===<!--13.4.1 Metallurgical Analysis=-->Testing Procedures for Power Engineering==

The main characteristic for the appraisal testing of contact materials electrical contacts for power engineering is applications serves on the one hand the optical evaluation of their microstructure in a metallographic mount. This provides a picture of continuous quality assurance, on the internal structure of other one the new and improvement development efforts for contact materials. It allows detecting structural in-homogeneityTo optimize the contact and switching performance, grain boundary enrichments, cracks, material separations, or defects in the brazing interfacecontact materials and device designs have to complement each other. The metallographic view success of such optimizing is however limited to the one two-dimensional plain in which the mounting cut was madeproven through switching tests.

Fig. 13.11 shows the microstructure The assessment of a Ag/CdO contact material after being affected by materials is performed using metallurgical test methods as well as switching tests in model test set-ups and in commercial switching devices. While physical properties such as melting and boiling point, electrical arcingconductivity etc. In are fundamental for the lower part the starting material structure is visible. In selection of the upper part base metals and the de-mixing additional components of the composite material through the effects materials, they cannot provide a clear indication of the contact and switching arc is clearly demonstratedbehavior. Metallurgical evaluations and tests are used primarily for determining material and working defects. This “switching structure” shows in certain areas depletion of metal oxide which increases the probability of The actual contact welding during subsequenbt make operations. Additional analysis by X-ray probing and switching behavior can however only be determined through switching tests in a scanning electron microscope (SEM) allows the micro analysis of the elements present model switch or preferably in the contact surface regionfinal electromechanical device.

Fig. 13.11:Microstructure Model testing devices offer the possibility of quick ratings of the make and break behavior and give a powdermetallurgical Ag/CdO material afterbeing affected by intense electricalarcingpreliminary classification of potential contact materials. Since such tests are performed under ideal conditions they cannot replace switching tests in actual devices.

===13The electrical testing of commercially produced switching devices should follow DIN EN or IEC standards and rules.4.2 Testing According to IEC/EN===Special test standards exist for each type of switching device which are differentiated by:

====13.4.2.1 * Make capacity* Break capacity* Electrical Life====life* Temperature rise

The following chapters are limited to metallurgical analysis and the testing of the most important properties of switching devices such as electrical life of contactors, motor switchestemperature rise, and auxiliary current switches used in power engineering is classified into use categories which are shown in table 13switching capacity.1:

The making and breaking currents for tests IEC/EN 60947===<!-4-1 are shown in Table 13.2 for the different use categories4.1-->Metallurgical Analysis===

The electrical life main characteristic for the appraisal of a motor switch is influenced primarily by arc erosion which is generated during make and break arcs on the contact surface. During AC-3 testing, materials for which the make current power engineering is six time the nominal rated current, optical evaluation of their microstructure in a metallographic mount. This provides a picture of the arc erosion is mainly caused by internal structure of the make arcs, especially if frequent contact bounces >2 ms occurmaterials. Therefore the bounce characteristic of switching devices primarily used for “normal” use It allows detecting structural in switching on and off electrical motors is of critical importance. If make and break currents are the same-homogeneity, grain boundary enrichments, cracks, as material separations or defects in the ultilisation categories ACbrazing interface. The metallographic view is however limited to the one two-1 and AC-4, the break erosion dominates dimensional plain in which the arc erosion so much that make erosion can be neglectedmounting cut was made.

Table <xr id="fig:Microstructure of a powder metallurgical Ag CdO material"/><!--(Fig. 13.111)--> shows the microstructure of a Ag/CdO contact material after being affected by electrical arcing. In the lower part the starting material structure is visible. In the upper part the de-mixing of the composite material through the effects of the switching arc is clearly demonstrated. This “switching structure” shows in certain areas depletion of metal oxide which increases the probability of contact welding during subsequent make operations. Additional analysis by X-ray probing in a scanning electron microscope (SEM) allows the micro analysis of the elements present in the contact surface region.<figure id="fig: Important Use Categories and Their Typical Applications for ContactorsMicrostructure of a powder metallurgical Ag CdO material">[[File:Microstructure of a powder metallurgical Ag CdO material.jpg|right|thumb|<caption>Microstructure of a powder metallurgical Ag/CdO material after being affected by intense electrical arcing</caption>]]and Power Switches</figure>

