low voltage insulation coordination
TRANSCRIPT
ENGR. MARITES R. PANGILINAN, P.E.E.
WHAT IS LOW VOLTAGE INSULATION COORDINATION
AND WHY IT IS IMPORTANT
WHERE DO SURGES COME FROM
HOW DO SPDs WORK/TYPE OF SPDs
SPD SPECIFICATIONS
SPD COORDINATION /CASCADING
COMPUTATIONS
WHAT IS LOW VOLTAGE INSULATION COORDINATION AND WHY
IT IS IMPORTANT
What is Low Voltage Insulation Coordination?
Insulation coordination aims at reducing the likelihood of
equipment dielectric failure brought about by voltage surges –
popularly known problem called overvoltage, where equipment or
a circuit is exposed to more voltage than it could handle.
It consists of matching the various surge levels that may appear on an
electrical installation with the surge withstand of the industrial or domestic
equipment within the system.
Why is Low Voltage Insulation Coordination Important?
This will ensure
safety of people,
protection of equipment,
and, to a certain extent continuity of supply.
To achieve this purpose, a surge protective device is added to an electrical
system to aid in managing these voltage surges.
ANSI/UL 1449 Third Edition ANSI/IEEE C62.41.1 (2002) IEC 61643-1
Type 1: 12,5-33kA
per Pole
Type 2: 8-65kA per Pole,
Up to 160kA in China
10-250kA Mode
20-500kA Phase
61643 -11 IEC “Low-
voltage surge protective
devices – Part 1: Surge
protective devices
connected to low-voltage
power systems –
Requirements and tests.”
1449 3rd ANSI/UL :
Standard for transient
Voltage
IEEE C62.41.1 (2002): Guide
On The Surge Environment
In Low-Voltage (1000V And
Less) AC Power Circuits
World Standards for Surge Protective Device
ccc
WHERE DO SURGES COME FROM
WAVEFORMS ARE USED TO TEST
SURGE PROTECTIVE DEVICES
Identifying the characteristic of the transient
voltage surges will lead to the correct
application of the SPD
WHERE DO SURGES COME FROM
Two Basic Types of transient Voltage Surges ( IEEE C62.41 Standard):
Lightning Induced Transients
(Combination Wave)
Switching - Example : Switching of breaker
(Ring wave)
The second waveform, called a “ring wave”.
It is important in testing SPD’s higher-
frequency response to transients created
within a facility by interrupted load currents.
First, a “combination-wave” transient.
A combination wave is associated with
lightning-induced transients on utility
power lines.
Closed Circuit Opening of Circuit
WHERE DO SURGES COME FROM
Combination Wave
The combination-wave transients that could be
expected from lightning were characterized,
One waveform shown comprises the test
CURRENT, and is defined by an 8 microsecond
(written 8μs) rise time, with a 20μs trailoff. At that
point, the wave has diminished to 50% of its peak
value.
The accompanying VOLTAGE waveform for
lightning has a 1.2μs rise time with a 50μs trail-off.
The test parameter just described is called a
combination wave because the test source must
provide both the current and voltage waveforms
simultaneously.
Ring Wave
A ring wave is an oscillatory surge with relatively
high voltage levels at relatively high frequency, but
with limited energy content.
As shown , the ring wave is characterized as having
a fast rise time of only 0.5μs along with a 10μs period,
which yields a natural frequency of 100 kHz.
Ring waves are associated with:
o fuses opening,
o power factor/capacitor switching action,
o load switching of motors, pumps, compressors,
other electrical loads.
The IEC Class I test for SPDs According to IEC 61643-1 (2002) [B10],
the “test impulse current” of the Class I test
is defined by its peak value and charge
transfer.
A further stipulation is that the specified
peak current and charge transfer be
reached within 10 µs. Because these
stresses are substantial, several levels of
peak current values are tabulated in that
IEC standard, allowing a case-by-case
decision on selecting the appropriate level.
