understanding electrical networks to enhance their protection

Understanding electrical networks to enhance their protection

? Situate the protection relay

Duration: 43:35 min

Expert: André TRUONGTraining: François BECHERET Layout: Bernadette ETIENNE

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Network disturbances

What exactly is protection

Network architecture

Points to remember

The various earthing system types

The various discrimination types

Network protection

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Understanding networks – June 04TOLED

Understanding networks – June 04 2TOLED

SITUATE THE PROTECTION RELAY

Industries

Production units

HV/MV substationsMV/MV

distribution

substations

MV/LV distribution substations

Generator

Overheadlines

Motors

Undergroundcables

Transformers


- Network disturbances

Natural phenomena

– branches

– lightning

Short-circuit

Short-circuit

Overloads

Short-circuit

Transient

surges

Transient

losses

Works

Use– capacity problem– reconfiguration– dust– insulators– machine start-up– pump/turbine

blocking ... – harmonics ...


WHAT EXACTLY IS PROTECTION

Sensorcurrentvoltage

A protection device does not prevent the fault from occurring, but limits the consequences ...

Trippingcoil

Trippingcoil

Trippingcoil

Detect and isolate the faultPreserve continuity of supply

MeasureCompareDecide


- The protection plan

Types of disturbance

Earthing systems

Network architectures

PROTECTION PLAN

Settings

Componentsto protect

Type of protection function

Discrimination

CHOICE OF

RELAY



NETWORK ARCHITECTURE


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Points to remember



Network protection

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Maintainability

Safety of equipmentand people

Technical andeconomic aspects

Open-endedness

Ease of operation

Maint Conti

Op

Safety

$ Open

- Choosing a network

Continuity ofoperation


Large distances

Maint Conti

Op

Safety

$ Open

Maint Conti

Op

Safety

$ Open

Strong point

Weak point

Supplied

Not supplied

Open loop Closed loop

Urban secondary networks= geographical areaand continuity of supply

Rural secondary networks= geographical areaand simplicity

- Loop distribution


Large to average distances

Single antenna

Maint Conti

Op

Safety

$ Open

Supplied

Not supplied

Maint Conti

Op

Safety

$ Open

Strong point

Weak point

Continuous process industries:continuity

Simple industries and tertiary: reduced costs

- Antenna distribution

Double antenna


Strong point

Weak point

Supplied

Not supplied

Maint Conti

Op

Safety

$ Open

Heavy process industries andlarge tertiary:continuity

- Double tap-off distribution


Maint Conti

Op

Safety

$ Open

Solution for cubicles

Strong point

Weak point

Supplied

Not supplied

Continuous process industriesOil & Gas: continuity

- Double busbar distribution


Main / standby production

Partial permanent production

Supplied

Not supplied

High consumption industryExpensive electricity

Sites with priority for continuity of supply

- Local production


Public distribution

Tertiary

Industry

Simple tertiary

Large tertiary

Simple processes

Continuous processes

« Heavy » continuous processes

Rural secondary Open loop

Urban secondary

Single antenna

Doubleantenna

Double tap-off

Doublebusbars

Continuity of supply /Ease of maintenanceComplexity of operation

Low costs

Closed loop Continuity of supply

Low costs

- Points to remember



DISTURBANCES


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Points to remember



Network protection

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- Network disturbances

Natural phenomena

Works

Use

Simple fault Complex fault

short-circuit

Surges

short-circuit

overloads

Transient

Losses

short-circuit

Transient

Effects– Customer

power supply suspended

– Incorrect network operation

– Material damage

– Bodily damage

– branches

– capacity problem

– lightning

– reconfiguration

– dust

– insulators

– machine start-up

– pump/turbine blocking ...

– harmonics


- The short-circuit

Origin

Rare but destructive

Duration Location– mechanical

– electrical

– human

– self-extinguishing

– transient

– permanent

– equipment

– link

phase-to-earth lsc

Isc: short-circuit– non-resistive

– impedant

The most common

Energy loss

phase-to-phase Isc

Isolated two-phase short-circuit Three-phase short-circuit (5% of cases)

Earth single-phase short-circuit Two-phase short-circuit (80% of cases)


- Other disturbances

Overload

In

time

Surges

Undervoltage and voltage sags

Frequency fluctuations, harmonics and transient phenomena

Ur

time

Temperature rise thus ageing

Voltage sag

Arcing

Saturation

Overspeed

Destruction

Current increase

Overload

Temperature rise


- Equipment short-circuit withstand

Disconnector

Switch

Contactor

Circuit-breaker

Fuse

Devices

noyes if draw-out

no

yes

no

noyes if draw-out

Isolationfunction

Main constraints

Input-output crossing withstandEarthing switch: making capacity on a fault

Breaking and making of normal load currentMaking capacity on short-circuit

In association with the fuse: breaking capacity in the fuse non-blowing zone

Nominal breaking and making capacityMaximum load capacity in breaking and making

Service and durability characteristics

Breaking capacity on short-circuitMaking capacity on short-circuit

Minimum breaking capacity on short-circuitMaximum breaking capacity on short-circuit

