Download Understanding networks

Understanding electrical networks to enhance
their protection
G
Points to remember
F
E
Network protection
The various discrimination types
D The various earthing system types
C
?
Situate the
protection relay
Duration: 43:35 min
TOLED
Network disturbances
B Network architecture
A What exactly is protection
Expert: André TRUONG
Training: François BECHERET
Layout: Bernadette ETIENNE
Understanding networks – June 04
SITUATE THE PROTECTION RELAY
Production units
Generator
Transformers
Overhead
lines
Underground
cables
MV/MV
distribution
substations
HV/MV substations
Motors
TOLED
Industries
MV/LV distribution
substations
Understanding networks – June 04
2
- Network disturbances
 Natural
phenomena
– branches
– lightning
 Works
Short-circuit
Transient
Short-circuit
 Use
–
–
–
–
–
–
capacity problem
reconfiguration
dust
insulators
machine start-up
pump/turbine
blocking ...
– harmonics ...
TOLED
Overloads
surges
Transient
Short-circuit
losses
Understanding networks – June 04
3
WHAT EXACTLY IS PROTECTION
Detect and isolate the fault
Preserve continuity of supply
Sensor
current
voltage
Measure
Compare
Decide
Tripping
coil
A protection device does not prevent the fault from
occurring, but limits the consequences ...
TOLED
Understanding networks – June 04
4
- The protection plan
Network
architectures
Types of
disturbance
PROTECTION PLAN
Type of protection function
Earthing
systems
CHOICE
OF
RELAY
Discrimination
Settings
Components
to protect
TOLED
Understanding networks – June 04
5
NETWORK ARCHITECTURE
G
Points to remember
F
E
Network protection
The various discrimination types
D The various earthing system types
C
?
TOLED
Situate the
protection relay
Network disturbances
B Network architecture
A What exactly is protection
Understanding networks – June 04
6
- Choosing a network
Safety of equipment
and people
Technical and
economic aspects
Open-endedness
Continuity of
operation
Maintainability
Safety
$
Open
Maint
Conti
Ease of operation
Op
TOLED
Understanding networks – June 04
7
- Loop distribution
Large distances
Open loop
Closed loop
Urban secondary networks
= geographical area
and continuity of supply
Rural secondary networks
= geographical area
and simplicity
Safety
Safety
$
Open
Maint
Conti
Op
TOLED
Supplied
Strong point
Not supplied
Weak point
$
Open
Maint
Conti
Op
Understanding networks – June 04
8
- Antenna distribution
Large to average distances
Single antenna
Safety
$
Open
Maint
Conti
Op
TOLED
Double antenna
Simple industries and tertiary:
reduced costs
Continuous process industries:
continuity
Supplied
Strong point
Not supplied
Weak point
Safety
$
Open
Maint
Conti
Op
Understanding networks – June 04
9
- Double tap-off distribution
Heavy process industries and
large tertiary:
continuity
Safety
$
Open
Maint
Conti
Op
TOLED
Supplied
Strong point
Not supplied
Weak point
Understanding networks – June 04
10
- Double busbar distribution
Solution for cubicles
Continuous process industries
Oil & Gas: continuity
Safety
$
Open
Maint
Conti
Op
TOLED
Strong point
Supplied
Weak point
Not supplied
Understanding networks – June 04
11
- Local production
Partial permanent production
High consumption industry
Expensive electricity
TOLED
Main / standby production
Supplied
Not supplied
Sites with priority for
continuity of supply
Understanding networks – June 04
12
- Points to remember
Public
distribution
Rural secondary
Open loop
Low costs
Urban secondary
Closed loop
Continuity of supply
Simple tertiary
Single antenna
Low costs
Tertiary
Large tertiary
Simple processes
Industry
Continuous processes
« Heavy » continuous
processes
TOLED
Double
antenna
Double tap-off
Double
busbars
Continuity of supply /
Ease of maintenance
Complexity of operation
Understanding networks – June 04
13
DISTURBANCES
G
Points to remember
F
E
Network protection
The various discrimination types
D The various earthing system types
C
?
TOLED
Situate the
protection relay
Network disturbances
B Network architecture
A What exactly is protection
Understanding networks – June 04
14
- Network disturbances
 Natural
phenomena
–
branches
–
lightning
 Works
Simple fault
Complex fault
short-circuit
Surges
short-circuit
 Use
– capacity problem
– reconfiguration
TOLED
overloads
Transient
Losses
–
–
dust
insulators
–
machine start-up
–
pump/turbine blocking ...
