Metrologically-certified mains power quality monitoring

The vol­ume of dig­i­tal data is increas­ing swift­ly and con­tin­ues to grow. One of the main caus­es are cryp­tocur­ren­cies like Bit­coin (XBT), Ether (ETH), Lite­coin (LTC) etc. or blockchain tech­nol­o­gy, which  to a cer­tain extent, is like a type of data­base which runs on sev­er­al net­worked servers. The grow­ing demand for data exchange is also spawn­ing the growth in the num­ber of data cen­tres, and they are being planned, built and main­tained at mas­sive scale around the globe. How­ev­er, data cen­tres have to deal with com­plex chal­lenges in terms of the sup­ply of elec­tric ener­gy, which can have an effect on secure (and legal­ly- com­pli­ant) 24/7 operation.

Problem description

Var­i­ous stud­ies have shown that mains pow­er qual­i­ty prob­lems gen­er­ate costs that run into the bil­lions each year. Already in 2007, the Pan-Euro­pean LPQI Pow­er Qual­i­ty Sur­vey 2007 esti­mat­ed that the dam­age was equiv­a­lent to 150 bil­lion Euros annu­al­ly. Mean­while, the chal­lenges for every­one have con­tin­ued to grow.

The solution

As described ear­li­er, pow­er qual­i­ty prob­lems can gen­er­ate dis­tur­bances and sys­tem fail­ures which inevitably result in addi­tion­al cost, time and effort. Pow­er sup­ply noise rep­re­sents a non-neg­li­gi­ble risk (see fig­ure 2) espe­cial­ly for data cen­tres, which are equipped with cap­i­tal-inten­sive redun­dan­cy (for exam­ple UPS sys­tems, gen­er­a­tors, mul­ti­ple pow­er sources) and which nor­mal­ly ought to pre­vent any down­time or poten­tial dam­age. Ide­al­ly, all the installed equip­ment should be com­pli­ant with the har­mon­ic dis­tor­tion and noise immu­ni­ty stan­dards, so it is prob­a­ble that they can oper­ate trou­ble-free. How­ev­er in an unfavourable oper­at­ing con­text, for exam­ple a large num­ber of sim­i­lar con­sumers, asym­met­ri­cal net load­ing, etc., sig­nif­i­cant­ly exces­sive noise lev­els can occur. To be able to esti­mate the risks as well as lim­it them on a per­ma­nent basis, pow­er qual­i­ty mon­i­tor­ing is thus essential.

The above-men­tioned stan­dards give guide­lines on how the mains pow­er should behave at the mon­i­tor­ing point in nor­mal oper­a­tion. Excep­tion­al sit­u­a­tions which could lead to the ener­gy sup­ply being tem­porar­i­ly restrict­ed are not cov­ered. It is com­pul­so­ry to record these types of dis­tur­bance, such as volt­age dips or inter­rup­tions, how­ev­er there is no spec­i­fied lim­it to their num­ber in order to be com­pli­ant with the stan­dard (see fig­ure 4). The func­tion of UPS or back­up pow­er sup­ply sys­tems is to be able to com­pen­sate for any pow­er sup­ply con­straints. These back­up solu­tions are how­ev­er lim­it­ed to the most impor­tant resources, so it may be that oth­er com­po­nents oper­ate with only reduced func­tion­al­i­ty. For this rea­son, it is crit­i­cal that oper­at­ing per­son­nel are quick­ly informed when an IEC 61000–4‑30 type event occurs. This can be imple­ment­ed by an auto­mat­ic noti­fi­ca­tion sent to the com­pe­tent peo­ple by email for example.

A further aspect: RCM

To pre­vent oper­a­tions being inter­rupt­ed unex­pect­ed­ly, data cen­tres avoid using resid­ual cur­rent mon­i­tor­ing devices (RCDs) with direct trig­ger­ing. In the con­trary, it is com­pul­so­ry to mon­i­tor resid­ual cur­rents on a per­ma­nent basis (see fig­ure 5). In this case, RCM (Resid­ual Cur­rent Mon­i­tor­ing) is used, which as well as its essen­tial func­tion of pro­tect­ing peo­ple’s safe­ty, also pro­tects the sys­tems from dam­age and aids fire pre­ven­tion. Fur­ther­more, changes in resid­ual cur­rents can pro­vide an ear­ly warn­ing of any dete­ri­o­ra­tion in the insu­la­tion and allow cor­rec­tive mea­sures to be under­tak­en. Errors occur­ring in the TN‑S sys­tem (for exam­ple ille­gal or addi­tion­al PE‑N con­nec­tions can also be in detect­ed ear­ly and cor­rect­ed as a result).

