TECHNICAL REQUIREMENTS FOR ELECTRICAL EQUIPMENT … · TECHNICAL REQUIREMENTS FOR ELECTRICAL EQUIPMENT Title ... IEEE Std 344 . Recommended Practices for Seismic Qualification of

Page 1 (13)

Document Issue Date Supersedes

TBE 102:2 4 (E) 2013-08-20 Issue 3 (E)

TECHNICAL REQUIREMENTS FOR ELECTRICAL EQUIPMENT

Title

Environmental specification for seismic conditions

Document

TBE 102:2

Issue

4 (E)

Contents

1 GENERAL.......................................................................................... 2

1.1 Background ......................................................................................... 2

1.2 Basic objectives regarding seismic capability .................................... 2

1.3 New design or replacement of equipment .......................................... 3

1.4 Applicable standards and regulations ................................................. 3

2 DEFINITIONS.................................................................................... 3

3 ENVIRONMENTAL CONDITIONS ................................................ 4

3.1 General ............................................................................................... 4

3.2 Design seismic environment ............................................................... 5

3.3 Response spectra ................................................................................ 5

3.4 Seismic environmental classes for Forsmark 3 and

Oskarshamn 3 (F3/O3) ....................................................................... 6

3.5 Seismic environmental classes for other units .................................... 6

3.6 Damping ............................................................................................. 7

3.7 Ground Response Spectra ................................................................... 8

3.8 Example of relationship between ground response, floor

response and response for installed equipment .................................. 10

3.9 Seismic environmental classes - 4 % damping ................................... 11



TBE 102:2 Issue 4 (E) Page 2 (13)

1 GENERAL

These Technical Requirements provide guidelines on how to specify and interpret

seismic requirements for electrical equipment to be used in Swedish nuclear power

plants.

1.1 Background

The first nuclear power plants in Sweden initially were designed with no seismic re-

quirements. A general robust design was considered to provide adequate protection

against seismic events. As a result of more stringent safety rules issued after the

construction, requirements on the ability to withstand earthquakes have been added.

For the two latest reactors, Forsmark 3 and Oskarshamn 3, (F3/O3), seismic

requirements according to American regulations have been applied for design and

construction.

Later, in a jointly project between SSM (Swedish Radiation Safety Authority) and the

Swedish utilities in 1985-1989 a characterisation of earthquakes was defined, in-

cluding ground response spectra with frequency content and duration applicable to

Swedish conditions. Ground response spectra were developed for frequencies of

1E-5/year, 1E-6/year and 1E-7/year. See section 3.7, Figure 1.

The frequencies 1E-5/year and 1E-7/year have been selected as requirements for the

evaluation of the safe shut down and cooling of the reactor and the reactor

containment integrity respectively.

During the continued evaluation of the seismic capabilities of the plants performed

by the Swedish utilities, problems have been identified as the specific Swedish re-

sponse spectra has higher acceleration levels than the corresponding American spec-

tra for frequencies above 10 Hz. This means that international experience and test re-

sults cannot be applied directly to the Swedish conditions. Especially for electrical

equipment, such as relays and contactors, which are sensitive to frequencies above

ca 33 Hz it has been difficult to analyse and to verify their capability and function,

since no international studies for this type of equipment have been made for these

higher frequencies.

In order to verify seismic capability for the older nuclear power plants the following

objectives have been outlined.

1.2 Basic objectives regarding seismic capability

Structures and components of essential importance for the safe shutdown and long

term core cooling of the reactor must have a seismic capability sufficient for the

seismic loads which can be expected at the frequency of 1E-5/year per unit. This

requirement also applies to seismic interaction, which means that structures, piping

or equipment not required to be seismically qualified must not cause damage to

equipment that are required for safe shut down during an earthquake.

As examples of seismic interaction requirements the structures, piping, or equipment

must not loosen, burn, explode, cause short circuits, etc, during an earthquake.

TBE 102:2 Issue 4 (E) Page 3 (13)

1.3 New design or replacement of equipment

For new design or replacement of component type (but not necessarily for repair of

excisting seismically qualified equipment) the guidelines in these Technical Re-

quirements must be followed. Applicable seismic requirements are to be specified in

the Technical Specification.

These requirements shall include specific required response spectra or response

spectra selected according to section 3.4 and 3.5. In the latter case response spectra

according to seismic environmental class SL1-SL6 shall envelop specific required

response spectra.

1.4 Applicable standards and regulations

IEC 60980

Recommended practices for seismic qualification of electrical equipment of the

safety system for nuclear generating stations.

