标准编号:	GB/T 13625-2018
中文名称:	核电厂安全级电气设备抗震鉴定
英文名称:	Seismic qualification of safety class electrical equipment for nuclear power plants
中标分类:	F65    核电厂核岛
行业分类:	GB    国家标准
ICS分类:	27.120.10 27.120.10    反应堆工程 27.120.10
发布机构:	国家市场监督管理总局、中国国家标准化管理委员会
发布日期:	2018-05-14
实施日期:	2018-12-1
标准状态:	现行
替代旧标准:	GB/T 13625-1992 核电厂 安全系统 电气设备 抗震鉴定
翻译语言:	英文
文件格式:	PDF
中文字符数:	45000 字
翻译价格(元):	4500.00 元
交付时间:	付款后 1 个工作日

Codeofchina.com is in charge of this English translation. In case of any doubt about the English translation, the Chinese original shall be considered authoritative.



This standard is developed in accordance with the rules given in GB/T 1.1-2009.



This standard replaces GB/T 13625-1992 Seismic qualification of electrical equipment of the safety system for nuclear power plants, and the following main technical changes have been made with respect to GB/T 13625-1992:



—— relevant contents are added for damping (see Clause 6 and Annex A);



—— the requirement is modified for TRS low frequency band so that the low-frequency displacement of the test device shall not be too large (see 8.6.3.2);



—— related contents are added for power spectral density envelope (see 8.6.3.2.1);



—— the seismic qualification approach combining analysis and test is added (see Clause 9);



—— the guidelines for seismic qualification using seismic experience data of reference equipment (see Annex G).



This standard was proposed by China National Nuclear Corporation.



This standard is under the jurisdiction of the National Technical Committee 30 on Nuclear Instruments of Standardization (SAC/TC 30).



The previous edition of this standard is as follows:



——GB/T 13625-1992.



Seismic qualification of safety class electrical equipment for nuclear power plants



1 Scope



This standard specifies the implementation method and documentation requirements of seismic qualification for verifying that safety level electrical equipment can perform its safety function during and/ or after an earthquake.



This standard is applicable to seismic qualification of safety level electrical equipment in nuclear power plants, including any interface components or equipment whose failure will have harmful effects on the performance of safety system.



2 Normative references



The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.



GB/T 12727 Qualification of safety class electrical equipment for nuclear power plants



3 Terms and definitions



For the purpose of this document, the following terms and definitions apply.



3.1

broadband response spectrum

response spectrum that describes motion in which amplified response occurs over a wide (broad) range of frequencies



3.2

coherence function

comparative relationship between two times histories. It provides a statistical estimate of how much two motions are related, as a function of frequency. The numerical range is from zero for unrelated, to +1.0 for related motions



3.3

correlation coefficient function

comparative relationship between two time histories. It provides a statistical estimate of how much two motions are related, as a function of time delay. The numerical range is from zero for unrelated, to +1.0 for related motions



3.4

critical seismic characteristics

design, material, and performance characteristics of an equipment item that provide assurance that the item will perform its required function under seismic loads



3.5

cutoff frequency

frequency in the response spectrum where the ZPA asymptote begins. This is the frequency beyond which the single-degree-of-freedom (SDOF) oscillators exhibit no amplification of motion and indicate the upper limit of the frequency content of the waveform being analyzed



3.6

damping

energy dissipation mechanism that reduces the amplification and broadens the vibratory response in the region of resonance. It is usually expressed as a percentage of critical damping. Critical damping is defined as the least amount of viscous damping that causes a SDOF system to return to its original position without oscillation after initial disturbance.



3.7

earthquake experience spectrum; EES

response spectrum that defines the seismic capacity of a reference equipment class based on earthquake experience data



3.8

flexible equipment

equipment, structures and components whose lowest resonant frequency is less than the cutoff frequency on the response spectrum



3.9

inclusion rules

rules that define the bounds of equipment included in a reference equipment class based on an acceptable range of equipment physical characteristics, dynamic characteristics, and functions for which seismic ruggedness has been demonstrated by experience data



3.10

independent items

components and equipment that (a) have different physical characteristics or (b) experienced different seismic motion characteristics, e.g., different earthquakes, different sites, different buildings, or different orientations/locations in the same building