–
harmonics
short-circuit
Transient
Effects
– Customer
power supply
suspended
– Incorrect
network
operation
– Material
damage
– Bodily damage
Understanding networks – June 04
15
- The short-circuit
 Origin
 Duration
 Location
–
mechanical
–
self-extinguishing –
–
electrical
–
transient
–
human
–
permanent
–
 Isc: short-circuit
equipment
–
non-resistive
link
–
impedant
phase-to-phase Isc
Rare but destructive
Isolated two-phase short-circuit
Energy loss
Three-phase short-circuit (5% of cases)
phase-to-earth lsc
The most common
Earth single-phase short-circuit
TOLED
Two-phase short-circuit (80% of cases)
Understanding networks – June 04
16
- Other disturbances
Overload
Temperature rise thus ageing
In
Voltage sag
time
Surges
Undervoltage and voltage sags
Arcing
Overspeed
Saturation
Destruction
Current increase
Overload
Ur
Temperature rise
time
Frequency fluctuations, harmonics and transient phenomena
TOLED
Understanding networks – June 04
17
- Equipment short-circuit withstand
Devices
Disconnector
Isolation
function
yes
Current switching
function
In service
no
Main constraints
On fault
no
Input-output crossing withstand
Earthing switch: making capacity on a fault
no
Breaking and making of normal load current
Making capacity on short-circuit
In association with the fuse: breaking capacity in the
fuse non-blowing zone
Switch
no
Contactor
no
yes if draw-out
yes
no
Nominal breaking and making capacity
Maximum load capacity in breaking and making
Service and durability characteristics
Circuit-breaker
no
yes if draw-out
yes
yes
Breaking capacity on short-circuit
Making capacity on short-circuit
Fuse
no
no
yes
Minimum breaking capacity on short-circuit
Maximum breaking capacity on short-circuit
TOLED
yes
Understanding networks – June 04
18
EARTHING SYSTEMS AND THEIR IMPACTS
G
Points to remember
F
E
Network protection
The various discrimination types
D The various earthing system types
C
?
TOLED
Situate the
protection relay
Network disturbances
B Network architecture
A What exactly is protection
Understanding networks – June 04
19
- Earthing systems and earthing
1 earthing type limits the
effects of network
disturbances
Continuity of supply
SERVICE
Simple protection
OPERATING COSTS
Personnel skills
Fault energy
Transient
phenomena
SAFETY OF PEOPLE
Surges
TOLED
Understanding networks – June 04
20
- 5 types of earthing system
R
L
Z
 Unearthed: no connection
 Earthed: connection
TOLED
R
 Earthed via a resistor
L
 Earthed via a reactance
Z
 Earthed via a compensated reactance
Understanding networks – June 04
21
- Unearthed neutral
Continuity of supply
SERVICE
Simple protection
OPERATING COSTS
Personnel
skills
 Advantages
–
Continuity of supply
 Drawbacks
–
2nd fault = Isc phase-to-phase
Fault energy
Transient
phenomena
SAFETY OF PEOPLE
surges & transients
–
Difficult discrimination
Surges
 Type of protection
–
–
Max. directional lo and
Max. residual Vo
Insulation monitor
 Applications
–
TOLED
Industry
Understanding networks – June 04
22
- Directly earthed neutral
Continuity of supply
SERVICE
Simple protection
OPERATING COSTS
Personnel skills
 Advantages
–
–
No surges
No specific protection
 Drawbacks
–
–
High lsc
No continuity of supply on
the 1st fault
Fault energy
Transient
phenomena
SAFETY OF PEOPLE
Surges
 Type of protection
–
Max. Io
 Applications
–
–
TOLED
US public distribution
For small lsc
Understanding networks – June 04
23
- Earthing via a resistor
Continuity of supply
SERVICE
Simple protection
R
Personnel
skills
 Advantages
–
Isc / surge compromise
–
Simple & selective protection
 Drawbacks
–
Breaking on 1st fault
–
Expensive resistor
OPERATING
COSTS
Fault energy
Transient
phenomena
SAFETY OF
PEOPLE
Surges
 Type of protection
–
Overcurrent
 Applications
–
TOLED
Public & industrial distribution
Understanding networks – June 04
24
- Earthing via a small reactance
Continuity of supply
SERVICE
Simple protection
L
Personnel
skills
 Advantages
–
Limited lsc
–
Inexpensive reactance
OPERATING
COSTS
Fault energy
Transient
phenomena
SAFETY OF
PEOPLE
 Drawbacks
–
Breaking on 1st fault
–
Surges
Surges
 Type of protection
–
Directional earth protection
 Applications
–
TOLED
Public distribution > 40 kV
Understanding networks – June 04
25
- Earthing via a compensation reactance
Continuity of supply
SERVICE
Simple protection
Z
Personnel
skills
 Advantages
– Limited lsc
– Continuity of supply
 Drawbacks
–
Expensive reactance
–
–
Surges
Discrimination implementation
OPERATING
COSTS
Fault energy
Transient
phenomena
SAFETY OF
PEOPLE
Surges
 Type of protection
–
Max. directional Io
 Applications
–
TOLED
Public distribution with high capacitive l
Understanding networks – June 04
26
- Summary of the 5 earthing systems
 Unearthed: no connection
 Earthed: connection
Transient
phenomena
 Earthed via a resistor
Simple protection
 Earthed via a reactance
Fault energy
 Earthed via a compensated
reactance
TOLED
Continuity of supply
Continuity of supply
Personnel
skills
Fault energy
Continuity of supply
Surges
Simple protection
Understanding networks – June 04
27
DISCRIMINATION
G
Points to remember
F
Network protection
E The various discrimination types
D The various earthing system types
C
?
