Elektroinstalateri: Električni strojevi. Bimetalna zaštita motora 3. razred.
Način spajanja, uloga i princip djelovanje bimetalne zaštite elektromotora.
Osnove elektrotehnike vežbe gradivo za 2. test
Literatura
Nadica Miljkovic ETF Instrumentacija za elektricna merenja
M.Mitrovic, A. Zekic, FF, Didaktika fizike
INternet
Three Point Starter: Diagram and Working PrincipleDr.Raja R
This document discusses the three point starter, which is a device that helps start and run DC shunt or compound wound motors. It consists of contact points called studs that gradually cut resistance from the armature circuit as the motor gains speed. Initially, high starting current is limited by the entire resistance being in series with the armature. As the handle moves from OFF to RUN, resistance is removed. The no voltage coil holds the handle in RUN position using magnetic force as long as power is supplied, but releases it to OFF if power fails, protecting the motor. However, three point starters have issues if field current decreases too much by field rheostat adjustment.
A battery charger is a device that puts energy into a rechargeable battery by forcing an electric current through it. The document discusses battery charger basics including definitions, battery chemistries, applications, and Microchip's portfolio of battery charger integrated circuits. Microchip offers various single-cell and dual-cell battery charger ICs supporting lithium-ion, lithium polymer, and lithium iron phosphate batteries with integrated or external MOSFETs and features like overvoltage protection and temperature monitoring.
Different methods of pwm for inverter controlTushar Pandagre
This document discusses different pulse width modulation (PWM) techniques for inverter control. It describes single pulse modulation, multiple pulse modulation, sinusoidal pulse modulation, and phase displacement control. PWM techniques allow for efficient internal control of the output voltage of an inverter by varying the pulse width. Using multiple pulses or sinusoidal pulses reduces harmonics in the output voltage. Phase displacement control combines the output of multiple inverters with phase shifts between them to control voltage. PWM techniques provide voltage regulation without additional stages but require fast switching devices and complex control circuits.
Osnove elektrotehnike vežbe gradivo za 2. test
Literatura
Nadica Miljkovic ETF Instrumentacija za elektricna merenja
M.Mitrovic, A. Zekic, FF, Didaktika fizike
INternet
Three Point Starter: Diagram and Working PrincipleDr.Raja R
This document discusses the three point starter, which is a device that helps start and run DC shunt or compound wound motors. It consists of contact points called studs that gradually cut resistance from the armature circuit as the motor gains speed. Initially, high starting current is limited by the entire resistance being in series with the armature. As the handle moves from OFF to RUN, resistance is removed. The no voltage coil holds the handle in RUN position using magnetic force as long as power is supplied, but releases it to OFF if power fails, protecting the motor. However, three point starters have issues if field current decreases too much by field rheostat adjustment.
A battery charger is a device that puts energy into a rechargeable battery by forcing an electric current through it. The document discusses battery charger basics including definitions, battery chemistries, applications, and Microchip's portfolio of battery charger integrated circuits. Microchip offers various single-cell and dual-cell battery charger ICs supporting lithium-ion, lithium polymer, and lithium iron phosphate batteries with integrated or external MOSFETs and features like overvoltage protection and temperature monitoring.
Different methods of pwm for inverter controlTushar Pandagre
This document discusses different pulse width modulation (PWM) techniques for inverter control. It describes single pulse modulation, multiple pulse modulation, sinusoidal pulse modulation, and phase displacement control. PWM techniques allow for efficient internal control of the output voltage of an inverter by varying the pulse width. Using multiple pulses or sinusoidal pulses reduces harmonics in the output voltage. Phase displacement control combines the output of multiple inverters with phase shifts between them to control voltage. PWM techniques provide voltage regulation without additional stages but require fast switching devices and complex control circuits.
3. Osnovni princip zaštite od preopterećenja je da zaštitni uređaj
prekine struju preopterećenja prije nego temperature prijeđu
dopuštene granice.
Sklopnik u kombinaciji s bimetalnim relejem također omogućuje
takvu zaštitu. Prolaskom velike struje bimetalne trake se
deformiraju i relej daje „signal” sklopniku da isklopi napajanje.
Manji sklopnici su tako konstruirani da se bimetalni relej može
direktno priključiti na sklopnik
pogledajmo
konkretan primjer
bimetalne zaštite
4. Osnovni dijelovi bimetalnog releja:
otvara NC kontakt i
prekida kontakte
sklopnika
NC kontakt za
feedback sklopniku
NO kontakt za
feedback/signalizaciju
Podešavanje struje
Manual/Auto reset, ručni reset
pritiskom na tipku. Auto reset
sam se resetira
Test kontakata (NC/NO), za
testiranje ispravnosti releja i
pomočnih krugova
6. Ovakva zaštita od preopterećenja prikladna je za elektromotore
U praksi se strujna preopterećenja motora najčešće pojavljuju zbog:
preniskog ili previsokog napona
preopterećenje stroja (blokada rotora)
smanjenje frekvencije
prečestog uklapanja
prekida jedne faze
Kod pojave preopterećenja sklopnik, na impuls bimetalnog
releja, na vrijeme isklapa motor.
7. Shema spajanja bimetalnog releja i sklopnika prikazana je na slici:
samodržanje sklopnika
tipkala
bimetalna
zaštita
stop
start
sklopnik
rastalni osigurači
svitak za upravljanje sklopnikom
trofazni motor
8. Primjer: ako dođe do pregaranja jednog osigurača (ili nestanka
napona jedne faze), motor će i dalje raditi dvofazno, struje druge
dvije faze porastu za 1.73 puta te ako to stanje potraje dulje,
namot motora će pregorjeti.
normalni uvjeti nedostaje jedna faza
9. Bimetalni releji podešavaju se u pravilu na vrijednost nazivne struje
motora.
Za zaštitu od kratkog spoja potrebno je ispred sklopnika dodati
trome osigurače (rastalni ili AIP).
Prema propisima bimetalni releji bi trebali isklopiti u sljedećim
vremenima prema tablici:
klase bimetalnih releja
11. Domaća zadaća:
1. Zbog čega najčešće dolazi do
preopterećenja motora?
2. Što se događa ako u radu trofaznog
motora nestane napon jedne faze?
3. Na koju struju je podešen bimetalni
relej prikazan na slici? Koje je klase?
4. Ako kroz bimetalni relej prikazan
slikom teče struja 0.675 A, u kojem
vremenu će relej isklopiti?
(pogledajte tablicu isklapanja)