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MCG Electronics, Inc.
12 Burt Drive
Deer Park, NY 11729, USA

Date:        August 27, 2001
日期: 2001年 8月27日
From:         Michael J. Coyle, President
发件人 Michael J. Coyle 先生,总裁
Subject    :    Questions from Mr. Lin Wei Yong of July 20, 2001
主题: (回复)林维勇先生2001年7月20日的问题


IEC 60364-1            Performance requirements and testing methods.
IEC 61312-1            Protection against Lightning Electromagnetic Impulse.
IEC 61643-5-534        Devices for protection against overvoltages.
ANSI C62.41-1991        IEEE Recommended Practice on Surge Voltages ....
                IEEE 所建议的电涌过电压防护措施......
Data Sheet no. 1 - Dec. 2000    French Lightning Protection Association (Appendix I)
第2000年12月的第一号数据表    法国防雷协会(附录 I)

1. LWY:  Should external electric and telecommunication lines entering structures with external lightning protection system (LPS) be protected against the effect of a direct lightning stroke striking that LPS?

MJC:  An external Lightning Protection System (LPS) means, to me, that lightning rods, related cabling and a building grounding method are already in place. So the only concern is the direct protection of the electric and telecommunication lines entering the building.

Surge protection should be provided at the point where the power and telecommunication lines enter and leave the building.

The AC power lines should be protected at the origin (building entry point) and at each of the succeeding protection zones within the building. The AC power lines and the telecommunication lines should be referenced together at the building entry point.

Because of the susceptibility of I/O ports to transient damage, from both power line and data line pathways, it has been MCG's practice to provide data line protection immediately at, and referenced to, the cabinet of the sensitive equipment. In essence this provides the ultimate zone protection!
由于电力线及数据线的I/O口容易受到瞬态电涌的损坏,MCG的一贯做法是:在敏感设备的机壳上直接安装数据线防护器,并将地线与机壳相连接地,此种做法为设备提供了最大的 区域保护。

2.    LWY:  How do we select or determine the parameters of a direct lightning stroke and how do we adequately protect against it.

MJC:  1st: Site surveys:

Here are some factors that might indicate the size of the problem.

* Does the site have a Lightning Protection System in place?
* 现场是否安装有雷击保护系统?
* Are there any visible arc marks on upper surfaces LPS rods?
* 避雷针的上部表面是否有可见的电弧放电痕迹?
* Does the site have a past history of equipment damage and its extent.
* 现场是否有遭受雷击而引起设备损坏的历史?设备的损坏程度?
* Do lights blink during lightning storms?
* 在雷暴期间,灯光是否会闪烁不定?
* Are computer operations disrupted during lightning storms?
* 在雷暴期间,计算机的操作是否中断过?
* Were transient measurements made at the site or during storms?
* 在正常天气或雷暴期间,是否对现场进行过电涌的测量?

Other factors to consider are:

2nd: Standards Committees:

A number of Standards Committees have addressed lightning and overvoltage conditions that appear on power lines.

The USA Standards are: ANSI - C62.41 and ANSI - C62.45 and others.
美国的标准为:ANSI - C62.41 及 ANSI - C62.45 及其他。
The European Standards are: IEC 60364 and IEC 61312 .
欧洲的标准为:IEC 60364 及 IEC 61312 .

* Some of the European community favors the 10/350 (s waveform for testing certain conditions, while the USA community has been using the 8/20 (s waveform, since the middle 1960's.
一些欧洲的机构倾向于使用10/350(s波形作为测试的一些条件, 而美国的机构从60年代中期起,就一直使用8/20 (s 波形。

* A French Standards Group, the Association Protection Foudre, in its Data Sheet no. 1 December 2000 under "Conditions of Use" lists a series of compelling arguments concerning the problems caused by Spark-gap protection on AC power systems. In particular, a system's operational reliability will be severely compromised as discussed in sections 4 and 7. See Appendix 1 for the complete article.
法国标准机构“防雷协会”(the Association Protection Foudre), 在其2000年12月的第一号数据表中的“使用条件”项目下,就火花间隙保护在交流电源系统中所造成的问题,列举了一系列令人不得不信服的论据。在第4节及第7节的讨论中,请参阅附录一全文,特别提及了(火花间隙保护)对系统运行可靠性的严重削减。