IEEE Std 344

Recommended Practices for Seismic Qualification of Class 1E Equipment for

Nuclear Power Generating Stations.

Other equivalent standards and regulations may be used after approval by the

Purchaser.

2 DEFINITIONS

Frequency

In this document frequency has two completely different meanings:

1) Occurrence frequency is given the unit 1/year. The occurrence frequency is the

inverse of the statistical mean time between earthquakes for a nuclear facility

with maximum ground acceleration (PGA) exceeding a certain value.

2) The frequency content expressed in Hz for the actual earthquakes.

Seismic loads

In this document acceleration forces are expressed with the unit m/s2 or g, where

1 g = 9,81 m/s2.

Damping

Damping is the generic name used for energy dissipation, which reduce the forces

and duration of the motions in mechanically oscillating systems. Damping occurs

primarily due to friction in mechanical joints and permanent deformation of struc-

tural materials. Damping is expressed as percent of critical damping, which means

that the next coming motion has x % less energy content than the previous motion.

Common damping values are 2-10 %.

Node

Node means the location in a building for which a response spectrum is generated.

TBE 102:2 Issue 4 (E) Page 4 (13)

PGA (Peak Ground Acceleration)

See definition of ZPA.

Response spectrum

A response spectrum is a diagram showing maximum response, e.g. in the form of

displacement, velocity or acceleration acting on all single degree of freedom systems,

caused by an applied motion (e.g. ground motions or building motions). Normally a

response spectrum is expressed for a given damping. The damping applies to a

certain affected oscillating system (installed equipment), when placed in the node for

which the response spectrum is generated. Example of response spectra is shown in

section 3.8. Response spectra are defined for the two horizontal axes x-, y- and

vertical z. For F3/O3 normally no distinction is made between response spectra for

the x– and y– axes. For the older nuclear units, which were not designed for seismic

influences, big differences in response spectra for x-, and y– axes may exist.

Normally one enveloping response spectrum for of the two axes x- and y- is

considered.

Time History

A diagram, with the unit “time” on the x-axis, and “acceleration” on the y-axis, de-

scribing the design basis ground motion. Section 3.7, Figure 2, shows a time history

for the ground motion. A time history may also be calculated for a certain level in a

building, including dynamic filter and amplification factors for the building and other

influencing structural elements.

ZPA (Zero Period Acceleration)

Acceleration level of the high frequencies in the part of the response spectrum where

no amplification effects occur. At increasing frequency the response curve flattens

out asymptotically to the ZPA level. ZPA is the maximum applied acceleration and

corresponds to the maximum peak value of the time history used to derive the re-

sponse spectrum. The higher acceleration levels of the response spectrum are caused

by resonance phenomena in the affected systems. For ground acceleration the

designation PGA (Peak Ground Acceleration) is often used instead of ZPA. Section

3.8 shows examples of response spectra with ZPA levels indicated.

3 ENVIRONMENTAL CONDITIONS

This section gives basic information about the seismic loads that buildings and

equipment are subjected to. Verification requirements for equipment with seismic

requirements are specified in KBE EP-147.

3.1 General

An earthquake causes both horizontal and vertical ground motions. These motions

are similar to random noise having the frequency content mainly below 50 Hz. The

duration of a major Swedish earthquake is about 10 seconds. See time history dia-

gram in section 3.7, Figure 2.

TBE 102:2 Issue 4 (E) Page 5 (13)

3.2 Design seismic environment

For Swedish nuclear power plants the so called S1 Earthquake according to

IEC 60980 or OBE Operating Basic Earthquake according to American regulations

(with the frequency 1E-2/year) need not to be considered. This means an earthquake

expected to occur during the operating life of the plants.

On the other hand S2 Earthquake according to IEC 60980 or SSE Safe Shutdown

Earthquake according to American regulations has to be considered.

This means that for seismic loads which can occur with an average frequency greater

than 1E-5/year and unit necessary safety functions must be demonstrated to fulfil the

intended functions.

The ground motions specified for Swedish nuclear power plants are shown in section

3.7, Figure 1.

For F3/O3 the curve based on Regulatory Guide 1.60, but modified for

PGA = 0,15 g horizontal acceleration, applies.

3.3 Response spectra

Based on the given ground response spectra in section 3.7, Figure 1, the relevant

floor response spectra are generated for the node (location) where the electrical

equipment is to be placed.

Applicable horizontal and vertical response spectra are given in the Technical Speci-

fication. In an early stage of design or purchase the damping for the actual electrical

equipment may not be known. Therefore, the response spectra for the node should be

generated for a number of different damping values. See also section 3.6.

