Analysis of Requirements for

Shipboard Voltage Spike

Suppressors

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Electronics and Electrical Engineering

Electrosystems Division

Washington, DC 20234

March 1 S84

Prepared for: Department of the Navy

Sea Systems Command

ngton, DC 20362

130

,1156

84-2844R

NBSIR 84-2844

ANALYSIS OF REQUIREMENTS FOR

SHIPBOARD VOLTAGE SPIKE

SUPPRESSORS

Owen B. Laug and David L. Hillhouse

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Electronics and Electrical Engineering

Electrosystems Division

Washington, DC 20234

March 1 984

Prepared for: Department of the Navy

Naval Sea Systems Command

Washington, DC 20362

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

TABLE OF CONTENTS

Page

LIST OF FIGURES iv

LIST OF TABLES v

Abstract . 1

1. INTRODUCTION 1

2. DEFINITION OF TERMS 2

3. SUPPRESSION PRINCIPLES AND DEVICES 2

4. SUPPRESSOR SELECTION CONSIDERATION 6

4.1 Steady-State Voltage Rating 6

4.2 Energy 8

4.3 Peak Transient Current. ..... 13

5. RELATING THE AVAILABLE- DATA TO THE REQUIREMENTS 14

5 . 1 Sag/Surge and Interrupt Data Analysis on Shipboard Power Lines

by Sachs/Freeman Associates, Inc., dated 12 June 1981 14

5 . 2 Energy Analysis of Transient Pulses on Shipboard Electric

Power Systems by Messrs. L. L. Grigsby and S. S. Kelkar of VPI,

dated July J.980 14

5.3 Investigation of Shore-based Powerline Transient s, by Naval

Electronic Systems Engineering Activity, dated 30 September 1981. . 14

5 . 4 Evaluation of Commercial Suppression Components and Comm e rcial

Suppressors , Preliminary Data, 5 volumes, by Naval Electronic

Activity, dated 10 March 1982 14

'

5.5 Ide ntification of Shipboard Powerline Transients , by Naval

Electronic Systems Engineering Activity, dated 1 March 1980 .... 15

5.6 USS ARKANSAS (C G N-41) ELECTRICAL POWER MONITOR ING, 2 volumes,

by Raytheon Service Company, dated September 1982 18

5.7 EPIC Measurement Program 19

5.8 Summary of Available Data 27

5.9 Measuring Power Line Disturbances 27

5.10 Different i al /Common Mode Measurements 30

5.11 Energy Measurements 30

6. CONCLUSIONS 32

7.

RECOMMENDATIONS 33

LIST OF FIGURES

Page

Figure 1. Comparison of the log-log voltage versus current (V-I) curves of MOVs and avalanche diodes 5

Figure 2. Attenuation of the transient source voltage V s by the

variable impedance Zc of a clamping-type suppressor 7

Figure 3. Steady-state power voltage wave (60 Hz or 400 Hz) with

superimposed transients, showing the effect of clamping-type

suppressors on such transients when the clamping level is

set correctly .

- 9

Figure 4. Steady-state power voltage wave (60 Hz or 400 Hz) with

superimposed transients, showing the effect of clamping-type

suppressors on such transients when the clamping level is

set too low 10

Figure 5. Circuit for calculating the current and energy dissipated in

a clamping suppressor 11

Figure 6. Graphical representation of the voltages in the clamping

suppressor circuit of Figure 5 12

Figure 7. Decaying exponential with initial value of 1200 V and large

initial spike of 2192 V. Duration to 50%, about 300 ms from

152 ms point. (Reproduced from St. Inigoes data) 16

Figure 8. Large 170 kHz oscillation riding on an apparent 7 kHz

"carrier." Duration unknown (goes off screen at about

175 ms). (Reproduced from St. Inigoes data) 17

Figure 9. Power system impedance and phase angle plotted as a function of frequency from the data of table 1. 21

Figure 10. Power system impedance and phase angle plotted as a function

of frequency from the data of table 2 22

Figure 11. Recording of a typical disturbance on the 440 V., 400 Hz

power system of the USS Kitty Hawk (CV-63), July 1983

(from the EPIC program, data furnished by NAVSSES) 26

Figure 12. The same disturbance may either decrease (a) or increase

(b) the instantaneous amplitude of the sine wave (sometimes

distinguished as a "notch" or a "spike," respectively).

The output response (c) of a high-pass filter to the

waveforms in (a) or (b) is the same 29

Figure 13 ^ Seven-day histogram of transient voltage versus number of

transients in 115- and 440-V systems 31

i v

LIST OF TABLES

Table 1

Table 2

Table 3

Page

Broadband impedance data from the CV-61 on phase A of the

120 V, 400 Hz power at the avionics shop location No. 667

with the AN/ASM 403 computer energized 23

Broadband impedance data from the CV-63 on the 120 V,

400 Hz system located in an aircraft electrical service station . . 24

Summary of spike suppressor data requirements and availability. . . 28

v

ANALYSIS OF REQUIREMENTS FOR

SHIPBOARD VOLTAGE SPIKE SUPPRESSORS

Owen B. Laug and David L. Hillhouse

Abstract

This report describes progress so far in a voltage spike

suppressor program, undertaken for the Naval Sea Systems (NAVSEA)

Command, with the objective of developing a sound technical basis on which a spike suppressor specification for shipboard equipment could

be written. The project contract stated that sufficient field data

for such a specification already existed, and needed only to be

correlated and analyzed. NBS investigation revealed that existing

data were far from adequate for this purpose. It was then recommended

that further testing already planned by the Navy be used to collect

the required data. Other as yet unreported data were also analyzed.

Neither effort succeeded in producing enough meaningful information

for carrying out the assigned task.

This report includes documentation of the analysis of all the

pertinent data above; a general discussion of the principles involved

and of the applicable suppression devices; a discussion of suppressor

selection considerations and the key parameters for this; and a review

and analysis of the reports provided by the Navy. Finally, the report

lists key parameters which must be known, and shows why the available

data cannot support the generation of a suppressor specification.

Key words: shipboard spikes; spikes; spike suppressors; suppressor

specification; voltage clamping; voltage spikes,

1. INTRODUCTION

In August 1982, a program to develop recommendations for voltage spike

suppressor specifications for Navy ships was undertaken by the National Bureau

of Standards (NBS). This program was funded by the Naval Sea Systems Command

(NAVSEA). The objective of the program was to provide a sound technical basis

for shipboard application of spike suppressors. Such specifications would

permit the Navy and the manuf acturers of suppression devices to determine

whether or not such devices met the requirements of the Navy.

The contract for this project stated that suppressor recommendations could

be based upon existing field data, which needed only to be correlated and

analyzed. In the first phase of the project, NBS investigation revealed that

the existing data were far from adequate for the purposes of this program. NBS

then recommended that further Navy testing, already planned in the EPIC program,

be utilized to collect the required data. In addition, other data previously

not made available to NBS were analyzed in an attempt to obtain sufficient

meaningful information. Neither the EPIC program nor this additional analysis

produced useful results.

