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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B
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D
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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
G
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
Understanding networks – June 04 3TOLED
- 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 ...
Understanding networks – June 04 4TOLED
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
Understanding networks – June 04 5TOLED
- The protection plan
Types of disturbance
Earthing systems
Network architectures
PROTECTION PLAN
Settings
Componentsto protect
Type of protection function
Discrimination
CHOICE OF
RELAY
Understanding networks – June 04 6TOLED
Network architecture
NETWORK ARCHITECTURE
? Situate the protection relay
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B
C
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Network disturbances
What exactly is protection
Points to remember
The various earthing system types
The various discrimination types
Network protection
G
Network architecture
Understanding networks – June 04 7TOLED
Maintainability
Safety of equipmentand people
Technical andeconomic aspects
Open-endedness
Ease of operation
Maint Conti
Op
Safety
$ Open
- Choosing a network
Continuity ofoperation
Understanding networks – June 04 8TOLED
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
Understanding networks – June 04 9TOLED
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
Understanding networks – June 04 10TOLED
Strong point
Weak point
Supplied
Not supplied
Maint Conti
Op
Safety
$ Open
Heavy process industries andlarge tertiary:continuity
- Double tap-off distribution
Understanding networks – June 04 11TOLED
Maint Conti
Op
Safety
$ Open
Solution for cubicles
Strong point
Weak point
Supplied
Not supplied
Continuous process industriesOil & Gas: continuity
- Double busbar distribution
Understanding networks – June 04 12TOLED
Main / standby production
Partial permanent production
Supplied
Not supplied
High consumption industryExpensive electricity
Sites with priority for continuity of supply
- Local production
Understanding networks – June 04 13TOLED
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
Understanding networks – June 04 14TOLED
Network disturbances
DISTURBANCES
? Situate the protection relay
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B
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What exactly is protection
Network architecture
Points to remember
The various earthing system types
The various discrimination types
Network protection
G
Network disturbances
Understanding networks – June 04 15TOLED
- 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
Understanding networks – June 04 16TOLED
- 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)
Understanding networks – June 04 17TOLED
- 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
Understanding networks – June 04 18TOLED
- 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
Understanding networks – June 04 19TOLED
The various earthing system types
EARTHING SYSTEMS AND THEIR IMPACTS
? Situate the protection relay
A
B
C
D
E
F
Network disturbances
What exactly is protection
Network architecture
Points to remember
The various discrimination types
Network protection
G
The various earthing system types
Understanding networks – June 04 20TOLED
- 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
Understanding networks – June 04 21TOLED
- 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
Understanding networks – June 04 22TOLED
- 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
Continuity of supply SERVICE
Fault energy
OPERATING COSTS
SAFETY OF PEOPLE
surges & transients
– Difficult discrimination
– Insulation monitor
Understanding networks – June 04 23TOLED
- 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
Continuity of supply SERVICE
Fault energy
OPERATING COSTS
SAFETY OF PEOPLE– No specific protection
– No continuity of supply on the 1st fault
– For small lsc
Understanding networks – June 04 24TOLED
- 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
Continuity of supply SERVICE
Fault energy
OPERATINGCOSTS
SAFETY OF PEOPLE
Understanding networks – June 04 25TOLED
- 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
Continuity of supply SERVICE
Fault energy
OPERATINGCOSTS
SAFETY OF PEOPLE
– Inexpensive reactance
– Surges
Understanding networks – June 04 26TOLED
- 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
Continuity of supply SERVICE
Fault energy
OPERATINGCOSTS
SAFETY OF PEOPLE– Continuity of supply
– Discrimination implementation
– Surges
Understanding networks – June 04 27TOLED
- 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
Understanding networks – June 04 28TOLED
The various discrimination types
DISCRIMINATION
? Situate the protection relay
A
B
C
D
E
F
Network disturbances
What exactly is protection
Network architecture
Points to remember
The various earthing system types
Network protection
G
The various discrimination types
Understanding networks – June 04 29TOLED
- 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
Understanding networks – June 04 30TOLED
- 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
Understanding networks – June 04 31TOLED
- 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
Understanding networks – June 04 32TOLED
- 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
Understanding networks – June 04 33TOLED
- 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.
Understanding networks – June 04 34TOLED
- Discrimination by differential protection
Source Principle: "differential"
Advantages – Sensitive
Drawbacks
– IA = IB ?
– Instantaneous
– Standby to provide
– Tripping on a difference!
– Implementation
– Cost
SectionProtectedarea
Understanding networks – June 04 35TOLED
- 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
Understanding networks – June 04 36TOLED
Network protection
NETWORK PROTECTION
? Situate the protection relay
A
B
C
D
E
F
Network disturbances
What exactly is protection
Network architecture
Points to remember
The various earthing system types
The various discrimination types
G
Network protection
Understanding networks – June 04 37TOLED
- 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
Understanding networks – June 04 38TOLED
- 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)
Understanding networks – June 04 39TOLED
- 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)
Understanding networks – June 04 40TOLED
- 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
Understanding networks – June 04 41TOLED
- 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
Understanding networks – June 04 42TOLED
- 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
Understanding networks – June 04 43TOLED
- 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
Understanding networks – June 04 44TOLED
- 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
Understanding networks – June 04 45TOLED
- 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
Understanding networks – June 04 46TOLED
POINTS TO REMEMBER
Types of disturbance
Earthing systems
Network architectures
Components to protect
PROTECTION PLAN
Settings
Type of protection function
Discrimination
CHOICE OF
RELAY