UPS-laitteen vian erotuskyvyn parantaminen

UPS devices are utilized to ensure a constant and undisturbed power supply for critical loads. If a fault occurs in the AC grid that normally supplies the load, the UPS device will instantly begin to supply power from its batteries via the inverter to the load. However, if a fault, such as a short circuit, occurs in the load side of the UPS when the UPS is supplying power from its batteries, the UPS must be able to supply enough fault current to clear the circuit breaker closest to the fault location and isolate the fault before the UPS itself trips to overcurrent. The maximum output current of the UPS is intentionally limited in time and magnitude to prevent power semiconductor components of the UPS inverter from suffering overcurrent damages. The problem is that UPS devices must be often oversized in terms of rated power so that a sufficient fault clearing capability of the UPS to clear respective circuit breakers in the load side is achieved. Thus, the spare power which results from oversizing the UPS is dispensable during normal operation of the UPS. This thesis aims to find economical ways to improve the fault clearing capability of a UPS device. Hence, a simulation model is developed which can be used to estimate how much the fault clearing capability of a UPS device may be improved by installing IGBTs and diodes in parallel to the main circuit of the UPS inverter. Current limit values of the UPS inverter and number of parallel connected IGBTs and diodes in the main circuit of the inverter are adjustable in the simulation model. Power losses and junction temperatures of IGBTs and diodes are calculated based on input data which may be obtained from datasheets of IGBTs and diodes. The solution to improve the fault clearing capability of a UPS device by adding IGBTs and diodes in parallel to the main circuit of the inverter is compared from economical and technical point of view to the use of an external fault clearing circuitry which is another worthy solution to improve the fault clearing capability of a UPS device. Cost comparison conducted between the two solutions revealed that improving the fault clearing capability of a 20 kW UPS device by adding IGBTs and diodes in parallel to the main circuit of the inverter may result in 20–30% higher costs than using the fault clearing circuitry. Furthermore, the fault clearing circuitry may be technically a more feasible solution to be applied for existing UPS devices than the change in IGBT and diode configuration.UPS-laitteita käytetään varmistamaan jatkuva ja häiriötön sähkönsyöttö kriittisille kuormille. UPS-laite alkaa välittömästi syöttää sähköä akustostaan vaihtosuuntaajan kautta kuormalle, jos kuormaa normaalisti syöttävässä vaihtosähköverkossa syntyy vika. Jos UPS laitteen kuormapuolella syntyy kuitenkin vika, kuten oikosulku, kun UPS laite syöttää sähköä kuormalle akustostaan, UPS-laitteen täytyy pystyä syöttämään tarpeeksi vikavirtaa, jotta lähinnä vikapaikkaa oleva katkaisija avautuu ja erottaa vian ennen kuin UPS-laite katkaisee sähkönsyötön ylivirran vuoksi. UPS-laitteen maksimilähtövirta on tarkoituksellisesti rajoitettu ajalliselta kestoltaan ja suuruudeltaan, mikä ehkäisee UPS-laitteen vaihtosuuntaajassa olevien tehopuolijohdekomponenttien vaurioitumista ylivirran vuoksi. Ongelmana on, että UPS-laitteita joudutaan ylimitoittamaan nimellisteholtaan, jotta niille saadaan riittävän korkea vian erotuskyky laukaisemaan kuormapuolen katkaisijat vikatilanteessa. Tällöin UPS-laitteen ylimitoittamisesta syntyvä lisäteho on kuitenkin tarpeetonta UPS-laitteen normaalin toiminnan aikana. Tämän työn tarkoituksena on löytää taloudellisia keinoja parantaa UPS-laitteen vian erotuskykyä. Työssä kehitettiin simulointimalli, jolla voidaan arvioida, kuinka paljon UPS-laitteen vian erotuskykyä voidaan parantaa kytkemällä IGBT- ja diodikomponentteja rinnan UPS-laitteen vaihtosuuntaajan pääpiiriin. Vaihtosuuntaajan virtarajoja ja rinnankytkettävien IGBT- ja diodikomponenttien määrää voidaan säädellä simulaatiomallissa. IGBT- ja diodikomponenttien tehohäviöiden ja liitoslämpötilojen laskenta perustuu niiden datalehdistä saataviin tietoihin, jotka syötetään simulaatiomallille. Ratkaisua, jossa UPS-laitteen vian erotuskykyä parannetaan kytkemällä IGBT- ja diodikomponentteja rinnan vaihtosuuntaajan pääpiiriin, verrataan taloudellisesta ja teknisestä näkökulmasta ulkoiseen vian erotuspiiriin, joka on toinen varteenotettava ratkaisu, jolla UPS-laitteen vian erotuskykyä voidaan parantaa. Ratkaisuille tehtiin kustannusvertailu, josta selvisi, että parantamalla nimellisteholtaan 20 kW:n UPS-laitteen vian erotuskykyä lisäämällä IGBT- ja diodikomponentteja rinnan vaihtosuuntaajan pääpiiriin lisää se kustannuksia 20–30% verrattuna ulkoisen vian erotuspiirin käyttöön. Vian erotuspiirin kytkeminen on lisäksi teknisesti helpompi toteuttaa jo olemassa oleviin UPS-laitteisiin verrattuna siihen, että niihin tehtäisiin vaadittavat IGBT- ja diodikomponenttien laitekokoonpanomuutokset

