformation at a frequency of 1575.42 MHz.

4.1.4 The GPS Receiver collects the data from the GPS Satellites and outputs a time basepulse (1PPS) every second in precise synchronisation with UTC/IST. Each 1PPS Pulse isaccompanied by a Serial Data packet output (A real time data comprising of Year,Month, Date, Hour, Minute and Second), which is a time stamp for that pulse. Thisoutput is utilized by a master clock to synchronize its time with UTC/IST with amaximum uncertainty of 1 micro second. The master clock can then generate varioustypes of outputs to synchronize any number of digital clock / microprocessor basedsystems.

4.1.5 See Annexure A for the relationship between GPS time and UTC time, when handlingLeap years and leap seconds.

4.1.6 A typical Master clock based on GPS consists of the following: GPS Antenna

GPS Receiver

Master Clock A & B

Redundant Comparator Clock

Signal Conditioner for Time Reference generation

Power Supply A&B


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4.1.7 The Master clock provides outputs such as Potential free contact (1 PPS, 1PPM), IRIGB-AM, IRIG B-TTL, NTP and SNTP. These are used to directly synchronise the Servers(SCADA, RMS, EMS) used in the electrical systems. The Servers then pass on the timesignal to their respective IEDs.

4.1.8 Stand-alone IEDS are also synchronised directly to the Master clock. The number ofsuch IEDs may be scaled up using Signal conditioners, which have multiple outputs. Theoutputs are usually of IRIG-B or Potential free contact type. The Signal conditioners arelocated near the clusters of client IEDs. The figure below pictorially represents all theavailable options.


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5.0 Time Synchronisation codes / protocols

5.1 Potential free contact

5.1.1 The GPS provides a pulse train via the potential free contact. The pulses are either 1pulse-per-second (1 PPS) or 1 pulse-per-minute (1 PPM). The pulse is synchronised withthe start of every second in the case of 1 PPS, and with the start of every minute in thecase of 1 PPM.

5.1.2 The pulses are used by the target device, to adjust its clock, as described here.

5.1.3 A binary input of the device is used to receive the pulses. The potential free contact ofthe Master clock is typically rated up to 250Vdc, 100mA. If the binary input of thedevice is galvanically isolated from its other circuits, it can be paralleled with the binaryinput of another device. It is possible then to drive several IEDs in parallel using one

Potential free contact.

5.1.4 Initially, the clock of the target device needs to be set manually to the correct minute andsecond. When the pulse train is activated, the clock will be rounded off to the nearestwhole second or minute, depending on the period of the pulse train. The rounding-offwill take place on the rising edge of the input. The time is corrected at every pulsereceived by the clock. In some cases, the synchronisation can be selected to be on thefalling edge.

5.1.5 In some cases, the time is adjusted by accelerating or decelerating the clock. By this waythe clock neither stops nor makes sudden jumps during the time adjustment.

5.1.6 The pulse is rejected if the error is large (typically > 0.05 seconds for second-pulse or

2 seconds for minute-pulse).

5.1.7 Typically, two detected pulses within acceptable time range are required for the targetdevice to activate pulse synchronisation. Similarly, if the synchronisation pulsesdisappear, the device deactivates pulse synchronisation after a delay corresponding to afew pulses.

5.1.8 The typical accuracy achievable with time synchronisation via a digital input is 2.5milliseconds for second-pulse and 5 milliseconds for minute-pulse synchronisation.The pulse length of the digital input signal does not affect time synchronisation.

5.2 IRIG B

5.2.1 IRIG stands for Inter Range Instrumentation Group. It is specified by theTelecommunications and Timing group of the US army and was originally developed forsending time or other data around missile test ranges. It now finds use in government,military and commercial fields.

5.2.2 Modern day electronic systems require time-of-day and year information for correlationof data with time. Serial formatted time codes are used to efficiently interface the timingsystem output with the user system.

5.2.3 Standardization of time codes is necessary to ensure system compatibility among the

various equipment suppliers. These digital codes are typically amplitude modulated onan audio sine wave carrier or transmitted as fast rise-time TTL signals. The use of the


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IRIG standard is to provide a standard protocol for serial time codes that are generatedfor correlation of data with time.

5.2.4 IRIG Standard 200-04 is the latest IRIG specification. The most common version is

IRIG-B. IRIG-B refers to a serial time code format. This is a timing signal that has a rateof 100 pulses per second. IRIG-B sends Day of Year, Hour, Minute and Second data ona 1 kHz carrier, with an update rate of one second. IRIG-B DCLS (DC level shift) isIRIG-B without the 1 kHz Carrier.