In order to avoid that a large number of response spectra are called for during design

or purchase of electrical equipment, a simplification may be made to allow for verifi-

cation according to a seismic environmental class shown in this document. Hence the

seismic environmental class becomes the requirement level that is verified by testing

according to KBE EP-147.

When using this type of broadened response spectra it should be noted that the

applied energy is proportional to the square root of the bandwidth. This implies that

equipment withstanding each single response spectrum may not withstand the applied

energy when tested with a broadened response spectrum making up an envelope of

the single response spectra.

TBE 102:2 Issue 4 (E) Page 6 (13)

3.4 Seismic environmental classes for Forsmark 3 and Oskarshamn 3 (F3/O3)

F3/O3 are designed for horizontal ground motion with PGA = 0,15 g.

See section 3.7, Figure 1. Vertical ground motion is assumed to 2/3 of the horizontal.

For F3/O3 there are stereotyped response spectra based on which height in the

building the equipment is located and depending on how the equipment is mounted.

There are three seismic environmental classes defined, class 3, 4 and 5. For class 3

and 4 the response spectra are given for horizontal and vertical acceleration respec-

tively. For class 5 no specific response spectra have been given. The combined

building responses are calculated according to Regulatory Guide 1.92, Rev 1.

For equipment mounted directly on walls or floors, current requirements specify

response spectra according to seismic environmental class SL1 or SL2. For

equipment mounted on other structures class SL5 applies. See Table 1 below.

Seismic environmental class, applicable for F3/O3 only

Seismic

Environ-

mental

Class

Equipment location Replaces

earlier class

SL1 Equipment mounted directly to building structure,

0-8 m above ground

Class 3

SL2 Equipment mounted directly to building structure,

8-20 m above ground

Class 4

SL5 Equipment mounted on e.g pipes, ventilation

drums, cable raceways or other structures

Class 5

Table 1

Response spectra for seismic environmental classes shown above are given in section

3.9, 3.10 and 3.11.

3.5 Seismic environmental classes for other units

For other units initially not designed for earthquakes, it is not permitted to use the

F3/O3 stereotyped classification.

For each equipment required response spectra must be generated for the equipment

mounting position. When the required response spectra have been generated for both

horizontal and vertical acceleration, one response spectrum shall be selected en-

veloping all horizontal and vertical required response spectra for the actual positions.

For equipment which can be expected to be used in a number of mounting positions

or buildings, the response spectrum is to be selected so that the qualification becomes

valid for all these positions and buildings. Primarily the response spectra are to be

selected from the seismic environmental classes SL1–SL6. In these classes the

response spectra curves are defined for the damping 4 %, 5 % and 7 %. The damping

value of the test spectrum shall not be higher than the lowest damping value of the

actual equipment.

For alternative damping values use IEC 60980 to determine amplification factor

(ratio between strong part and ZPA) at different damping values for a typical “time-

history”.

TBE 102:2 Issue 4 (E) Page 7 (13)

The classes SL1–SL6 make no distinction between vertical and horizontal accelera-

tion with respect to the test spectrum that is to be used.

If no broadened response spectrum according to class SL1–SL6 envelopes actual

spectra for specific mounting positions, or if the broadened spectrum is considered

too conservative, then the horizontal and vertical spectra for specific mounting

positions could be used instead as required response spectra.

Seismic environmental class, applicable to all units except F3/O3

Seismic

Environ-

mental

Class

Equipment location Comment

SL1 Equipment mounted directly to

building structure

Response spectra based on

calculated maximum building

response spectra

SL2 - " - - " -

SL3 - " - - " -

SL4 - " - - " -

SL5 Lowest class for equipment

mounted on e.g. pipes, ventilation

ducts, cable raceways or other

installed structures

Response spectra based on

calculated maximum response

spectra for structures

SL6 Equipment mounted on e.g.

pipes, ventilation ducts, cable

raceways or other installed

structures

- " –

Table 2

Response spectra for seismic environmental classes shown above are given in section

3.9, 3.10 and 3.11.

3.6 Damping

Damping values for verification by test or analysis are to be selected according to

approved standard, e.g. those referred to in section 1.4, or according to documented

recognised practice.

If damping values can not be established 5 % must be used.

TBE 102:2 Issue 4 (E) Page 8 (13)

3.7 Ground Response Spectra

Figure 1

The broken line in the diagram represents the F3/O3 design requirements for a

ground response spectrum, based on Regulatory Guide 1.60, modified for PGA =

0,15 g horizontal acceleration. The other curves represent later defined design criteria

for ground response spectra, based on specific swedish conditions, with the

frequencies 1E-5/year, 1E-6/year and 1E-7/year.

All curves represent 5% damping.

TBE 102:2 Issue 4 (E) Page 9 (13)

Figure 2

Illustration of a swedish earthquake

TBE 102:2 Issue 4 (E) Page 10 (13)

3.8 Example of relationship between ground response, floor response and response

for installed equipment

Example of repeated response spectra calculations. The ground response spectrum,

which is characterised by the local geological conditions, is amplified in the building

resulting in a floor response spectrum. A cabinet for electrical equipment is placed on

the floor. The cabinet contains electronics and other electrical components. The floor

response spectrum is amplified by the cabinet to a new response spectrum for a

specific position in the cabinet. The ground response spectrum in this case is for 5 %

damping at a maximum ground acceleration of 1,5 m/s2 and is used for analysis of

buildings. The floor response spectrum in this case is for 4 % damping at the

maximum floor acceleration of 5,5 m/s2.

The cabinet is exposed to an acceleration characterised by the floor response spec-

trum. A position in the cabinet give accelerations designated “Skåprespons” in the

response spectrum, in this case calculated for 5 % damping. The maximum acce-

leration is 8,0 m/s2. The cabinet has a resonance frequency at 24 Hz, which gives

acceleration values of 36 m/s2.

The cabinet response spectrum according to the diagram illustrates the effect on af-

fected components (single degree of freedom models with 5 % damping) in the ana-

lysed position in the cabinet. If the affected component has a resonance frequency at

11 Hz, we read the acceleration 19 m/s2, but if the resonance frequency is 15 Hz, we

read 36 m/s2. These accelerations are the result of a ground motion as shown in

section 3.7, Figure 2.

Ground Response

Floor Response

Cubicle Response

TBE 102:2 Issue 4 (E) Page 11 (13)

0

1

2

3

4

5

6

7

8

9

10

11

12

1 10 100

SL1

SL2

SL6

SL4

SL3

SL5

g

Hz

3.9 Seismic environmental classes - 4 % damping

Hz

SL1

g

SL2

g

SL3

g

SL4

g

SL5

g

SL6

g

1 0,1 0,2 0,2 0,3 0,4 0,4

1,6 0,4 1,3 1,6 2,0 2,7 3,5

3 1,7 2,8 3,4 4,2 6,0 7,8

4 2,3 2,8 3,9 6,0 7,5 11,2

25 2,3 2,8 3,9 6,0 7,5 11,2

50 0,4 0,7 1,1 1,7 3,0 3,2

60 0,4 0,7 1,1 1,7 3,0 3,2

TBE 102:2 Issue 4 (E) Page 12 (13)

0

1

2

3

4

5

6

7

8

9

10

11

12

1 10 100

SL1

SL2

SL6

SL4

SL3

SL5

g

Hz


Hz

SL1

g

SL2

g

SL3

g

SL4

g

SL5

g

SL6

g

1 0,1 0,2 0,2 0,3 0,4 0,4

1,6 0,4 1,2 1,6 2,0 2,7 3,5

3 1,5 2,5 3,4 4,2 5,5 7,8

4 2,1 2,5 3,4 5,2 6,8 9,9

25 2,1 2,5 3,4 5,2 6,8 9,9

50 0,4 0,7 1,1 1,7 3.0 3,2

60 0,4 0,7 1,1 1,7 3.0 3,2

TBE 102:2 Issue 4 (E) Page 13 (13)

0

1

2

3

4

5

6

7

8

9

10

11

12

1 10 100

SL1

SL2

SL6

SL4

SL3

SL5

g

Hz


Hz

SL1

g

SL2

g

SL3

g

SL4

g

SL5

g

SL6

g

1 0,1 0,2 0,2 0,3 0,4 0,4

1,6 0,4 1,1 1,6 2,0 2,4 3,5

3 1,4 2,24 3,0 4,2 4,9 7,8

4 1,84 2,24 3,0 4,6 6,0 8,6

25 1,84 2,24 3,0 4,6 6,0 8,6

50 0,4 0,7 1,1 1,7 3,0 3,2

60 0,4 0,7 1,1 1,7 3,0 3,2

TECHNICAL REQUIREMENTS FOR ELECTRICAL EQUIPMENT … · TECHNICAL REQUIREMENTS FOR ELECTRICAL EQUIPMENT Title ... IEEE Std 344 . Recommended Practices for Seismic Qualification of

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