Triage and urgent dental care for COVID-19 patients in the Hospital District of Helsinki and Uusimaa

Objective This paper describes and reports the patient-specific characteristics of an urgent dental care clinic for COVID-19 infected, suspected, exposed or quarantined patients from March to December 2020 in the Hospital District of Helsinki and Uusimaa, Finland. Material and methods The triage and the treatment protocol were established based on the scientific data. Patient files were evaluated from the hospital district's electronic medical record system. IBM SPSS software was used for statistical analysis. Results There were 1114 consultations and 257 visits at the clinic. Most of the patients were generally healthy with mean age of 35, had toothache and were suspected to be SARS-CoV-2 positive. Seventeen of the patients received positive tests for COVID-19 infection. The main treatment was tooth extraction, mostly due to caries. Statistically significant differences between COVID-19 infected and other patients occurred in age (45 vs 34 years-of-age, p = .009) and number of teeth (25 vs 28, p = .031). No SARS-CoV-2 infection transmission chains were traced to the clinic. Conclusion During the challenging pandemic time, patients were carefully screened by specialists in clinical dentistry and treated safely and effectively. Patient-specific characteristics revealed no differences between COVID-19 infected and other patients in terms of symptoms or treatment needs.Peer reviewe

Emissions of DEHP-free PVC flooring

Degrading 2-ethylhexyl-containing PVC floorings (eg DEHP-PVC floorings) and adhesives emit 2-ethylhexanol (2-EH) in the indoor air. The danger of flooring degradation comes from exposing occupants to harmful phthalates plasticisers (eg DEHP), but not from 2-EH as such. Since the EU banned the use of phthalates in sensitive applications, the market is shifting to use DEHP-free and alternative types of plasticisers in PVC products. However, data on emissions from DEHP-free PVC floorings are scarce. This study aimed at assessing the surface and bulk emissions of two DEHP-free PVC floorings over three years. The floorings were glued on the screed layer of concrete casts at 75%, 85%, and 95% RH. The volatile organic compounds (VOCs) were actively sampled using FLEC (surface emissions) and micro-chamber/thermal extractor (µ-CTE, bulk emissions) onto Tenax TA adsorbents and analyzed with TD-GC-MS. 2-EH, C9-alcohols, and total volatile organic compound (TVOC) emissions are reported. Emissions at 75% and 85% RH were similar. As expected, the highest emissions occurred at 95% RH. 2-EH emissions originated from the adhesive. Because the two DEHP-free floorings tested emitted C9-alcohols at all tested RH, it makes the detection of flooring degradation harder, particularly if the adhesive used does not emit 2-EH.Peer reviewe