5.2.5 There are other formats in the IRIG Standard 200-04, which have other pulse rates (IRIGA, D, E, G and H). They are not used for our application.

5.2.6 The available IRIG B formats are IRIG B000, IRIG B003, IRIG B120, IRIG B122 andIRIG B123. The 3 digits are coded as below. For more details on IRIG-B format and onBCD, SBS and CF, refer to Annexure-B.

Format Modulation Coded expressionB000 BCD, CF. SBS

B003

DC Level Shift (DCLS),width coded, no carrier BCD, SBS

B120 BCD, CF, SBS

B122 BCD

B123

1kHz Sine wave carrier,amplitude modulated, 1

millisecond resolution BCD, SBS

BCD - Binary Coded Decimal, coding of time (HH, MM, SS, DDD)

SBS - Straight Binary Second of day (0....86400)

CF - Control Functions depending on the user application

5.3 Network Time Protocol (NTP)

5.3.1 NTP is a protocol for synchronizing computer clocks across a network to standard time.The NTP client software runs continuously as a background task that periodicallyreceives updates from one or more servers.

5.3.2 With the appropriate hardware, NTP is capable of achieving synchronisation to withinmicroseconds, depending on the synchronisation source and the network paths. Due tocomplexity, this protocol is not used for electrical systems. Refer to Annexure C formore details.

5.4 Simple Network Time Protocol (SNTP)

5.4.1 SNTP is a basic version of NTP. It provides a simplified access strategy for servers andclients that do not require the degree of accuracy of the NTP protocol. SNTP is meant tooperate in a dedicated server configuration, that is, one in which the server provides onlyone function. With careful design and control of the various latencies that are typical insuch network design, it is possible to deliver time accurate to the order of milliseconds.Because the network packet formats of both protocols are identical, the two areinteroperable. The main difference between the two is that SNTP does not have the errormanagement and complex filtering systems that NTP provides. The SNTP protocolallows room for error and might not be suitable for some applications such as those inthe financial industry that have very strict accuracy requirements.


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5.4.2 Here the IED functions as a SNTP client. For clock synchronization one can selectbetween the operating modes Broadcast-from-SNTP-Server or Request-from-Server.With the first operating mode, synchronisation occurs by a broadcast message sent fromthe SNTP server to all devices in the network. In the Request-from-Server mode, the

IED requests the device specific time signal during a settable cycle.

5.4.3 The device requesting synchronization (the Client), formats a request data packet andsends this to the synchronization server at time T1. The server records the receptiontime, T2, and transmits a response data packet at time T3 containing time values for bothT2 and T3. Finally, the client receives at the time T4 and decodes the other two timescontained in the packet. The four times are used to compute estimates of both the end-to-end network latency and the offset between the clocks.

5.5 Time synchronisation options in Relays

5.5.1 IRIG-B and Potential free contact are the most common options available in relays.

5.5.2 The time synchronisation options in Numerical relays which are commonly in use aretabulated in Annexure -E. Some of the features are optional and they need to be specifiedat the time of ordering.

5.5.3 The relays can communicate with the RMS or SMS (Substation management system /SCADA for switchyard) through a number of Network communication options, listed inthe last column of Annexure -E. Some of these are proprietary. The networks are usedfor data collection, and sometimes control and interlock. The relays get timesynchronised, as an added benefit.

6.0 Signal Cabling

6.1.1 IRIG-B TTL : Un-modulated IRIG B is normally distributed using copper cabling,


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which may be either coaxial (typically RG-58 type) or shielded twisted pair.

6.1.2 IRIG-B AM : The best practice for modulated IRIG B is to use shielded twisted paircable to connect the IED to the clock. This is adequate for all installations within a

substation. Fibre-optic cables have the advantage of immunity to electromagneticinterference. However, while substations may reasonably be considered high-EMIenvironments, the expense of fibre optic cable and drivers is generally not justified formost connections, particularly between clock and IEDs in the same rack or control room.

6.1.3 Potential free contact : Coaxial Cable or twisted pair cable can be used.

6.1.4 NTP / SNTP : Twisted pair cable can be used for NTP / SNTP.

6.1.5 The choice of cable type, gauge, stranding etc. is up to the station designer based onother considerations, such as ease of routing and termination, and minimising costs.