Certain commercial instruments are identified in this report to provide the

sponsor with the analysis requested in the work statement. NBS has merely

reproduced information in reports supplied by the sponsor and has conducted no evaluation on the instruments identified. Identification does not imply

recommendation or endorsement by NBS for any purpose, nor does it imply that any

identified instruments are the best available for a given purpose.

1
This report documents the analysis of all the pertinent data made available

to NBS. A brief general discussion of the principles of transient suppression

is also provided, with emphasis on the types of suppressors which appear to be

most suitable for shipboard applications. Selection considerations are given,

outlining the key parameters which must be known with some assurance in order to

apply suppression devices. Shipboard transient data provided in five Navy

reports are reviewed and analyzed, with emphasis on the quality of the data

relative to their use in the development of transient suppressor

specifications. The report explains which key parameters must be known in order

to generate a spike suppressor scheme. It also shows why the available data

base cannot support the generation of performance specifications.

2. DEFINITION OF TERMS

The DOD-STD-1399 (NAVY) standard entitled Interface Standards for Shipboard

Systems (section 30 0) defines some of the terms pertinent to this subject

somewhat diff erent ly than they are commonly defined in industry standards.

Specifically, DOD-STD-1399 defines a Voltage Spike as a voltage change of very

short (less than one millisecond) duration compared with one cycle of the power

system voltage. For definition and test purposes the standard 2500 V 1.2 x 50 ysec lightning impulse is used. But in reality, spike forms can range

from single pulses with extremely short rise time and exponential decay to

oscillating disturbances persisting for several oscillations within an exponentially decaying envelope.

On the other hand, a Voltage Transient (excluding spikes) is defined as a sudden change in voltage which exceeds the user voltage tolerance limits and

returns to and remains within these limits within a specified recovery time

after the initiation of the disturbance. In other words, transients are considered to be relatively long-term voltage excursions outside the nominal

steady-state voltage level, which may persist from a few to many cycles of the

power frequency without significant alteration of the waveform. Often the term

"sag-surge" is used as well and has the same general meaning as voltage

transient.

Thus, the Navy defines voltage spikes as "short-time" transients that .are less than one millisecond in' duration. Industry's standards related to

protective devices or arrestors do not make a time distinction in power system

disturbances. The common term used by industry standards is Surge Voltage . The

devices used to limit surges are commonly referred to in industry as Surge

Protectiv e De vices . Transient over-voltage is a term commonly used

interchangeably with Surge Voltage by authors in the field and manuf acturers of

protective devices. This report will generally adhere to the use of the term

voltage spike as defined in DOD-STD-1399, although the word transient may at times be used to refer to a general disturbance of the power waveform without

any reference to its duration.

3. SUPPRESSION PRINCIPLES AND DEVICES

The failure and operational upset of electronic equipment caused by spikes

and transients on shipboard power systems has been recognized as a significant

obstacle to maintaining reliable equipment operation and to the development of new systems. Of particular concern in the surveys taken aboard ships has been

the observation of over-voltage spikes and transients. Equipment designers have

2
recognized the problem and have taken steps to deal with it in their own systems. Another and perhaps more efficient means of dealing with this problem

is through the concept of "primary" transient protection on a shipboard power

distribution system. Such protection could be implemented by specifying

appropriate suppression devices strategically located throughout a given power

distribution system to reduce high amplitude spikes to harmless levels. Not

only would such a scheme make it unnecessary for every equipment to protect

itself but it would allow predictable voltage levels to be maintained. Residual

noise or interference on the power line which causes problems to a particular

piece of equipment could then be dealt with separately to the degree required.

The brief technical discussion of suppression principles and devices which

follows is based on the concept of applying suppression devices in a "primary"

protection scheme.

Transient suppressors can be divided into two general categories: those

that attenuate transients, and those that divert transients away from sensitive

loads.

Attenuating a transient is usually accomplished with some type of filter

inserted in the circuit. The filter allows the desirable signal to pass while

attenuating the undesirable (high frequency) energy contained in a transient.

The simplest form of filter is a capacitor placed across the line. The

impedance of the capacitor forms a voltage divider with the source impedance,

resulting in attenuation of the transient at high frequencies. While such

simple filters can offer effective transient protection, they may produce

undesirable side effects such as unwanted resonances, high in-rush currents

during switching, or excessive reactive loading of the power system. These

undesirable effects can be reduced by adding a resistor in series with the

capacitor, thus forming the popular RC-type suppression network; but the added

resistance tends to make the network a less effective suppressor.

More complex filters comprised of resistors, capacitors, and inductors are often located at the equipment/power line interface, serving the dual function

of transient and interference protection. Although such filters can be quite

effective, they may be unsuitable for a general primary protective scheme

because each network must be specifically designed for the circuit in which it

is to be used. For example, filters that employ series reactive elements must

be designed to pass the currents of the power system over a wide range without

excessive dissipation or compromised performance.

The second method of suppression operates by diverting all or part of the

spike away from the circuit to be protected. Diversion devices fall roughly

into two categories: (1) voltage-clamping, and (2) voltage-shorting or "crowbar.

As the jargon implies, the "crowbar"-type devices involve a switching

action, either by the breakdown of a gas between two electrodes or the firing of

a thyristor. After switching on, this device approaches a short circuit or very

low impedance, which diverts the transients away from the load. Its primary

limitation when used in power circuits is the "follow current" or "power follow"

effect. This phenomenon occurs when the current from the power circuit follows

an overvoltage spike or transient. Since the "crowbar" effectively

short-circuits the source, the current may be very large, and may produce a significant disturbance on the line. Furthermore, the device may or may not

3
clear itself at zero current. Thus, additional devices such as fuses or circuit

breakers must be provided if there is no provision for self-clearing action.

Because such a suppressor can create significant line disturbances itself, this

type is probably not suitable for shipboard application, and will not be

discussed any further.

The voltage-clamping suppressor is so named because it "clamps" the voltage

across its terminals at an approximately fixed level over a wide range of

currents 1 through them. This suppressor has a nonlinear impedance which depends

upon the voltage across its terminals. With this device, the protected circuit

is unaffected before and after the transient at any voltage level below the

clamping level. When a transient exceeds the clamping voltage level, the excess energy of the transient is dissipated in the suppressor and in the resistance of

the electrical network source impedance. There are a number of voltage-clamping

devices, but the two types most used today are avalanche junction semiconductors

and Metal -Oxide-Vari stors (MOVs).

Avalanche semiconductor diodes, often referred to as zener diodes, are very

effective at clamping and come closest to an ideal constant voltage clamp.

These diodes switch abruptly (subnanosecond times) from a non-conducting to a conducting state. Their major limitation is their small energy dissipation

capability. However, this has been overcome by several manuf acturers by

packaging many junctions in a network that is able to dissipate considerable

energy.

Although the physics involved are quite different, the MOV has an electrical behavior similar to that of back-to-back avalanche semiconductor

(zener) diodes. The physical difference is that the MOV does not clamp by diode

switching action, but acts instead as a resistor whose resistance varies

inversely with voltage in a highly nonlinear manner. The breakdown into the

clamping region is therefore not as sharp, and the MOV switching speed

(nanosecond times) is slightly slower than avalanche diode switching speed.

However, the energy absorption capability is much greater than for avalanche

diodes. Some larger units can absorb several kilojoules.

