NUMERICAL RELAYS

ASHUTOSH BHATTACHARJEEDEPUTY MANAGERPROTECTION CELL, AEGCLGUWAHATINUMERICAL RELAYSAn Approach To Modern Relaying..WHAT IS A PROTECTION RELAY ??A protective relayis anelectricallyoperatedswitch.Detect and isolate faults on transmission and distribution lines by opening and closingcircuit breakers.Relays allow one circuit to switch a second circuit which can be completely separate from the first.Relays help us to monitor, manage & control our Power System Network in an intelligent manner.

BASIC RELAY OPERATIONSTAGE I : ELECTROMECHANICAL RELAYS

EARLY DESIGNS USING ELECTROMAGNETIC INDUCTION PRINCIPLE..HOW DO THEY OPERATE ?An electric current through a conductor will produce a magnetic field at right angles to the direction of electron flow. If that conductor is wrapped into a coil shape, the magnetic field produced will be oriented along the length of the coil. The greater the current, the greater the strength of the magnetic field, all other factors being equal.

The magnetic field produced by a coil of current-carrying wire can be used to exert a mechanical force on any magnetic object, just as we can use a permanent magnet to attract magnetic objects, except that this magnet (formed by the coil) can be turned on or off by switching the current on or off through the coil.

And a negative torque restrains rotation.STAGE II : SOLID STATE OR STATIC RELAYS

THESE RELAYS CAME TO EXISTENCE IN LATE 70s & STARTED REPLACING THE EM RELAYS BY ELIMINATING THE SERIOUS PROBLEM OF HANDLING MOVING PARTS & BURNING CONTACTS.

Static relays require a very little volt-ampere for their operation. HOW DO THEY OPERATE ?In a solid state relay, the incoming voltage and current waveforms are monitored by analog circuits. The analog values are compared to settings made by the user via potentiometers in the relay, and in some case, taps on transformers.The incoming AC current is first converted into a small signal AC value, then the AC is fed into a rectifier and filter that converts the AC to a DC value proportionate to the AC waveform. An op-amp and comparator is used to create a DC that rises when a trip point is reached.

THESE RELAYS MOSTLY USE REED CONTACTS. THEREFORE RELIABILITY IS PRACTICALLY ENHANCED.

DEFICITS WITH STAGE I & IIDEPENDABILITY & SECURITY NOT ENOUGHSPEED & ACCURACYNO SELF CHECKING FACILITYHIGHER BURDENSNOT IMMUNE TO VARIATION IN PARAMETERS OF INDIVIDUAL COMPONENTS [CT/PT ETC.]CAN NOT BE PROGRAMMED IN ACCORDANCE WITH NEEDHISTORICAL DATA STORAGE AND MANY MORE.

STAGE III : NUMERICAL RELAYSThese are microprocessor-based relays in contrast to other relays that are electromechanically or electronically controlled. These relays provide great precision and convenience in application in the sophisticated electronic products. By combining several functions in one case, numerical relays also save capital cost and maintenance cost over electromechanical & static relays.The first protection devices based on microprocessors were employed in 1985. The widespread acceptance of numerical technology by the customer and the experiences of the user helped in developing the second generation numerical relays in 1990.Today Numerical Relays are believed to be the heart & soul of balanced Power System Engineering.

Why Numerical Relaying ?

IN ADDITION :

OPERATION IN BRIEF

BASIC BLOCK DIAGRAM OF INTERNAL ARCHITECTURE OF A NUMERICAL RELAY

** NPR IS NUMERICAL PROTECTION RELAYIt is clear from the previous slide that Relaying Hardware of Numerical Relays can also be used for the measurement purpose.

Analog input is feed into the anti aliasing filter which is a low pass filter. Output of this filter is feed into the sample and hold circuit , frequency of sampling should be twice of our highest frequency of interest (according to the nyquist criterion). If sampling frequency kept low than aliasing input may occur.after the sampling, signal are feed into the multiplexer, where all the signal get multiplexed and we have a single signal. this signal is feed into the analog to digital converter. this digital signal is feed into the microprocessor and microprocessor generates control signal according to its input.

Newer technologies are becoming more complex to achieve a zero error status of operation of modern Numerical Relays.

What did we learn ?

IN ASEB PRESENTLY NUMERICAL RELAYS ARE MAINLY BEING USED FOR THREE DIFFERENT PROTECTION SCHEMES: -

1. DISTANCE PROTECTION2. TRANSFORMER DIFFERENTIAL PROTECTION 3. BACK UP OVER CURRENT & EARTH FAULT PROTECTION

MAKETYPE OF RELAYS USEDSIEMENSDISTANCE/DIFFERENTIALAREVA / MICOMDISTANCE/DIFFERENTIAL/ BACK UP

SWITZER ENGG. LTD.(SEL)DISTANCETOSHIBADISTANCE/DIFFERENTIAL

ABBDISTANCE/DIFFERENTIAL

GENERAL ELECTRICDISTANCE/DIFFERENTIAL /BACK UP

SIEMENSABBTOSHIBAGESELMICOM / AREVASINCE NUMERICAL RELAYS ARE MOST VERSATILE DEVICES IN ANY POWER SYSTEMTHEY ARE ALWAYS REQUIRED TO BE SET & PROGRAMMED ACCORDINGLY. BASICCOMMUNICATION OF THESE RELAYS ARE MOSTLY DONE THROUGH COMPUTERS.