The standard also states that a typical
waveshape that can achieve these
parameters is that of a “unipolar impulse
current.” A proposed additional note states
that one of the possible waveshapes
meeting these parameters may be the
10/350 μs waveshape defined in the IEC
documents dealing with lightning
protection. DIRECT HIT
Three Important Waveforms
1.Combination wave 8/20µs , 1.2/50µs
2.Ring wave 0.5 /10µs
3. IEC 10/350µs
IMPULSE WITHSTAND CATEGORY (IEC) Impulse
withstand
category
Example of equipment in category Required impulse
withstand voltage
I
(low impulse
voltage)
Sensitive electronic equipment connected to the fixed installation 1.5KV
II
(normal impulse
voltage)
Domestic appliances and portable tools connected to fixed installations 2.5kV
III
(high impulse
voltage)
Equipment intended to be installed in a part of the fixed installation where
a high degree of availability of overvoltages is expected, such as
distribution boards, circuit breakers and wiring systems
4.0KV
IV
(very high impulse
voltage)
Equipment intended to be installed at or near the intake to the
installation, such as the energy meter
6.0KV
Required minimum
withstand voltage for equipment where installation Rated voltage is 230V
Category C environments are located on the
LINE side of the service disconnect.
• Outside and service entrance
• Service drop from pole to building
• Run between meter and panel
• Overhead line to detached building
• Underground line to well pump
Category B environments are immediately adjacent
on the LOAD side of the service disconnect breaker.
Category B environments are characterized as
having short branch circuits and feeder lines.
• Distribution panel devices
• Bus and feeder industrial plants
• Heavy appliance outlets with “short” connections to
service entrance
• Lighting systems in large buildings
Category A : Outlets and Long Branch Circuits
--All outlets at more that 10 m (30 ft.) from Category B.
--All outlets at more than 20 m (60 ft.) from Category C.
IEEE 62.41 LOCATION CATEGORY
Notice that Category C environments are subjected only to
combination wave transients,
Category B environments are tested using both ring waves and
combination waves.
Category A environments are tested with ring
waves only.
Comparison between IEC and UL Surge Protective Devices
Protection IEC Use linked to /based on risk
assessment
UL 3rd
edition
Use linked to /based on point
of installation
Line side Type1
Used to protect against the
effects caused by direct or close-
up strikes
Type1
Used after service transformer
but before the first circuit
breaker
Line /Load side Type2
Used to protect against the
effects caused by remote strikes,
inductive or capacitive coupling,
and switching surge voltages
Type2
Permanently connected SPDs
after the circuit breaker
(most of products)
Load side Type 3 Used to protect
particularly sensitive termination Type3 Cord Connected, Direct Plug-in
Component - Type4 Used as discrete components
COMPARISON OF DIFFERENT STANDARDS
ANSI/IEEE62.41 Category C Outside, service
entrance equipment
10KV or more
Category B Service equipment, Major
feeders, and short branch circuits
6KV
Category A Long branch circuits and
receptacles
4 KV
Classification of SPD
(UL 1449 3rd Edition)
SPD Type 1
In=10kA, 20kA
SPD Type 2
In=3kA, 5kA, 10kA, 20kA
SPD Type 3
In= 3kA
wave Combination wave (8 x 20 μs ) &
(1.2 x 50 μs )
Combination wave / Ring
wave
Ring wave
IEC 61643 TEST CLASS Class I (10 x 350 μs)
Class II (8 x 20 μs )
Class III (0.5./10μs)
Overvoltage Category Category IV Category III Category II Category I
Overvoltage withstand 6KV 4KV 2.5KV 1.5KV
Classification of SPD (IEC) SPD Type 1
Impulse discharge current (Iimp):
maximal discharge current for
impulse wave 10/350S, which SPD
can withstand at least 1 time.
SPD Type 2
Maximum discharge
current (Imax): maximal
discharge current for
impulse wave 8/20S, which
SPD can withstand at least 1
time.
SPD Type 3
Open circuit
voltage (Uoc):
open circuit voltage
of the combination
wave generator at
the point of
connection of the
device under test
HOW DOES SPD WORK/ TYPES OF SPDs
HOW DOES SPD WORKS?