The manner in which voltage-clamping suppressors operate may be clarified

by inspection of the log-log voltage versus current (V-I) curves of these

devices, shown schematically in figure 1 (not to scale). For each device there

exists a very small idling or standby current below the breakdown or clamping

voltage. Thus the suppressor looks essentially like an open circuit over this

voltage range. At the entrance to the breakdown voltage region (the "knee" of

the V-I curve) both devices change very rapidly from an essentially

nonconducting to a highly conducting state. Stated another way, the incremental

resistance, AV/Al, becomes very small, effectively creating a very low

resistance for voltages higher than the clamping voltage. Beyond a certain

current, the V-I curves turn up again, ending the clamping voltage region. This

upturn region is of interest here only in that circuit design must keep the

suppressor current below this level. The two curves are shown with different

shapes to emphasize that the avalanche diode switches more abruptly (sharper

"knee") and clamps more firmly (less slope in the clamping region) than the MOV.

l An ideal clamping suppressor would maintain an absolutely fixed voltage over an infinite range of current.

4

i
Loc,

Voltage

Lo& Current

Figure 1. Comparison of the log-log voltage versus current (V-I) curves of

MOVs and avalanche diodes (not. to scale).

5
Either clamping-type suppressor can be represented schematically as a variable impedance that attenuates the open-circuit transient voltage as shown

in figure 2. As the open-circuit voltage approaches the voltage level where the

impedance of the suppressor begins to lower abruptly, voltage division begins to

take place. It is important to understand that the device depends on the source impedance (Z s ) to produce the clamping. If the source impedance is low

compared to the dynamic clamping resistance of the device, the division ratio

will be low, i.e., the clamping action will be poor. As the equation in

figure 2 shows, if Z s = 0, Vc = Vs , and there is _no clamping action. In

other words, a suppressor cannot be effective with a zero source impedance. As

will be shown, it is the source impedance of the transient which governs the

sharing of energy dissipated between the suppressor and the source impedance.

Thus, the performance and limitation of a suppression system is directly

influenced by the source impedance of the transient.

The function and effectiveness of a clamping-type suppressor can perhaps be

visualized more clearly by reference to figure 3, which shows a power system

sinusoidal voltage wave with five different types of disturbances impressed upon

it. The upper and lower (positive and negative) clamping voltage levels,

established by a MOV or by back-to-back avalanche diodes, create an envelope

which bounds the voltage that can appear across the protected circuit. Whereas

the voltage trace with disturbances superimposed represents the applied voltage

in the absence of the suppressor, the trace less the shaded portions represents

the applied voltage in the presence of the suppressor. Note that "spikes" 1, 3,

and 5 are partially suppressed, whereas "notches" 2 and 4 are not, even though

"spike" 2 is comparable in size and "notch" 4 is much larger. Note also that

although spike 3 is the largest of all, a large part of it remains unaffected.

Thus, clamping-type suppressors are only effective in reducing overvoltage

transients which rise above the peak voltage of the power system. As will be

explained in the subsequent section, the clamping level cannot be set at exactly

the peak level of the power system voltage, hence, by necessity there will

always be some overvoltage residuals. If necessary, the additional suppression

techniques referred to earlier could deal with the residual disturbances shown

in figure 3.

4. SUPPRESSOR SELECTION CONSIDERATION

A voltage-clamping suppressor should operate under steady-state conditions

with a very small standby current, and in transient conditions without

degradation or failure when subjected to very large peak current and very large

energy dissipation. The selection process for a particular suppressor requires

specific knowledge of the electrical environment in which it will operate. When

the environment is not fully defined, some assumptions can be made but at the

risk of possible failures or economic penalties. Among the factors which must

be considered in the selection of an appropriate voltage-clamping device for a given circuit are:

(1) Steady-state voltage rating

(2) Transient energy absorbed by the device

(3) Peak transient current through the device

4.1 Steady-State Voltage Rating

The steady-state voltage rating is the voltage that may be applied to the

device under normal conditions with allowance for surges (a voltage increase

6
Figure 2. Attenuation of the transient source voltage V

s by the variable

impedance Zc of a clamping-type suppressor.

i 7
above the normal operating level persisting for several cycles). The regulation

of the line voltage is an important factor, since poor regulation can lead to

surges that may cause the device to begin clamping. This can lead to failure

since the power capability of the system can greatly exceed the power

dissipation capability of any suppressor. Refer again to figure 3, which shows

a case in which the steady-state ac voltage of the suppressor has been selected

properly, i.e., the clamping voltage is always above the peak of the sine wave.

On the other hand, figure 4 represents a case in which the steady-state ac voltage is too high, i.e., the peak of the sine wave exceeds the clamping

voltage. In this case, the clamping level is set too low, and the suppressor

begins to conduct appreciable current during the peak of the fundamental wave

itself. This will cause the suppressor to dissipate excessive amounts of energy

even in the absence of spikes, thereby either destroying it or permanently

altering its characterise cs. The temperature coefficient of the clamping level

of most MOVs is negative, so that increased heating of the device causes a subsequent lowering of the clamping level which can lead to thermal runaway

f ai lure.

A design tradeoff is involved in the selection of the steady-state voltage

rating, in that too high a value (over-conservative design) results in a transient clamping voltage which is too high, i.e., a "clamp ratio" which is too

low. 2 The steady-state voltage rating must be selected so as to minimize the

idling, or stand-by current, while at the same time holding the clamping voltage

as low as possible without allowing a "surge" to push the peak of the sine wave

into the clamping region. In systems likely to be subject to surges (most ship

systems), selecting a steady-state voltage rating too low is probably the more

serious of the two problems.

4.2 Energy

The energy rating of the device is perhaps the single most important

parameter, and must be considered carefully in relation to the potential

transient energy that can exist in a given electrical environment. The energy

rating refers to the energy that must be dissipated in the suppressor during a spike. A circuit which illustrates this concept is shown in figure 5, in which

a spike voltage, V s , is superimposed on a steady-state voltage, V ss . A

total voltage, (V s + V ss ), is thus imposed upon a circuit which is protected

by a clamping suppressor whose clamping voltage is Vc , through the source impedance Z s

. The circuit conditions as shown apply during the time for which

(V s + V ss ) is greater than the clamping voltage.

Figure 6 represents the graph of the generalized voltage versus time for

figure 5. Figure 6 assumes that the spike duration is short relative to the

period of the power system voltage, V ss , so that the base line voltage of the

spike can be considered constant over the interval of the spike. The

crosshatched area delineates the voltage wave during the time it is above

clamping voltage Vc

. During this time, i s flows, and the suppressor must

absorb energy, E s where

2 The "clamp ratio" is defined in industry as the clamping voltage divided by the

peak value of the steady state voltage.

8
©

Figure 3. Steady- st at e power voltage wave (60 Hz or 400 Hz) with superimposed

transients, showing the effect of cl ampi ng-type suppressors on such

transients when the clamping level is set correctly.

9
i

Figure 4. Steady-state power voltage wave (60 Hz or 400 Hz) with superimposed nsients, showing the effect of -clamping-type suppressors on such transients when the clamping level is set too low.

10
Figure 5. Circuit for calculating the current and the energy dissipated in

a clamping suppressor.
Figure 6. Graphical representation of the voltages in the clamping suppressor

circuit of Fig. 5.

