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Telecommunications Industry Association
TR41.9-06-02-008
Document Cover Sheet
Project Number
Document Title
Type A Surge Generator Tolerance
Source
Bourns Ltd.
Contact
Name: Mick Maytum
Complete Address: Bourns Ltd.,
Manton Lane, Bedford, MK41 7BJ, UK
Distribution
TR-41.9
Intended Purpose
of Document
(Select one)
X
Phone: +44 7879 697652
Fax: +44 8700 521810
Email: [email protected]
For Incorporation Into TIA Publication
For Information
Other (describe) -
The document to which this cover statement is attached is submitted to a Formulating Group or
sub-element thereof of the Telecommunications Industry Association (TIA) in accordance with the
provisions of Sections 6.4.1–6.4.6 inclusive of the TIA Engineering Manual dated March 2005, all of
which provisions are hereby incorporated by reference.
Abstract
This contribution analyses CR and L/R rise-controlled capacitive discharge generator designs. The
waveshape tolerance is controlled by generator component tolerances and the ratio (a) of external to
internal discharge currents. For CR rise-controlled capacitive discharge generator designs the output
resistor split () has a major influence on the rise time tolerance. The proposed tolerance values are:
10/160
200 A –0 +30 A, 10 µs +0 –5 µs/ 160 µs -0 +50 µs
1500 V –0 +150 V, 10 µs +0 –3 µs/ 160 µs -0 +100 µs
10/560
100 A –0 +15 A, 10 µs +0 –5 µs/ 560 µs -0 +150 µs
800 V –0 +80 V, 10 µs +0 –3 µs/ 560 µs -0 +300 µs
v1.0 – 20050426
Telecommunications Industry Association
TR41.9-06-02-008
Type A Surge Generator Tolerance – A Mathematical Analysis
1
Introduction
Much of the content here was published either as Applications I nformation in Bourns TISP® data
sheets or submissions to NIPP-NEP (T1E1.7 that was). This contribution analyses CR and L/R
rise-controlled capacitive discharge generator designs. The waveshape tolerance is controlled by
generator component tolerances and the ratio () of external to internal discharge currents.
Those short of time should skip to clauses 9, Summary Table, and 10, Comments and Proposals.
2
Generator Categories
There are three categories of surge generator having defined open -circuit and short-circuit
waveshapes: single waveshape, combination waveshape and circuit defined. Single waveshape
generators have the same nominal waveshape for the open -circuit voltage and short-circuit
current (e.g. <10/>160 open-circuit voltage and short-circuit current). Combination generators
have two waveshapes, one for the open-circuit voltage and the other for short-circuit current
(e.g. 1.2/50 open-circuit voltage and 8/20 short-circuit current) Circuit specified generators
usually equate to a combination generator (e.g. the Type B surge generator that gives an 9/720
open-circuit voltage and a 5/320 short-circuit current). If the combination or circuit -defined
generators operate into a finite resistance the waveshape produced is intermediate between the
open-circuit and short-circuit values.
3
Waveshape and Waveform Notation
Most lightning tests, used for equipment verification, specify a unidirectional waveform that has
defined peak amplitude with an exponential rise and an exponential decay. Waveshapes are
classified in terms of rise time in microseconds and a decay time in microseconds to 50% of the
peak amplitude. The notation used for the waveshape is rise time/decay time, without the
microseconds quantity and the “/” between the two values has no mathematical sign ificance. A
50A, 5/320 waveform would have a peak current value of 50 A, a rise time of 5 µs and a decay
time of 320 µs.
3.1
Waveshape Rise and Decay Definition
Current waveshape rise time is normally expressed as a line drawn through the 10 % to 90 %
rising edge points extrapolated to the 0 (virtual zero time) and 100 % levels. The current decay
time is measured from the virtual zero time until the current has decayed to 50 % of the
maximum amplitude.
Voltage waveshapes are normally expressed in one of two wa ys. As the rising edge of the
voltage often has ringing, the voltage rise time is expressed as a line drawn through the 30 % to
90 % rising edge points extrapolated to the 0 (virtual zero time) and 100 % levels.
The second way is to use the current waveshape method with a line drawn through the 10 % to
90 % rising edge points extrapolated to the 0 (virtual zero time) and 100 % levels (Telcordia GR 1089-CORE, Issue 3 Annex A). In both voltage waveshape cases, the voltage decay time is
measured from the virtual zero time until the current has decayed to 50 % of the maximum
amplitude.