TOLED
Situate the
protection relay
Network disturbances
B Network architecture
A What exactly is protection
Understanding networks – June 04
28
- 6 types of discrimination to optimise
continuity of supply
Discrimination:
Isolate only the faulty part
Supply the healthy sector
Choice of protection relay as
per:
Network
6 discrimination principles:





time
current
logic
by directional protection
by differential protection
 combined
Disturbances incurred
Earthing system
TOLED
Understanding networks – June 04
29
- Time discrimination
 Principle: “time”
– time delays increasingly short as we
move away from the source
Source
TA =1.1 s.
TB =0.8 s.
– tripping as close as possible to the fault
 Advantages
– simple
– automatic standby
TC =0.5 s.
TD =0.2 s.
Phase-to-phase fault
TOLED
 Drawbacks
– tripping too long in A, in event of fault at
this level
Understanding networks – June 04
30
- Current discrimination
 Principle: “current”
Source
– The further the fault from the source,
the weaker the fault current
IscBmax
Section A
 Advantages
– Each relay monitors its section
– Simple, inexpensive and fast
 Drawbacks
Section B
IsA > IscAmin
TOLED
– No « standby » protection
Condition
IsA > IscBmax
Understanding networks – June 04
31
- Logic discrimination
 Principle: “ … ”
Source
–
A (blue) additional network connects all
the protection relays to allow exchanges
and decisions as to « which relay is
concerned ».
 Advantages
Logic wait
–
Avoids over long tripping times
–
Tripping time not dependent on
number of protection devices
–
Standby system
 Drawbacks
Phase-to-phase
fault
–
An additional wiring network is
required
Additional wiring
TOLED
Understanding networks – June 04
32
- Discrimination by directional protection
 Principle: “directional”
Cable
Cable
– Measures flow direction
– Network in loop on 2 sources
 Advantages
Vref.
– Preserves 1 out of the 2 power
supplies in event of fault in 1
– Simple solution
Busbar
 Drawback
– The cost of the voltage transformers
TOLED
Understanding networks – June 04
33
- Discrimination by differential protection
 Principle: "differential"
Source
–
IA = IB ?
–
Tripping on a difference!
 Advantages
Protected
area
Section
–
Sensitive
–
Instantaneous
 Drawbacks
TOLED
–
Cost
–
Implementation
–
Standby to provide
Understanding networks – June 04
34
- In short, discrimination is ...
 1 … time
 2 … current
 Discrimination applies to
– I phase
– Io earth
 3 … logic
 4 … direction
 5 … difference
 6
TOLED
?
 Global discrimination and
redundancy
– Mix discrimination types
 6 Discrimination combination
Understanding networks – June 04
35
NETWORK PROTECTION
G
Points to remember
F
E
Network protection
The various discrimination types
D The various earthing system types
C
?
TOLED
Situate the
protection relay
Network disturbances
B Network architecture
A What exactly is protection
Understanding networks – June 04
36
- Connection protection: overhead lines
Overhead lines: 80 % of problems
Downstream faults:
Short-circuits
Breakage of a phase
 Recommended protections:
X
X
X
incomer
–
–
–
–
–
overcurrent protection (50/51)
max. Io protection (50N/51N)
phase unbalance protection (46)
distance protection (21)
line differential protection (87L)
line feeder
 Protection provided by other devices
– Against lightning: overvoltage protection devices
– Against transient contacts: automation
TOLED
Understanding networks – June 04
37
- Connection protection: underground cables
Underground distribution in urban
environments
Downstream faults:
short-circuits
breakage of a phase
 No reclosing
X
X
X
 Recommended protections:
incomer
cable feeder
TOLED
–
–
–
–
–
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
38
- Connection protection: busbars
Electrical switchboards
– « energy concentration » !