12
( 1 )

t 2

i _ dt

assuming an ideal suppressor, for which Vc

is constant.

The most desirable way to determine the above energy would be to measure

V c and i s at the suppressor, and then perform the indicated integration of

the voltage-current, product. Since this determination cannot be done in

practice, an alternate method is to use the voltage spike recording of figure 6

along with the measured source impedance as a function of frequency. Then from

figures 5 and 6, i s = (V ss + V s - Vc )/Z s , and equation (1) becomes,

f 2 v (V + V - V ) = J c

'

ss s c

'

ti z

c

dt ( 2 )

where V c > v ss> and Z s is assumed to be constant between times ti and t2

.

Thus, with a knowledge of the transient voltage as a function of time and

of the source impedance, appropriate algorithms can be used to calculate

energy. To summarize, energy calculations require two pieces of information:

1. Transient voltage recordings as a function of time (Fig. 6).

2. Source impedance (Z s ) of the network as a function of frequency

(1 kHz to 500 kHz).

Inspection of figure 6 and of equation (2) will show why data on voltage wave shape and duration are important. Since energy is a voltage-squared-time

function, it should be apparent that the larger spike voltage V s is, and the

longer its duration above clamping voltage Vc , the larger the energy which

must be absorbed by the suppressor. Stated another way, a very large but short

spike may represent less energy than a much smaller but much longer spike.

Also, the longer spike tends to contain more energy because source impedance

Z s is usually predominantly inductive-resistive in nature, hence increases

very significantly with frequency, making it much larger for short spikes than

for long ones. From equation (2) energy is inversely proportional to Z s

.

4.3 Peak Transient Current

For reasons only indirectly related to the total energy absorbed during any

one pulse, the lifetime of a clamping-type suppressor is related inversely to

the peak current through the suppressor. This relationship is quite strong,

e.g., a MOV rated for one 2000 A pulse of a given length might typically

withstand 2,000 200 A pulses of the same length without degradation. Peak

current rating is usually stated as the peak value of a single pulse of

current. Repetitive pulsing requires a significant derating of peak pulse

current. Thus, the peak current and expected frequency of occurrence of the

transients must be considered in relation to the expected life of a given

suppressor. Peak current can be determined when the open-circuit peak transient

voltage, the clamping voltage, and the source impedance are known (see Fig. 5).

Therefore, as was true for energy rating, voltage pulse and circuit impedance

data are essential.

13
5. RELATING THE AVAILABLE DATA TO THE REQUIREMENTS

Part of the data on which this report is based are contained in five

reports (5.1 through 5.5) which were provided by NAVSEA at the beginning of the

project. These five documents were to be the basis for establishing a suppressor specification for shipboard use. Each report is summarized briefly

below, and those which bear most directly on the problem are discussed in more detail. In addition, the data made available from the USS Arkansas (CGN-41) and

the data acquired from the EPIC program during the project period are discussed

(5.6 and 5.7). A tabular summary of the 5.1 to 5.7 discussion is presented in

Section 5.8. Also discussed (5.9 through 5.11) are some of the general problems

identified as common to most of the data analyzed thus far.

5 .

1

Sag/Surge and Interrupt Data Analysis on Shipboard Power Lines by Sachs/Freeman Associates, Inc.,

dated 12 June 1981.

This document contains sag/surge and interrupt data collected from thirteen

ships and analyzed for compliance with DOD STD-1399. These data involve very

slow rises and falls (cycles to many seconds) in system voltages, and thus are

not applicable to spike voltage characteri sties . However, the report does have some relevance to selecting the steady-state voltage rating of a suppressor.

For the 115- V system studied, most of the surges were under 130 V.

5.2

Energy Analysis of Transient Pulses on Shipboard Electric Power Systems by Messrs. L. L. Grigsby

and S. S. Kelkar of VPI, dated July 1980.

This report is basically theoretical. It develops an algorithm for

calculating transient energy from voltage pulse data in the time domain, and the

source impedance as a function of frequency. The technique appears useful for

calculating the energy of a voltage spike, but as the report points out,

considerably more impedance data are necessary before the method can be applied

to shipboard systems.

5 .

3

Investigation of Shore-based Powerline Transients,

by Naval Electronic Systems Engineering Activity,

dated 30 September 1981.

This report summarizes the results of a transient measurement program on Navy shore-based power very similar to the program discussed in Section 5.5.

This program contained much more data (135,000 hours; 27,500 transients).

Ninety-four percent of the data were taken with Dranetz recorders. The

discussion under section 5.5 also applies to these data.

5.4

Evaluation of Commercial Suppression Components and

Commercial Suppressors , Preliminary Data, 5 volumes,

by Naval Electronic Activity, dated 10 March 1982.

These documents provide an independent analysis of the characteristics of

various suppression components and packaged suppression systems, apart from any

equipment they might protect. Three generic types of suppressors (metal oxide

varistors, silicon pn junction devices, and gas tubes) were tested to determine

if their performances changed with energy ratings, steady-state application

14
ratings, or different manufacturers. The data and the descriptions of the

particular packaged off-the-shelf suppression systems may be useful in

determining whether a suppressor design can be supplied by an existing

commercial unit or by minimal modification of such a unit. However, much more

detailed circuit data than those given would be necessary in order to evaluate

these commercial packages. Some of the units failed. The report does not make

clear whether these failures were due to transients alone, to heating due to

excessive idling current (e.g., epoxied "series" suppressors ) , or to combined

causes .

5.5 Identification of Shipboard Powerline Transients , by Naval Electronic Systems Engineering Activity,

dated 1 March 1980.

This report presents an extensive survey of transients on thirteen Navy

ships, totaling over 9400 monitoring hours and over 2300 transients. The bulk

of these data (80%) were obtained using Dranetz Model 606-3 recorders. These

recorders give useful general information on the frequency of occurrence,

location, and apparent peak voltages of transients in these Navy systems. They

record no waveform data (i.e. s duration and shape). Due to their somewhat

limited bandwidth, it is also possible that they fail to reproduce the full

amplitude of the faster transients. Some 5% of the data were taken with a fast

digital storage oscilloscope. Because the storage oscilloscope records the

complete waveform, both waveshape (duration) and peak voltage can be obtained.

These data represent a total of approximately 125 spikes of several different

types. In an initial review of the data compiled in the report, a number of

discrepancies were noted, particularly in the reported durations of the

transients.

As a result, NBS personnel made a trip to the Naval Electronic Systems

Engineering Activity (NESEA), St. Inigoes, MD, to reexamine the waveform data

stored on magnetic floppy disks. All 125 spikes were reviewed. Only 34 were of

possible significance in terms of amplitude or duration. These 34 "worst cases" were copied and returned to NBS for further analysis. They included data from

only three of the thirteen ships--LST1188, DDG41, and FF1092. This analysis

revealed significant disagreement with the NESEA report, and showed that report

to be very pessimistic regarding the significance of the spikes recorded, as related to waveshape and duration (which, in turn, are strongly correlated with

the energy dissipated in the suppressor).