3.11

narrowband response spectrum

response spectrum that describes the motion in which amplified response occurs over a limited (narrow) range of frequencies



3.12

natural frequency

frequency(s) at which a body vibrates due to its own physical characteristics (mass and stiffness) when the body is distorted in a specific direction and then released



3.13

operating basis earthquake; OBE

earthquake that could reasonably be expected to occur at the plant site during the operating life of the power plant considering the regional and local geology and seismology and specific characteristics of local subsurface material



Note: For the vibratory ground motion produced by the earthquake, those features of the nuclear power plant, necessary for continued operation without undue risk to the health and safety of the public, are designed to remain functional.



3.14

power spectral density; PSD

mean squared amplitude per unit frequency of a waveform, and it is expressed in g2/Hz versus frequency



3.15

prohibited features

design details, materials, construction features, or installation characteristics that have resulted in seismic induced failure or malfunction of the equipment to maintain its structural integrity and perform its specified function at earthquake or test excitations with defined seismic capacity



3.16

qualified life

period of time, prior to the start of a design basis event (DBE), for which the equipment was demonstrated to meet the design requirements for the specified service conditions



3.17

reference equipment

equipment used to establish a reference equipment class



3.18

reference equipment class

a group of equipment sharing common attributes as defined by a set of inclusion rules and prohibited features





3.19

reference site

site containing equipment or items used to establish a reference equipment class



3.20

required response spectrum; RRS

response spectrum issued by the user or the user's agent as part of the specifications for qualification or artificially created to cover future application



3.21

resonant frequency

frequency at which a response peak occurs in a system subjected to forced vibration. This frequency is accompanied by a phase shift of response relative to the excitation



3.22

response spectrum

plot of the maximum response, as a function of oscillator frequency, of an array of SDOF damped oscillators subjected to the same base excitation



3.23

rigid equipment

equipment, structures and components whose lowest resonance frequency is greater than the cutoff frequency on the response spectrum



3.24

safe shutdown earthquake; SSE

earthquake that is based upon an evaluation of the maximum earthquake potential considering the regional and local geology and seismology and specific characteristics of local subsurface material



Note: Some certain structures, systems, and components need to remain their functions under the maximum vibratory ground motion caused by the earthquake. These structures, systems and components are those necessary to ensure the following requirements:



a) Integrity of the reactor coolant pressure boundary;



b) Capability to shut down the reactor and maintain it in a safe shutdown condition;



c) Capability to prevent or mitigate the consequence of off-plant irradiation accidents.



3.25

seismic capacity

highest seismic level for which required adequacy has been verified



3.26

sine beats

continuous sinusoid of one frequency, amplitude modulated by a sinusoid of a lower frequency



3.27

stationarity

condition that exists when a waveform is stationary and when its amplitude distribution, frequency content, and other descriptive parameters are statistically constant with time



3.28

test experience spectra; TES

test-based response spectra that define the seismic capacity of a reference equipment class



3.29

test response spectrum; TRS

response spectrum that is developed from the actual time history of the motion of the shake table



3.30

transfer function

complex frequency response function that defines the dynamic characteristics of constant parameter linear system



Note: For an ideal system, the transfer function is the ratio of the Fourier transform of the output to that of a given input.



3.31

zero period acceleration; ZPA

acceleration level of the high-frequency, unamplified portion of the response spectrum



Note: This acceleration corresponds to the maximum peak acceleration of the time history used to derive the response spectrum.



4 General discussion of earthquake environment and equipment response



4.1 Earthquake environment



Three-dimensional (3D) random ground motion caused by earthquakes may be characterized by simultaneous but statistically independent horizontal and vertical components. The strong motion portion of the earthquake may last from 10 s to 15 s, although the complete event may be considerably longer. The ground motion is typically broadband random and produces potentially damaging effects over a frequency range from 1 Hz to the cutoff frequency of response spectrum.



4.2 Equipment on foundations



The vibratory nature of the ground motion (both horizontal and vertical) can be amplified or attenuated in foundation-mounted equipment. For any given ground motion, the amplification or attenuation depends on the system’s natural frequencies (soil, foundation, and equipment) and the damping dissipation mechanisms. The typical broadband response spectra that describe the ground motion indicate that multiple-frequency excitation predominates.



