Essential questions and answers on UPS (part 2)

During its useful life the UPS must face innumerable challenges to guarantee the correct operation of the Data Center and the activity of the company.

 

What are the power supply problems?

The low quality of the power supply is one of the main problems that results in data loss. When we talk about problems of this nature, the most significant include voltage dips and cuts, surges, frequency variations, harmonics and voltage imbalance.

All these occurrences on the grid cause damage and reduce the useful life of IT equipment and components, as well as date losses.

 

What are voltage dips and cuts?

Nominal voltage must have an effective value of 230 V between phase and neutral, and 400 V between phases. Variations of ±10% are permitted 95% of the time and up to +10/-15% 100% of the time.

A voltage dip is a sudden drop in voltage at a point of a power grid, up to a value comprising (by agreement) between 90% and 1% (CENELEC EN 50160), followed by a re-establishment of the grid voltage after a short period of time comprising between 100 and 1000 ms.

What problems can it cause? Data loss, file damage, operating errors in the equipment devices, component damage and reducing its useful life.

 

What is a surge?

A surge is an abnormal voltage value. The most usual ones are due to excess, but can also be due to absence (undervoltage). Surges are caused sporadically and can reach up to several kV of crest value in milliseconds or microseconds.

There are three types of surge:

  • Temporary, at industrial frequency.
  • Switching.
  • Atmospheric origin (lightning).

 

They can occur:

  • In differential mode (between active phase/phase or phase/neutral conductors),
  • In common mode (between active conductors and the mass or ground).

They can damage IT equipment hardware and cause data loss. UPS, along with solutions such as surge arresters, will help control these faults.

 

Frequency variation?

The frequency must be 50 Hz, with variations below ±2% 95% of the time and up to ±15% 100% of the time.

The double conversion on-line UPS keeps the frequency constant in conditions suitable for the consumption of equipment.

 

What are harmonics?

Any periodical function (of frequency f) can be broken down into a sum of sine waves of frequency h x f (h: full); h is called order or range of the harmonic (h > 1). The first order component is the basic component.

Total Harmonic Distortion (THD) provides a measurement of the deformation of the signal.

Harmonics primarily come from non-linear loads, whose characteristic is to absorb a current that does not have the same form as the voltage supplying them.

These high frequency harmonic currents can cause serious problems in the usual operation of the facilities, warming up, untimely trips, errors in IT equipment.

In this respect, UPS have evolved quite a lot by generating TDHi < 3% in high range double conversation on-line equipment.

Harmonic currents can be transmitted through ground networks, reinjected through low impedances and cause problems in parts of the facility that beforehand have nothing to do with the harmonic generation zone.

 

What is a voltage imbalance?

Voltage imbalance is caused either when the effective values of the phases are not the same or when there is an excessive delay between them. It establishes as a limit that 95% of the effective values calculated in 10 minutes from the reverse component of the voltage must be between 0% and 2% of the direct component.

The purpose of this standard is to define and describe the values characterising the voltage of the power supplied:

  • Frequency
  • Amplitude
  • Wave form
  • Symmetry

 

These characteristics are subject to variations due to:

  • Modification of the network load
  • Disturbances issued by certain equipment
  • Absences due to external causes

Selecting the best UPS system for our data center will be motivated by different circumstances, but it is essential to have specialist engineers and technicians, who can assess the current situation of the DPC and its potential needs in the future.

To mitigate the aforementioned power supply problems to a large extent, not only must the most suitable UPS be selected, but also a set of technical solutions related said UPS.