Current switching function

In service On fault

no

yes

yes

no

yes

no

no

no

yes

yes



EARTHING SYSTEMS AND THEIR IMPACTS


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Points to remember


Network protection

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- Earthing systems and earthing

Surges

1 earthing type limits the effects of network disturbances

Transient phenomena

Simple protection

Personnel skills

Continuity of supply SERVICE

Fault energy

OPERATING COSTS

SAFETY OF PEOPLE


- 5 types of earthing system

Unearthed: no connection

Earthed: connection

R

R Earthed via a resistor

L Earthed via a reactance

L

Z Earthed via a compensated reactance

Z


- Unearthed neutral

Advantages – Continuity of supply

Drawbacks

Type of protection

Applications

– 2nd fault = Isc phase-to-phase

– Max. directional lo and Max. residual Vo

– Industry

Surges

Transient phenomena

Simple protection

Personnel skills


Fault energy

OPERATING COSTS

SAFETY OF PEOPLE

surges & transients

– Difficult discrimination

– Insulation monitor


- Directly earthed neutral

Advantages – No surges

Drawbacks

Type of protection

Applications

– High lsc

– Max. Io

– US public distribution

Surges

Transient phenomena

Simple protection

Personnel skills


Fault energy

OPERATING COSTS

SAFETY OF PEOPLE– No specific protection

– No continuity of supply on the 1st fault

– For small lsc


- Earthing via a resistor

R

Advantages

Drawbacks

Type of protection

Applications

– Breaking on 1st fault

– Overcurrent

– Public & industrial distribution

– Isc / surge compromise

– Simple & selective protection

– Expensive resistorSurges

Transient phenomena

Simple protection

Personnel skills


Fault energy

OPERATINGCOSTS

SAFETY OF PEOPLE


- Earthing via a small reactance

Advantages

Drawbacks

Type of protection

Applications – Directional earth protection

– Public distribution > 40 kV

– Limited lsc

– Breaking on 1st fault

L

Surges

Transient phenomena

Simple protection

Personnel skills


Fault energy

OPERATINGCOSTS

SAFETY OF PEOPLE

– Inexpensive reactance

– Surges


- Earthing via a compensation reactance

Advantages

Drawbacks

Type of protection

Applications

– Expensive reactance

– Max. directional Io

– Public distribution with high capacitive l

– Limited lsc

Z

Surges

Transient phenomena

Simple protection

Personnel skills


Fault energy

OPERATINGCOSTS

SAFETY OF PEOPLE– Continuity of supply

– Discrimination implementation

– Surges


- Summary of the 5 earthing systems

Unearthed: no connection Continuity of supply Personnel skills

Surges Earthed via a reactance Fault energy

Earthed: connection Transient phenomena

Fault energy

Earthed via a resistor Continuity of supplySimple protection

Earthed via a compensated reactanceContinuity of supply Simple protection



DISCRIMINATION


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Points to remember


Network protection

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- 6 types of discrimination to optimise continuity of supply

Isolate only the faulty part

Choice of protection relay as per:

Supply the healthy sector

Network

Disturbances incurred

Earthing system

Discrimination:

6 discrimination principles:

time current logic by directional protection by differential protection

combined


- Time discrimination

Principle: “time”

Advantages – simple

Drawbacks – tripping too long in A, in event of fault at this

level

– time delays increasingly short as we move away from the source

TA =1.1 s.

TB =0.8 s.

TC =0.5 s.

TD =0.2 s.

– tripping as close as possible to the fault

– automatic standby

Source

Phase-to-phase fault


- Current discrimination

Principle: “current”

Advantages – Each relay monitors its section

Drawbacks

– No « standby » protection

– The further the fault from the source, the weaker the fault current

– Simple, inexpensive and fast

Section A

Section B

Source

ConditionIsA > IscBmaxIsA > IscAmin

IscBmax


- Logic discrimination

Principle: “ … ”

Advantages

– Avoids over long tripping times

Drawbacks

– Standby system

– A (blue) additional network connects all the protection relays to allow exchanges and decisions as to « which relay is concerned ».

– Tripping time not dependent on number of protection devices

– An additional wiring network is required

Additional wiring

Source

Logic wait

Phase-to-phasefault


- Discrimination by directional protection

Principle: “directional”

Advantages – Preserves 1 out of the 2 power supplies in

event of fault in 1

Drawback

– Simple solution

– Measures flow direction

– The cost of the voltage transformers

– Network in loop on 2 sources

Busbar

Cable Cable

Vref.


- Discrimination by differential protection

Source Principle: "differential"

Advantages – Sensitive

Drawbacks

– IA = IB ?