Further analysis showed that of the 34 "worst cases" above, all the

"significant" spikes were on 440 V lines. Assuming a 450 V MOV, whose clamping

voltage is about 1350 V, plus spike occurrence on the peak of the steady-state

voltage wave (an additional worst case), only five of the 34 (or 125) spikes

recorded would even trigger the suppressor, i.e-. , exceed the clamping voltage.

Furthermore, only two would appear to dissipate significant energy in the

suppressor. These two spikes are reproduced in figures 7 and 8. However, the

appearance of even these two spikes leads to the suspicion that they are not

real, but are artifacts of some sort. There is no obvious mechanism in a Navy

power system which would be able to generate transients of this size and

duration. Nevertheless, the presence of these two spikes in a relatively small

data base means that the possibility of transient problems in Naval shipboard

15
Figure 7. Decaying exponential with initial value of

1200 V and large initial spike of 2192 V. Duration to 50%, about 300 ys from 152 ys

point. (Reproduced from St. Inigoes data).

h’ 16
TIME IN MICROSECONDS .

Figure 8. Large 170 kHz oscillation riding on an apparanet

7 kHz "carrier." Duration unknown (goes off screen at about 175 ys). (Reproduced from

St. Inigoes data).

17
power circuits cannot be ruled out. On the other hand, the data base is far too

small to be useful in suppressor design.

The total data body probably contains enough information to generate a preliminary specification for the frequency of occurrence of increasing peak

voltages, although the Dranetz data may be low by as much as 50% for very fast

spikes. Even allowing for this, the highest peak voltage found among 1250

transients on 440 V lines was 1500 V. Among 1100 transients on 120 V lines, the

highest peak was 675 V. Since the Dranetz results (95% of the total data)

include no data on waveshape or source impedance, they are of use only for

analysis of worst case transient amplitude and frequency of occurrence.

In summary, no firm conclusions can be drawn from the very limited data

available from this report, and most certainly, no development of suppressor

specifications can even be considered.

5.6 USS ARKANSAS (C6N-41) ELECTRICAL POWER MONITORING , 2 volumes, by Raytheon Service Company,

dated September 1982.

Two reports present the results of monitoring the electrical power system

on CGN-41, under various at-sea conditions. Some data were recorded with

Dranetz Model 606-3 and 626 recorders, and the remainder with a HP-3964A

magnetic tape recorder. Both models of the Dranetz recorders were designed to

enable a direct measure of the differential or phase-to-phase voltage. The

magnetic tape recorder, however, because of its single-ended input configuration

could only record the common mode or phase-to-ground voltage of each phase on individual channels. Each phase-to-phase voltage had to be reconstructed from

the phase-to-ground potential of two channels by appropriate summing and scaling

networks and then recorded on an oscillograph.

Approximately 1900 impulses were recorded. The highest transient voltage

reported was 2030 V, and a sizable number of durations (about 20%) were greater

than 2048 us (the time base limit of the Dranetz recorder), all on the 440-V

lines. No source impedance data were gathered. Only 25 oscillograms were presented and none of these included the "worst" cases; hence, there is little

usable waveshape information. Although there were, in many cases, large

amplitude and long duration phase-to-ground impulses, the reconstructed

phase-to-phase voltage produced practically no transients. The report surmised

that transient changes in line-to-ground impedance were the cause for the

observed line-to-ground voltage disturbances. Some of the pulses presented

appear to be square, or nearly so. If the worst-case pulse voltage and duration

cases should happen to be square or triangular waves, they would represent a very severe design requirement for a suppressor. The reports recommend that

continued transient monitoring should be conduc-ted under controlled conditions

to further determine the cause of transients. Of particular concern is the

apparent long duration transients (greater than 2048 ys) indicated by the

Dranetz recorders. If these are real, rather than artifacts of the

instrumentation, such transients pose a threat to user equipment as well as severe requirements for suppression devices.

It is suspected, however, that the apparent long duration transients are due to the technique utilized by the Dranetz recorder which operates as follows:

18
the recorder commences clocking a disturbance at the time that the voltage

exceeds or falls below a designated threshold value. This threshold value may

be well below the peak value, e.g., 20 V or 50 V. When the voltage maximum or minimum is attained, that level is recorded. The duration of the transient is

clocked until the voltage level returns to the original threshold value and this

time interval is recorded. Thus, the time that is measured is that time from

the initial threshold excursion up to the time at which the same threshold level

is reacquired. The length of time that the transient remained at the maximum or minimum value (or above the conventional 50% of peak definition for duration) is

not recorded.

Since not all of the data taken on magnetic tape had been reviewed and

analyzed, it was recommended in the Phase I report that this data be analyzed to

help resolve the question of the apparent unusually long duration transients.

This recommendation was addressed by the David Taylor Naval Ship Research and

Development Center (DTNSRDC). They transcribed the data from magnetic tapes to

obtain voltage waveform plots. Analysis of the plots showed no large spikes.

However, some unexplained sudden line-to-line voltage offsets were recorded.

Thus, the additional data on magnetic tape did not help to resolve or provide

any plausible explanation for the long duration transients indicated by the

Dranetz instrumentation. Finally, even if one were confident of the data, the

data base in these reports is small and involves only one ship.

5.7 EPIC Measurement Program

The Electric Power Interface Compatibility (EPIC) program was established

within the Navy to identify, if possible, the sources of incompatibility between

power systems and user equipment. Some of the main areas of study identified by

the EPIC program were voltage interruptions, voltage drops, harmonic distortion,

and voltage spikes. The dat.a-gathering phase of the program consisted of

monitoring a number of ship's service power supplies, including measurements at

the shore power installation points, selected power distribution points, and

selected user equipment locations. Also, the test procedures had outlined where

practical the simulation of certain operating scenarios, such as an Automatic

Bus Transfer operation or a large motor start up. The data from all the ships

monitored was to be used to identify and develop solutions to the documented

EPIC problems. For the voltage spike program, the EPIC test procedures called

for specific measurements of spike amplitude, waveshape, and frequency of

occurrence. Also, the measurement of power system broadband impedance was established as part of the total test procedures.

It was anticipated that the measurements related to voltage spikes from the

EPIC program would add significantly to the data base required for the

development of a suppressor specification. However, the data from the EPIC

program has contributed minimally to the Voltage Spike program discussed here.

The result has been that only a very limited amount of impedance data from two

ships and a total of 75 power system waveform recordings from one ship have been

made available to NBS. These data are discussed in more detail below.

A broadband impedance-measuring system (BIMS) was developed for the Navy by

a private contractor. This system automatically measures the complex impedance

at multiple points in a shipboard power system without deenergizing the line or interfering with it. The instrument is a one-of-a-kind device that claims to be

19
able to measure the power line impedance on systems up to 440 V over a frequency

range from 5 Hz to 700 kHz with accuracies in the order of ±5% of full scale and

±5% of reading.

The first test run of the BIMS was made aboard the USS Ranger (CV-61) in

April 1983. Impedance data were recorded from two different test stations on each of the three phases of a 120 V, 400 Hz power circuit. Measurements from

the first test station were conducted under two conditions: with the AN/ASM 403

computer energized and with it unenergized. These measurements resulted in a total of nine impedance data sets from the CV-61.

