Solid-State Switching Devices for Switching Motors Solid-State Contactors General data ■ Function ■ Integration Switching functions The contactors to switch motors are "Instantaneous switching", because this method is particularly suited for inductive loads. By distributing the ON point over the entire sine curve of the mains voltage, disturbances are reduced to a minimum. Notes on integration in the load feeders The SIRIUS solid-state switching devices are very easy to inte- grate into the load feeders thanks to their industrial connection method and design.
Particular attention must however be paid to the circumstances of the installation and ambient conditions, as the performance of the solid-state switching devices is largely dependent on these. Depending on the version, certain restrictions must be obser- ved. Detailed information about the minimum spacing can be found in the technical specifications and the product data sheets. Performance characteristics The performance of the solid-state switching devices is substan- tially determined by the type of power semiconductors used and the internal design. In the case of the SIRIUS solid-state contac- tors and solid-state relays, only thyristors are used in place of less powerful Triacs.
Despite the rugged power semiconductors that are used, solid- state switching devices respond more sensitively to short-cir- cuits in the load feeder. Consequently, special precautions have to be taken against destruction, depending on the type of design. Two of the most important features of thyristors are the blocking voltage and the maximum load integral: Blocking voltage Thyristors with a high blocking voltage can also be operated without difficulty in networks with high interference voltages. Se- parate protective measures, such as a protective circuit with a varistor, are not necessary in most cases. Siemens generally recommends using SITOR semiconductor fuses.
These fuses also provide protection against destruction in the event of a short-circuit even when the solid-state contactors and solid-state relays are fully utilized. For example, for the SIRIUS solid-state switching devices e. g. thyristors with 800 V blocking voltage are built in for operation in networks up to 230 V. Thyristors with up to 1600 V are used for power systems with higher voltages. Alternatively, if there is lower loading, protection can also be pro- vided by standard fuses or miniature circuit breakers. This pro- tection is achieved by overdimensioning the solid-state swit- ching devices accordingly.
The technical specifications and the product data sheets contain details both about the solid-state fuse protection itself and about use of the SIRIUS devices with conventional protection equipment. Maximum load integral One of the purposes of specifying the maximum load integral ( I І t ) is to determine the rating of the short-circuit protection. Only a large power semiconductor with a correspondingly high I І t va- lue can be given appropriate protection against destruction from a short-circuit by means of a protective device matched to the application.
However, the SIRIUS solid-state switching devices are also characterized by the optimum matching of the thyristors ( I І t value) to the rated currents. The rated currents specified on the devices according to EN 60947-4-3 were confirmed by ex- tensive testing. Semiconductor motor and reversing contactors can be easily combined with the 3RV motor starter protectors and 3RB2 over- load relay from the SIRIUS modular system. Thus, fuseless and fuse motor feeders can be designed easily and in a space-sa- ving manner. Note: You can find more information on the Internet at:
The operation of wye-connected three-phase induction motors (especially with ratings tors can lead to very high EMC interference. Solid-state swit- ching devices being used in the vicinity may be affected by this interference which lies above the permissible limit values. http://www.siemens.com/cd/is_schalten/html_76/schalt.htm In case of high EMC interference we recommend that motors up to 5.5 kW controlled by 3RT10 1. electromechanical contactors be equipped with EMC suppressor circuits. The best filtering ef- fect is achieved with three-phase RC interference suppression modules such as 3RT19 16-1PA1 up to 400 V.
Suitable modules for the contactors can be found in Chapter 3 under "Accessories and Spare Parts". Varistor interference suppression modules should not be used because they are unsatisfactory at filtering out rapid transients. 54 Siemens · 2009