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Wattmeter
Definition
The wattmeter is an instrument for measuring the electric power (or the supply rate of electrical energy) in watts of any given circuit.Electric power is measured by means of a wattmeter. This instrument is of the electrodynamic type. It consists of a pair of fixed coils, known as current coils, and a movable coil known as the potential coil. The fixed coils are made up of a few turns of a comparatively large conductor. The potential coil consists of many turns of fine wire. It is mounted on a shaft, carried in jeweled bearings, so that it may turn inside the stationary coils. The movable coil carries a needle which moves over a suitably marked scale. Spiral coil springs hold the needle to a zero position.The figure below shows the circuit of a simple wattmeter.
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It will not. This relay is a Normally Open relay construction. The contacts are closed only when power is applied to the relay coil. You must use either an SPST-NC (Single Pole Single Throw – Nor?
It will not. This relay is a Normally Open relay construction. The contacts are closed only when power is applied to the relay coil. You must use either an SPST-NC (Single Pole Single Throw – Normally Closed) construction or an SPDT (Single Pole Double Throw) type of construction so a contact closure is presented when there is no power applied to the relay coil.
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The burgler's contrivance was very well thought out, he had planned every single detail.
Why use two wattmeter to calculate the power of a three phase load?
Two wattmeter method is used in a three phase sysstem to measure the true power without regard to the balance ie. It can be used to measure both balanced loads and unbalanced loads.The three phase power could be measured using single phase wattmeters in each loads of the system. But using three wattmeters is quite unnecessary as we can measure it by using only two wattmeters.The three phase power could be measued by using single phase wattmeters , haing a current coil in one line and a potential coil connected between the line and some arbitrary common junction point. If that arbitrary common point is chosen on one of the three lines, then the wattmeter connected to that line will indicate zero power because it's potential coil has no voltage across it. hence, that wattmeter may be eliminated, and the three phase power can be determined by means of only two single phase wattmeters.
Explain the Two wattmeter method of power measurement in a 3 phase circuit?
A single wattmeter can measure power due to one phase only. But circuit arrangements , popularly called: 1) 2-wattmeter method (requiring two wattmeters) 2)3-wattmeter method (requiring 3 wattmeters) can be used for measuring power inn 3-phase circuit. The details of these method can be found in any standard book on electrical engineering.
State the meaning of multiplying factor of wattmeter and with suitable example explain how it is determined?
watt meter is constructed such that it read only power on a single scale. Only single scale will available to read the measured power. In order to take the accurate reading just we measure the reading and we will multiple along with factor called multiplication factor. That's depends on on which voltage knob we connected and also the current. Multiplication factor can be determined by: Multiplication factor =(voltage range*current range*pf)/Max scale deflection.
