Interlocks - spec30210019

DOE-SPEC-3021-97

within the specified limits. Upon restoration of the Owner's

electrical distribution system frequency to within specified limits,

the inverter shall automatically synchronize with it at a slew rate

of 1 Hz/s or less. Indication of synchronism shall be provided on

the UPS system control panel.

ATTENTION:

Synchronization is usually based on the frequency difference of the two sources being within less than 0.5 Hz

and the phase difference being less than 2 degrees.

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b. Synchronization between the inverter output and internal bypass

source shall be defined to be coincidence of frequency

[ ] Hz and coincidence of phase [ ] degrees.

3.3.2.7

Interlocks. Provide interlocks to prevent a manual transfer from the

inverter output to the external maintenance bypass source and

internal bypass under normal conditions if it is outside the following

limits:

a. Bypass voltage (internal or external) is more than 10% higher or

lower than nominal

b. Voltage difference between inverter output and bypass source

(internal or external) is greater than 10% of the bypass voltage

c. Bypass frequency (internal or external) is more than 0.5 Hz

from the nominal value specified in 3.2.2

d. The two sources are not synchronized to within 2 degrees

Current limiting. The UPS system inverter shall be equipped with a

3.3.2.8

complete automatic current limiting feature which prevents the

output from exceeding the maximum safe rating of the inverter and

protects it against overloads or short circuits at the output. As long

as the overload is present, the limiting feature shall limit the output

current to a value which will not damage the inverter or cause its

protective devices to operate. Once the overload is removed, the

inverter shall automatically resume operation at normal voltage. In

the event of the load limiting feature failure, backup protection shall

be provided which will trip the inverter and transfer the load to the

internal bypass source. This condition shall be indicated locally and

through a set of alarm contacts for the Owner's annunciator.