Correct measurement data through metrological traceability

An old lock­smith’s say­ing is “cen­time­tres are a clock­mak­er’s mea­sure­ment”. Put anoth­er way, “he who mea­sures, mea­sures garbage”. Tech­ni­cians and econ­o­mists know this and they take heed of this well-known and still use­ful warn­ing, mak­ing sure they use the right method for each type of mea­sure­ment. How­ev­er in spite of the fact that the required spec­i­fi­ca­tions of a pow­er qual­i­ty device are pre­cise­ly defined in terms of mea­sure­ment method­ol­o­gy (IEC 61000–4‑30), device char­ac­ter­is­tics (IEC 62586–1) and val­i­da­tion of com­pli­ance with the stan­dards (IEC 62586–2), there are still dif­fer­ences between the man­u­fac­tur­ers. Sup­pli­ers are often unable to prove why their analy­sis device meets the spec­i­fi­ca­tions and mea­sures cor­rect­ly. Proof of a tru­ly cor­rect mea­sure­ment can only be obtained from an inde­pen­dent cer­ti­fi­ca­tion lab, ide­al­ly a metro­log­i­cal insti­tute. Non-cer­ti­fied test labs, or even the man­u­fac­tur­ers own state­ments can­not be a sub­sti­tute for metro­log­i­cal cer­tifi­cate and thus should be viewed with a crit­i­cal eye. This is espe­cial­ly true where sen­si­tive activ­i­ties such as data cen­tres are con­cerned, which are asso­ci­at­ed with high costs and risks.

The benefits of metrologically-certified power quality monitoring

The main ben­e­fit of a pro­fes­sion­al and per­ma­nent pow­er qual­i­ty mon­i­tor­ing is the increased oper­a­tional avail­abil­i­ty of data cen­tres. Where­by pow­er qual­i­ty is defined as a key com­po­nent of sup­ply qual­i­ty (see fig­ure 6) and is nat­u­ral­ly applic­a­ble for many oth­er sen­si­tive areas oth­er than data cen­tres (for exam­ple hos­pi­tals, sen­si­tive indus­tri­al sites, in trans­port infra­struc­ture such as air­ports, pub­licly-acces­si­ble build­ing com­plex­es such as shop­ping cen­tres, etc.). The ben­e­fit is obtained by analysing the record­ed long-term data to observe the changes and iden­ti­fy cor­re­la­tions. Com­pli­ance with the con­trac­tu­al sup­ply guide­lines is just one of the impor­tant aspects.

Results

Draw­ing the cor­rect con­clu­sions from metro­log­i­cal­ly-cer­ti­fied pow­er qual­i­ty mon­i­tor­ing includ­ing RCM, results in the durable pro­tec­tion of invest­ments, reduced oper­at­ing costs, max­imi­sa­tion of data avail­abil­i­ty and very impor­tant­ly, the sat­is­fac­tion of all stake­hold­ers. These include cus­tomers, employ­ees, ener­gy sup­pli­ers, oper­a­tors, investors, ser­vice con­trac­tors, author­i­ties, asso­ci­a­tions, etc. And last­ly, it helps to low­er CO2 emis­sions because it makes it pos­si­ble to oper­ate the data cen­tre more effi­cient­ly and securely.

Outlook

A fur­ther aspect to be con­sid­ered is whether con­tin­u­ous and qual­i­fied mon­i­tor­ing of the mains pow­er could also be used to pre­vent cyber attacks on the ener­gy sup­ply of data cen­tres or oth­er sen­si­tive activ­i­ties. This would be qua­si-redun­dant to the exist­ing mon­i­tor­ing sys­tems which are already imple­ment­ed as soft­ware solu­tions, but which are how­ev­er sub­ject to enor­mous dynam­ics. The pur­pose is to research whether a con­nec­tion can be found between changes in pow­er qual­i­ty and cyber attacks on a data cen­tre’s servers and infra­struc­ture, and as a result be able to fend them off early.