7.0 Information to be provided to C&I for Master Clockspecification

7.1.1 Successful implementation of time synchronisation depends on the correct designing ofthe interface between the Master clock and the Electrical systems. The systemrequirement needs to be identified and conveyed correctly to C&I. The architecture ofthe Master clock including the specifications and locations of signal conditioners isdecided accordingly.

7.1.2 The format of Annexure D may be used for this purpose. It conveys the followingbasic information.

7.1.3 Systems and IEDs to be synchronized Finalise the list of equipment which need synchronisation. The decision is techno-

commercial in nature, and the aspects were dealt with, in section 2.1 above.

7.1.4 Synchronisation options After the list of equipment is finalised, look for the available synchronisation

options in each. IRIG-B and Potential free contact are the commonly availableoptions.

It is incomplete to simply mention IRIG-B. Please obtain from the relaymanufacturer the full format number (IRIG-Bxxx). At the very least, the type (AM

Amplitude Modulated / TTL Transistor-Transistor-Logic, 5V) shall be informed. Similarly, the type of Potential Free Contact (PPS Pulse per Second / PPM Pulse per

Minute) shall be informed.

Wherever possible, the IRIG-B may be used. When it is not available, the Potential

free contact, PPM/PPS may be used. If both options are available, this shall beindicated in the table.

If both options are not available, the system has to be engineered in greater detail,

so that there are no communication problems during commissioning.

7.1.5 Number of signals required The number of signals required, can be indicated in the table after giving due

consideration to the possibility of paralleling of IEDs.


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If a number of IEDs are located in the same switchgear panel, it is possible to

connect their IRIG-B inputs in parallel and drive them from a common source.Similarly, the Binary inputs of a number of IEDs may be paralleled and driven with

a single Potential free contact. Since we are looking for accuracy only at the 1mS level (rather than micro-second),

this is allowed.

The other consideration is that ground loops shall be avoided. Please confirm from

the IED manufacturer that the inputs of the IEDs are galvanically isolated.

The number of IEDs which may be paralleled is not very definite. For practical

reasons, this is presently limited to 8 IEDs.

7.1.6 Location and Distance from the Master Clock The location of the client device and its distance from the Master clock also govern

the choice of signal conditioner.

7.1.7 Detailed engineering considerations The limit on the number of IEDs in parallel needs to be confirmed by the Master

Clock manufacturer. The main considerations are the loss of accuracy, eliminationof ground loops and the loading on the signal source.


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Annexure A : Leap year / Leap second

A.1. Leap Year Convention

A.1.1. The U.S. Naval Observatory Astronomical Applications Department defines the leap yearaccording to the Gregorian calendar, which was instituted by Pope Gregory VIII in 1582 to

keep the year in a cycle with the seasons. The average Gregorian calendar year, technicallyknown as the Tropical Year, is approximately 365.2425 days in length and it will take about

3,326 years before the Gregorian calendar is as much as one day out of step with theseasons.

A.1.2. According to the Gregorian calendar, which is the civil calendar in use today, years that areevenly divisible by 4 are leap years with the exception of century years that are not evenly

divisible by 400. This means that years 1700, 1800, 1900, 2100, 2200, and 2500 are NOTleap years. Years 1600, 2000, and 2400 are leap years.

A.1.3. All clocks, including GPS follow the same leap year calendar. Hence the dates areconsistent.

A.2. Leap Second Convention

A.2.1. Civil time is occasionally adjusted by one-second increments to insure that the differencebetween a uniform time-scale defined by International Atomic Time (TAI) does not differ

from the Earths rotational time by more than 0.9 seconds. Consequently, Coordinated

Universal Time (UTC), also an atomic time, was established in 1972 and is adjusted for theEarths rotation and forms the basis for civil time.

A.2.2. Twenty four leap seconds (as on 01-01-2009) have been added to keep UTC in

synchronization with the rotation of the earth. In 1980, when the Global PositioningSystem (GPS) came into being, it was initially synchronized to UTC. However, GPS timedoes not add leap seconds, and consequently, GPS time is fifteen seconds ahead (as on 01-

01-2009) of UTC. The relationship between (TAI) and UTC is given by a simpleaccumulation of leap seconds occurring approximately once per year. If required, time

changes are made on December 31 and on June 30 at 2400 hours.

A.3. See the linkhttp://tycho.usno.navy.mil/leapsec.html for further information.