4.3 Equipment on structures



The ground motion (horizontal and vertical) may be filtered by intervening building structures to produce amplified or attenuated narrowband motions within the structure. The dynamic response of equipment on structures may be further amplified or attenuated to an acceleration level many times more or less than that of the maximum ground acceleration, depending upon the equipment damping and natural frequencies. The narrowband response spectra that typically describe a building floor motion indicate that single-frequency excitation of equipment components can predominate. Similar filtering of in-structure motion may occur in flexible piping systems. For components mounted away from supports, the resultant motion may be predominantly single frequency in nature and centered near or at the resonant frequency of the piping system. This resonance condition may produce the most critical seismic load on components mounted on the line.



4.4 Simulating earthquake



4.4.1 General



The goal of seismic simulation is to reproduce the postulated earthquake environment in a realistic manner. The form of the simulated seismic motion used for the qualification of equipment by analysis or testing can be described by one of the following functions:



a) Response spectrum;



b) Time history;



c) Power spectral density (PSD).



The simulated seismic motion may be generated for the foundation, floor of the building, or substructure upon which the equipment is to be mounted. The simulated seismic motion is usually supplied by the user or the user’s agent as a part of the specifications.



Because of the directional nature of seismic motion and the filtered output motion of building and equipment structures, the directional components of the motion and their application to the equipment shall be specified or accounted for in some other appropriate manner.



4.4.2 Response spectrum



The response spectrum provides information on the maximum response of single-degree-of-freedom (SDOF) oscillators as a function of oscillator frequency and damping when subjected to an input motion. The response spectrum can indicate the frequency content and the peak value of the input motion (namely the ZPA).



It should be pointed out that the response spectrum cannot provide the following information:



a) The waveform or time history of the excitation that produced it;



b) The duration of motion (this shall be defined in the corresponding appraisal technical requirements document);



c) The dynamic response of any specific equipment.



4.4.3 Time history



A time history displays the earthquake-induced motion (usually in terms of acceleration) as a function of time. The simulated motion in seismic qualification test is derived from existing or artificially generated earthquake records. For any floor, the time history generated includes the dynamic filtering and amplification effects of the structures and other intervening support structures.



4.4.4 PSD function



The mean squared amplitude per unit frequency of the vibratory motion is characterized in terms of the PSD as a function of frequency.



Note: Although the response spectrum and the PSD function do not define the exact waveform or duration of the excitation, they are valuable tools. They enable significant frequency-dependent properties of the motion to be seen at a glance from one curve. The PSD provides information regarding the excitation directly without including the effects on an array of SDOF oscillators as is done for the response spectrum. As a result, the PSD allows application of relationships between excitation and response by way of the transfer functions for linear systems.







4.5 Supporting structure and interactions



Seismic qualification of equipment requires consideration of installation features, such as:



a) The seismic adequacy of the supporting structure (supporting assembly, structure, anchorage, floors, walls or foundation);



b) The potential for adverse seismic interactions (such as falling of overhead components, proximity impacts, differential displacements, spray, flood, or fire).

Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 General discussion of earthquake environment and equipment response
5 Seismic qualification approach
6 Damping
7 Analysis
8 Testing
9 Combined analysis and testing
10 Experience
11 Documentation
Annex A (Informative) Recommended damping ratio of typical electrical equipment in seismic analysis
Annex B (Informative) Statistically independent motions
Annex C (Informative) Test duration and number of cycles
Annex D (Informative) Fragility testing
Annex E (Informative) Measurement of ZPA
Annex F (Informative) Frequency content and stationarity
Annex G (Informative) Method of seismic qualification with reference to experience data