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Telecommunications Industry Association
TR41.9-06-02-008
VOLTAGE WAVEFORM DEFINITION
CURRENT WAVEFORM DEFINITION
90
90
80
80
70
70
60
60
Amplitude %
100
Amplitude - %
100
50
40
30
20
10
50
40
30
20
10
0
VIRTUAL FRONT
TIME
VIRTUAL
ORIGIN
0
VIRTUAL TIME
TO HALF VALUE
VIRTUAL FRONT
TIME
VIRTUAL
ORIGIN
VIRTUAL TIME
TO HALF VALUE
IEC 60099-1 (1994)
Designation of impulse shape: A combination of two numbers, the first representing the virtual front time (T1) and the second the
virtual time to half value of the tail (T2). It is written as T1/T2, both in microseconds, the sign "/" having no mathematical meaning.
Figure 1 Current Waveshape and 30% to 90 % Voltage Waveshape
3.2
Waveshape Rise and Decay times from Surge Generator Circuit Time Constants
3.2.1
Rise time
When a single CR or L/R time constant, , controls the waveshape rise time, the 10 % to 90 %
method gives a rise time of 2.75. The 30 % to 90 % method gives a rise time of 3.24 . Thus the
two methods of measurement do not give the same value for the same rise waveshape, as the
mathematical treatment assumes a linear and not an exponential rise.
3.2.2
Decay time
When a single CR constant, , controls the waveshape decay time, the decay time is given by
0.697.
4
Generator Components
People who build their own generators have the problem of fin ding reliable, high-voltage, highcurrent components. A 2 kV, 100 µF capacitor is hard to find and often the most economic
capacitance tolerance will be ±10 %. Small value capacitors, used for rise time control, may be
obtained with ±5 % values. Resistors can normally be obtained in ±5 % values. These tolerance
values will be used for the circuit calculations.
5
Type A Surge Waveforms
5.1
Metallic, >800 V, 100 A, <10/>560 Waveform
Applied between any pair of connections on which lightning surges may occur.
5.1.1
Open-circuit Voltage
The surge shall have an open-circuit voltage waveform with minimum peak amplitude of 800 V, a
maximum 30 % to 90 % method rise (front) time of 10 µs and a minimum decay time of 560 µs.
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Telecommunications Industry Association
5.1.2
TR41.9-06-02-008
Short-circuit Current
The surge shall have an short-circuit current waveform with minimum peak amplitude of 100 A, a
maximum 10 % to 90 % method rise (front) time of 10 µs and a minimum decay time of 560 µs.
5.2
Longitudinal, >1500 V, >200 A, <10/>160 Waveform
Applied to any pair of connections on which lightning s urges may occur.
5.2.1
Open-circuit Voltage
The surge shall have an open-circuit voltage waveform with minimum peak amplitude of 1500 V,
a maximum 30 % to 90 % method rise (front) time of 10 µs and a minimum decay time of 160 µs.
5.2.2
Short-circuit Current
The surge shall have an short-circuit current waveform with minimum peak amplitude of 200 A, a
maximum 10 % to 90 % method rise (front) time of 10 µs and a minimum decay time of 160 µs.
6
Generator Circuits
There are two common types of generator circuit; CR rise time controlled and L/R rise time
controlled.
6.1
CR Rise Time Controlled Generator
Figure 2 shows a CR rise time controlled generator and the two circuit simplifications used to
calculate the decay and rise times.
VC
R2
SW
R1
C1
R3
C2
CR Rise Time Controlled Generator
VC
C1
R2
SW
R3
R1
R2
R3
C2
Decay Time Circuit
Rise Time Circuit
Figure 2. CR rise time controlled generator circuits
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Telecommunications Industry Association
TR41.9-06-02-008
The energy storage capacitance, C 1 , and the circuit shunt resistance control the waveshape
decay time. The shunt resistance is resistor R 1 for the open-circuit output condition and resistor
R 1 in parallel with the series combination of resistors R 2 and R 3 for the short-circuit output
condition.
In the open-circuit output case, capacitor C 2 and resistor R 2 control the rise time. For shortcircuit output condition, capacitor C 2 and resistor R 2 and R 3 in parallel control the rise time.
6.2
LR Rise Time Controlled Generator
Figure 2 shows a LR rise time controlled generator and the two circuit simplifications used to
calculate the decay and rise times.
VC
L
SW
R2
R1
C1
L/R Rise Time Controlled Generator
VC
C1
R2
SW
R1
L
R2
R1
Decay Time Circuit
Rise Time Circuit
Figure 3. LR rise time controlled generator circuits
The energy storage capacitance, C 1 , and the circuit shunt resistance control the waveshape
decay time. The shunt resistance is resistor R 1 for open-circuit output condition and resistor R 1 in
parallel with resistors R 2 for the short-circuit output condition.