• Connected in parallel to the
incoming SPD has big
impedance
•When the overvoltage
comes, SPD conducts and
drives the surge current to
the earth
For efficient protection of
installation and
equipment use SPD!
TECHNOLOGIES USED IN SPDs
Spark Gap
without trigger
Triggered
Spark Gap
Type1
Gas discharge
tube
Type1 or 2
MOV
Type1 / 2 /
3 Type1
Fast Response Discharge Capability
Zener
diode
Type3
₱
₱ ₱ ₱
Due to high MOV current withstand capacity technology can be used in Type1 SPD
Flashover happens in Spark gap used technology -> limited number of applications of
use
SPD SPECIFICATIONS
available in 30kA, 60kA, 100kA and
150kA per phase peak surge capacity
with 200kAIC short circuit current
rating.
IEC STANDARD COMPLIANT SPD UL/ANSI STANDARD COMPLIANT SPD
SPD SPECIFICATIONS
Surge Protective Device Specifications
1. DEVICE CIRCUIT DESCRIPTION:
This defines the components within the Surge Protective Device
that actually suppress transient voltage surges. Examples include
• Metal Oxide Varistors (MOV’s),
• gas-tube design.
2. MAXIMUM SURGE CURRENT: (IMAX) This is the maximum discharge current for impulse wave 8/20S, which SPD can
withstand at least 1 time.
3. Nominal discharge current : (In)
Crest Value of Surge current of 8/20 μs waveform associated with Type 2 spd’s
During the test SPD shall withstand this value ~20 times.
4. Impulse discharge current: (Iimp)
Impulse current of 10/350S waveform associated with Type 1 spd’s and can
withstand at least 1 time
5. Maximum continuous operating voltage: (Uc)
Maximum r.m.s. voltage, which may be continuously applied to the SPD's mode of
protection without it conducting – the higher, the better
6.Voltage protection level : (Up)
Maximum voltage to be expected at the SPD terminals due to an impulse stress In
and or Iimp – the lower the better (<1,5kV)
7. PROTECTION MODES:
three modes of surge protection should be provided: line to neutral, ine to ground,
and neutral to ground. Of course, clamping data should be furnished for each
mode. In the case of panel-mounted units, especially those installed on delta
systems or at service entrances where ground and neutral are bonded, the devices
may provide adequate protection even though every possible suppression mode is
not applicable.
8. SAFETY AGENCY APPROVALS:
Certification organizations like UL, IEEE, IEC, CSA, and NOM, should be
specified along with their appropriate test standards, product categories, and
reference file numbers.
The peak value of
an 8/20 μs (Type
1 or) remains
functional after 15
surges
UL 1449 TYPE 1
UL 1449 TYPE 2
Type 2 devices
can be tested
using a 3, 5, 10 or
20 kA.
SPD COORDINATION/ CASCADING
Cascading is the term used to describe the method of combining several levels of surge
protective devices into the one installation.
This takes advantage of the best features of each device to improve the protection level for
the equipment. Often manufacturer recommends using a high surge current capacity device to
divert the bulk of the transient over-voltage at the origin of the installation.
In the case of a Class 1 & 2 device this would be either the spark gap arrester or a high
current capacity MOV. Should finer protection be required, the next step is to install a Class 3
device near the terminal equipment.
Cascading increases the current diverting capacity of the SPD system whilst maintaining a
low voltage (Up) to ensure the best protection for valuable equipment.
Selecting SPD of the same manufacturer or make will ensure correct coordination between
devices
CASCADING
FACILITY-WIDE PROTECTION SOLUTIONS – IEEE EMERALD BOOK
RECOMMENDS A CASCADE (OR 2-STAGE ) APPROACH
PROTECTION DISTRIBUTED LEVELS
Type 1: when the
building is fitted with a
lightning protection
system and located at
the incoming end of the
installation, it absorbs a
very large quantity of
energy;
Type 2: absorbs residual
overvoltages;
Type 3: provides "fine"
protection if necessary
for the most sensitive
equipmentlocated very
close to the loads.