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Annexure B : IRIG-B

B.1. IRIG-B format

B.1.1. The beginning of each 1.0 second time frame is identified by two consecutive 8.0 ms bits,P0 and Pr. The leading edge of Pr is the on-time reference point for the succeeding time

code words. Position identifiers P0 and P1 through P9, (8 ms duration) occur every 10th bitand 10 ms before the leading edge of each succeeding 10 pps "on-time" bits (see Figure).

B.1.2. The three time code words and the control functions presented during the time frame arepulse width coded. The binary zero and the index markers have duration of 2.0 ms, and a

binary one has duration of 5.0 ms. The 100 pps leading edge is the on-time reference pointfor all bits.

B.1.3. The BCD time-of-year code word consists of 30 bits beginning at index count one. Thesub-word bits occur between position identifiers P0 and P5; there are 7 bits for seconds, 7

for minutes, 6 for hours, and 10 for days. Nine bits for year information occur betweenposition identifiers P5 and P6 to complete the BCD time code word. An index marker

occurs between the decimal digits in each sub-word to provide separation for visualresolution. The LSB occurs first. The BCD time-of-year code recycles yearly.

B.1.4. Eighteen control functions occur between position identifiers P6 and P8. Any controlfunction bit or combination of bits can be programmed to read a binary one or zero during

any specified number of time frames.

B.1.5. The SB seconds-of-day word occurs between position identifier P8 and P0. A position

identifier occurs between the 9th and 10th binary coded bit.


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B.2. IRIG-B Wiring considerations

B.2.1. Un-modulated IRIG-B Wiring

B.2.1.1.Un-modulated or level-shift IRIG-B time code is generally developed by a system clock at

a level of approximately 5 volts peak, i.e. the high level is approximately +5V and thelow level approximately zero volts. Most clock outputs are often coaxial (typically BNC).

B.2.1.2.For applications requiring the ultimate in accuracy (i.e. sub-microsecond), issues such ascable delay (1 to 1.5 nanosecond/foot or 3 to 5 ns/meter) and ringing caused by the fast rise

and fall times of the signal coupled with imperfect line termination (which causesreflections) must be considered. For such applications, it is customary to use direct coaxialconnections with one load per driver, and lines are generally terminated at either the source

or load to reduce ringing if the line length exceeds a few feet. Since the characteristicimpedance of coaxial cable is typically 50 (sometimes 75 or 93) ohms, compared with the

input impedance of the opto-coupler circuit of around 1000 ohms, overloading of the driveroften precludes more than one load being used per output when the load includes a 50-ohmtermination.

B.2.1.3.However, in most applications it is possible to connect an un-modulated IRIG-B driver to

numerous IEDs, using any reasonably-clean setup of either coaxial or twisted-pair lines.For accuracies at the level of one microsecond this is sufficient, provided the cable lengthsare not excessive. In particular, at the one-millisecond level of performance, it can be said

with relative certainty that any setup providing a signal that can be decoded at all will give

adequate performance.

B.2.2. Modulated IRIG-B Wiring

B.2.2.1.The modulated IRIG-B signal is similar in many ways to a voice-grade audio or telephonesignal, and it can be distributed with similar methods. The rise and fa ll times of the signal

are low, and the decoders generally use an automatic gain-control amplifier to compensatefor varying input signal levels, so there are no significant considerations with respect toreflections or signal loss. Similarly, delays are small compared with the achievable

accuracy of perhaps 50-100 microseconds at best, so cable delays are not an issue. IEDinputs are normally transformer-isolated, so earth loops will also not be a problem.

B.2.2.2.The best practice for modulated IRIG-B adequate for all installations within a sub-station,is to use shielded twisted pair cable to connect the IEDs to the clock.

B.3. Earthing Considerations for IED and System Design

B.3.1. The best engineering practice generally requires any signal line to be earthed at some point.For most analogue signals, including time-code signals, this is normally the signal source.

B.3.2. Since earth loops are to be avoided, it is important to earth each signal at one point only.

This must be the source end, if there is the possibility to have multiple loads attached to a

given source. Therefore, IRIG-B inputs in IEDs must provide galvanic isolation.


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Annexure C : Network Time Protocol (NTP)

C.1. NTP is a protocol for synchronizing computer clocks across a network to standard time.The NTP client software runs continuously as a background task that periodically receivesupdates from one or more servers. The client software ignores responses from servers thatappear to be sending the wrong time and averages the results from those that appear to be

correct.