In the open-circuit output case, inductor L and resistor R 1 control the rise time. For short-circuit
output condition, inductor L and resistor R 1 and R 2 in parallel control the rise time.
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Telecommunications Industry Association
7
TR41.9-06-02-008
Decay Time t D Calculation
The calculation will be done on the generic circuit of Figure 4.
T SC = CSxa RO/(1+a )
T OC = CSxa RO
RO
CS
a RO
CS
Short-Circuit Decay Time Circuit
a RO
Open-Circuit Decay Time Circuit
Figure 4 Open- and Short-circuit Decay time constants
R O is the resistance between the energy storage capacitor, C S , and the output. The ratio of
external to internal discharge currents is defined as . This makes the energy storage capacitor
internal shunt resistance R O .
The minimum short-circuit decay time, t DSCMIN is given by:
t DSCMIN = 0.697x0.9x0.95xC S xR O /(1+)
The maximum open-circuit decay time, t DOCMAX is given by:
t DOCMAX = 0.697x1.1x1.05xC S xR O
Hence:
t DOCMAX / t DSCMIN = 1.1x1.05x(1+)/(0.9x0.95) = 1.35(1+)
The value of  is critical to the waveshape tolerance. If  were 0.1, the open-circuit voltage
maximum tolerance would be +49 % and the short-circuit current maximum tolerance becomes
+35 %. However, for every 100 A of short-circuit current, the capacitor would have to supply
1100 A of current. Thus would dramatically increase the capacitor size and cost.
If  was set to 0.3, the open-circuit voltage maximum tolerance becomes +76 % and the shortcircuit current maximum tolerance is still +35 %.
Using a ±5 % capacitor, for an  of 0.1, would give an open-circuit voltage maximum tolerance of
+34 % and the short-circuit current maximum tolerance becomes +22 %. Similarly, for an  of
0.3, the open-circuit voltage maximum tolerance is +59 % and the short-circuit current maximum
tolerance is +22 %.
The generator component tolerance controls short-circuit current tolerance. The generator
component tolerance and the design value of  controls open-circuit voltage tolerance.
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Telecommunications Industry Association
8
8.1
TR41.9-06-02-008
Rise Time t R Calculation
L/R controlled rise
The calculation will be done on the generic circuit of Figure 5.
t RSC = (1+a )L/(a RO)
t ROC = L/(a RO)
L
L
RO
a RO
a RO
Short-Circuit Rise Time Circuit
Open-Circuit Rise Time Circuit
Figure 5 Open- and Short-circuit Rise time constants
R O is the resistance connected to the output terminal. The internal shunt resistance is R O . The
short-circuit condition will have the largest time constant and the open-circuit condition will have
the smallest time constant. However there are different multipliers used to calculate the current
and voltage rise times.
The short-circuit current rise time, t R is given by:
t RSC = 2.75x(1+)L/(R O )
For a = 0.1, t RSC = 3.03xL/(R O )
For a = 0.3, t RSC = 3.58xL/(R O )
The open-circuit rise time, t R is given by:
t ROC = 3.24xL/(R O )
An  value of 0.18 equalises the t RSC and t ROC values. Below 0.18, t RSC is the shortest rise time.
Above 0.18, t ROC is the shortest rise time.
For  < 0.18
t RSCMIN /t ROCMAX = (0.9x0.95x2.75x(1+)L/(R O )/(1.1x1.05x3.24xL/(R O ))
= (0.9x0.95/(1.1x1.05))x0.85x(1+)
For  > 0.18
t ROCMIN /t RSCMAX = (0.9x0.95x3.24xL/(R O ))/(1.1x1.05x2.75x(1+)L/(R O ))
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Telecommunications Industry Association
TR41.9-06-02-008
= (0.9x0.95/(1.1x1.05))x1.18/(1+)
8.2
CR controlled rise
The calculation will be done on the generic circuit of Figure 6.
t RSC = (1-b )CRxb RO)
bR O
t ROC = CRxb RO
(1-b )R O
bR O
CR
CR
Short-Circuit Rise Time Circuit
Open-Circuit Rise Time Circuit
Figure 6 Open- and Short-circuit Rise time constants
R O is the resistance connected to the output terminal. The rise shaping circuit splits R O into R O
and (1-)R O . The shaping capacitor, C R , is connected between common and the resistors
junction. The short-circuit condition will have the smallest time constant and the open -circuit
condition will have the largest time constant.
