Kuliah Teknik Tegangan Tinggi (1)
TKE 474
High Voltage Engineering
~High
Engineering~
O e o tage
Overvoltage
and
Insulation Coordination
06/12/2011
Overvoltage ‐‐‐‐‐‐> Insulation coordination
Insulation coordination:
1. Insulation coordination is the selection of the
insulation strength.
insulation strength
2. The "selection of the insulation strength
consistent with the expected overvoltages to
obtain an acceptable risk of failure.
3. Insulation coordination is the "process of
bringing the insulation strengths of electrical
equipment into the proper relationship with
expected overvoltages
t d
lt
and with the
d ith th
characteristics of surge protective devices"
06/12/2011
Types of Overvoltages
Overvoltages stressing a power system can
generally be classified into two main types:
1. External overvoltages:
Generated by atmospheric disturbances i.e:
li ht i t ik
lightning strike
2 Internal overvoltages:
2.
Generated by changes in the operating
conditions of the network and can be divided
into two types i.e:
(a) switching overvoltages and
(b)
(b) temporary overvoltages
l
06/12/2011
ÖTypically :
yp
y
• straight hit to conductor
• back flashover via grounded component
• induced
The Lightning Discharge
06/12/2011
Nature of Danger of Lightning Strike
06/12/2011
The Lightning Discharge
06/12/2011
The Lightning Voltage Surge
Ö Propagating overvoltage into both directions along
the conductor
• Typically Z0 = 250 – 500 Ω
Ö overvoltage ~
lt MV
0 m
U
620 m
1600
1300 m
3
2200 m
kV
1200
800
400
0
06/12/2011
0
1
2
3
4
t / μ s
Back flashover via grounded component
g
p
Ö flashover from grounded component to
phase conductor and called back flashover
06/12/2011
Induced Overvoltages
lightning current cause a rapidly changing
magnetic field into the LC loops of the line inducing a
voltage
i
Vinduced
h
= k i Z0
d
d
h
k = considers propagation speed of discharge current. Typically 1.2 – 1.3
i = peak lightning current
h h i h f
h = height of conductor,
d
d = distance of stroke from conductor
06/12/2011
Internal Overvoltages
busbar short circuit
asynchronous network
disruption of capacitive current
06/12/2011
line fault
disruption of small inductive current
voltage applied to no load line
voltage applied to no‐load line
Power System Overview (HV aspect)
Insulation Over‐voltages
Electric insulation is a vital part of an
electrical power system, a careful
analysis of the line insulation to ensure
an adequate line design is needed
(
(Stewart et al, 1992).
l
)
Power System Overview (HV aspect)
* Continuous Power Frequency Voltages
The insulation has to withstand normal
Th i
l i h i h
d
l
operating voltages. The voltage may
fluctuates caused changing the load. The
normal range of fluctuation is around
+10%.
Power System Overview (HV aspect)
The voltage Vmax is used for the selection of number of insulators for line
application.
Typical number of
string glass insulator
Power System Overview (HV aspect)
• Basic Switching Impulse Insulation Level
(BSL)
The BSL
e BS is the electrical strength of insulation
s t e e ect ca st e gt o su at o
expressed in terms of the crest value of a
sta da d s tc g pu se. e stat st ca
standard switching impulse. The statistical
BSL, insulation exhibits a 90% probability of
withstands a 10% probability of failure. In IEEE
%p
y
Std 1313.1‐1996, the BSL is called the switching
impulse withstand voltage.
p
g
Power System Overview (HV aspect)
B i Li h i I
l
• Basic Lightning Impulse
(
)
Insulation Level (BIL)
The BIL or basic lightning impulse
insulation level is the electrical
strength of insulation expressed in
terms of the crest value of the
standard lightning impulse.
Power System Overview (HV aspect)
I
Impulse Insulation Strength
l I
l i S
h
Insulation strength is expressed in terms of
conventional or statistical BILs and BSLs.
For every application of an impulse having the
standard waveshape and whose crest is equal
to the BIL or BSL the probability of a
to the BIL or BSL, the probability of a
flashover or failure is 10%.
The mean of this distribution or characteristic
is defined as the critical flashover voltage or
critical flash over (CFO)
critical flash over (CFO).
Impulse Insulation Strength
Power System Overview (HV aspect)
For the transmission line insulation strength is
Power System Overview (HV aspect)
usually statistically described by a CFO voltage at
which the insulation exhibits a 50% probability of
flashover and by a standard deviation
fl h
d b t d d d i ti σ which is
hi h i
approximately 5% of the CFO (IEEE Std. 62.22, 1997)
Power System Overview (HV aspect)
• Switching Impulse Strength of Tower
p
Conversion three to six‐phase transmission lines will
effect on the existing tower insulation i.e. striking
distance (clearance) and the insulator string length
(number of insulator). The statistical withstand
voltage for line insulation V3 is defined as:
Power System Overview (HV aspect)
Clearance area is depending on horizontal
and vertical distance between conductor and
tower.
Horizontal and vertical distance is 4.42
meter and 1.78 meter. Relationship between
the CFO and the strike distance can be
approximated by
pp
y :
Power System Overview (HV aspect)
S
kg
h
W
is the flash distance (meter)
is gap factor. For a lattice steel
t
tower,
kg is about 1.2
i b t
(IEEE Std 1313.2‐1999),
is conductor height, and
is tower width (horizontal distance
DH)
Power System Overview (HV aspect)
Minimum clearance based on lightning impulse
In the clearances calculation based on lightning impulse (LI),
clearances are calculated by dividing the highest equivalent
crest voltage for the 1.2/50 μs impulse wave shape. Clearance
phase‐to‐ground can be calculated by using:
High Voltage Engineering
~High
Engineering~
O e o tage
Overvoltage
and
Insulation Coordination
06/12/2011
Overvoltage ‐‐‐‐‐‐> Insulation coordination
Insulation coordination:
1. Insulation coordination is the selection of the
insulation strength.
insulation strength
2. The "selection of the insulation strength
consistent with the expected overvoltages to
obtain an acceptable risk of failure.
