3RB2 Solid-State Overload RelaysOverview
SIRIUS 3RB2113?4RB0 solid-state overload relay
The 3RB20 and 3RB21 solid-state overload relays up to 630 A with internal power supply have been designed for current-sensitive protection of loads with normal and heavy starting (for "Function" see reference manual "Protection Equipment – 3RU1 and 3RB2 Overload Relays", http://support.automation.siemens.com/WW/view/en/35681830) against excessive temperature rises due to overload, phase unbalance or phase failure.
An overload, phase unbalance or phase failure result in an increase of the motor current beyond the set rated motor current. This rise in current is detected by the current transformers integrated into the devices and evaluated by corresponding solid-state circuits which then output a pulse to the auxiliary contacts. The auxiliary contacts then switch off the load by means of a contactor. The break time depends on the ratio between the tripping current and current setting Ie and is stored in the form of a long-term stable tripping characteristic (see "Characteristic Curves" http://support.automation.siemens.com/WW/view/en/20357046/134300).
In addition to inverse-time delayed protection of loads against excessive temperature rises due to overload, phase unbalance and phase failure, the 3RB21 solid-state overload relays also allow internal ground-fault detection (not possible in conjunction with contactor assemblies for wye-delta starting). This provides protection of loads against high-resistance short circuits due to damage to the insulation material, moisture, condensed water etc.
The "tripped" status is signaled by means of a switch position indicator. Resetting takes place either manually or automatically after the recovery time has elapsed (for "Function", see reference manual "Protection Equipment – 3RU1 and 3RB2 Overload Relays", http://support.automation.siemens.com/WW/view/en/35681830).
The 3RB2 electronic overload relays are suitable for operation with frequency converters. Please to refer to the instructions in the reference manual "Protection Equipment – 3RU1 and 3RB2 Overload Relays", see http://support.automation.siemens.com/WW/view/en/35681830.
The devices are manufactured in accordance with environmental guidelines and contain environmentally-friendly and reusable materials. They comply with all important worldwide standards and approvals.
Overload relay 3RB30 and 3RB31 in sizes S00 and S0, see "SIRIUS 3RB3 Solid-State Overload Relays".
"Increased safety" type of protection EEx e according to ATEX Directive 94/9/EC
The 3RB20/3RB21 solid-state overload relays are suitable for the overload protection of explosion-proof motors with "increased safety" type of protection EEx e.
The relays meet the requirements of IEC 60079-7 (Electrical apparatus for areas subject to explosion hazards – Increased safety "e").
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