© Siemens AG 2009 As well as the overload protective devices, the contactors and short-circuit protection devices must also be designed for these long starting times. This is why combinations according to CLASS 5 and CLASS 10 are generally more cost-effective. CLASS 20, CLASS 30 and CLASS 40 are generally used only if genuinely necessitated by the application. solutions under overload and short-circuit conditions is techni- cally comparable. For fuseless load feeders with solid-state overload relay, and for higher trip classes, CLASS 20, CLASS 30 and CLASS 40 in particular, a motor-protective circuit breaker is often used in- stead of a motor starter protector. This is due to the following:
from the point of view of thermal destruction limits, starter cir- cuit breakers are generally designed for CLASS 10 motor starts. The current measurement of solid-state overload relays usually moves into saturation upwards of a 10-fold rated current, so that the intrinsic protection of the motor starter protector is no longer guaranteed for higher trip classes. In order to ensure thermal intrinsic protection, it is advisable to use a motor start- er protector that protects itself over the overload release.
The motor-protective circuit breaker is selected so that the point at which the characteristic curve of the overload relay intersects with the a-tripping characteristic of the motor-protective cir- cuit breaker is more than 10 times the set current. This ensures that, in the case of motor faults, such as overload or blocking, the overload relay always trips and not the motor starter pro- tector. Type of coordination 1 or 2 When selecting the combinations, in many cases, either type of coordination 1 or 2 can be selected. According to IEC 60947-4-1, the type of coordination defines the permissi- ble degree of damage for a device following a short-circuit. ■ Type of coordination "1" 1) :
After a short-circuit, it is permissible for the starter to be inopera- tive, in particular, damage to the contactor, solid-state switching devices and overload relay is permissible. ■ Type of coordination "2" 1) : The starter is still operative. There must be no signs of damage to the devices, with the exception of slightly welded contactor con- tacts if these can be easily separated again without any notice- able deformation. 1) Combinations are color coded according to the respective type of coordina- tion as shown above. In this situation, combinations with motor starter protector and contactor offer the most cost-effective solution.
However, combinations with overload relays offer distinct advantages for certain applications: In both cases, the short-circuit is reliably and safely cleared. Combinations of coordination type 2 are therefore of a higher quality and are rapidly available for reuse after a short-circuit. In the case of solid-state switching devices, the same applies as for type of coordination 2, that the short-circuit is cleared without any damage to the power semiconductors. Combina- tions of coordination type 1 are generally the more favorably priced solution. Combinations of coordination type 2 auto- matically fulfill the requirements of coordination type 1.
■ Using 3RB20/3RB21 and 3RB22/3RB23 solid-state overload relays, as well as SIMOCODE pro 3UF7, enables users to achieve not only trip classes CLASS 5 and CLASS 10, but also solutions for heavy starting, such as CLASS 20, CLASS 30 and CLASS 40. ■ Using solid-state overload relays offers a wide setting range of 1:4 or 1:10. This offers advantages during configuration (e. g. if the exact motor current is not known) and enables us to reduce the number of variants required. Tests All of the specified combinations are tested in compliance with IEC 60947-4-1. ■ Overload and short-circuit protection are carried out sepa- rately and can also be signaled separately.
Alternatively, the 3RV19 21-1M signaling block can be used for the 3RV mo- tor starter protector instead of the overload relay. This also supports the separate signaling of overloads and short-cir- cuits. With or without overload relay In addition to the combinations comprising a motor starter protector (for motor protection) and contactor, combinations are also available with circuit breaker (for starter protection), contactor and overload relay. ■ Setting of the overload relay to "Automatic Reset" can also save a walk to the control cabinet in the case of overload tripping, as a manual reset in the control cabinet is not re- quired.
Alternatively, this function can also be imple- mented with the "3RV11 motor starter protector with over- load relay function". These devices can be used in the motor starter protector + contactor tables instead of the 3RV10 motor starter protector. In the first case, the motor starter protector assumes the dual function of overload protection and short-circuit protection, while in the second case, the circuit breaker assumes only the short-circuit protection function and the overload relay the overload protection function. The tripping behavior of both Introduction 7