C.2. With the appropriate hardware, NTP is capable of achieving synchronisation to withinmicroseconds, depending on the synchronisation source and the network paths.

C.3. NTP synchronisation is part of a software package that includes a full suite of NTP optionsand algorithms, which are relatively complex, real-time applications. The sheer size and

complexity of the NTP suite is not appropriate for many environments that do not havestringent accuracy requirements.

C.4. The NTP daemon is an operating system programme which sets and maintains the systemtime of day in synchronism with time servers. When it starts, it checks its configuration file

(/etc/ntp.conf) to determine synchronisation sources, authentication options, monitoringoptions, access control and other operating options. It also checks the frequency file(/etc/ntp/drift) that contains the latest estimate of clock frequency error. If specified, it will

also look for a file containing the authentication keys (/etc/ntp/keys).

C.5. Once the NTP daemon is up and running, it will operate by exchanging packets (time and

sanity check exchanges) with its configured servers at poll intervals and its behaviour willdepend on the delay between the local time and its reference servers. Basically, the process

starts when the NTP client sends a packet containing its timestamp to a server. When theserver receives such a packet, it will in turn store its own timestamp and a transmit

timestamp into the packet and send it back to the client. When the client receives the packetit will log its receipt time in order to estimate the travelling time of the packet.

C.6. The packet exchange takes place until a NTP server is accepted as a synchronizationsource, which takes about five minutes. The NTP daemon tries to adjust the clock in small

steps and will continue until the client gets the accurate time. If the delay between both theserver and client is big enough the daemon will terminate and we will need to adjust thetime manually and start the daemon again.

C.7. The NTP is fully specified in a document Request for Count 1305.See

www.faqs.org/rfcs/rfc1305.htmlfor further information.


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Annexure D : Format of Data to be provided to C&I

The following format may be used to communicate the time synchronisation requirements ofElectrical systems. The data is filled in, on sample basis.

Time synchronisationoptionsSystems and IEDs to

be synchronised IRIG BType

PFCType

Others

No. ofsignalrequired

Location

Distancefrom MasterClock panel

in metres

Switchyard SCADA,Relays, Bay Controlunits, Energy meters

IRIG-B000

--- --- 1

Relay managementsystem

--- --- SNTP 1

Energy managementsystem

--- --- SNTP 1

Generator Protection

panel

IRIG-

B120

--- --- 4 per unit

GeneratorFault Recorder panel

--- PPS --- 1 per unit

GT UAT protection

panel

IRIG-

B000

PPS --- 4 per unit

ST protection panel IRIG-

B000

PPS --- 2 per unit

Automatic Bus

transfer panel

--- PPS SNTP 1 per unit

MV switchgear 0CA IRIG-B000

PPS --- 3

LV Switchgear U-

PMCC#1

--- PPS --- 3


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Annexure E : Time Synchronisation protocols available inrelays

RelayMake

RelayType

Direct synchronisationoptions (IRIG B / PPM, PPS)

Network communication options

ABB (IED 670)

REB 670REC 670RED 670

RET 670REG 670

REL 670

PPM, PPS

IRIG-B 12x via galvanicBNC connector

IRIG-B 00x via galvanicconnector or optical ST

connector

IEC61850

IEC60870-5-103

SPA (no time synch)

LON

DNP 3.0

GPS satellite clock connected to thestation bus communication switch, in

NTP format Synchronisation from IED 670

equipped with a GPS module, actinglike a SNTP server

ABB REF 615 IRIG-B (format not

obtained)

Ethernet station bus using SNTP

ABB REU 610REF 610

REM610

PPM, PPS SPA (no time synch)

IEC60870-5-103

Modbus (no time synch)

DNP 3.0

Profibus DP

LON

IEC 61850

ABB RET 54_

REF 54_ PPM, PPS SPA (no time synch)

DNP 3.0

ABB REX521 PPM, PPS SPA (no time synch)

IEC 60870-5-103

LON

Siemens 7UT63 IRIG-B (format not

obtained)

DCF 77 (only time synch)

Siemens 6MD663 PPM

IRIG-B (format notobtained)


Siemens 7SA63

7SA6137SA61

IRIG-B (format not

obtained)


IEC 60870-5-103

Profibus FMS-DP

DNP 3.0

IEC 61850


19/20


20/20

Design Guide for Time ion of Electrical System 21-07-2009

Documents

Transcript of Design Guide for Time ion of Electrical System 21-07-2009