The short-circuit current rise time, t R is given by:
t RSC = 2.75x(1-)C R xR O
The open-circuit rise time, t R is given by:
t ROC = 3.24xC R xR O
The short-circuit condition will always have the shortest rise time. The rise time ratio is:
t RSCMIN /t ROCMAX = (0.95x0.95)(2.75x(1-)C R xR O )/((1.05x1.05)x(3.24xC R xRO ))
= ((0.95x0.95)/(1.05x1.05))x0.85x(1-)
= 0.82x0.85x(1-) = 0.7x(1-)
Table 1 shows how the resistor split ratio, , strongly controls the rise time ratio, t RSCMIN /t ROCMAX .
Table 1

0.1
0.2
0.3
t RSCMIN /
t ROCMAX
0.63
0.56
0.49
Tolerance
%
-37
-44
-51

0.4
0.5
0.6
t RSCMIN /
t ROCMAX
0.42
0.35
0.28
Page 8
Tolerance
%
-58
-65
-72

0.7
0.8
0.9
t RSCMIN /
t ROCMAX
0.21
0.14
0.07
Tolerance
%
-79
-86
-93
Telecommunications Industry Association
TR41.9-06-02-008
The Type B surge generator uses a  ratio of 0.375 for metallic testing and 0.545 for longitudinal
testing.
9
Summary Table
Table 2 uses the equations of clauses 7 and 8 to calculate the tolerance percentage of the wave
shape. As an application example, consider the <10/>160 waveshape and the tolerance values
shown in the blue text row (L/R rise controlled generator with a ±10 % capacitor tolerance and an
 of 0.3).
Open-circuit voltage waveshape = 10 µs 0 % –33 %/160 µs 0 % +76 %
= 10 µs +0 –3.3 µs/ 160 µs -0 +120 µs
Short-circuit current waveshape = 10 µs 0 % –26 %/160 µs 0 % +35 %
= 10 µs +0 –2.6 µs/ 160 µs -0 +56 µs
Table 2
Generator
Type
Tolerance
of C S ,
Energy
Storage
Capacitor
%
±10
L/R
rise
controlled
±5
CR
rise
controlled
t RSC is for
 = 0.5. For
other 
values see
Table 1
±10
±5

Ratio of
External to
Internal
Current
Open-Circuit Voltage
Short-Circuit Current
t ROC
%
t DOC
%
t RSC
%
t DSC
%
0.1
-26
49
-31
35
0.2
-27
62
-26
35
0.3
-33
76
-26
35
0.1
-18
34
-23
22
0.2
-20
47
-18
22
0.3
-26
59
-18
22
0.1
-18
49
-65
35
0.2
-18
62
-65
35
0.3
-18
76
-65
35
0.1
-18
34
-65
22
0.2
-18
47
-65
22
0.3
-18
59
-65
22
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Telecommunications Industry Association
TR41.9-06-02-008
10 Comments and Proposals
10.1
Amplitude
The use of ±5 % resistors components to connect to the output terminal gives a 10 % possible
amplitude variation in current. Add to that a voltage setting accuracy of 5 % and the output
current variation is 15 %. The open-circuit voltage should be capable of be set within a 10 %
range.
10.2
Decay Time
If only 5 % components are considered in Table 2, the (rounded) decay time tolerance becomes
+30 % for current and +60 % for voltage.
10.3
Rise Time
If only 5 % components are considered in Table 2, the (rounded) rise time tolerance for L/R rise
time controlled generators becomes -30 % for current and -30 % for voltage. CR rise time
controlled generators show -70 % for current and -20 % for voltage at a  value of 0.5. Changing
the  to 0.3 would give -50 % for current and -20 % for voltage.
10.4
Proposal
The decay time tolerance is about +30 % for current and +60 % for voltage.
The rise time tolerance is about -50 % for current and -30 % for voltage.
The amplitude tolerance is +15 % for current and +10 % for voltage.
10.4.1
<10/>160 Proposal
200 A –0 +30 A, 10 µs +0 –5 µs/ 160 µs -0 +50 µs
1500 V –0 +150 V, 10 µs +0 –3 µs/ 160 µs -0 +100 µs
10.4.2
<10/>560 Proposal
100 A –0 +15 A, 10 µs +0 –5 µs/ 560 µs -0 +150 µs
800 V –0 +80 V, 10 µs +0 –3 µs/ 560 µs -0 +300 µs
Page 10