* In Class II, III and IV applications, both the ANSI and IEC groups are in agreement that an 8/20 waveform is appropriate. Data Sheet no. 1 - Dec. 2000    French Lightning Protection Association (Appendix I) indicates, in section 10, that a 20kA, 8/20 us waveform is appropriate on lightning rod fitted buildings.
ANSI及IEC两个组织在II、III及IV级的应用中,都同意使用8/20(s波形是合适的。 法国防雷协会,2000年12月第一号数据表(见附录一)中第10节指出:20KA,8/20 us波形适用于安装了避雷针的建筑物。

3rd: Field experience.

Since the 1960's, surge protectors, employing MOV and MOV-hybrid technology, have been widely deployed in the USA to suppress lightning and overvoltage surges based on the ANSI - C62.41 8/20(s waveform standards.
自从60年代以来,根据ANSI C-62.41,8/20(s波形的标准,采用MOV(金属氧化物可变电 阻--译者注)及MOV混合技术的电涌防护器在美国已被广泛地应用,用于抑制雷击和过电 压电涌。

Lightning activity, in the United States, varies widely, from very little to extensive year-round activity. In fact it is equal to the lightning activity of China. The failure rate of SPD equipment in the U.S. has been remarkably low, when using the 8/20(s waveform as a guide, even in high exposure situations.

4th: Independent 3rd Party Assessment: Bell Telephone Laboratories

Technical arguments can be made about the validity of the 8/20 (s or the 10/350 (s waveform to properly approximates the transient waveforms that might appear at the building entry.

* In the 1960's, Bell Telephone Laboratories had occasion to investigate lightning transient damage that occurred at a number of their highly automated telephone Central Office sites.

* This study resulted in a Bellcore Protection Standard document being issued that defined the building entry protection characteristics for their Central Office sites to be a 20kA, 1.2/50(s -8/20 (s combination wave .
调查研究的结果致使了“贝尔防护标准”的发表,标准中定义:它们的中心现场建筑物的进口端的防范对象为20kA、 1.2/50(s 及8/20 (s的混合波形。

* A copy of the Bellcore specification can be made available if you are interested. This Standard has been in effect for over 20 years with excellent results.

5th : Computer Equipment Designs:.
第 5:计算机设备的设计:

In the United States, an independent industry group, the Computer Business Equipment Manufacturers Association (CBEMA) issued design guidelines for equipment connected to the AC power lines.
在美国,“计算机商用设备制造协会”(CBEMA)是独立的工业团体,发表了 与交流供电系统连接的设备之设计准则。

This standard was designed to reduce the susceptibility of their sensitive equipment to AC power line transients and long duration overvoltages. On a 120VAC power line, for example, the computer equipment would be required to withstand, at least, a 841V peak transient voltage for 100 (s. Figure 2 in Mr. Dion Neri's article indicates the transient voltage withstand levels for other AC rms line voltages.
此标准的设计目的是:降低敏感设备对来自交流电源的电涌及长时延过电压的敏感性。例如:对于120V的交流供电系统,计算机设备对峰值为841V瞬态过电压至少,应能承受100 微秒。Dion Neri 先生的文章中,插图2指出其它交流电源的有效值线电压对瞬态过电压 的承受水平。

MCG designs its SPD's to operate safely above the longer duration AC power line surges (Uc >= 1.5 x Io) and yet below the CBEMA developed voltage withstand levels. Our protectors are operated in this narrow protection window by our use of our low voltage drop Micro-Z (tm)cable. The Micro-Z (tm) cable is supplied as part of our SPD without extra charge.
MCG对其电涌防护产品的设计,使其能在长时延的交流电源线电涌(Uc >= 1.5 x lo ) 下安全工作,但低于CBEMA规定的过电压承受水平。由于使用了我们的专利产品-低压降Micro-Z (tm)线缆,我们的防护器工作在这样狭小的保护范围内。 Micro-Z (tm)线缆, 作为 我们SPD产品的一部分,不另外收费。

6th Recommended Lightning Surge protection
第 6:被推荐的雷电电涌保护

The final decision depends on the answers to several questions.
* How critical is the facility?
* 被保护设备的重要性?
* What is the likely severity of the transient impulse current?
* 瞬态脉冲电流的强度有多大?
* What is the voltage sensitivity of down stream equipment?
* 下游负载设备耐过压的能力有多高?

To guard against direct, or nearby lightning strikes to the building or on the secondary side of the utility power transformer, install one of MCG's substantial SPDs at the site's main distribution panel. A typical model is MCG's 405XT models, which are capable of diverting up to 400 kA, 8/20 us and will easily meet any requirements at a reasonable cost.
为防护建筑物受直接雷击、或邻近雷击或供电变压器低压端受雷击(引起的电涌-译者注),可在建筑物主配电盘上安装一个MCG的重型防护器,典型的型号为405XT, 它能分流高达400kA, 8/20 us的电涌, 合理的价格,轻松的满足任何标准的要求。

If a site is unlikely to be directly hit but needs protection from remote strikes to utility transmission lines, then a moderately sized protector at the building entry point or main distribution panel will generally be sufficient to provide excellent protection. MCG's SPD models, 205XT and 305XT would be suitable. Smaller protectors can be employed deeper within the building.

7th: Mandatory IEC compliance
第 7:强制与 IEC一致

In territories bound to comply with IEC European standards, a survey, similar to the one suggested above may help indicate which situations require use of an SPD tested to IEC's Class I 10/350(s test standard. In such cases I would suggest that consideration be given to the following approach:
在必须执行IEC欧洲标准的地区,一个类似于上面所提及的问答也许会有助于明确在何种情况下应使用经IEC Class I 10/350(s波形测试过的电涌防护器。在这种情况下, 我建议对下述方法给予考虑:

For any site requiring an SPD tested to IEC's Class I requirements (10/350(s) - to the recommended lighting protection given above, merely add a suitable a spark-gap protector that is mounted at the power entry point of the building.
任何地方,如果需要采用符合 IEC Class I 测试要求(10/350(s)的电涌防护器,按以上 建议的雷电防护措施,只在建筑物电源线进口端加装一个适当的火花间隙保护器 。

A spark gap-mov coordination activity would be needed to assure proper performance per IEC 61643, Working Group 37A, Annex A 6.3. This coordination exercise could easily be developed into a standard instruction set for site preparation.
根据 IEC 61643,“工作组合”37A,附录 A 6.3,火花间隙和MOV之间需要协调配合, 以确保真正的保护性能。这种协调配合的步骤可容易地被编为标准指南,作为现场应用规范。

3. LWY:  How do we select the rated values of Uc, Up, In, Imax, Iimp (according to IEC 61312 - for a direct lightning strike).
如何选择设定值 Up, In, Imax, Iimp(根据IEC 61312-直击雷击)?

MJC:  If the site is being protected by a Class I spark-gap protector, the device's specifications will be set for Imax, In and Q. These levels are set by having an appreciation of the factors outlined under question 2.
如果现场安装有一个等级 I 的火花间隙保护器,设备的技术规格将被设为Imax、In 及 Q, 这些值的设定取决于如上问题 2中所提及的因素。

The proper selection criteria for Uc would depend on the site's equipment susceptibility to upset or damage. Either IEC standards or MCG's CBEMA based standards would be applied

If the entire site were to protect using Class II, III and/or IV criteria, we would suggest limiting voltage levels based on CBEMA criteria.
如果整个现场需要采用Class II,III 及/或 IV标准进行保护,我们建议根据CBEMA标准 来限定电压水平。

4. LWY:  What are the current views in USA about IEC 61312 protection against LEMP.

MJC:  My opinion and some discussions I've had with knowledgeable surge protection people, in the USA, leads me to believe that the Class I 10/350 (s criteria are probably excessive, in many cases. This belief is grounded on the successful application of the ANSI C62.41 -1991 combination waveforms in the USA and other countries.
我个人的意见以及和美国本土一些电涌防护人士所作过的讨论使我相信Class I 10/350(s标准在很多情况下,可能过于极端,这种观点建立的基础是ANSI.C62.41-1991组 合波形 标准在美国和其他国家的成功应用。

Mr. Donald Worden, a leading member of the IEEE Surge Protection Committees would be much better qualified to discuss this issue.
Donald Worden先生- IEEE电涌防护委员会的核心成员,更具资格讨论这方面的问题。

The French Lightning Protection Association cautions against the use of Spark Gap protectors in most applications. A copy of the Association's technical data sheet on this subject can be supplied to you.

