4_IEC_EN_61800-5-1_Thermal_energy_hazards

Successful product safety design for equipments covered by IEC/EN 61800-5-1 Thermal and energy Hazard Section
presented by Zhengdong Ma, Medical group leader TUV SUD Jiangsu
EN 61800-5-1 3.22 prospective short-circuit current current which flows when the supply conductors to the circuit are short-circuited by a conductor of negligible impedance located as near as possible to the supply terminals of the PDS/CDM/BDM 4.3.9 For co-ordination with upstream protection devices, the manufacturer shall specify a maximum prospective short-circuit current rating corresponding to each power output of the CDM/BDM. If protection devices with particular characteristics are necessary, these shall also be specified. NOTE The maximum prospective short-circuit current rating refers to the capability of the power source which supplies the PDS.
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The short-circuit stresses may be reduced by the use of current-limiting devices (inductances, current-limiting fuses or other current-limiting switching devices).
IEC 60439-1 2.10.3 cut-off current; let-through current the maximum instantaneous value of current attained during the breaking operation of a switching device or a fuse [IEV 441-17-12] NOTE This concept is of particular importance when the switching device or the fuse operates in such a manner that the prospective peak current of the circuit is not reached. That means, when short circuit occurred, fuse may reduce/limit prospective peak current to a expected limit.
TÜ V SÜ D Group
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21 November 2008
Short circuit
All electrical systems are susceptible to short circuits and the abnormal current levels they create. These currents can produce considerable thermal and mechanical stresses in electrical distribution equipment. Therefore, it's important to protect personnel and equipment by calculating short-circuit currents during system upgrade and design. Because these calculations are life-safety related, they're mandated by 110.9 of the NEC, which states: “Equipment intended to interrupt current at fault levels shall have an interrupting rating sufficient for the nominal circuit voltage and the current that is available at the line terminals of the equipment. Equipment intended to interrupt current at other than fault levels shall have an interrupting rating at nominal circuit voltage sufficient for the current that must be interrupted.”
TÜ V SÜ D Group
Department name 21 November 2008
Ip
TÜ V SÜ D Group
Department name
21 November 2008
Ip
Short circuit in system is expected; Short circuit results in thermal and dynamic Stresses with huge of current. We wish the system and components is so constructed as to be capable of withstanding the thermal and dynamic stresses resulting from shortcircuit currents up to the rated values. Then how to do?
TÜ V SÜ D Group
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21 November 2008
Fusing protection
2.3.2 prospective current (of a circuit and with respect to a fuse) current that would flow in the circuit if each pole of the fuse were replaced by a conductor of negligible impedance For a.c., the prospective current is expressed by the r.m.s. value of the a.c. component. NOTE The prospective current is the quantity to which the breaking capacity and characteristics of the fuse are normally referred, e.g. I 2t and cut-off current characteristics (see 8.5.7).
电路 预 期 电流(相对于熔断器) 假 定 电路 内的熔断器由阻抗可忽略不计的接线所取代时，电路所流过的电流。 预期 电 流 是熔断器分断能力和特性的参照量，例如尸t和截断电流特性(见8.5. 7 ),
TÜ V SÜ D Group
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21 November 2008
Short-circuit consideration
TÜ V SÜ D Group
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21 November 2008
Ip
What is cut-off current? IEC 60269-1:2006 requires: cut-off current (Ip)= peak let-through current: maximum instantaneous value reached by the current during the breaking operation of a fuse-link when it operates in such a manner as to prevent the current from reaching the otherwise attainable maximum. Determined as a function of the prospective current under stated conditions of operation. prospective current ≤breaking capacity of a fuse. 截 断 电 流cut-offc urrent 在熔 断 体 分断期间，所能达到的最大瞬时电流;这样可防止电流达到最大值。
21 November 2008
Fuse famous function: current limit characteristic
5.8.1 Cut-off current characteristics The cut-off current characteristics shall represent the maximum instantaneous values of current likely to be experienced in service (see 8.6.1 and Annex C). Where the cut-off current characteristics are required, and unless specified in subsequent parts, they should be given by the manufacturer according to the example shown in Figure 4, in a double logarithmic presentation with the prospective current as abscissa.
TÜ V SÜ D Group
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21 November 2008
Fuse famous function: current limit characteristic
Then how to use this function?
TÜ V SÜ D Group
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TÜ V SÜ D Group
Department name
21 November 2008
Short-circuit consideration
EN 61800-5-1 5.2.3.6.2.1 For the Short-circuit test, the supply shall be capable of delivering the specified prospective short-circuit current (see 4.3.9) at the connection to the PDS, unless circuit analysis demonstrates that a lesser value may be used. For the Breakdown of components test, the supply shall be capable of delivering a prospective short-circuit current of between 1 kA and 5 kA, unless the analysis of 4.2 shows that a different value is required. 6.2 prospective short-circuit current rating(s) and protective device characteristics