NETA Battery and UPS Systems Testing 5 — Questions and Answers
Question 1: Which NETA MTS test verifies that a UPS static transfer switch correctly transfers the load to bypass within the specified time when output voltage deviates beyond tolerance?
- Overcurrent coordination test
- Automatic transfer time test (Correct answer)
- Harmonic injection test
- Ground fault impedance test
Correct answer: Automatic transfer time test
The automatic transfer time test confirms the static bypass switch operates within manufacturer-specified milliseconds when UPS output falls outside the acceptable voltage or frequency window.
Question 2: Nickel-cadmium (NiCd) stationary batteries require a different maintenance approach than VRLA batteries primarily because NiCd cells:
- Have a higher self-discharge rate requiring more frequent equalization
- Require electrolyte level checks and periodic water additions (Correct answer)
- Cannot be tested with ohmic measurement devices
- Operate at lower float voltages making voltage measurement unreliable
Correct answer: Require electrolyte level checks and periodic water additions
NiCd batteries use a liquid potassium hydroxide electrolyte that can deplete through gassing, requiring periodic inspection and distilled water additions unlike sealed VRLA designs.
Question 3: What does the 'C-rate' designation C/8 mean when applied to a battery discharge test?
- The battery is discharged at a current equal to its rated capacity divided by 8, over an 8-hour period (Correct answer)
- The battery delivers 8 times its rated capacity in one hour
- The test requires 8 charge-discharge cycles
- The charger output is limited to 8 amperes
Correct answer: The battery is discharged at a current equal to its rated capacity divided by 8, over an 8-hour period
C/8 means the discharge current equals the rated ampere-hour capacity divided by 8, resulting in a complete discharge over approximately 8 hours under ideal conditions.
Question 4: During UPS commissioning, the input current total harmonic distortion (THD-I) is measured at 28%. Which standard provides the limits that should be used to evaluate this result?
- NFPA 70E Article 130
- IEEE 519 (Correct answer)
- ANSI C84.1
- NETA MTS Section 7
Correct answer: IEEE 519
IEEE 519 establishes harmonic current and voltage distortion limits at the point of common coupling for power electronic equipment including UPS systems.
Question 5: A VRLA battery float voltage is found to be 0.05 V/cell above the manufacturer's recommended maximum. The long-term consequence of operating in this condition is:
- Reduced self-discharge and extended shelf life
- Accelerated water loss, dry-out, and thermal runaway risk (Correct answer)
- Improved capacity recovery and reduced sulfation
- No significant effect within a ±0.1 V/cell tolerance band
Correct answer: Accelerated water loss, dry-out, and thermal runaway risk
Chronic over-voltage on VRLA cells drives excessive electrolysis, depleting the recombination capacity, drying out the separator, and increasing thermal runaway susceptibility.
Question 6: When testing UPS battery charger output under a fully discharged battery condition, which parameter must be verified to prevent battery damage?
- Output ripple voltage stays below 1 Vrms
- Bulk charge current does not exceed the manufacturer's maximum charge rate (Correct answer)
- Charger output frequency matches utility frequency
- DC bus voltage matches nominal battery voltage within 0.1%
Correct answer: Bulk charge current does not exceed the manufacturer's maximum charge rate
Exceeding the maximum recommended charge current causes excessive heat, gassing, and potential plate damage, so the charger's current-limiting function must be verified during bulk charging.
Question 7: Which condition would cause a conductance tester to give an artificially high (falsely good) reading on a lead-acid battery cell?
- Cell temperature below 25°C
- Cell at a low state of charge
- Cell with a partially shorted plate group
- Surface charge present on recently charged cell (Correct answer)
Correct answer: Surface charge present on recently charged cell
Surface charge from a recent charge cycle elevates the apparent open-circuit voltage and can cause conductance testers to read higher than the true rested-state value, masking degradation.
NETA Battery and UPS Systems Testing 5
Which NETA MTS test verifies that a UPS static transfer switch correctly transfers the load to bypass within the specified time when output voltage deviates beyond tolerance?