What is UPS (Uninterruptible Power Supply)?

An Uninterruptible Power Supply (UPS) is a device that offers emergency backup power to electrical equipment in the event of a failure or fluctuation in the main power supply.

ISO/IEC Standards for UPS

• IEC/ISO 62040-1 – General and Safety Requirements
  Discusses the structure, protection, and user safety of UPS systems. Applies to UPS used in normal and abnormal operating conditions.
• IEC/ISO 62040-2 – Electromagnetic Compatibility (EMC)
  Defines EMC requirements (immunity and emissions). Ensures the UPS doesn't interfere with or suffer from other electronic equipment.
• IEC/ISO 62040-3 – Performance and Testing
  Specifies UPS classification (VFI, VI, VFD). Describes testing methods: output stability, transfer time, overload capacity, etc.
• IEC/ISO 62040-4 – Environmental Aspects – Requirements and Reporting
  Addresses environmental impacts, efficiency, and sustainability. Includes reporting guidelines for lifecycle and energy.
• IEC/ISO 62040-5 Series – DC UPS Systems
  Focuses on UPS systems providing DC output (used in telecom, industrial control). Part 5-1: Safety requirements for DC UPS. Other parts may define performance and installation requirements (as released).

Testing of Load Bank through UPS

To evaluate the state of your Uninterruptible Power Supply, load bank testing is used. It assesses battery performance as well as life. The purpose of this test is to confirm that your system is capable of handling the necessary load.

Using Standard Titles for Load Bank Tests

• IEC/ISO 62040-3 – Performance and Test Requirements for UPS
  When testing UPS systems with a load (such as a load bank), this is the main criterion. It covers:
  • Load step response
  • Output voltage/frequency under load
  • Overload capability
  • Transfer time to/from battery
  • Efficiency and thermal limits under load
  • Battery backup time under specified loads
• IEC/ISO 62040-1 – General and Safety Conditions
  Guarantees secure functioning throughout load testing. Defines protection and fault response when UPS is under load.
• IEC/ISO 62040-4 – Environmental Aspects
  Focuses on energy and thermal performance during testing loads. Crucial for monitoring heat dissipation during testing with continuous loads.

Dynamic Features for UPS-Based Load Bank Testing

When testing a UPS using a load bank, dynamic characteristics refer to how the UPS responds to sudden or varying load changes. These are critical for assessing UPS reliability, performance, and its ability to protect sensitive equipment.
Based on IEC/ISO 62040-3, here are the key dynamic characteristics to evaluate:

• Transient Response
  Definition: The UPS's response to abrupt variations in load.
  Test: Apply a load step (e.g., from 0% to 50% or 50% to 100%) and measure:
  • Voltage deviation (%)
  • Time to recover to steady-state (in milliseconds)
• Voltage Regulation under Load
  Definition: The capacity to keep the output voltage within predetermined bounds when the load fluctuates.
  Test: Apply different load levels (0%, 25%, 50%, 75%, 100%) and measure output voltage variation.
• Frequency Stability
  Definition: The capacity to sustain output frequency while loads fluctuate, particularly in online or VFI mode.
  Test: Track changes in frequency while the step load is changed.
• Transfer Time
  Definition: Time taken to switch from normal to battery mode or bypass under dynamic conditions.
  Test: Simulate a power failure and measure transfer time (should be near-zero for online UPS).
• Overload Response
  Definition: UPS behavior when the load beyond the rated capacity is defined as follows.
  Test: Apply an overload (e.g., 125% load for 10 minutes) and observe if UPS can sustain or shut down safely.
• Harmonic Distortion (THD)
  Quality of the output waveform under dynamic load is defined as follows.
  Test: Measure THD of voltage and current especially during load transitions.
• Battery Response
  Definition: Battery performance during sudden transitions (e.g., full load during blackout).
  Test: Examine the runtime, discharge rate, and voltage drop.
• Recovery Time
  Definition: The amount of time it takes for frequency and voltage to return to normal following a transient.

Static Characteristics for Load Bank Testing through UPS

Static characteristics describe a UPS system's performance under constant load, without fluctuations. These parameters assess the baseline output quality, stability, and efficiency.
Based on IEC/ISO 62040-3, key static characteristics include:

• Output Voltage Regulation
  Definition: The UPS's ability to maintain stable output voltage under constant load.
  Test: Assess the output voltage under different steady loads (0%, 25%, 50%, 75%, 100%).
  Requirement: Deviation within ±1% to ±5%, depending on UPS class (VFI, VI, VFD).
• Output Frequency Regulation
  Definition: Output frequency stability under constant load.
  Test: Measure frequency during steady operation.
  Typical value: ±0.5 Hz (depends on UPS class and input conditions).
• Output Waveform Quality (THD)
  Definition: Total Harmonic Distortion (THD) is the voltage waveform’s definition.
  Test: Analyze the voltage waveform at full load.
  Limit: THD < 3% (for high-performance VFI UPS).
• Efficiency
  Definition: The output to input power ratio when the load is constant.
  Test: Measure input and output power at different loads.
  Typical value: 95%+ for online UPS (VFI) at full load; 98%+ for line-interactive UPS (VI).
• Input Power Factor
  Definition: Real to perceived power ratio derived from the mains.
  Test: Measure power factor at various loads.
  Typical: > 0.95 for modern UPS systems.
• Heat Dissipation (Thermal Performance)
  Definition: Heat generated under continuous load.
  Test: Measure exhaust air temperature and cooling system performance.
• Static Stability
  Definition: The UPS’s ability to maintain output parameters without drift over time under constant conditions.

Difference Between Static and Dynamic Characteristics: