Instrument AC

Question 1

Why is the blocking diode placed on the DC output feeding into the inverter?

Answer 1

So if rectifier output (from ac) is higher than dc output current doesn’t flow back to dc source acting as battery charger

Question 2

What are the different conditions that will give you “failure” alarm on UPS mimic board (instrument AC)?

Answer 2

• loss batt source (volt downstream dc low) - invert failure (invert output, ovrld, fail, high freq) - bypass source (static switch swapped to TRY) - loss ac output (ac from UPS lost) - manual bypass (manual bypass in bypass)

Question 3

Power supplies to instrument ac (PY11, 11a, 12, 13, 13a, 14)?

Answer 3

Panel dc ac TRY(pri) PY11 SD11 F F PY11a SD11 F F PY12 SD12 G G PY13 SD13 H H PY13a SD13 H H PY14 SD12 H H

Question 4

What conditions will transfer static switch of inverter to “bypass”?

Answer 4

• Loss of inverter output (loss inverter) - inverter high current (burn off fault) - dc voltage into inverter < 100 vdc (damage inverter trying to boost current)

Question 5

What conditions will put you in t.s.? (Inst ac) Loss dc input to IY- 1 Loss ac input to IY- 2 Static switch xfr to bypass- 3 Bypass switch xfr to bypass- 4 TRY xfr to backup- 5

Answer 5

1, 3, 4

Question 6

Describe basic layout of Vital inverter (UPS)

Answer 6

• vital 480 vac provides power to transformer rectifier (ac->dc)(480->134)
• backup dc thru blocking diode comes in downstream of rectifier
• dc inverted (dc->ac)
• goes through static switch (alt power via TRY)
• goes through maint switch
• goes to PY-…….panels