Digital Relay Hard Copy

7/30/2019 Digital Relay Hard Copy

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HISTORY OF PROTECTIVE RELAYS


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DISCOVERY OF DIGITAL RELAY

INTRODUCTION

Digital relays that uses a microprocessor to analyze power system voltages, currents or other process

quantities for the purpose of detection of faults in an industrial process system.The digital relay is a

multifunctional device using numerical algorithms that can easily duplicate any of the ANSI protection

functions with simple software modifications. Digital relays are those in which the measured ac

quantities are manipulated in analog form and subsequently converted into square-wave (binary)

voltages. Logic circuits or microprocessors compare the phase relation-ships of the square waves tomake a trip decision. A multifunction digital relay is a microprocessor-based unit that uses Digital Signal

Processing technology in order to provide multiple protective relaying functions for generator

protection in one unit. Since many functions are incorporated into one package, much less panel space

and wiring is required than would be if individual relays were used.


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PARTS OF DIGITAL RELAY BASED IN OPERATION

Low voltage and low current signals (i.e., at the secondary of a voltage transformers and current transformers) are

brought into a low pass filter that removes frequency content above about 1/3 of the sampling frequency (a

relay A/D converter needs to sample faster than 2x per cycle of the highest frequency that it is to monitor). The AC

signal is then sampled by the relay's analog to digital converter from 4 to 64 (varies by relay) samples per power

system cycle. In some relays, a short history of the entire sampled data is kept for oscillographic records. Only the

fundamental component is needed for most protection algorithms, unless a high speed algorithm is used that uses

subcycle data to monitor for fast changing issues. The sampled data is then passed through a low pass filter that

numerically removes the frequency content that is above the fundamental frequency of interest (i.e., nominal

system frequency), and uses Fourier transform algorithms to extract the fundamental frequency magnitude and

angle. Next the microprocessor passes the data into a set of protection algorithms, which are a set of logic

equations in part designed by the protection engineer, and in part designed by the relay manufacturer, that

monitor for abnormal conditions that indicate a fault. If a fault condition is detected, output contacts operate to

trip the associated circuit breaker(s).

PARTS OF DIGITAL RELAY BASED IN CONSTRUCTION

FRONT PANEL REAR PANEL
http://en.wikipedia.org/wiki/Transformer_types#Voltage_transformershttp://en.wikipedia.org/wiki/Current_transformerhttp://en.wikipedia.org/wiki/Low_pass_filterhttp://en.wikipedia.org/wiki/A/D_converterhttp://en.wikipedia.org/wiki/A/D_converterhttp://en.wikipedia.org/wiki/Low_pass_filterhttp://en.wikipedia.org/wiki/Current_transformerhttp://en.wikipedia.org/wiki/Transformer_types#Voltage_transformers


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FRONT PANEL OPERATION

ENERGIZING: When initially energized or re-energized, the digital relay automatically restarts

in the following sequence:

the green on LED and red self-diagnostic LED light

the red self-diagnostic LED goes out

the watchdog relay contacts reset

the digital relay displays the version name followed by the version letter, for

example, DR LXS01 KNote: To test the indicators and the display, press simultaneously on the meters and

device buttons. All indicators and LCDs will activate.

MODES OF OPERATION:The digital relay has two basic modes: Standard and Setup. An overview of these

modes follows.

Setup ModeThe digital relays settings are defined and modified in the

Setup mode. While in this mode, you can:

scroll through all display pages

use the value buttons (, +, and enter) to define or modify the relays

configuration

Standard ModeThis is the digital relays basic operating mode. While in this

mode, you can:

scroll through all display pages

use the meter, device, and settings buttons to display metered values and

settings (the value buttons are inoperable in the Standard mode)

Note: Settings cannot be altered in the Standard mode. Settings must be defined or

changed in the Setup mode. See Setting Parameters, page 35.

After Settings And Metered Values, which explains how to access the settings

and metered values available on the digital relay, the Setup and Standard modes

are detailed more fully.

REAR PANEL OPERATIONProtective Output : The digital relay has three output relay contacts (1), which operate when a phase

Relay Contacts fault or ground fault is detected:

output 1terminals 8 and 7 (normally open)

output 2terminals 6 and 5 (normally open)

output 3terminals 4 and 3 (normally closed)

These relays connect to the trip circuit.Control Power: Both ac and dc models of the digital relay are available. The dc model of the

digital relay supports 48125 Vdc power supplies; the ac model supports

100127 Vac power supplies.

The control power is connected to the two control power terminals and the

grounding screw (2).