Table 1 shows an impedance data set obtained from the CV-61 on phase A of

the 120 V 400 Hz power at Avionics Shop No. 6 and 7 with the AN/ASM 403 computer

energized. Figure 9 is a plot of the data of Table 1 showing impedance and

phase angle as a function of frequency. The impedance varies from a low of

0.29ft at 150 Hz to about 17ft at 175 kHz. Although the phase angle is

predominately positive, indicating an equivalent inductive reactance, the phase

varies considerably over the 200 kHz bandwidth. This variation implies a fairly

complex impedance which cannot be reduced to a single lumped resistance and

inductance over the entire bandwidth. The impedance is not greatly affected

(especially above 1 kHz) by whether the AN/ASM 403 computer is on or off, and

does not vary much among the three phases.

These measurements on the CV-61 and the small amount of data which resulted

were intended primarily to demonstrate the operation, installation, and

dependability of the BIMS. Although the results seem reasonable, no independent

measurements have been reported on the BIMS accuracy, particularly at low

impedance and large phase angles.

Subsequent to the above impedance measurements, a limited amount of power

system impedance data were obtained from the USS Kitty Hawk (CV- 63), during

July 1983. Measurements were made at two main stations: 440 V, 60 Hz and

120 V, 400 Hz power. The 60 Hz distribution system was being supplied by shore

power. The measurements resulted in a total of seven impedance data sets for

the CV-63

.

Table 2 shows an impedance data set taken from the 120 V, 400 Hz system

located in an aircraft electrical service station of the CV-63. Figure 10 is a plot of the data showing impedance and phase angle as a function of frequency.

The impedance varies from a low of 0.02ft at 90 Hz to about 20ft at 200 kHz.

Comparison of the two data sets of Tables 1 and 2 (CV-61 vs CV-63) shows that

the impedance measurements from the CV-63 are lower by as much as a factor of seven at the low frequencies and about the same at frequencies above 100 kHz.

However, in the frequency range around 10 kHz where it is believed that

considerable spike energy may exist, the CV-63 .impedance is three to four times

lower than the CV-61 impedance. The significance of the difference in these two

impedance data sets cannot be properly evaluated yet because there is

insufficient information about the two systems. In particular, no information

was made available as to the distances of the measurement system from the

generator. Such an evaluation requires a complete mapping of broadband

impedance of all representative circuits from the generator to the end of the

line on a number of ships. This has not been done. The impedance data provided

thus far can only be regarded as trial measurements which demonstrate the

20
- 90.

0

90

O

RNGLE<+>

0

IHPEBRNCECO

1O.O0O 20.000

150. G

1S4.7

22?.

4

279.9

344.6

' 450.4

522,3

643. 1

' 791.7

974.7

1200.0

1477.4

•1618.

9

2239.3

2756.8

3394.

1

4178,6

5144.5

7797.6

9600.

8

11S19.G

14550.8

17914,2

22054.9

27152.8

33429.0

41156.0

50668 .

9

£» 2 3 8 0 • S

76799.

7

94551.6

1 1 6406,

6

143313.4

176439.4

Figure 9. Power system impedance and phase angle plotted as a function of frequency from the data of Table 1.
99.

110.

136 . 167 . 206.

254.

313. 350 . 475 . ET O J JC' l

r . 720 .

2G36.

2507.

3036.

3800.

4678.

5760.

7091

.

3 f 3 0 . 10743.

1 3233 . 16291

.

20857.

24693.

30401

37428.

46079.

56733

69344.

1 85363.

130333.

160459.

197548.

Figure 10. Power system impedance and phase angle plotted as a function of frequency from the data of Table 2.

22
Table 1 Broadband

120 V, 400

No. 6 and

impedance data from the CV-61 on phase A

Hz power at the avionics shop location

7 with the AN/ASM 403 computer energized,

FREQ. IMPEDANCE ANGLE

(Hertz

)

(Ohms

)

(Degrees)

150.0 0.29 51.5

184.7 0.29 52.6

227.4 0.32 61.3

279.9 0.40 66.0

344.6 0.53 67.0

450.4 0.97 71.1

522.3 0.95 56.3

643.1 1.57 44.4

791.7 0.59 35.1

974.7 0.52 . -12.1

1200.0 0.90 62.1

1477.4 0.95 32.8

1818.9 1.32 43.9

2239.3 1.74 18.7

2756.9 1.45 14.0

3394.1 1.55 -0.6

4178.6 1.03 -10.2

5144.5 0.64 15.7

6333.6 0.85 46.1

7797.6 1.08 58.1

9600.0 1.68 60.1

11819.0 1.56 45.7

14550.8 1.77 75.4

17914.2 2.55 75.6

22054.9 3.65 63.7

27152.8 4.29 37.3

33429.0 2.29 57.9

41156.0 3.64 73.4

50668.9 4.41 73.4

62380.8 5.50 80.5

76799.7 7.08 - 82.2

94551.6 8.87 83.4

116406.6 11.15 85.5

143313.4 14.07 86.9

176439.4 17.46 86.7

23
Table 2. Broadband impedance data from the CV-63 on the

120 V, 400 Hz system located in an aircraft

electrical service station.

FREQ. IMPEDANCE ANGLE

(Hertz

)

(Ohms

)

(Degrees

)

90.0 0.02 42.6

110.8 0.03 50.8

136.4 0.04 59.6

167.9 0.04 64.4

206.8 0.06 71.6

254.6 0.06 69.2

313.4 0.07 72.6

350.4 0.10 66.0

475.0 0.13 72.7

584.8 0.15 70.9

720.0 0.19 73.6

886.4 0.24 68.4

1091.3 0.23 67.7

1343.6 0.33 71.5

1654.1 0.38 59.7

2036.5 0.43 69.8

2507.2 0.58 60.2

3086.7 0.54 61.3

3800.2 0.70 64.3

4678.6 0.90 60.2

5760.0 1.22 54.5

7091.4 2.07 17.0

8730.5 0.36 65.2

10748.5 0.44 36.1

13233.0 0.81 70.5

16291.7 1.14 76.6

20057.5 1.46 77.6

24693.6 1.79 78.1

30401.4 2.19 78.5

37428.5 2.76 79.4

46079.9 3.34 80.3

56731.0 4.11 79.4

69844.1 5.17 78.9

85988.2 6.41 77.9

105863.9 8.00 77.4

130333.7 10.13 71.0

160459.6 13.59 72.2

197548.9 20.12 43.8

24
operability of the BIMS. Also, independent calibrations should be made on the

BINS to provide some indication of accuracy.

From the standpoint of worst-case suppressor design requirements, an equivalent lumped model of impedance may be sufficient. Perhaps the impedances

of the various major power circuits can be reduced to a few simple equivalent

lumped models. However, far more impedance data would be required to determine

this. Computer algorithms are also available for calculating energy and peak

current from voltage spike waveform data in the time domain, and discrete

impedance data in the frequency domain, similar to the data provided by the

BIMS. Correlation of these two approaches would be very useful.

