Design and construction.

DOE-SPEC-3021-97

3.3

3.3.1

General. The UPS system shall consist of a UPS module and storage battery

rated to supply the requirements for the critical load as specified herein.

3.3.1.1

Source and output. The internal bypass source and the inverter

output shall be connected to the ac bus via a high-speed static

transfer switch. The static transfer switch shall automatically

transfer the ac bus to the internal bypass source only if it is available

within the tolerances noted in paragraph 3.2.2 or upon a drop in

output voltage or variation of frequency as specified in paragraph

3.3.2.1.

Power interruption interval. The power-interruption interval during

3.3.1.2

the transfer from the inverter to the internal bypass source shall not

exceed the limits defined in paragraph 3.3.5.4. If specified in

paragraph 3.3.5.2, the transfer switch shall automatically retransfer

the ac bus back to the inverter output upon restoration of normal

conditions and after a suitable time delay to avoid cycling during

slow clearing of external faults and during inrush conditions. This

transfer shall always take place for the inrush loads listed in

paragraph 3.3.5.3. A transfer in either direction shall not cause a

disturbance to the critical loads. Provide the means for the Owner

to manually inhibit automatic retransfer via the static transfer switch.

Transfer in either direction shall not cause a disturbance to the ac

load(s). Transfer shall require the inverter output to be in

synchronism with the bypass ac source, except for an inverter

failure. For inverter failure, the transfer shall complete regardless of

phase angle. The UPS module shall provide an alarm whenever a

transfer to the internal bypass source takes place. Include a

suitable time delay for this alarm to avoid alarming on momentary

transfer.

Manual transfer. Make provisions to transfer the ac bus manually to

3.3.1.3

the external maintenance bypass source for maintenance of the

static switch with a make-before-break switch for uninterrupted

transfer of power to the critical loads.

3.3.2

Inverter.

ATTENTION:

The following are guidelines for providing information about inverters, below:

The voltage regulation of most UPS systems is around 5%.

The transient response to a 100% step change in load should hold the output voltage to within 10% of

nominal and the output should recover to within 3% of nominal in 3-5 cycles.

As a guideline, the total harmonic distortion (THD) should not exceed 5%, and the maximum content of

any single harmonic should not exceed 3%.