5.     LWY:  If SPDs are to be installed at more than one location in a building, what issues must be considered in coordinating the SPDs at building entrance and others connected to the same line?

If SPDs are installed throughout the site, using ANSI C62.41-1991 Standards, then no coordination of MCG's equipment is required.

Our experience in using SPD's connected on the same power line, but located at different points within a building has been very favorable.

This coordination issue has been documented in Mr. Dion Neri's article 'Surge Protection: Where and How Much?" that appeared in the March 1999 issue of EC&M magazine. A copy can be forward if necessary.
关于这个协调配合的问题已在 Dion Neri 先生的题为:“电涌保护:哪里和多少?”的文章中阐述并发表在1999年3月的EC&M杂志中。 如果需要可提供一份复印件。

The article reported on a study undertaken in MCG's facility to determine the interactions between various combinations of SPDs connected on the same power line and at different distances from the building entry. All units had the same clamping voltage MOV's.

The conclusion : No special coordination activities need to be undertaken because the power line's inherent resistance and inductance parameters, which vary with length, eliminates the need for any special coordination activities."

If SPDs are installed using IEC Standards, then coordination activities would need to be considered between IEC Class I SPD's and any use of MCG's Class II, III and IV protectors.

The IEC documentation is very clear on the need for isolating inductance, between Class I and Class II locations. Coordination of SPD's can be achieved, but it would entail considerable, and we believe to be unnecessary, building rewiring costs.
IEC的文件非常清楚地指出:需要在Class I 和 Class II之间使用隔离电感。 做到了SPD的协调配合,其花费也相当可观,我们相信重新布线的费用是不必要的。

6. LWY:  When protecting a building it is permitted to install a separate grounding electrode for special equipment? If an equipment manufacturer requires this , how do we deal with this problem?

MJC:  If the installation does not adhere to the IEC "zone" protection concept, then we recommend the following.

Normally, the equipment to be protected is enclosed in a metal cabinet, which is essentially a Faraday cage. The only access points for transients are the AC power line wires and any data and telecommunication wiring.

The SPDs, both AC power and Data Line protectors, are installed at the point where the wires enter the cabinet. The SPDs must be referenced to the metal cabinet by very short leads.

This approach protects the internal circuitry independently of whatever grounding arrangements are made.

7.    LWY:  In the NEC of USA, it is permitted to use the isolated / insulated grounding method. What is the current view in the USA about this method. What is its application scope? What are its advantages and its shortcomings? Since this method is a contradiction to the bonding required at the same place or in the same room, how do we treat this contradiction?   

MJC:  This question is similar to Question 6 above.                

Manufacturers will attempt to isolate their equipment from disturbances of a transient nature that may appear on the AC lines and data lines (I/O ports), or on the building ground system. A manufacturer will often require that an isolation transformer be connected in front of their equipment, and that their equipment be connected to a separate, isolated ground.

The manufacturer is, in effect, attempting to create a protected zone environment for his equipment, so as to avoid site problems. Frequently, this quasi-zone approach fails because coaxial cables will be extend from their equipment to equipment grounded at other locations. Thus, sneak transient pathways are reintroduced into the system. I believe the site problems need to be more directly addressed, with much more attention given to the zone concept.
设备生产商试图为其设备创建一个保护区环境以避免现场环境所产生的问题。通常, 这种类似的方法都失败了,因为同轴线将从他们的设备延伸到在其他地方接地的设备。由此,电涌进入的路径又被重新引入到系统中来。 我认为,现场的问题需要被更直接地论述,并对”区域”概念给予更多的考虑。

8. LWY:  In a building, how do we provide for protection against overvoltage switching? What are its origins and magnitude? How do we protect against it?