Other than the BIMS, the instrumentation required for the data-gatheri ng

phase of the EPIC program has been under the purview of the Naval Ship System

Engineering Station (NAVSSES) in Philadelphia, PA. Their responsibility has

been to procure the appropriate instrumentation, design the required interfaces,

reduce the data, and report the results. The instrumentation for recording

voltage spikes on the power waveform at each station consisted of a commercial

four-channel digital storage oscilloscope coupled to custom-designed external

attenuators and trigger circuitry. NBS personnel travelled to NAVSSES in July

1983 to discuss problems with the instrumentation. Personnel at NAVSSES

indicated that most of their inability to obtain reliable spike voltage data

aboard ship was due to three problems:

1. Interface circuitry troubles and limitations.

2. Reliability difficulties with the digital oscilloscopes.

3. Equipment operator inexperience aboard ship.

Apparently the external trigger circuitry was bandwidth limited to 150 kHz,

but NAVSSES maintained that this was not a severe limitation to capturing

voltage spikes. Although the basic problems were never completely solved, the

system worked well enough to get some voltage spike data aboard ship. To date

the total results of voltage spike waveform measurements made available to NBS

from the EPIC program consist of 75 records of spike voltages obtained from the

CV-63 at four measurement stations. These data were transcribed by NBS from

magnetic disks into waveform plots. Figure 11 shows one of the typical

recordings, consisting of about one cycle of each phase of the 440 V, 400 Hz

power with voltage spikes on each waveform. None of the records showed spikes

much greater than shown in figure 11. In fact, none of the recorded spikes

would be affected by a simple clamping type of suppressor. In short, these data

showed no significant spikes.

Although impedance and spike waveform data are considered essential for

determining energy and peak current requirements of suppression devices, other

data that could be used to support a suppressor specification were to be

generated from the EPIC program. The program called for measurement of line

disturbances and the frequency of occurrence of voltage spikes. As emphasized

before, a data base of line disturbance measurements, particularly surges or rises in the line voltage, is important in establishing the minimum steady-state

operating voltage of clamping-type suppressors. Also, voltage spike frequency

25
v-/

U!2

\r

i 26

Figure

11.

Recording

of

a

typical

disturbance

on

the

440

V,

400

Hz

power

system

of

the

USS

Kitty

Hawk

(CV-63),

July

1983

(from

the

EPIC

program,

data

furnished

by

NAVSSES).
of occurrence data is helpful in establishing suppressor lifetime operating

requirements. No such data from the EPIC program have been made available to

NBS.

5.8 Summary of Available Oat a

Table 3 presents a comparative summary of the data required for suppressor

specifications and the data available from the reports just discussed in

sections 5.1 through 5.7. This summary demonstrates that the data base for the

two key parameters, source impedance and spike waveform, is extremely limited.

Table 3 also points up the necessity for further investigation of surges, since

excessive surges can destroy otherwise properly applied suppressors (see

figure 4 and the accompanying discussion), and make a practical spike

suppression system very difficult to obtain.

5.9 Measuring Power Line Disturbances

Practically all of the voltage spike data from ships reviewed thus far by

NBS, with the exception of the 75 waveform recordings from the CV-63 and some

data from the CGN-41, were recorded without the disturbance being superimposed

on the power voltage waveform. The phase of a disturbance with respect to the

power line waveform is important both from the standpoint of user equipment

susceptibility and suppressor requirements. As shown in figures 12a and 12b, a disturbance may either decrease or increase the instantaneous amplitude of the

sinusoidal power voltage waveform (sometimes distinguished as a "notch" or "spike," respectively). However, if the recording equipment uses high-pass

filtering to attenuate the power system waveform, then only the disturbance

(high frequency information) is preserved and the distinction between a "notch"

and a "spike" is lost. Most of the commercial power line disturbance analyzers

record the peak value of a transient excluding the ac line voltage.

All of the spike waveforms recorded on storage oscilloscopes by Naval

Electronic Systems Engineering Activity (NESEA) were processed through high-pass

filters. Figure 12c shows that the response to high-pass filtering is identical

for each type of disturbance. However, the effect on a user equipment and

suppressor could be quite different. The disturbance or "notch" of figure 12a

is entirely inside the envelope of the power system waveform that may not

produce a direct overvoltage threat to equipment. A clamping-type suppressor

certainly would have no effect. On the other hand, the spike of figure 12b

produces an overvoltage and would be clipped by a clamping-type suppressor. As

an extreme example of the necessity to locate the spike on the steady-state

waveform, a 440 V power system could conceivably have a 1200 V instantaneous

amplitude decrease and rapid recovery at the peak of the waveform (a "notch")

and still be within the envelope of the waveform, yet recording equipment

preceded by high-pass filtering would record such a "notch" as a voltage spike.

Thus, the question arises as to whether disturbances that are within the

peak-to-peak system voltage envelope should be considered the same as true

overvoltage spikes. From the standpoint of worst-case design for clamping-type

suppressors, all spikes could be considered as causing an instantaneous voltage

increase at the peak of the power system waveform.

But the point of this discussion is that if surveys are conducted to

measure the extent and severity of power line transients, these transients

27
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28

Certain

commercial

instruments

are

identified

in

this

report

to

provide

the

sponsor

with

the

analysis

requested

in

the

work

statement.

NBS

has

merely

reproduced

information

in

reports

supplied

by

the

sponsor

and

has

conducted

no

evaluation

on

the

instruments

identified.

Identification

does

not

imply

recommendation

or

endorsement

by

NBS

for

any

purpose,

nor

does

it

imply

that

any

identified

instruments

are

the

best

available

fora

given

purpose.
29

Figure

12.

The

same

disturbance

may

either

decrease

(a)

or

increase

(b)

the

instantaneous

amplitude

of

the

sine

wave

(sometimes

distinguished

as

a

"notch"

or

a

"spike,"

respectively).

The

output

response

(c)

of

a
should be considered in relation to the instantaneous power system voltage, or

at least correlated with the different system voltages. A case in point is

figure 10 of D0D-STD-1399 (shown here as fig. 13), which shows a seven-day

histogram of transient voltage versus number of transients in 115 and 440 V systems. Here the number of transients plotted are the combined totals, without

regard to the power system in which they occurred. Obviously, a 1200-V spike on

a 115- V system would be more serious than on a 440 V system, but may be a lesser

problem on either system if it is a "notch" near the peak.

5.10 Differential/Common Mode Measurements

In all the data made available to NBS thus far, there appears to be an inconsistency in the modes for which data are recorded. There are two possible

modes of monitoring the transients, referred to as differential mode

(line-to-line) or common mode (1 i ne-to-common ) . According to the NESEA reports,

when the Dranetz recorders were connected in the common mode configuration no transients were detected. Therefore, all the spikes recorded were monitored in

the differential, mode, or line-to-line. Similar measurements in the

differential mode recorded by the Raytheon Service Co. indicated transients

whose duration exceeded the range (2048 ysec) of the Dranetz monitoring

equipment, whereas common mode data taken with magnetic tape recorders showed

mostly large, long-duration offset voltages. When the line-to-line potentials were subsequently reconstructed from the common mode voltage differential

recordings, no significant spikes were observed.

Furthermore, the data taken with a digital storage oscilloscope are mixed,

consisting primarily of differential measurements taken under shipboard power

and common mode measurements taken under shore power. It is not clear why this

disparity exists, but these inconsistencies cast further suspicion on the

reliability and usefulness of the data. This also raises the question as to

whether the line-to-line or the 1 ine-to-common mode must be protected. The

issue is not clear, and would have to be addressed in a comprehensive

specification.

