What framework conditions are required on the grid side to enable trouble-free operation of an r750?
SSC_min.=RSCE*Srück_.
A minimum factor of 35 was defined for the short-circuit power ratio (RSCE).
Important!
It should be noted here that the overload case must also be covered when calculating the mains short-circuit apparent power.
If several r750 units are connected in parallel at the same connection point, the minimum apparent mains short-circuit power (SSC_min.) must be designed for the sum of the regenerative powers.
The inductance effective at the mains input terminals of the regenerative feeder must not exceed 0.6mH.
The following table provides information on the minimum required mains short-circuit apparent power for a regenerative feeder at nominal load and overload.
| Device | Prück_N [kW] | Srück_N [kVA] | SSC_min._N. [kVA] (without overload) | Srück_max. [kVA] (max. overload) *1 | SSC_min_Überlast. [kVA] (max. overload) *1 |
| r750-C13/400-3 | 13 kW | 14 kVA | 490 kVA | 25,9 kVA | 907 kVA |
| r750-C26/400-3 | 26 kW | 28 kVA | 980 kVA | 51,8 kVA | 1813kVA |
Prück_N = Rated regenerative power
Srück_N = Rated apparent regenerative power
SSC_min._N= Minimum required mains short-circuit apparent power (without overload)
Prück_max.= Maximum apparent regenerative power in overload operation
SSC_min_Überlast. = Minimum required mains short-circuit apparent power (maximum overload)
*1= For the overload case, the maximum overload time must be taken into account. (see load cycles)
Related to other operating points of the r750 (e.g. for operation with peak power or with parallel connection of several r750s on the same DC link), the minimum required mains short-circuit apparent power can be linearly converted from the rated data.
You can estimate the apparent short-circuit power from the data of the feed-in transformer. To do this, you need the uk (relative short-circuit voltage of the transformer) and the apparent power of the transformer. Both values are typical nameplate data of the transformer.
The apparent short-circuit power of the transformer at its connection terminals is calculated as follows:
Ssc=UL * Irated x 100 / uk(%)
Important!
The current-limiting components between the transformer output and the connection terminals of the r750 (e.g. line resistances, choke/mains filter, etc.) must also be taken into account.
As an alternative to the estimation via the transformer data, a measurement of the loop impedance at the terminals of the regenerator can provide information about the resulting short-circuit current Isc. Isc results from UL/ZNet. Isc is typically displayed directly by the measuring device.
This method has the advantage that the current-limiting components between the transformer output and the control cabinet terminals are also estimated.
Mains feedback/EMC aspects
The mains perturbations arising with an RSCE=35 (soft mains) are generally not relevant for use in the industrial mains, as EMC limits must usually be complied with at the transfer point.
The statements made in the product documentation regarding conducted interference emission during operation on the public low-voltage network assume an RSCE ≥ 240.