*Contactors, Motor Starters according ===<!--13.4.2-->Testing According to IEC/N60947-4-1EN===

*Auxiliary Current The electrical life of contactors, motor switches, and auxiliary current switches used in power engineering is classified into use categories which are shown in <xr id="tab:Important Use Categories and Their Typical Applications for Contactors and Power Switches according to IEC"/EN 160947><!-5-(Tab. 13.1)-->.

bildThe making and breaking currents for tests IEC/EN 60947-4-1 are shown in <xr id="tab:Verification of Electrical Life Conditions for Make and Break Tests of Contactors and Motor Starters by Utilization Category"/><!--(Tab. 13.2)--> for the different use categories. The electrical life of a motor switch is influenced primarily by arc erosion which is generated during make and break arcs on the contact surface. During AC-3 testing, for which the make current is six time the nominal rated current, the arc erosion is mainly caused by the make arcs, especially if frequent contact bounces > 2 ms occur. Therefore the bounce characteristic of switching devices primarily used for “normal” use in switching on and off electrical motors is of critical importance. If make and break currents are the same, as in the ultilisation categories AC-1 and AC-4, the break erosion dominates the arc erosion so much that make erosion can be neglected.<br style="clear:both;"/>  <figtable id="tab:Important Use Categories and Their Typical Applications for Contactorsand Power Switches"><caption>'''<!--Table 13.1:-->Important Use Categories and Their Typical Applications for Contactors and Power Switches'''</caption> {| class="twocolortable" style="text-align: left; font-size: 12px"|-!colspan="6" style="text-align:left"| Contactors, Motor Starters according to IEC/N60947-4-1|- !Type of current!Utilisation category!Typical application|-|Alternating current (AC)|AC-1|Non-inductive or slightly inductive loads, resistance furnaces|-||AC-2|Slip ring motors: starting, switch-off|-||AC-3|Squirrel-cage motors: starting, switch-off, switch-off during running⁴⁾|-||AC-4|Sqirrel-cage motors: starting, plugging, reversing, inching|-|Direct current (DC)|DC-1|Non-inductive or slightly inductive loads, resistance furnaces|-||DC-3|Shunt motors: starting, plugging, reversing, inching, dynamic braking|-||DC-5|Series motors: starting, plugging, reversing, inching, dynamic braking|-!colspan="6" style="text-align:left"| Auxiliary Current Switches according to IEC/EN 160947-5-1|-!Type of current!Utilisation category!Typical application|-|Alternating current (AC)|AC-12|Controlling resistive semiconductor loads in feed circuits of optoelectronics|-||AC-14|Controlling small electromagnetic loads (72 VA max)|-||AC-15|Controlling electromagnetic loads (> 72 VA)|-|Direct Current (DC)|DC-12|Controlling resistive semiconductor loads in feed circuits of optoelectronics|-||DC-13|Controlling of electro magnets under direct current|-||DC-14|Controlling of electromagnetic loads under direct current with power saving resistors in circuits|}</figtable>

Fig. <figtable id="tab:Verification of Electrical Life Conditions for Make and Break Tests of Contactors and Motor Starters by Utilization Category"><caption>'''<!--Table 13.2:AC-3 contact arc erosion ->Verification of Electrical Life Conditions for Make and Break Tests of two differentlyproduced Ag/SnO contact materials 2in a 37 kW contactorAg/SnO 88/12, produced Contactors and Motor Starters by conventional 2powder metallurgy with MoO additive, 3extrudedAg/SnO 88Utilization Category'''</12, powder manufacturing by 2the reaction-spray process with CuO andBi O additives, extrudedcaption>