3. Insulation coordination is the "process of
bringing the insulation strengths of electrical
equipment into the proper relationship with
expected overvoltages
t d
lt
and with the
d ith th
characteristics of surge protective devices"
06/12/2011
Types of Overvoltages
Overvoltages stressing a power system can
generally be classified into two main types:
1. External overvoltages:
Generated by atmospheric disturbances i.e:
li ht i t ik
lightning strike
2 Internal overvoltages:
2.
Generated by changes in the operating
conditions of the network and can be divided
into two types i.e:
(a) switching overvoltages and
(b)
(b) temporary overvoltages
l
06/12/2011
ÖTypically :
yp
y
• straight hit to conductor
• back flashover via grounded component
• induced
The Lightning Discharge
06/12/2011
Nature of Danger of Lightning Strike
06/12/2011
The Lightning Discharge
06/12/2011
The Lightning Voltage Surge
Ö Propagating overvoltage into both directions along
the conductor
• Typically Z0 = 250 – 500 Ω
Ö overvoltage ~
lt MV
0 m
U
620 m
1600
1300 m
3
2200 m
kV
1200
800
400
0
06/12/2011
0
1
2
3
4
t / μ s
Back flashover via grounded component
g
p
Ö flashover from grounded component to
phase conductor and called back flashover
06/12/2011
Induced Overvoltages
lightning current cause a rapidly changing
magnetic field into the LC loops of the line inducing a
voltage
i
Vinduced
h
= k i Z0
d
d
h
k = considers propagation speed of discharge current. Typically 1.2 – 1.3
i = peak lightning current
h h i h f
h = height of conductor,
d
d = distance of stroke from conductor
06/12/2011
Internal Overvoltages
busbar short circuit
asynchronous network
disruption of capacitive current
06/12/2011
line fault
disruption of small inductive current
voltage applied to no load line
voltage applied to no‐load line
Power System Overview (HV aspect)
Insulation Over‐voltages
Electric insulation is a vital part of an
electrical power system, a careful
analysis of the line insulation to ensure
an adequate line design is needed
(
(Stewart et al, 1992).
l
)
Power System Overview (HV aspect)
* Continuous Power Frequency Voltages
The insulation has to withstand normal
Th i
l i h i h
d
l
operating voltages. The voltage may
fluctuates caused changing the load. The
normal range of fluctuation is around
+10%.
Power System Overview (HV aspect)
The voltage Vmax is used for the selection of number of insulators for line
application.
Typical number of
string glass insulator
Power System Overview (HV aspect)
• Basic Switching Impulse Insulation Level
(BSL)
The BSL
e BS is the electrical strength of insulation
s t e e ect ca st e gt o su at o
expressed in terms of the crest value of a
sta da d s tc g pu se. e stat st ca
standard switching impulse. The statistical
BSL, insulation exhibits a 90% probability of
withstands a 10% probability of failure. In IEEE
%p
y
Std 1313.1‐1996, the BSL is called the switching
impulse withstand voltage.
p
g
Power System Overview (HV aspect)
B i Li h i I
l
• Basic Lightning Impulse
(
)
Insulation Level (BIL)
The BIL or basic lightning impulse
insulation level is the electrical
strength of insulation expressed in
terms of the crest value of the
standard lightning impulse.
Power System Overview (HV aspect)
I
Impulse Insulation Strength
l I
l i S
h
Insulation strength is expressed in terms of
conventional or statistical BILs and BSLs.
For every application of an impulse having the
standard waveshape and whose crest is equal
to the BIL or BSL the probability of a
to the BIL or BSL, the probability of a
flashover or failure is 10%.
The mean of this distribution or characteristic
is defined as the critical flashover voltage or
critical flash over (CFO)
critical flash over (CFO).
Impulse Insulation Strength
Power System Overview (HV aspect)
For the transmission line insulation strength is
Power System Overview (HV aspect)
usually statistically described by a CFO voltage at
which the insulation exhibits a 50% probability of
flashover and by a standard deviation
fl h
d b t d d d i ti σ which is
hi h i
approximately 5% of the CFO (IEEE Std. 62.22, 1997)
Power System Overview (HV aspect)
• Switching Impulse Strength of Tower
p
Conversion three to six‐phase transmission lines will
effect on the existing tower insulation i.e. striking
distance (clearance) and the insulator string length
(number of insulator). The statistical withstand
voltage for line insulation V3 is defined as:
Power System Overview (HV aspect)
Clearance area is depending on horizontal
and vertical distance between conductor and
tower.
Horizontal and vertical distance is 4.42
meter and 1.78 meter. Relationship between
the CFO and the strike distance can be
approximated by
pp
y :
Power System Overview (HV aspect)
S
kg
h
W
is the flash distance (meter)
is gap factor. For a lattice steel
t
tower,
kg is about 1.2
i b t
(IEEE Std 1313.2‐1999),
is conductor height, and
is tower width (horizontal distance
DH)
Power System Overview (HV aspect)
Minimum clearance based on lightning impulse
In the clearances calculation based on lightning impulse (LI),
clearances are calculated by dividing the highest equivalent
crest voltage for the 1.2/50 μs impulse wave shape. Clearance
phase‐to‐ground can be calculated by using: