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Voltage sag and interruption are commonly related to power quality problems. Voltage sag refers to voltage dips typically for 0.5 to 30 cycles.
During sag, RMS voltage dips with 10% to 90% (Fig. 1). They usually occur due to switching faults on heavy loads. A transitory interruption lasts from 2 seconds to 5 seconds. This sag affects power electronic loads and computer system adjustable speed drives.
Fig. 1: Waveform explaining voltage sag.
Before we go into the circuit details of CSI we must know the difference between a VSI and a CSI. The voltage and current sources are as shown in Figs .1(a) and (b) respectively.
(a) Voltage source
(b) Current source
Fig.1: Different types of sources.
The current source is derived from the voltage source by connecting a large value inductance in series with the voltage source as shown in Fig. 1(b). The important points to be remembered about a current source are:
In this topic, you study the Difference Between Voltage Source Inverter (VSI) and Current Source Inverter (CSI).
The transient overvoltages can switch on the thyristor. In some cases, the thyristor can be damaged due to these transient voltages. These transient voltages are very common when the converter is having inductive loads. The thyristors T1 can be protected against transient voltages by a RC network as shown in Fig. l. This RC network … Read more
The online UPS is also called inverter preferred UPS.
Fig. 1 shows the block diagram of online UPS.
Fig. 1: Block diagram of the online UPS system.
The offline UPS is also called line preferred UPS.
Fig. 1 shows the block diagram of an offline UPS. When mains supply is present, the charger charges the battery. The inverter is off and UPS static switch is off. The load is connected to mains through mains static switch.
Fig. 1: Block diagram of offline UPS.
Moving Coil Microphone works on Faraday’s law of electromagnetic induction, which states that, “when a conductor moves in a magnetic field, it cuts the flux line and an emf is generated.” Therefore, Electro-dynamic microphones are also called as Electro-magnetic microphones.
Fig. 1: Moving Coil Microphone
Carbon microphone consists of a thin moving diaphragm, used as primary (first) transducer, which senses the sound pressure waves and convert them into displacement of diaphragm. Moving diaphragm is connected to a capsule having flexible bellows to allow compression or expansion. A capsule containing granules of carbon acts as a secondary transducer in this microphone. The device is externally powered by a constant voltage source (battery). Therefore, carbon microphone is not a self-generating type instrument, like Electro-dynamic microphone (Fig. 1).
Fig. 1: Carbon Microphone.
Hair hygrometer is a type of absorption hygrometer, which works on the principle that, “change in moisture content causes change in physical and chemical properties of certain materials”, such as, human hair, animal membrane, wood, paper etc. As human hairs are used in this hygrometer, this type is called as hair hygrometer.
Bourdon tube pressure gauge consists of bourdon tube bent into an arc of circle. Cross-section of the tube is elliptical. One end of tube is connected to the point, whose pressure is to be measured. Other end is connected to the rack and pinion through mechanical linkage. The pointer is pivoted on the pinion (Fig. 1).
(a) Schematic view of Bourdon Tube Pressure Gauge.