DESIGNATED SOFTWARES ARE PROVIDED BY THE MANUFACTURERS TO COMMUNICATE AS WELL AS SET THE RELAYS IN ACCORDANCE WITH ONES NEED.

THOUGH IT IS SIMPLE & CONVENIENT TO ACCESS ANY NUMERICAL RELAY USING A COMPUTER, FRONT PANEL ACCESS IS ALSO PROVIDED FOR INSTANT READING OF VARIOUS DATA AS WELL AS DOING SOME MINIMAL CHANGES IN THE RELAY SETTINGS. DIFFERENT SCROLL BUTTONS ALONGWITH FUNCTION KEYS ARE THERE TO PROVIDE A SUITABLE HMI.

AT ANY MOMENT OF TIME A PERSON CAN READ ANY REQUIRED DATA FROM THE RELAY BY PRESSING THE FRONT PANEL KEYS IN A PRE - REQUISITE SEQUENCE.

FOR EXAMPLE: IN SIEMENS RELAYS YOU CAN READ THE FAULT RECORD INSTANTLY BY PRESSING THE F3 KEY ON THE FRONT PANEL.

A SMALL DISPLAY IN THE FRONT PANEL ALSO HELPS USER IN RECORDING AND MONITORING DIFFERENT DATA.

SOFTWARESA SNAPSHOT OF A FEW SOFTWARES USED FOR COMMUNICATING NUMERICAL RELAYS

DIGSI FROM SIEMENSENERVISTA UR FROM GEPROTECTION FEATURES OF NUMERICAL RELAYS

1. NUMERICAL DISTANCE PROTECTION22

In this case also, the relay has many different functions in one single unit:DIFFERENTIAL PROTECTION WITH VECTOR COMPENSATION & ADAPTABILITY TOWARDS ANY AVAILABLE CT RATIO.

ADD ON STABILIZATION WITH INRUSH RESTRAIN (2ND & 3RD ) OVERFLUXING PROTECTIONRESTRICTED EARTH FAULT PROTECTIONBACK UP O/C & E/F PROTECTIONTHERMAL OVERLOAD PROTECTIONUNDERFREQUENCY / (dF/dT) PROTECTION

2. NUMERICAL DIFFERENTIAL PROTECTION

A Typical Differential Curve3. BACK UP (O/C & E/F PROTECTION)The micro-controller continuously monitors the magnitude of the phase current and the neutral current .whenever the phase current or the earth current magnitude exceeds the present value corresponding line / earth element will pick up and relay will trip after time interval calculated by the selected IDMT curves. Whenever the fault level exceeds the selected high set range, the relay will trip for high set, ignoring the selected IDMT curves. The timer logic is processed and after comparison with set time schedules, tripping signals are issued accordingly. The output relays are programmable.

The relay rating (In) is field selectable either 1A or 5A. The relay has RS 485 com port which can be used with Modbus protocol for communication purposes.

The auxiliary supply for the numeric relay is provided by a switch mode power supply unit with input voltage either AC or DC with a wide operating voltage from 21-130 volts or 85-275 volts. And in case of AC, the power supply is designed operate from 45HZ - 65HZ.Again it is worth mentioning here that unlike EM relays no external connection is required for zero sequence current / voltage calculation . The relay micro processor does it internallysaving substantial amount of complexity in the relay circuit.

Numerical back up protection goes way ahead in selecting any conventional operating curvesuggested by IEC or any other organization.

RELAY INPUT / OUTPUT CONTACTSNUMERICAL RELAYS HAVE HIGH PRECISION INPUTS & OUTPUTS FOR ACHIEVING CONTROL & INDICATIONS. THESE CONTACTS ARE CALLED BINARY CONTACTS AND INVOLVE TRANSISTORS & FLIP-FLOPS. DISCRETE CHANGES IN THEIR STATES (0 OR 1) DECIDE FLOW OF DC CURRENTS AS & WHEN REQUIRED. THESE CONTACTS CAN EASILY BE COFIGURED THROUGH SOFTWARE WITH A FEW MOUSE CLICKS.

28FAULT & EVENT RECORDING

SCADA & REMOTE OPERATION USING CARRIER/TELECOMEACH NUMERICAL RELAY IS PROVIDED WITH COMMUNICATION INTERFACE ENABLING IT TO CONNECT TO ONE OR MANY SUB-STATION LEVEL SYSTEMS OR EQUIPMENTS EITHER ON THE SUB STATION AUTOMATION BUS OR SUB-STATION MONITORING BUS. THESE COMMUNICATION PROTOCOLS ARE ALSO PUT IN USE FOR REMOTE OPERATION AND CONTROL OF THESE RELAYS.

IMAGINE HERE SITTING IN GUWAHATI WE CAN CONFIGURE / MONITOR A RELAY IN DIBRUGARH.TESTING & COMMISSIONING OF NUMERICAL RELAYSIN AEGCL WE ARE PRESENTLY USING OMICRON CMC 256 KIT FOR TESTING OF DIFFERENT NUMERICAL RELAYS. TESTING IS OF MUCH IMPORTANCE TO AVOID ANY FUTURE MAL-OPERATIONS OF THE RELAY. THIS KIT IS A HIGHLY SOPHISTICATED ONE & CAN ONLY BE OPERATED THROUGH COMPUTER.

TESTING PLAN OF A NUMERICAL DISTANCE RELAY :

LAST WORDS

Thank You..