MJC:  The sources of these internal transients are everyday items, such as air compressors, arc welders, pumps, elevators, switching power supplies and other inductive loads.
这些内部电涌的根源是每天都会使用的设备, 如空气压缩机,电弧焊接机,泵,电梯,开关电源和其他的感应负载。

Each piece of machinery will place unique transient waveforms on the AC power line. These transient amplitudes depend on the rms current interrupted, the point on the sine wave when the interruption occurred, the speed of the disconnection etc.

For example, a 20 hp induction motor (230vac line to line, 4 pole, wye connected) contains about 39 joules of stored energy per phase (assuming maximum torque). Such a motor can produce a transient overvoltage, reaching many thousands of volts, when the normal rms current is interrupted. Considering that switching occurs often, any loads connected to the same distribution / branch panel will be vulnerable to damage or disruption.
例如,一个20匹马力的感应电机(230VAC 线对线,4极,Y形连接)包括了大约每相39焦耳的储存电能(假设最大的扭矩)。当通常的均方根电流被打断,这样的一个电机可以产生一个可达几千伏的电涌过压。考虑到开关操作经常发生,与同一个配电柜/分线箱连接的负载都会很容易受到损害或中断。

The proper and most cost-effective method to protect against locally generated transients is to use smaller and less expensive SPDs directly at the local service panels. These smaller units are exceptionally rugged and will handle virtually any internally generated transient.
最经济有效的方法是在本地配电盘处直接使用小型低成本的SPD防护局部产生的电涌。 这些小型的装置特别结实,能有效地应付任何内部产生的电涌。

Since the SPD device is located at the intersection point of many pieces of equipment, it is a very cost-effective approach since it is not often necessary to protect individual pieces of equipment.

You might wonder if the surge protector installed at the service entrance would also protect equipment within the facility. Unfortunately, it doesn't. The heavy-duty service entrance protector is too far away, inductance-wise, to be able to limit locally developed transients.
你可能想知道安装在总进线端的电涌保护器是否也会保护建筑内的设备。很遗憾,不会。 因为这个重型的进线端的保护器,由于距离太远、电感的原因,不能有效地抑制局部 产生的电涌。

9. LWY:  What is the application scope of star bonding ( single point grounding) and meshed bonding ( multipoint grounding) networks. What items need to be noted between them?

MJC:  Building steel, when properly bonded together, approximates an ideal Faraday cage. Inside the building, all the metal cabinets are wired to a common ground plate located where the power lines (and telecommunication lines) enter the building. This ground plate is then connected to a ground rod and building steel at this point of entry. This approach provides excellent shielding, for the equipment within the building, from direct lightning strikes.

Meshed bonding enables a site to achieve a considerably lower ground resistance pathway for diverting direct lightning strikes to earth ground. In essence, it is a Faraday cage with an entire side connected to earth via multiple ground rods.

SPDs connected at the power entry point will continue to clamp transient voltages on the AC power lines to safe levels. SPDs located at interior zones will also function effectively. 连接在电源入口处的SPD会持续将交流电源线上的电涌电压,钳制到安全的水平。位于内部各区域的SPD也将有效地发挥作用。

10. LWY:  For telecommunication lines, when its outside part uses optical fiber cable and at the entrance of building it is then changed to metallic line, such as twisted pair or coaxial cable. Does it also need to consider the coordination between the power side and the signal side of a single piece of equipment? And how to consider the protection of the above metallic line in the building against overvoltage?

MJC:  Normally an equipment's circuitry is enclosed in a metal cabinet and its IC's, microprocessors etc. are protected as if in a Faraday cage.

The only access points for transients are via the AC or DC power line wires and all of the data and telcom signal wiring that enters and leaves the cabinet.

If we protect each wire as it passes through the metal cabinet wall and reference it directly, with a wire less than 6 inches (15 cm) to the metal cabinet, then excellent protection is assured.

If the optical fiber were brought directly into the cabinet, then it would be unnecessary to provide any data line or telecom protection, since there would not be a metallic pathway for transient voltage to enter into the equipment.

It is recommended that twisted pair wiring and coaxial cabling be provided with suitable data line protection, at the point where the signals penetrate the metal cabinet walls, with the protectors referenced to the metal cabinet by a short wire (< 15cm).

