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 !!!