核电厂安全级电气设备抗震鉴定
1范围
本标准规定了为验证安全级电气设备在发生地震期间和(或)地震后能执行其安全功能而进行的抗震鉴定的实施方法及其文件要求。
本标准适用于核电厂安全级电气设备的抗震鉴定，包括其故障会对安全系统的性能产生有害影响的任何接口部件或设备。
2规范性引用文件
下列文件对于本文件的应用是必不可少的。凡是注日期的引用文件，仅注日期的版本适用于本文件。凡是不注日期的引用文件，其最新版本(包括所有的修改单)适用于本文件。
GB/T 12727核电厂安全级电气设备鉴定
3术语和定义
下列术语和定义适用于本文件。
3.1
宽频带反应谱broadband response spectrum
描述在宽频范围内产生放大反应运动的反应谱。
3.2
相干函数 coherence function
表征两个时程在频域上的相互关系。相干函数给出了两个运动统计上的相关程度，为频率的函数。其数值范围从0～+1.0，其中完全不相关运动为0，完全相关运动为+1.0。
3.3
相关系数函数 correlation coefficient function
表征两个时程在时域上的相互关系。相关系数函数给出两个运动统计上的相关程度，是以时间延迟为自变量的函数。其数值范围从0～+1.0，其中完全不相关运动为0，完全相关运动为+1.0。
3.4
关键抗震特性critical seismic characteristics
能够确保设备在地震载荷作用下执行要求功能的设计、材料和性能特性。
3.5
截止频率cutoff frequency
反应谱中零周期加速度渐近线开始处的频率。单自由度振子的频率在超过该频率后将不再放大输入运动，这是所分析波形的频率上限。
3.6
阻尼damping
一种在共振区域中减少放大量和拓宽振动反应的能量耗散机理。阻尼通常以临界阻尼的百分数来表示。临界阻尼定义为单自由度系统在初始扰动后来经振荡回复到其原来位置的最小黏性阻尼值。
3.7
地震经验谱earthquake experience spectrum；EES
根据地震经验数据来确定表征参考设备抗震能力的反应谱。
3.8
柔性设备 flexible equipment
最低共振频率小于反应谱截止频率的设备、构筑物和部件。
3.9
范围规则 inclusion rules
根据经验数据已证明为耐震设备的物理特性、动态特性和功能的可接受范围来确定参考设备组的规则。
3.10
独立物项 independent items
具有不同的物理特性或经受不同的地震运动特性[例如，不同的地震、不同的厂址、不同的构筑物，或同一构筑物的不同方向和(或)位置]的部件和设备。
3.11
窄频带反应谱narrowband response spectrum
描述一个有限(窄带)频率范围内产生放大反应运动的反应谱。
3.12
自振频率natural frequency
物体在特定的方向上受到变形然后释放时，由于其自身的物理特性(质量和刚度)使物体发生振动的频率。
3.13
运行基准地震operating basis earthquake；OBE
结合地区和当地的地质和地震情况以及当地地层材料的具体特性，在电厂正常运行寿期内可合理预期在厂址会发生的地震。
注：对于该地震产生的地震动，那些需继续运行而不对公众的健康与安全产生过度风险的核电厂设施可以保持其功能。
3.14
功率谱密度power spectral density PSD
一个波形每单位频率的均方幅值，用g2/Hz与频率的关系表示。
3.15
禁止特征prohibited features
在规定抗震能力的地震或试验激励下，会导致设备发生结构完整性及功能失效或异常的详细设计、材料、结构特征或安装特性。
3.16
鉴定寿命qualified life
证明设备在设计基准事件(DBE)之前对于规定的使用工况能满足设计要求的时间期限。
3.17
参考设备 reference equipment
用于建立参考设备组的设备。
3.18
参考设备组reference equipment class
由范围规则和禁止特征确定的一组具有相同属性的设备。