Parameter Setup Mode Pressing the button located in the parameter setup mode access hole P (3)

Access Hole activates the parameter setup mode. The digital relay settings are entered in

this mode using the value + and value buttons.

Watchdog Relay The digital relay continually performs a self-diagnostics check. If the unit detects

an internal failure, the protective output relay contacts are then inhibited and a

watchdog relay releases. The watchdog relay consists of two output relay

contacts (4):

output 4terminals 4 and 3 (normally open position when digital relay de-energized)

output 5terminals 2 and 1 (normally closed position when digital relay de-energized)The watchdog output relay contacts can be connected to an alarm (e.g., a light or

a bell) to indicate when an internal failure occurs

Sensing Connections The line currents are sensed by three external 1 A or 5 A standard phase CTs. The

CT secondary leads are connected to the CCA 660 phase current sensor module,

which contains the digital relay current sensors and attaches to the rear of the

digital relay by the DB-9 connector (7).

There are two methods for sensing the ground fault current:

internal summation of the three phase currents (default)

an optional method using an external CSH core balance CT connected to the


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back of the digital relay (8); the CSH core balance CT is purchased separately

Communications The POWERLOGIC communicating version of the digital relay has the following

capabilities:

POWERLOGIC software compatibility

can share RS-485 communications link (9) with circuit monitors

operates at a baud rate from 1,200 to 19,200 bps

can be daisy-chained with up to 31 additional POWERLOGIC devices over a

10,000 foot (3,048 m) spanCommunication Indicator Lights There are three communication indicator lights (11), which show the status of the

optional communications card as follows:

red CPU LED alternates one second on/one second off when the

communications card central processing unit (CPU) is operating normally

yellow RX LED flashes when a master device is sending a message to a device

on the network

green TX LED flashes when the digital relay is acknowledging a message received

REASONS TO TEST DIGITAL RELAY


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DIGITAL RELAY AREA OF USE

DISTRIBUTION FEEDER PROTECTION

CIRCUIT BREAKER PROTECTIONThis implies a current flow that keeps on feeding the fault which can be used to detect the breaker failure itself.

In those applications which even though the mechanical failure exist, the current could not be high enough to be

detected, the opening must also be verified by means of breaker auxiliary contacts.

OPERATION: A tripping order for the circuit breaker initiates the time delay count down for the protection.Once the

time delay is over , if the breaker is not yet open, the protection sends a tripping order to all the adjacent breakers,

including those at the end of the lines if necessary. Sometimes two time delays are used, the first one to repeat the

tripping order for the breaker itself, and the second for the other breakers.

GENERATOR PROTECTION

REAL TIME ABILITY OF DIGITAL RELAY

FAULT LOCATION AND FAULT TYPE

PRE-FAULT,FAULT, AND POST-FAULT CURRENT AND VOLTAGES

RELAY INTERNAL ELEMENT STATUS

RELAY CONTROL INPUT AND OUTPUT STATUS

INSTANTANEOUS AND DEMAND METERING

BREAKER OPERATION DATA

RELAY SELF STATUS

EVOLUTION OF DIGITAL RELAY COMMUNICATION INTERFACE


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Conclusion

Digital relays are presently available that provide highly reliable protection for generators. These units

utilize the latest digital signal processing technology to accomplish many relaying functions

simultaneously. By appropriate use of multiple multifunction digital relays, or by using multifunction

digital relays in combination with single-function relays, protection engineers can provide the reliabilityand security level needed for their specific applications.

Digital relays provide many extra features that are quickly becoming priority items. These include self-

checking, digital fault recording, metering and remote communications. The self calibration and special

test programs included with the relays simplify test and checkout of installations using these devices.


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TECHNOLOGICAL UNIVERSITY OF THE PHILIPPINES

AYALA BLVD. ERMITA MANILA

COLLEGE OF ENGINEERING

ELECTRICAL ENGINEERING DEPARTMENT

DIGITAL RELAY

SUBMITTED BY:

BENEDICT C. FORTEZA

JEFFREY D. FRIO

BSEE 4C

SUBMITTED TO:

ENGR.GILBERT B. HOLLMAN

PEE 3009

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Digital Relay Hard Copy