NTMU02
标准IEC 60947-3定义的隔离开关是一种机械开关装置，当处于断开位置时，它执行断开功能，并确保隔离距离（触点之间的距离）足以保证安全。必须通过正向操作来保证和验证断开的安全性：操作杆必须始终指示设备移动触点的实际位置。机械开关装置必须能够在正常电路条件下产生、携带和断开电流，包括正常使用中的任何过载电流，并在规定的时间内携带异常电路条件下的电流，例如短路条件。隔离开关通常用作：•主副配电盘设备；•线路、母线或负载装置的开关和断开装置巴士领带。隔离开关应确保整个装置或其部分不带电，安全地与任何电源断开。例如，使用这种隔离开关可以使人员在工厂上进行工作，而不会有电气性质的风险。即使不禁止并排使用单极装置，标准建议使用多极装置，以保证电路中所有极的同时隔离。标准IEC 60947-3规定了隔离开关的特定额定特性，详情如下：•Icw【kA】：额定短时耐受电流：是指开关能够承载的电流，不会造成损坏，在特定持续时间的闭合位置2.7隔离开关的电气特性108保护和控制装置| ABB 2一般特性使用类别的特性详见下表1。交流电流中要求高的类别是AC23A，该设备必须能够连接等于设备额定电流10倍的电流，并能够断开等于设备额定电流8倍的电流。从结构的角度来看，隔离开关是一种非常简单的装置。它没有安装过电流检测装置和随后的电流自动中断装置。因此，隔离开关不能用于故障情况下可能发生的过电流自动保护，必须由协调断路器提供保护。这两种装置的组合允许在短路电流值大于定义隔离开关性能的电气参数的系统中使用隔离开关（后备保护见第3.4章。这仅对Isomax和Tmax隔离开关有效。对于Emax/MS空气隔离开关，必须验证Icw和Icm的值分别高于电厂短路和相应峰值的值。•Icm[kA]：额定短路接通容量：是指断路器可以闭合而不损坏的短路电流的大峰值。当制造商未给出该值时，必须将其视为至少等于对应于Icw的峰值电流。由于不需要隔离开关来断开短路电流，因此无法定义断开容量Icu[kA]•交流和直流的使用类别：定义使用条件的类型，用两个字母表示设备可能安装的电路类型（交流为交流电，直流为直流电），两位数字表示必须操作的负载类型，另外一个字母（a或B）表示使用频率。根据使用类别，产品标准定义了在异常条件下，隔离开关必须能够断开和闭合的电流值。

NTMU02
switch disconnector as defined by the standard IEC 60947-3 is a mechanical switching device which, when in the open position, carries out a disconnecting function and ensures an isolating distance (distance between contacts) sufficient to guarantee safety. This safety of disconnection must be guaranteed and verified by the positive operation: the operating lever must always indicate the actual position of the mobile contacts of the device. The mechanical switching device must be able to make, carry and break currents in normal circuit conditions, including any overload currents in normal service, and to carry, for a specified duration, currents in abnormal circuit conditions, such as, for example, short-circuit conditions. Switch disconnectors are often used as: • main sub-switchboard devices; • switching and disconnecting devices for lines, busbars or load units; • bus-tie. The switch disconnector shall ensure that the whole plant or part of it is not live, safely disconnecting from any electrical supply. The use of such a switch disconnector allows, for example, personnel to carry out work on the plant without risks of electrical nature. Even if the use of a single pole devices side by side is not forbidden, the standards recommend the use of multi-pole devices so as to guarantee the simultaneous isolation of all poles in the circuit. The specific rated characteristics of switch disconnectors are defined by the standard IEC 60947-3, as detailed below: • Icw [kA]: rated short-time withstand current: is the current that a switch is capable of carrying, without damage, in the closed position for a specific duration 2.7 Electrical characteristics of switch disconnectors 108 Protection and control devices | ABB 2 General characteristics The characteristics of the utilization categories are detailed in Table 1 below. The most demanding category in alternating current is AC23A, for which the device must be capable of connecting a current equal to 10 times the rated current of the device, and of disconnecting a current equal to 8 times the rated current of the device. From the point of view of construction, the switch disconnector is a very simple device. It is not fitted with devices for overcurrent detection and the consequent automatic interruption of the current. Therefore the switch disconnector cannot be used for automatic protection against overcurrent which may occur in the case of failure, protection must be provided by a coordinated circuit-breaker. The combination of the two devices allows the use of switch disconnectors in systems in which the short-circuit current value is greater than the electrical parameters which define the performance of the disconnector (back-up protection see Chapter 3.4. This is valid only for Isomax and Tmax switch-disconnectors. For the Emax/MS air disconnectors, it must be verified that the values for Icw and Icm are higher to the values for short-circuit in the plant and correspondent peak, respectively. • Icm [kA]: rated short-circuit making capacity: is the maximum peak value of a short-circuit current which the switch disconnector can close without damages. When this value is not given by the manufacturer it must be taken to be at least equal to the peak current corresponding to Icw. It is not possible to define a breaking capacity Icu [kA] since switch disconnectors are not required to break short-circuit currents • utilization categories with alternating current AC and with direct current DC: define the kind of the conditions of using which are represented by two letters to indicate the type of circuit in which the device may be installed (AC for alternating current and DC for direct current), with a two digit number for the type of load which must be operated, and an additional letter (A or B) which represents the frequency in the using. With reference to the utilization categories, the product standard defines the current values which the switch disconnector must be able to break and make under abnormal conditions.