– Instantaneous

– Standby to provide

– Tripping on a difference!

– Implementation

– Cost

SectionProtectedarea


- In short, discrimination is ...

1 … time

2 … current

3 … logic

5 … difference

4 … direction

6 ?

Discrimination applies to – I phase

– Io earth

Global discrimination and redundancy

– Mix discrimination types

6 Discrimination combination


Network protection

NETWORK PROTECTION


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Points to remember



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Network protection


- Connection protection: overhead lines

X X X

line feeder

incomer

Overhead lines: 80 % of problems

– Against transient contacts: automation

Downstream faults:Short-circuitsBreakage of a phase

Recommended protections:– overcurrent protection (50/51)– max. Io protection (50N/51N)– phase unbalance protection (46)– distance protection (21)– line differential protection (87L)

Protection provided by other devices– Against lightning: overvoltage protection devices


- Connection protection: underground cables

Underground distribution in urban environments

cable feeder

X X X

incomer

Downstream faults:short-circuitsbreakage of a phase

No reclosing

Recommended protections:– Directional earth protection (67N)– Overcurrent protection (50/51)– Residual overcurrent protection (50N/51N)– Phase unbalance protection (46)– Line differential protection (87L)


- Connection protection: busbars

Electrical switchboards

Schéma F2

– « energy concentration » !– need to eliminate the fault quickly

X X X X X X X

busbar

Fault– short-circuits (between bars and

with the earth)– temperature rise– insulation loss

Recommended protections– Logic discrimination: overcurrent (50/51) and

residual overcurrent protection (50N/51N)

– Time discrimination: busbar differential protection (87B)


- Protection example of substation busbars with 2 incomers

discrimination

Directional protection set if fault

protections– Overcurrent protection (50/51)– Residual overcurrent protection (50N/51N) – Directional phase protection (67)

– current


- Switchgear protection: the transformer

Protections Faults

Short-circuit

Earth fault

Overload

• Max. Io 50N/51N

• Restricted differential 64REF• Tank earth

50N/51N, 50G/51G

• Overcurrent 50/51• transformer differential• 87T• Buchholz• DGPT 63

• Overcurrent 50/51• Thermal overload

49RMS• Temperature 49T

• Coiling• Tank• Magnetic circuit

• Coiling• Magnetic circuit

• Insulators

Impacts


- Switchgear protection: the motor

• Voltage sag• Unbalance

• Short-circuit • Earth fault• Loss of synchronism

• Overload• Starting too long• Locked rotor

• Frequent starting

• Overcurrent 50/51 • Machine differential 87M• Max. Io 50N/51N,

78PS

• Undervoltage 27• Max. reverse component 46• Overpower32P

• Thermal overload 49RMS

• 48• 51LR• Min. I 37, P, 37P

• Limited number of start-ups 66

• Active power return: voltage sag

• Destruction of coiling and magnetic circuit• Motor deceleration

• Overcurrent• Stator temperature rise• Pump unpriming• Mechanical breakage

• Temperature rise

Protections Faults Impacts

Upstream

Internal

Downstream

Use


- Switchgear protection: the generator

Short-circuit

• Overcurrent 50/51• Machine differential 87M• Overcurrent with voltage retention 50V/51V

Active power returnUnbalanceSurge

32P, 46, 59

Loss of synchronism • 78PS• Min. impedance

21B

Earth fault • Max. Io 50N/51N• Restricted earth differential 64REF•Residual overvoltage 59N

Faults relating to incorrect regulation

• Over and under frequency 81H/81L• Undervoltage 27

• Destruction of coiling & magnetic circuit

• Mechanical danger for turbine + rotor

temperature rise

• Overspeed Absorption Reactive power

(operates as motor) then temperature rise

• Temperature rise and poor efficiency

• Destruction of coiling & destruction of magnetic circuit

Protections Faults Impacts Internal

Upstream


- Switchgear protection: the capacitor

Internal short-circuit

• Overcurrent 50/51• Thermal overload49RMS• Max. reverse component 46

• Overvoltage 59

Earth fault • Max. Io 50N/51N• Residual overvoltage 59N• Max. reverse component 46

• Destruction of insulators

Unbalance

Surge • Destruction of insulators

• Thermal overload 49RMS• Max. reverse component 46• Specific

• Reduction in capacity

Short-circuit in the connection

Protections Faults Impacts

• Destruction of connections with capacitors


- The protection guide will provide you with more details

Networks

Earthing systems

Isc

Sensors

Protection functions

Discrimination

Network protection

Electrical network protection

Protection Guide

network


POINTS TO REMEMBER

Types of disturbance

Earthing systems

Network architectures

Components to protect

PROTECTION PLAN

Settings

Type of protection function

Discrimination

CHOICE OF

RELAY

understanding electrical networks to enhance their protection

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