3.19
参考厂址reference site
具有确定参考设备组设备或物项的厂址。
3.20
要求反应谱required response spectrum；RRS
由用户或其委托人在鉴定技术要求文件中规定的反应谱，或人工生成能够覆盖将来应用的反应谱。
3.21
共振频率resonant frequency
受到强迫振动的系统中出现反应峰值处的频率。该频率下，反应相对于激励有相位差。
3.22
反应谱response spectrum
一组单自由度(SDOF)有阻尼振子在受相同基础激励情况下最大反应与振子频率的关系曲线。
3.23
刚性设备 rigid equipment
最低共振频率大于反应谱截止频率的设备、构筑物和部件。
3.24
安全停堆地震safe shutdown earthquake；SSE
结合地区和当地的地质和地震情况以及当地地层材料的具体特性，对可能的最大地震作出评估后确定的一个地震。
注：在该地震产生的最大地震动下一些特定的构筑物、系统和部件需保持其功能。这些构筑物、系统和部件对保证下列要求是必需的：
a)反应堆冷却剂压力边界的完整性；
b)使反应堆停堆并维持反应堆在安全停堆状态的能力；
c)防止或减轻厂外辐照事故后果的能力。
3.25
抗震能力 seismic capacity
经过验证的设备所能经受的最大地震水平。
3.26
正弦拍波sine beats
幅值受较低频率正弦波调制的某一频率的连续正弦波。
3.27
稳定性stationarity
波形是稳定时，其幅值分布、频率成分和其他特征参数不随时间而变化。
3.28
试验经验谱test experience spectra；TES
确定参考设备组抗震能力的、基于试验的反应谱。
3.29
试验反应谱test response spectrum；TRS
由地震台面运动的实际时程得到的反应谱。
3.30
传递函数transfer function
一个用来确定常系数线性系统动态特性的复频响应函数。
注：对于一个理想系统，传递函数为输出与给定输入的傅里叶变换之比。
3.31
零周期加速度zero period acceleration；ZPA
反应谱高频、未被放大部分的加速度水平。
注：该加速度相当于用来推导反应谱的时程的最大峰值加速度。
4地震环境和设备反应概论
4.1 地震环境
地震产生的三维随机地而运动可用同时发生且统计上相互独立的水平和垂直分量来表征。虽然整个地震事件可能持续较长的时间，但其强震持续时间可能仅10 s～15 s。地面运动是典型的宽频带随机运动，在1 Hz至反应谱截止频率的频率范围内可能产生破坏作用。
4.2基础上的设备
对安装在基础上的设备，地面运动(水平和垂直)的振动特性可能被放大或衰减。对于任何给定的地面运动，放大或衰减取决于系统(土壤、基础和设备)的自振频率和阻尼耗散机理。地面运动大都采用宽带反应谱进行描述，说明多频激励起了主导作用。
4.3结构上的设备
地面运动(水平和垂直)可因相关结构的滤波作用而在结构中产生放大或衰减的窄带运动。结构上设备的动态反应加速度则会得到进一步的放大或衰减，可达最大地面加速度的数倍或若干分之一，具体取决于设备的阻尼和自振频率。通常采用窄频带反应谱来描述构筑物的楼面运动，表明对设备部件的单频激励起主导作用。构筑物运动中的类似滤波作用在柔性管道系统中也会发生。对于不在支承上安装的部件，最终的运动可能是以管系共振频率(或其附近)为主的单频。这种共振条件会对安装在管线上的部件产生最苛刻的地震载荷。
4.4模拟地震
4.4.1概述
地震模拟的目的是用可行的方式复现假定的地震环境。采用分析或试验方法鉴定设备时所用的模拟地震运动，可由下列任何一种形式给出：
a)反应谱；
b)时程；
c)功率谱密度(PSD)。
可为基础、构筑物楼面或安装设备的子结构生成模拟地震运动。这些模拟地震运动通常由用户或其委托人在设备规格书中规定。
由于地震运动的方向性以及构筑物和设备结构滤波后输出运动的方向性，运动的方向分量及其对设备的作用应加以规定，或以其他适当的方式进行说明。
4.4.2 反应谱
