Data Centre Power Quality, Efficiency and Reliability:

Data centre are very critical to operation of any successful business. They are growing larger and complex. The way to control costs, availability and reliability, while maintaining flexibility and scalability is to take full advantage of innovation and modularity.

Mission critical electronic digital equipment such as servers, programmable logic controllers, electrical supply must guarantee safe secure, clean and continuous uninterruptible power at the input terminals. The risks are high and could cost the business dear if external power is compromised in terms of quality or availability. If the power Quality is not maintained to standards, such as the IEEE-519 2014 or even better, the consequences can be serious, and could be a potential financial losses.

Power quality is characterized by parameters that express harmonic pollution, reactive power and load imbalance. By employing the right technology, a variety of power quality problems can be solved rendering installations trouble free, efficient and reliable, while complying with global standards of IEEE-519 2014.

Power Quality Problems

Ideally the power supply should be a constant sinusoidal voltage waveform. However the reality is different, due to inductive and capacitive inductances in electrical networks which are inevitable, data centre will experience power quality issues such as transients and outages. Hence maximizing power quality closer to a ideal supply system of a sinusoidal waveform, should be the goal of any data centre managers.

If the power quality standards and bench marks are set high, then loads connected will run with optimum efficiency, reliability. Reduction of carbon print will also be the additional benefit.

On the contrary to good clean power quality in the network is bad power quality, the loads connected would fail, energy cost can be high, operating cost( Capex) will inflate, enhanced carbon footprint. In some extreme case operation of the data centre may become economically unviable.

The possible consequences of poor power quality include:

1. Unexpected power failure due to tripping of MCBs.
2. Failure of servers, communication equipment, flickering of lights.
3. Electro magnetic Interferences in communication equipment (EM) can cause error in data.
4. Increase system losses.
5. Increase in capital expenditure as a result of oversizing of UPS , batteries, cables and transformers.
6. Penalty for not maintaining Power factor and excess billing due to faulty metering.
7. Disturbance and unsteadiness of visual sensation induced by light stimulus, where spectral distribution fluctuates with time, commonly called flicker.
8. Health issues of personnel working in the data centre.

The following are the main contributors of Poor or bad Power quality:

1.      Reactive Power

2.      Load imbalance caused by single phase load.

3.      Zero sequence currents (3rd Harmonics) generated by single phase electronic loads like lighting control gears and power supplies. The Harmonics generated can add to the neutral and load the neutral. Snapping of neutral wire can be dangerous and cause high voltage in single phase electronic equipments. It is also a potential fire Hazard.

4.      UPS and AC drives of chiller Plants and cooling fans will generate 5th and 7th Harmonics in sizable quantities and can have a deleterious effect on sensitive connected loads.

How do cost add up:

 Most Harmonic pollution now a days is created by harmonic producing non linear loads. The harmonic currents injected into the electrical network impedences transfers in to voltage distortion (Ohms Law Ih X Zh) which gets applied to all loads, consequently the loads are subjected to stress, and eventually fail due to these power quality issues.

Unfiltered harmonic currents that are not mitigated and attenuated by Harmonic filters flows through the cables and transformers to and fro along with the fundamental will distort the voltage waveform in the public network.

In order to limit the pollution that affect other users in the utility, IEEE-519 standards have been drawn to prevent Pollution of electrical network of other users. The philosophy and logic behind is that you shall not pollute your neighbor electrical network.

Power quality Parameters:

Reactive Power and Power factor:

The active power (KW) which is the energy converted into usefull work, whose phase current waveform is in phase and symmetrical to the voltage waveform.

The reactive power Q (KVAR) which is required to sustain the electromagnetic field like in the case of a motors, capacitor and reactor (which are basically energy storage devices) make up the losses of reactive energy, that does not translate energy into usefull work (KW).

The apparent Power S (KVA) which gives a geometric combination of the active and reactive power drawn from the network.

The capacitor stores energy in the form of electrical field, and the reactors stores energy as magnetic field. Capacitors and reactors are phase shifted by 90 degree and are inversely related and is reciprocal to each other. The formula below shows the inverse relationship.

Inductor L = 2 phiFL

Capacitor = 1/ 2phi FC

The ratio between active power and apparent power is referred to as displacement power factor or COS phi and is the indication of the efficiency of the electrical system. A cos phi of 0 indicates the most inefficient system and cos phi =1 indicates the most efficient electrical system.

Harmonic Distortion:

Harmonic pollution is referred to as Total Harmonic Distortion, THD V is voltage distortion and THDI is current distortion. By definition equal to the ratio of Harmonics to the fundamental frequency (50 Hz)\

These quantities are referred to as a percentage of the fundamental (50 HZ) and is the integer multiple of 50Hz. 3rd harmonics is 3x50Hz = 150 hz, 5th harmonics is 5x50=250hz, 7th harmonics is 7x50hz=350hz and so on.

The distorted Harmonics adds 3rd dimension to power and is called distorted power factor, this is besides the displacement power factors caused by inductive loads. The Total factor will then be distorted Pf x Displacement Power factor.

Distorted Power Factor complicates and adds 3rd dimension in calculation of reactive energy (KVAR).

Distorted power factor are caused by Non Linear loads like UPS, SMPS, lighting control gears and AC drives.

In the presence of Harmonics Installing automatic Power factor control Panel, will not improve power factor, in fact they may worsen the situation and may cause low power factor and Harmonic resonance. Capacitor Banks will act as low impedence path for harmonic currents and damage capacitors. Instead of providing energy and improve power factor, they act as Harmonic sink and amplify harmonic signals and currents.

However anti resonant filters in series with the capacitors will act as high impedence to these harmonics and will improve power factor. But the ideal and good electrical practice is to mitigate Harmonics at source and prevent resonance.

They are multiple , simple, robust and cost effective techniques to deal with these complex harmonics effectively, thereby improving Power quality, electrical efficiency and reliability.

Some of the techniques are simple devices like the Zero sequence impedence transformer, Advance Passive harmonic filter and Harmonic mitigation transformer.

If are you are curious to know more about the impact of PQ the detailed article will be provide drop your mail in comments

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