5.11 Energy Measurements

It was noted that in both the shipboard and shore-based transient

investigations (sec. 5.3 and 5.5), energy levels of transients were determined

from simultaneous recordings of voltage and current waveforms at a given test

location. Energy levels were then obtained by multiplying the voltage and

current and integrating over time. The reported energy levels calculated with

this technique yielded values that were in the mi Hi joule range and below. The

report concludes from these few measurements that the energy levels are much

less than previously believed. There is a question as to the meaning of these

measurements. It is true that such a measurement gives the dissipated energy in

the equivalent load at the point of measurement, but it does not indicate the

current or energy that a given suppression device would need to withstand at that point. The magnitude of the transient current as reported above depends

entirely on the load impedance at the particular test location. To appreciate

this contention, consider the extreme case where the voltage and current of a transient are monitored at the end of a branch circuit that has no load. Under

this condition the observed transient current would be zero regardless of the

transient voltage amplitude, hence would yield zero energy. However, if a voltage-clamping suppressor were placed at this point, the current through the

30
°0 6G0 GOO 1200 1000 2000 PEAK AMPLITUDE. VOLTS

Figure 13. Seven-day histogram of transient voltage versus number of transients in 115- and 440-V' systems.

31
suppressor would be determined by the difference between the transient voltage

amplitude (V ss +V s ) and the clamping voltage of the suppressor (V c ) divided

by the effective source impedance (Z$), i.e., (Vc s +V s -V c )/Z s , as discussed in sec. 4.2 and shown in figs. 5 and 6). This example emphasizes once

again that the effective impedance of the circuit which introduces the transient

is an extremely important parameter in designing a protection scheme.

6. CONCLUSIONS

This report has summarized the work done so far by NBS in the voltage spike

suppressor program. Selection considerations for suppression devices have been

discussed in relation to the key parameters which must be known. A review of

the reports provided by the Navy has been given with a detailed analysis of all

known existing shipboard data relevant to suppressor applications. A number of

specific conclusions may be derived from this work. These are summarized as fol lows

:

1. Voltage-clamping devices which provide clipping of spikes above

the peak value of the line voltage appear to be the most likely

candidates for protecting shipboard electrical power systems.

2. The three primary electrical specifications which must be considered

in the selection and/or design of a suppressor are:

a. Steady-state voltage rating.

b. Transient energy absorbed by the device.

c. Peak transient current through the device.

3. The two key measurements required to determine the energy that a candidate suppressor must be able to absorb are:

a. Transient voltage recordings as a function of time, at the

suppressor application point.

b. Source impedance of the network, looking in at the suppressor

application point, as a function of frequency.

4. The reliability of the existing data base is questionable for the

following reasons:

a. There is evidence of incorrectly reported transient waveform data

from the 125 records reported in Section 5.5.

b. Some reported values of spike durations seem unusually long

(greater than 2 ms).

c. There are inconsistencies in the results obtained from both common mode and differential mode measurements.

5. The spike voltage waveform, broadband impedance, and surge data base is

too small to form a spike suppressor specification that would

economically and reliably serve the entire Navy.

32
7. RECOMMENDATIONS

Recognizing the inadequacy of the present data base for the development of

a suppressor specification, and further recognizing that data gathering from

operational ships of the fleet is difficult, time consuming, and does not lend

itself to a series of well-controlled experiments, an alternate approach is

recommended.

Basically the approach consists of developing the theoretical model of a simple shipboard power system, coupled with laboratory measurements to determine

the practical limits of observed and potential voltage spikes. This approach

attempts to develop a technical basis for a specification of spike suppressors

through a judicious combination of laboratory experiments using key components

of shipboard power systems, and circuit modeling using a wel 1 -developed

interactive electromagnetic transient program (EMTP).

To accomplish the goal of developing a clear understanding of the

generation and suppression of voltage spikes through modeling and laboratory

measurements, a test facility with appropriate power system components, manned

by personnel familiar with this problem, must be available and committed to

providing support.

A proposal based on this approach was submitted to NAVSEA on October 21, 1983.

It is anticipated that the proposed study would yield substantial

information on some of the questions which must be answered before

recommendations for a suppressor specification can be generated. Some of these

questions are:

1. What are the worst case limits (voltage and current amplitude,

duration, waveshape) of spikes in shipboard circuits containing no suppressors?

2. What is the range of broadband source impedances in shipboard power

systems?

3. What is the relationship between line-to-line spikes and line-to-ground

spikes? Must suppression be provided in both modes?

4. Are there optimal suppressor numbers, ratings, and locations?

5. How effective will simple clamping suppressors be for the worst case

spikes, i.e., what will be the residual spike voltage?

6. Are suppressors needed other than those installed in susceptible

equipment by the manufacturer needed at all?

33

N OS-1 14A »<i v. -'-PC) 1. PUBLICATION OR 2. Performing Organ. Report No. 3. Publication Date REPORT NO.. NBSIR 84-2844 March 1984

U.">. DCHT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

4. TITLE AND SUBTITLE

Analysis of Requirements for Shipboard Voltage Spike Suppressors

5. AUTHOR(S)

Owen B. Laug and David L. Hi 11 house

6. PERFORMING ORGANIZATION (If joint or other than NBS. see instructions)

NATIONAL BUREAU OF STANDARDS

7. Contract/Grant No.

DEPARTMENT OF COMMERCE 8. Type of Report & Period Covered

WASHINGTON, D.C. 20234

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City, Slate, ZIP)

Electrical Equipment Division

Ship Systems Directorate

Naval Sea Systems Command

Department of the Navy, Washington, DC 20362

10. SUPPLEMENTARY NOTES

1 Document describes a computer program; SF-185, FIPS Software Summary, is attached

11.

ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here)

This report describes progress so far in a voltage spike suppressor program,

undertaken for the Naval Sea Systems (NAVSEA) Command, with the objective of

developing a sound technical basis on which a spike suppressor specification for

shipboard equipment could be written. The project contract stated that sufficient

field data for such a specification already existed, and needed only to be correlated

and analyzed. N8S investigation revealed that existing data were far from adequate

for this purpose. It was then recommended that further testing already planned by the

Navy be used to collect the required data. Other as yet unreported data were also

analyzed. Neither effort succeeded in producing enough meaningful information for

carrying out the assigned task.

This report includes documentation of the analysis of all the pertinent data above;

a general discussion of the principles involved and of the applicable suppression

devices; a discussion of suppressor selection considerations and the key parameters

for this; and a review and analysis of the reports provided by the Navy. Finally, ti

(

report lists key parameters which must be known, and shows why the available data

cannot support the generation of a suppressor specification.

12.

KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and sepjrate hey words ty • Shipboard spikes; spikes; spike suppressors; suppressor specification;

voltage clamping; voltage spikes .

13.

AVAILABILITY

F]y] Unl imited EX] not Official Distribution. Do Not Release to NTiS

EU Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C

20 402.

] Order From Nacional Technical Information Service (NTiS), Springfield, VA. 22161

] 4. N i. PRINTED PAGE

39

15. P.