User manual

Static Transfer Switch

UNB

User Manual

Page 11 (28)

3.3 Electrical Connectors

3.3.1 Input terminals

The UNB is equipped with two AC inputs, one for the inverter and the other for the substitute-mains. Both sources

must have the same frequency and the same nominal voltage level. Because there are no protection fuses

integrated in the unit, both sources must be protected externally.

If several inverters are connected in parallel, the parallel connection of the inverter outputs has to be arranged

externally.



REMARK: If inverters of series PWS are connected in parallel, a symmetry-choke per inverter additionally is to

be installed into the L-phase.

The AC input connectors are located on the rear side of the unit. Because of the limited load capacity of the con-

nector pins the UNB with an output power of 23.0kVA is equipped with two connectors, the 30.0 & 40.0kVA unit

with three connectors with several contact pins connected in parallel accordingly. In that case the contact pins

require an identical cable diameter and length. This applies also to the AC output connection terminal which is

described in the following.

Additional the UNB is equipped with a DC input for the connection with the battery of the system. The internal

electronic circuit of the UNB is supplied by mains and additionally by the battery (redundancy). The voltage level

of the battery is monitored by the UNB; the result is used for switching off the inverters in case of over/under

voltage.

The UNB measures and monitors the voltage level of both input sources (real effective values) and additional the

frequencies. The thresholds of those measuring values are programmable (factory setting, only practicable by

skilled service personnel).

3.3.2 Output terminals

The unit is equipped with a plug-in AC output connection terminal. In case of short circuit, the short circuit power is

transferred to the UNB input, which causes the fuse of source 1 or 2 to blow. The UNB may be overloaded only for

short-time (see technical data). In particular this is to be observed for the correct dimensioning of the pre-fuse. The

pre-fuse must be dimensioned according to the nominal output power of the UNB. If the pre-fuse is

overdimensioned, the resultant delayed fuse tripping may destroy the internal thyristors of the UNB.

The operation of the UNB in combination with inverters of series UNV:

The UNB measures and monitors the current of the consumer load. In order to avoid a permanent overload of the

inverters the UNB verifies the availability of the connected inverters and anew calculates the allowed total current

of the consumer load. If one of the inverters in parallel operation fails, the overload threshold value automatically is

reduced.