反应谱给出了单自由度振子在给定输入运动下的最大反应信息，它是振子频率和阻尼的函数。反应谱能给出输入运动的频率成分和运动峰值(即零周期加速度)。
需要指出的是反应谱不能提供下列信息：
a)产生反应谱的激励波形或时程；
b)运动持续时间(这应在相应的鉴定技术要求文件中规定)；
c)任何特定设备的动态反应。
4.4.3时程
地震引起的运动(通常为加速度)随时间变化的函数即为时程。抗震鉴定试验时所模拟的运动来自实际或人工产生的地震记录。对任一楼面，所生成的时程包括了构筑物和其他中间支承结构的动态滤波和放火效应。
4.4.4功率谱密度函数
功率谱密度表征某一运动参数单位频率内振动幅值的均方值，它是频率的函数。
注：尽管反应谱和功率谱密度函数不能确定确切的激励波形或持续时间，它们依然是有用的工具，能从一根曲线上得到运动的重要频率特性。功率谱密度直接给出了关于激励的信息，但并来像反应谱那样考虑激励对一组单自由度振子的作用。因此，利用线性系统的传递函数理论，可以根据功率谱密度确定激励和反应之间的关系。
4.5支承结构和相互作用
设备抗震鉴定需考虑安装特性，如：
a)支承结构(支承组件、结构、锚固件、楼面、墙或基础)抗震适用性；
b)有害的地震相互作用可能性(如上部部件的跌落、邻近的撞击、不同的位移、喷淋、水淹或火灾)。
5抗震鉴定方法
5.1 概述
设备的抗震鉴定应证明在承受由一个安全停堆地震产生的作用力期间和(或)之后设备执行其安全功能的能力。另外。在承受安全停堆地震之前，设备应承受若干运行基准地震的作用。
5.2抗震鉴定技术条件
抗震鉴定需明确规定被鉴定设备的技术条件，具体详见第11章。
应明确规定抗震要求的技术条件至少包括：持续时间、频率范围和加速度值。提供这些数据信息的可以是：
a)以功率谱密度(频率的函数)表示的振动运动；
b)地震强震部分的持续时间；
c)设备安装点上的要求反应谱，要求反应谱必需包括主水平轴和垂直轴的数据，以及不同阻尼比(如2％、5％和7％)的数据；
d)设备安装点(楼板或构筑物)上的最大加速度与重要频率的关系曲线或时程曲线。
对于运行基准地震(OBE)和安全停堆地震(SSE)，其反应谱的形状和幅值均可能不同。故为了对试验件进行鉴定，应知道这些地震水平所相应的加速度谱。技术条件应说明所用反应谱的合理性。
5.3 常用抗震鉴定方法
常用的抗震鉴定方法通常有四种：
a)通过分析来预测设备性能；
b)在模拟地震条件下对设备进行试验；
c)采用试验和分析相结合的方法来鉴定设备；
d)通过使用经验数据来鉴定设备。
上述每一种方法，或其他证明合理的方法均适用于验证设备的抗震性能。选择适用的鉴定方法至少需考虑以下因素：
a)设备结构的类型、尺寸、形状和复杂程度；
b)是通过(设备)可操作性，还是仅仅通过结构完整性验证安全功能；
c)结论的可靠性。
被鉴定的设备应能够证明在地震期间和(或)之后能执行其安全功能。要求的安全功能不仅取决于设备本身，还取决于设备在系统和电厂中的作用。地震期间的安全功能可能与地震之后所要求的安全功能相同，也可能不同。例如，可能要求某一电气设备在地震期间不误动作，或在地震期间和之后都能执行能动功能，或可能要求它在地震期间保持完好而在地震之后要求执行能动功能，或是上面这些要求的任意组合。而对另一设备，可能只要求在地震期间和之后保持结构完整性。这些给定要求应是明确的，并且对安全功能的定义应作为设备鉴定技术要求文件的一部分给出。验证所选用的鉴定方法符合要求是用户和(或)委托方的职责。
当设备安全功能要求证实设备在地震期间的可运行性时，应在鉴定模拟的强震运动持续部分进行。
作为总的鉴定大纲的一部分，抗震试验应按GB/T 12727或其他适用标准指明的顺序进行，并注意按相关标准中所讨论的试验裕度来确定和考虑显著的老化机理。在这些导则中，应证明设备在其整个鉴定寿期中能执行其安全功能，包括在鉴定寿期末发生安全停堆地震期间和(或)之后的功能可运行性。
6 阻尼
6.1概述
