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8/10/2019 PowerPoint - Introduction to Protection Relay_RevB

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Introduction to Protection Relay

Presented by: Ir.S.Gopinath

Date: 07/11/2012


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Contents (cont.)

2.3 Principle of Relay

( Case study: CX-M Relay operation for

11kV VCB)3. Current Transformer ( CT) & Voltage

Transformer (VT)

4. Relation between Relay and CT/VT


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Contents (cont.)

5. I.D.M.T setting of Phase Overcurrent Protection

relay

( Case study: Calculation on Electromechanicalrelay ( Overcurrent ) for Radial distribution

system)


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1. Renewable Energy: Concentrated Solar

Power (CSP) CSP systems use mirrors or lenses to concentrate

a large area of sunlight, or solar thermal energy,

onto a small area.

Concentrated light is converted to heat, which

drives a heat engine(usually a steam turbine)

connected to an electrical power generator.

Example: 11MW PS10 & PS20 Solar Power Plant
http://en.wikipedia.org/wiki/Solar_thermal_energyhttp://en.wikipedia.org/wiki/Heat_enginehttp://en.wikipedia.org/wiki/Steam_turbinehttp://en.wikipedia.org/wiki/Steam_turbinehttp://en.wikipedia.org/wiki/Heat_enginehttp://en.wikipedia.org/wiki/Solar_thermal_energy


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2. Introduction to Protection Relay

IEEE defines a relay as an electric device that is

designed to input conditions in a prescribed

manner and after specified conditions are met, to

cause contact operation


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2.1 Electrical system Protection

isolation of a problem area in the system quickly

so that the rest of the system as much as possible

is left continue service.

The five(5) basic features are:

- Reliability

- Selectivity

- Speed of Operation

- Simplicity

- Economics


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Some related device numbers are: ( stated in

IEEE C37.2-2008)- undervoltage relay (27)

- field circuit breaker (41)

- thermal relay (49)- instantaneous overcurrent relay (50)

- lockout relay (86)

- differential protective relay (87)


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2.2 Causes & Types of Fault

faults can interrupt the healty operation of the

power system.

The type and nature of faults in a three-phase

system are normally classified as:

- Phase & ground

- Permanent

- Transient

- Semitransient


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Phase & Ground fault


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Permenant Faults

- created by punturing or breaking insulators,breaking conductors and objects falling on the

ground conductor

Trasient Faults

- created by transient overvoltages such as

lightning.


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2.3 Principle of Relay

Relay has two mechanical parts:.

- Firstly, the contact(s) of the relay


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- Secondly, the device that forces the terminal tomove so-called an electromagnet


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Types of relay:

- Electromechanical relay

- Static relay- Digital relay

- Numerical relay


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Electromagnetic Relay

convert a magnetic flux generated by the

application of a low voltage electrical control

signal either AC or DC across the relay terminals,

into a pulling mechanical force which operatesthe electrical contacts within the relay.


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- Electromechanical relay construction


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Relay contact types

Electrical relays can be made up of one or moreindividual switch contacts with each "contact"

being referred to as a "pole

Description of the contact types:

SPST - Single Pole Single Throw

SPDT - Single Pole Double Throw

DPST - Double Pole Single Throw

DPDT - Double Pole Double Throw with the action of the contacts being described as

"Make" (M) or "Break" (B)


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- Relay Contact Configuration


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- Relays at Jimah MV Switchgear

Example of Protection relays at Jimah electrical

system:

- Lockout relay

- Power relay

- Thermal overload relay


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Power relay:

- 11kV & 3.3kV switchgear panel uses MM type

OMRON Power relay for control circuits.


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Case study: CX-M relay operation in VCB

control circuit


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Lockout relay

- Protect our main system and safeguard our

personnel with the industry standard for

safety and reliability. This lockout relay

applied for protection of:

Generator Transformer & Generator

Unit Auxliary transformer (UAT)

Excitation Transformer


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3. Current Transformer ( CT) & Voltage

Transformer (VT)

CT Principle:

- The alternating currentflowing in the primary

produces a magnetic field in the core, which then

induces a current in the secondary winding

circuit.
http://en.wikipedia.org/wiki/Alternating_currenthttp://en.wikipedia.org/wiki/Alternating_current


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CT symbol:


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- CT types applied for medium voltage system

Window or Ring type CT

Bar type CT

Bushing Type Or Busduct

Current Transformers ( BCT )

Wound type Primary CT


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VT Principle:

- to produce the system votlages, accurately at low

voltage suitable for the operation of measuring

instruments

- The primary winding is connected across the

supply voltage and low range voltmeter (0-110V)

is connected across the secondary windingterminals.


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- VT types applied for medium voltage system

Cast iron in-resin VT

Capacitor VT

Electromagnetic VT

Cast iron VT with Build-in Fuse type


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4. Relation between Relay and CT/VT

The relays are connected to the power system

through the CT and VT.

CT and VT are used to measure the current

and voltage in a circuit of the order of

hundreds of amperes and volts respectively.


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- Basic configuration of protection relay in a circuit


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- Basic scheme of protection relay and circuit breaker

When current exceeds the normal value, torque produced

will overcome the spring tension to rotate the disc about a

vertical spindle to which a long arm is attached.

The arm moves in the anticlockwise direction till it closes

the terminals 1& 2, and completes the circuit comprising

of a battery and the trip coil of the circuit breaker.


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5. I.D.M.T Overcurrent relay

In inverse definite minimum time (IDMT) relay its

operating is inversely proportional to fault

current and also a characteristic of minimum

time after which this relay definitely operates.


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- Relay coordination

a. whenever possible, use relays with the same

operating characteristic in series with each other

b. make sure that the relay fastest from the

source has current settings equal to or less than

the relays behind it.

using either time or overcurrent, or a

combination of both.


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IEC 60255 defines a number of standard

characteristics as follows:

- Standard Inverse (SI)

- Very Inverse (VI)

- Extremely Inverse (EI)

- Definite Time (DT)


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- Relay characteristics & equations


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- Relay Time Grading Margin (GM)

The time interval that must be allowed between

the operation of two adjacent relays in order to

achieve correct discrimination between them.


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The grading margin depends on a number of

factors:

the fault current interrupting time of the circuit

breaker

relay timing errors

the overshoot time of the relay

CT errors

final margin on completion of operation


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- Important terms for I.D.M.T relay setting


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The important parameters required for relay setting are

such as:(i) Pick-up current- It is the minimum current in the

relay coil at which the relay starts to operate

[ Pickup current = Rated secondary current of CT

x Current setting]

(ii) Current settingIt is often desirable to adjust

the pickup current to any value.


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(iv) Plug setting (P.S.M)- determines the current at

which the relay will start to operate.

(v) Time-setting multiplier (T.M) - controls the

relays disc movement. The position of the

moving contact is usually adjusted by turning

the time multiplier knob, which ranges from 0.1

to 1.0. Calculated by multiplying the time

setting multiplier with the time obtained from

time/ p.s.m curve of the relay.

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