11. LWY:  In USA, what are the views about requirements of 534.2.3.1 and how should they be dealt with?

MJC:  In TT systems, according to figure B.1, Uc shall be >= 1.5*Uo.
在TT系统中,根据图B.1,Uc应 >=1.5*Uo。
In TN and TT systems, according to figure B.2 Uc shall be >= 1.1* Uo.
在TN和TT系统中,根据图B.2,Uc应 >=1.1*Uo。
In IT systems, Uc shall be at least as high as the line to line voltage U.
在 IT系统中,Uc应至少与线-线 电压 U相等。

We are in agreement with 534.2.3.1 that the maximum continuous voltage Uc of SPD's shall be not less than the maximum actual continuous voltage between the terminals of the SPD.
我们赞同534.2.3.1 -- SPD的最大持续电压Uc必须不少于SPD端点间的最大实际持续电压。

It is our experience that SPDs, properly sized for transient surges, are much more likely to fail in service because of longer duration, multi-cycle surges that occur on some AC power systems.

For TT, TN, and IT systems, Our SPDs will be Uc >= 1.5 x Uo.    
对于TT、TN和 IT系统,我们的SPD会是Uc >= 1.5 x Uo。

In the USA, our minimum Uc >= 1.15 x Uo.
在美国,我们最小的Uc >= 1.15 x Uo。

A typical model no. is 205XT-120Y, with Uc >= 1.15 x Uo.
典型的型号是205XT-120Y,其Uc >= 1.15 x Uo。

Overseas, we normally supply Uc >= 1.5 x Uo.
在海外,我们通常提供Uc >= 1.5 x Uo的产品。

A typical model no. is 205XT-120Y (180), with Uc >= 1.5 x Uo.
典型的型号是205XT-120Y (180),其Uc >= 1.5 x Uo。

12.   LWY:  In USA, what are your views about requirements of 534.2.3.4 and how should they be dealt with? If the SPD is installed at the origin of an electrical installation supplied by the public distribution system, the rated discharge current shall not be less than 5 kA.   

MJC:  This appears to be a Class II application, since Imax, Iimp and Q were not mentioned. Class II performance, to 20 kA, 8/20us and higher, is easily achieved by MCG's line of surge protection devices.
这似乎是一个II 级应用,因为没有提及Imax,Iimp和Q。II 级的性能要求20KA,8/20 us或更高,MCG的电涌防护产品系列很容易做到。

Note 2- in the presence of a lightning protection system the discharge current will be substantially higher and an assessment will lead to the choice of a higher rated discharge current for the SPD.
注2---有雷击防护系统的情形下,放电电流会明显较高,因而应选择更高额定放电电流 的 SPD。

Mention of an external LPS was made, but no mention of Imax, Iimp or Q were made. Note 2 seems to imply a possible Class I situation. If so then, any Class II protector should be located at the main distribution panel and suitable steps taken to insure coordination between the SPD's.
曾提到过外部的LPS,但未提及LMAX,LIMP或Q。注2似乎在暗指一个可能的Class I 情形。如果是这样的话,那么任何Class II 保护器都必须放在主配电盘上并采取适当的步骤以确保SPD间的协调配合。

If Note 2- isn't requiring a Class I (10/350 us) waveform, then MCG's line of XT models, which are capable to 400 kA (8/20us) and higher, third party tested will easily meet any requirements at a reasonable cost.

13. LWY:  In the USA, what are the views about coordination of SPD's (per requirement of 534.2.3.6) and how should it be dealt with?   

MJC:  Generally the view about coordination is that it should be adhered to, if the situation warrants it. However, in the USA, it is much less of a problem since the use of spark gaps and MOV's, in concert, seldom occurs. This greatly reduces the installation costs

For SPDs, with a protective level different from that provided at the origin, as in the IEC standards, then coordination is mandatory. For coordination to be effective an inductance is inserted between the origin installed SPD and the downstream SPD's. The IEC documentation appears to be useful in this regard. MCG would certainly provide suitable instructions for installing our equipment in such a situation.   

Incidentally, MCG has always been engaged in coordinating activities within our Data line protectors. We use a isolating impedance between the gas diode and the silicon avalanche diodes, to permit the gas tube to operate properly and to permit the low energy avalanche diode to perform its voltage limiting function - without being damaged.

 本页最后修改时间:2011年08月26日 09:17:00