Transcript AVOP-ELEKTRO-SMI-007

Tutorial: Mechanik - elektrotechnik
Topic:
Basics of electrical engineering
the 2nd. year
Measuring inductance
Prepared by: Ing. Jiří Smílek
Projekt Anglicky v odborných předmětech, CZ.1.07/1.3.09/04.0002
je spolufinancován Evropským sociálním fondem a státním rozpočtem České republiky.
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Definition:
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Inductance is the ratio of the coupled induction
flux to the current which passes through the coil.
Coupled magnetic flux to the current that flows
through the coil
The basic unit - 1 H (henry)
◦ L- inductance coil
◦ M - magnetic flux coupled coils
◦ I – current passing through the coil
◦ N – number of turns in the coils
The mutual inductance M of two close coils is
the ratio of the induced emf in the first coil caused
by a current in the second coil
or vice versa - M1 = M2
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The used method:
Deviation method – inductance is measured by an A-metre and Vmetre to determine the value of the measured resistance deviation
or determine the numeric value.
a) Connection for the measurement of smaller inductance/ coils
b) Connection for the measurement of larger inductance/coils
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Calculation:
Self inductance can be determined from the definition of
impedance:
Apparent power coils:
Coil impedance:
Coil resistance
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The measurement procedure:
• To measure inductance using the indirect method we must know
the voltage and the current – calculate RX and ZLX ⇒calculate LX
• To measure the resistance a DC current must flow in the circuit
• To measure the inductance an AC current must flow in the circuit
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Method suitable for measuring air coils in operation
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The used method:
Deviation method – inductance is measured by an A-metre, Vmetre and a W-metre - Inductance coils with an iron core are not
constant because they depend on the magnetic flux, that is the
current passing through the coil
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The measurement procedure:
Resistance Rreg adjusted current for example of 0.25 A and read
current I, voltage U and power P (losses in the turns and the iron).
From the measured values we calculate the coils impedance:
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Calculations:
From the measured values we calculate:
• Coil impedance:
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Active resistance:
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Inductance:
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Inductance can also be calculated from the relationship:
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Of which
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The used method:
Bridge method– inductance with a Maxwell-Wien bridge
The condition of the bridge balance:
After treatment and separation of real and imaginary members:
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Describe how induction is defined
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Describe how mutual inductance is defined
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Write how you know the types of coils
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Write what methods can measure inductance
◦ direct –
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◦ indirect –
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Explain why an inductance coil with an iron
core is not constant
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Write a procedure to measure inductance with
an iron core
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Write the procedure to calculate the
inductance from the measured values
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Mužík, J. Management ve vzdělávání dospělých. Praha: EUROLEX BOHEMIA, 2000. ISBN
80-7361-269-7.
Operační program Vzdělávání pro konkurenceschopnost, ESF 2007 – 2013.
Dostupné na: http://www.msmt.cz/eu/provadeci-dokument-k-op-vzdelavani-prokonkurenceschopnost
Učebnice Elektrická měření – Ing. Pavel Vylegala, SŠE Ostrava, 2006
Učebnice Elektrické měření – SNTL, 1981
Elektrotechnika - Laboratorní cvičení pro bakalářské studium - Doc. Ing. Miloš Hammer,
CSc.