{| class="twocolortable" style="text-align: left; font-size: 12px"|-!Ultilisation Category!Current!colspan="3" style=13"text-align:center"| Make operation!colspan="3" style="text-align:center"| Break Operation|-!!I_e/A!I/I_e!U/U_e!cos &phi; !I_c/I_e!U_r/U_e!cos &phi; |-|AC-1|Alle Werte|1|1|0.95|1|1|0.95|-|AC-2|Alle Werte|2.5|1|0.65|2.5|1|0.65|-|AC-3|I_e &le; 17<br />I_e > 17|6<br />6|1<br />1|0.65<br />0.35|1<br />1|0.17<br />0.17|0.65<br />0.35|-|AC-4|I_e &le; 17<br />I_e > 17|6<br />6|1<br />1|0.65<br />0.35|6<br />6|1<br />1|0.65<br />0.35|-!!I_e/A!I/I_e!U/U_e!L/R [ms]!I_c/I_e!U_r/U_e!L/R [ms]|-|DC-1|All values|1|1|1|1|1|1|-|DC-3|All values|2.5|1|2|2.5|1|2|-|DC-5|All values|2.5|1|7.5|2 Temperature Rise====.5|1|7.5|}</figtable>

FigU_e = Rated operational voltage <br />U = Voltage<br />U_r = Recovery voltage<figure id="fig:AC3 contact arc erosion of two differently produced Ag SnO2 contact materials">[[File:AC3 contact arc erosion of two differently produced Ag SnO2 contact materials.jpg|right|thumb|<caption>AC-3 contact arc erosion of two differently produced Ag/SnO₂ contact materials in a 37 kW contactor <b>1</b> Ag/SnO₂ 88/12, produced by conventional powder metallurgy with MoO₃ additive, extruded <b>2</b> Ag/SnO₂ 88/12, powder manufacturing by the reaction-spray process with CuO and Bi₂ O₃ additives, extruded</caption>]]</figure>====<!--13.134.2.2-->Temperature Rise==== Testing for temperature rise is required only for switching devices in the new stage. During use however over the entire life of the device no damages due to temperature rise are allowed in the device or at its terminal points.<figure id="fig:Maximum movable bridge temperature rise for different contact materials">[[File:Maximum movable bridge temperature rise for different contact materials.jpg|right|thumb|<caption>Maximum movable bridgetemperature rise for different contactmaterials in a 132 kW contactor afterhigh load (AC-4) switching<b>1</b> Ag/CdO 88/12 sintered

<b>2</b> Ag/SnO2 7SnO27.5In2O3 25In2O32.5

<b>3</b> Ag/SnO2 88/12

<b>4</b> Ag/SnO2 11.5 WO3 0.5sintered and extruded<b>5</b> Ag/SnO SnO2 11.6 MO MO4 0.4sintered and extruded</caption>]]</figure>For the assessment of contact materials a temperature rise test is frequently performed after a specified number of switching operations accompanied by arcing (<xr id="fig:Maximum movable bridge temperature rise for different contact materials"/><!--(Fig. 13.13)-->). The most important characteristic is the measured temeperature rise of the movable bridge contacts. If a certain upper limit of temperature is reached, adjacent plastic components may be irreversibly damaged.

For the assessment of contact materials a temperature rise test is frequently performed after a specified number of switching operations accompanied by arcing (Fig. 13.13). The most important characteristic is the measured temeperature rise of the movable bridge contacts. If a certain upper limit of temperature is reached, adjacent plastic components may be irreversibly damaged. ====<!--13.4.2.3 -->Analysis of the Switching Sequence====