MDB SDB FDB
Type1 Type2 Type3
90% 9% 1%
•Three phase TT, TNS, IT (with neutral) systems: 100kA /2 = 12.5kA/wire
4 wires •Three phase TNC, IT (without neutral) systems: 100kA/2 =18.7 kA/wire
3 wires •Single phase TT, TNC system: 100kA =50kA/wire
2wires
100kA
200kA
100kA
50%
50%
IEC 62305-1.
Maximum lightning
current parameter for
LPL 1 is fixed at 200kA
COMPUTATIONS
COMPUTATIONS
ΔV = L di/dt
COMPUTATION
ΔV = L di/dt
High-energy transients occur whenever a current is interrupted. The higher the current, the
greater the amplitude of the transient. The following formula can be used to determine the
transient voltage level (represented by ΔV in the equation):
“L “ - is the circuit’s total inductance.
“di” - represents the rate of change in the current.
“dt” - is the interval of time over which the current changed.
Note that since dt is the denominator in this fraction, the faster the transient (meaning the smaller
the number represented by dt), the larger the transient amplitude (represented by V) becomes.
Example - Computation for Determining voltage protection level (Uprotec) at at
the Installation point of SPD
Step 1 : Connections of a SPD to the loads should be as short as possible in order to reduce the value of the
voltage protection level (installed Uprotec) on the terminals of the protected equipment. The total length of SPD
connections to the network and the earth terminal block should not exceed 50cm.
Step 2: The voltage Uprot is the sum of protection level of the SPD Up and inductive voltage drop appearing on the
conductors connecting SPD and protective device :
Uprot = Up + Uind = Up + Ldi/dt ≤ Ui
The voltage sensed by the device Uprot has to be less than dielectric strength:
Uprot ≤ Uw
The protection level of the SPD (kV) is determined as:
Up = Uprot - Uind = Uprot - Ldi/dt ≤ Ui
Step 3: To calculate using example above:
a) Assuming that the total length of the conductor is L = L1 + L2+L3 = <50 cm
b) The load to be protected is a sensitive load
For the conductor
A distributed inductance of a typical conductor is approximately 1μH/m, which at the current rate of rise of 1
kA/μs contributed approximately with 1kV per meter length.
Hence applying Lenz’s law to this connection: ΔU= L di/dt
ΔU - the transient voltage level
L - is the circuit’s total inductance.
di - represents the rate of change in the current
dt - is the interval of time over which the current changed.
The normalized 8/20 μs current wave, with a current amplitude of 8kA, accordingly creates voltage rise of
1000V/m of cable.
ΔU=L di/dt = (0.5m) 1 x 10-6 x 8 x103
8 x 10-6
= 500V
For the voltage protection level
The required protection level of SPD at termination board is determined as overvoltage category II which is
2.5 KV.
Up as per manufacturer brochure is 1.5kV. Hence
Uprotec = Up + U1 + U2
= 1.5kV + 500V
=2kV
Uprot ≤ Ui
Hence 2kv < 2.5kv The device is protected by the SPD
Example 2 - Coordination of surge protective device
The fine-protection device P2 is installed in parallel with the incoming protection device P1.
If the distance L is too small, at the incoming overvoltage, P2 with a protection
level of U2 = 1500 V will operate before P1 with a level of U1 = 2000 V.
P2 will not withstand an excessively high current. The protection devices must therefore be coordinated to ensure that
P1 activates before P2.
To do this, we shall experiment with the length L of the cable, i.e. the value of the self-inductance between the two
protection devices. This self-inductance will block the current flow to P2 and cause a certain delay, which will force P1
to operate before P2.
A metre of cable gives a self- inductance of approximately 1μH.
P1 P2
The rule ΔU= Ldi /dt causes a voltage drop of approximately 1000 V/m/kA, 8/20 μs wave.
For L = 10 m, we get UL1 = UL2 ≈ 1000 V.
ΔU=L di/dt = (10m) 1 x 10-6 x 8 x103
8 x 10-6
= 1000V
To ensure that P2 operates with a level of protection of 1500 V requires
U1 = UL1 + UL2 + U2 = 1000 + 1000 + 1500 V = 3500 V.
Consequently, P1 operates before 2000 V and therefore protects P2.
THANK YOU !!!