阻尼是系统中多种能量耗散机理的统称。实际上，阻尼取决于许多参数，如结构系统、振型、应变、法向力、速度、材料、连接方式和滑动量。按线性振动理论，简化假设为阻尼是纯黏性的，或与运动部件的相对速度成正比。因此，当涉及一个实际系统的阻尼值时，通常假定它是等效于黏性或是线性的。通常这是采用线性分析理论方法来描述具有某种程度非线性的实际硬件性能的一种简化方法。
对于由许多部件组成的设备，阻尼常常不是单一值，阻尼与设备的每一个部件都有关系，从螺栓连接或焊接结构到材料性质。在确定设备阻尼值时，通常给出典型值的范围。由于在多数情况下，设备、构筑物、部件各振型的阻尼值是不同的，因此在分析中常常在所研究的频率范围内采用一个综合的阻尼值。
6.2 阻尼测量
6.2.1 概述
线性振动理论表明有许多测量阻尼的方法。应特别注意实际系统与理论模型之间的对应关系。例如，几乎不可能找出设备中与模型集中质量单元严格一致的精确位置。一些计算模态阻尼的方法，如Q值法，完全依赖于单自由度的假设。
注：Q值是单自由度振子传递函数幅值的峰值，与阻尼比存在如下关系：Q=0.5ξ-1。通过测量半功率带宽可确定Q=fn/Δf，其中fa为共振频率，Δf为半功率带宽。
由于设备中各点的反应通常由振型向量和每个振型的参与因子确定，所以直接由在设备中任何点上测得的最大共振反应峰值和正弦扫描输入激励幅值计算阻尼通常是不可接受的。为估计阻尼，常用下列方法，但也可采用其他证明是合理的方法。这些方法假设在设备中能激励起单一振型，且运动传感器安装在非零运动位置上。任何情况下都应仔细考虑，针对不同的反应幅值是否存在明显的阻尼非线性。
6.2.2通过测量衰减来确定阻尼
等效黏性阻尼可通过记录特定振型的衰减率进行计算。这个方法通常称作对数衰减法。
6.2.3通过测量半功率带宽确定阻尼
以慢速正弦扫描激励设备，测量设备中任意要求位置的反应并绘制成频率函数的曲线。从这些反应曲线上，与每个振型有关的阻尼可通过测量其半功率点处相应共振峰的宽度进行计算。这个方法常称为半功率带宽法。
6.2.4通过曲线拟合法确定阻尼
用正弦扫描、随机或瞬态激励对设备进行激振，并通过反应获得相应的传递函数。利用数学模型对实际频率反应数据(传递函数)进行拟合，即能得到各阶频率下的模态阻尼。这种曲线拟合通过平滑处理能去除噪声或小的实验误差。
6.3 阻尼的应用
6.3.1 分析中阻尼的应用
分析中，为预计设备对地震运动的反应建立设备的数学模型，该模型中所用的阻尼值需对应于设备中实际的能量耗散，以便能精确地预估反应。另一个方法是用一个保守的线性阻尼值来得到保守的反应。在任何情况下，都需要知道具体设备的阻尼范围和非线性的性质及它们对反应的影响。合适的阻尼值可从试验或其他经证明是合理的来源获得。
实际阻尼本质上是非线性的。在大多数设备中，由于如材料内摩擦或部件之间连接处的内摩擦，或库仑型滑动摩擦等因素，实际阻尼是反应幅值的函数。对分析而言，可采用线性阻尼进行近似，但需注意阻尼实际上是随反应增加而变化的。
一般来说，对结构系统的主要处理方法是假定阻尼是黏性的。然而，某些机柜或壳体可能表现出非黏性阻尼的特征，分析中对此需加以关注。
除非另有规定，分析中典型的电气设备阻尼比推荐值可参见附录A。
6.3.2试验中阻尼的应用
试验中，可使设备经受由要求反应谱(RRS)所确定的人工模拟地震运动时程来鉴定设备。反应谱通过一组单自由度有阻尼振子的峰值反应来确定地震运动。由于振子是假设的，在用于试验的要求反应谱中可采用任何可行的阻尼值，例如5％，并且不需要与设备的实际阻尼相一致(注意与分析中使用的要求反应谱的区别，分析时采用的阻尼值应与实际设备相对应)。在8.6.1中给出了在选择可接受的试验运动中要求反应谱(RRS)和试验反应谱(TRS)的应用。对于反应谱中的阻尼值，有下列关系：
a)在比较要求反应谱和试验反应谱时，两个反应谱的阻尼应相同；
b)在不同阻尼下比较要求反应谱和试验反应谱时，则需考虑以下情况：
1)当试验反应谱的阻尼大于要求反应谱且满足8.6.1中的准则时，这种情况是保守的，鉴定结果可以接受；
2)当试验反应谱的阻尼小于要求反应谱的阻尼时，则应进行进一步的评估。一种可能性是对试验运动进行重新分析以产生一个可接受阻尼值的试验反应谱，并应用a)或b)的1)中给出的准则。