Page 87 - Uninterruptible Power Supplies

Interconnecting the Standby and Normal Supplies
Interconnecting the Standby and Normal Supplies 85

High-Voltage Switchgear
For high-voltage installations, the switchgear should comply with BS EN
60298. The enclosures should protect the equipment against the ingress
of solid foreign objects, and persons against touching hazardous parts, to
one of the degrees of protection in BS EN 60529. (BS EN 60298 invokes
BS EN 60694 which in turn invokes BS EN 60529).

Prospective Fault Current Level
For a set providing an alternative supply and not arranged to run in
parallel with the normal supply, the prospective fault level will be
the higher of the two supplies, which will almost certainly be that of the
normal supply. For sets running in parallel with the normal supply,
the prospective fault current will be the sum of the two fault cur-
rents. The mechanical and thermal stresses imposed on the busbars
are proportional to the square of the current, it follows that a modest
additional current from a generator can have a significant effect
within the switchboards.

Information to Be Displayed at the
Switchboard
Single-Set Installations The generator panel of a single set, not
intended to run in parallel with another set or the normal supply, is
required by ISO8528 to display the following information:

Voltage, with provision for indication of phase-to-phase and phase-
to-neutral voltages
Current, with provision for indication of each phase

Other indications which should be considered includes:

The frequency of the ac output
Operating hours, that is, a cumulative hours-run counter
For large sets only, indication of kW, kVAr, power factor, and cumu-
lative kWh.

Multiple-Set Installations Each generator panel of a multiple-set instal-
lation not intended to run in parallel with the normal supply should
display the following:

Voltage, with provision for indication of phase-to-phase and phase-
to-neutral voltages
Current, with provision for indication of each phase
kW indication for each set

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