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Entry type: FAQ Entry ID: 44854338, Entry date: 08/30/2010
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SIRIUS 3RW30 / 3RW40 and 3RR2: Application of current monitoring relays 3RR2 in association with Soft Starters 3RW30 and 3RW40

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QUESTION:

What shall one consider with an application of current monitoring relays 3RR2 in association with Soft Starters 3RW30 and 3RW40?


ANSWER:

Due to the mechanical design and the significant heating of the Soft Starter, direct mounting of a current monitoring relay 3RR2 to a Soft Starter 3RW30 / 3RW40 is regrettably not permitted. The current monitoring relay shall be mounted separately on the DIN rail by means of the terminal brackets for standalone installation.

During the starting and stopping periods of the Soft Starter (phase cut) the current monitoring relay shall be inactive.

Difficulty:

As a matter of function the current monitoring relay 3RR2 must determine the system frequency for an appropriate current measurement. This is achieved through permanent measuring the time intervals between the phase zero passes.

During starting and stopping periods of the Soft Starters 3RW it is not possible to take this measurement with sufficient accuracy as a result of the variable phase control. The current monitoring relay 3RR2 would mistake a phase control as a phase loss. For that reason the current monitoring relay shall be inactive during starting and stopping periods of the Soft Starter.

Remedy with Soft Starter 3RW40:

The supply voltage of the current monitoring relay 3RR2 can be toggled on / off via the bypass output for start ramp detection of the Soft Starter 3RW40.

After the start period is finished and the bypass contacts are closed, the current monitoring relay 3RR2 is switched on and it can incur monitoring of the application without further delay. With the begin of the stopping period the bypass contacts are opened and the current monitoring relay 3RR2 is switched off.

Remedy with Soft Starter 3RW30:

In association with Soft Starters 3RW30 without bypass output the engaging / disengaging of the monitoring relay can be carried out by means of an on-delayed timing relay, e.g. 3RP1511. The time delay should be preset slightly longer than the ramp time of the soft start and then activated simultaneously with the motor start. Coevally with the disengagement of the Soft Starter there is also the supply voltage of the current monitoring relay 3RR2 switched off through the timing relay.

Remark:

In both situations it has to be ensured by the superordinated control system, that the control voltage of the current monitoring relay 3RR2 is not disengaged when the current monitoring relay itself has provoked the shutdown of the Soft Starter e.g. by exceeding a preset treshold. In that circumstance no detail diagnosis at the current monitoring relay would be feasible anymore.