– need to eliminate the fault quickly
Schéma F2
busbar
Fault
– short-circuits (between bars and with
the earth)
– temperature rise
– insulation loss
 Recommended protections
X X X X
X X X
– Logic discrimination: overcurrent (50/51) and
residual overcurrent protection (50N/51N)
– Time discrimination: busbar differential
protection (87B)
TOLED
Understanding networks – June 04
39
- Protection example of substation busbars
with 2 incomers
Directional protection set if
fault
 protections
– Overcurrent protection (50/51)
– Residual overcurrent protection (50N/51N)
– Directional phase protection (67)
 discrimination
– current
TOLED
Understanding networks – June 04
40
- Switchgear protection: the transformer
Faults
Protections
Short-circuit
• Coiling
• Tank
• Magnetic circuit
• Overcurrent 50/51
• transformer
differential
• 87T
• Buchholz
• DGPT 63
Earth fault
• Coiling
• Magnetic circuit
• Max. Io
50N/51N
• Restricted
differential 64REF
• Tank earth
50N/51N, 50G/51G
• Insulators
• Overcurrent 50/51
• Thermal overload
49RMS
• Temperature 49T
Overload
TOLED
Impacts
Understanding networks – June 04
41
- Switchgear protection: the motor
Faults
Upstream
• Voltage sag
• Unbalance
Impacts
• Active power return:
voltage sag
• Undervoltage 27
• Max. reverse
component 46
• Overpower
32P
• Destruction of coiling
and magnetic circuit
• Motor deceleration
• Overcurrent 50/51
• Machine differential
87M
• Max. Io 50N/51N,
78PS
• Overcurrent
• Stator temperature
rise
• Pump unpriming
• Mechanical
breakage
• Thermal overload
49RMS
• 48
• 51LR
• Min. I 37, P, 37P
• Temperature rise
• Limited number of
start-ups 66
Internal
• Short-circuit
• Earth fault
• Loss of synchronism
Downstream
• Overload
• Starting too long
• Locked rotor
Use
• Frequent starting
TOLED
Protections
Understanding networks – June 04
42
- Switchgear protection: the generator
Faults
Internal
Impacts
• Overcurrent 50/51
• Machine differential
87M
• Overcurrent with
voltage retention
50V/51V
Short-circuit
• Destruction
of coiling & magnetic
circuit
Earth fault
• Destruction of
coiling & destruction
of magnetic circuit
• Max. Io 50N/51N
• Restricted earth
differential 64REF
•Residual overvoltage
59N
• Overspeed
Absorption
Reactive power
(operates as motor)
then temperature rise
• 78PS
• Min. impedance
21B
• Temperature rise
and poor efficiency
• Over and under
frequency 81H/81L
• Undervoltage 27
• Mechanical danger
for turbine + rotor
temperature rise
32P, 46, 59
Loss of synchronism
Faults relating to
incorrect regulation
Upstream
Active power return
Unbalance
Surge
TOLED
Protections
Understanding networks – June 04
43
- Switchgear protection: the capacitor
Faults
TOLED
Impacts
Protections
Internal short-circuit
• Reduction in
capacity
• Thermal overload
49RMS
• Max. reverse
component 46
• Specific
Short-circuit in the
connection
• Destruction of
connections with
capacitors
• Overcurrent 50/51
• Thermal overload
49RMS
• Max. reverse
component 46
Earth fault
• Destruction of
insulators
Unbalance
• Max. Io 50N/51N
• Residual
overvoltage 59N
• Max. reverse
component 46
Surge
• Destruction of
insulators
• Overvoltage 59
Understanding networks – June 04
44
- The protection guide
will provide you with more details
Electrical network protection
 Networks
Protection Guide
 Earthing systems
 Isc
 Sensors
 Protection functions
 Discrimination
network
TOLED
 Network protection
Understanding networks – June 04
45
POINTS TO REMEMBER
Network
architectures
Types of
disturbance
PROTECTION PLAN
Type of protection function
Earthing
systems
CHOICE
OF
RELAY
Discrimination
Settings
Components to protect
TOLED
Understanding networks – June 04
46