lead to extreme damage, especially on at least one of the phases or poles. They are the cause of early failure of this phase and therefore the complete switching device and can happen as early as after only 30% of the normally expected lifetime. Because of variations in the mechanical characteristics of switching devices from manufacturing processes life testing cannot be performed on one device alone. Only statistical analysis of tests from multiple device samples can be used as reliable results. Such a procedure is however time consuming and costly. If however every single switching operation during a test is monitored for bounce behavior, on- and off-switching synchronization and related phase sequencing and phase delays, the arc moving behavior, and especially arc energy which is transferred during make and break arcing to the contact pieces, and then these data are properly analyzed, it is it possible to assess a specific contact material from a test in only one device alone. Only statistical analysis  ====<!--13.4.2.4-->Switching Capacity==== The main requirement for low voltage power switches is the withstanding of high short circuit currents. The short circuit switching capacity of power switches is determined in tests from multiple device samples according to IEC/EN 60947-2 (<xr id="tab:Testing for the Short Circuit Breaking Capacity of Low Voltage Power Switches According to IECEN 60947-2 (Shortened Summary)"/><!--(Tab. 13.3)-->). These tests differentiate between the maximum short circuit current switching capacity (ultimate current limit) I_CU and the operational (or service) short circuit current capacity I_CS . When specifying I_CU it must be guaranteed that short circuit current up to the maximum limit value can be used as reliable resultsinterrupted safely. Such a procedure is however After its occurrence it must be possible to switch on one additional time consuming onto the not yet eliminated short circuit and again interrupt this short circuit current again safely. The switch does not have to be functional any more after this second interruption. A switch specified for I_CS must still be capable to protect the circuit and costlybe further usable within certain limitations. If however every single  To safely withstand short circuit currents high requirements are imposed on the weld resistance of the materials used for the mating contacts. During short circuit switching operation the contact force between the contacts pairing is reduced by electromagnetic forces. Above a certain device specific current value the contacts will separate. This generates an electrical arc with contact material melting at its root points. During the next closing of the contacts this can cause contact welding, prohibiting the opening of the contacts during a subsequent short circuit and therefore eliminating the safety function of the switching device.<br style="clear:both;"/>  <figtable id="tab:Testing for the Short Circuit Breaking Capacity of Low Voltage Power Switches According to IECEN 60947-2 (Shortened Summary)"><caption>'''<!--Table 13.3:-->Testing for the Short Circuit Breaking Capacity of Low Voltage Power Switches According to IEC/EN 60947-2 (Shortened Summary)'''</caption> {| class="twocolortable" style="text-align: left; font-size: 12px"|-!Test characteristics!Rated ultimate short circuit breaking capacity I_CU!Service short circuit breaking capacity I_CS|-|Test conditions|Ue<br />cosn depends on value of current I in kA, i.e {| class="innertable" style=" border: none"|6 < l &le; 10| cos&phi; 0.5|- |10 < l &le; 20|cos&phi; 0.3|-|20 < l &le; 50 | cos&phi; 0.25 |-| 50 < l |cos&phi; 0.2 |-|}|Ue<br />cosn depends on value of current I in kA, i.e {| class="innertable" style=" border: none"|6 < l &le; 10| cos&phi; 0.5|- |10 < l &le; 20|cos&phi; 0.3|-|20 < l &le; 50 | cos&phi; 0.25 |-| 50 < l |cos&phi; 0.2 |-|}|-|Testing sequence|O - t - CO|O - t - CO - CO|-|Subsequent isolation test is monitored for bounce behavior|2 x U_e, with min. 1.000 V|2 x U_e, with min. 1.000 V|-|Subsequent temperature rise test||Temperature not exceed temperature rise limit|}</figtable> U_e = Rated operational voltage<br />U = Current<br />O = Switch off<br />T = Pause<br />CO = Switch onand off ===<!-- 13.4.3-->Testing According to UL and CSA=== The test standards for North America according to UL (USA) and offswitching synchronization CSA (Canada) differ in part substantially from those of the IEC and related phase sequencing harmonized European EN standards. In the US and phase delaysCanada the standards differentiate between switchgear for power distribution, the arc moving behaviorfor example low voltage circuit breakers and power switches covered by UL 489 (UL = Underwriters Laboratories) and CSAC22.2 No. 5-02 (CSA = Canadian Standard Association) and those for industrial switching devices, for example contactors covered by UL 508 and especially arc energy which is transferred during make CSA-C22.2 No. 14 respectively. For industrial controls, contactors and break arcing other switching devices are often classified in the USA according to NEMA (National Electrical Manufacturers Association) current rating. North American standards emphasize the contact pieces, prevention of fires and therefore has high limit requirements on temperature rise. They also require larger air and then these data are properly analyzedcreep gaps than those of IEC, is it possible which leads to assess a specific significant differences in the design of the switches and their contact material from a test in only one devicesystems. ==References==[[Testing Procedures#References|References]] [[de:Prüfverfahren_in_der_Energietechnik]]