Skip to main content

POWER QUALITY MEASURABLE QUANTITIES

VOLTAGE DIP

is a reduction in the RMS voltage in the range of 0.1 to 0.9 pu (retained) for duration greater than hall a mains cycle and less than 1 minute, Often referred to as a ‘sag’, Caused by faults, increased load demand and transitional events such as large motor starting.

VOLTAGE SWELL

is an increase in the RMS voltage in the range of 1.1 to 1.8 pu for a duration greater than half a mains cycle and less than 1 minute, Caused by system faults, load switching and capacitor switching.

TRANSIENT

is an undesirable momentary deviation of the supply voltage or load current. Transients are generally classified into two categories: impulsive and oscillatory.

HARMONICS

are periodic sinusoidal distortions of the supply voltage or load current caused by non-linear loads. Harmonics are measured in integer multiples of the fundamental supply frequency. Using Fourier series analysis the individual frequency components of the distorted waveform can be described in terms of the harmonic order, magnitude and phase of each component.

INTER HARMONICS

Distorted voltage or current wave-forms containing periodic distortions of a sinusoidal nature that are not integer multiples of the fundamental supply frequencies are termed inter harmonics.

FLICKER

is a term used to describe the visual effect of small voltage variations on electrical lighting equipment (particularly tungsten filament lamps). The frequency range of disturbances affecting lighting appliances, which are detectable by the human eye, is 1-30 Hz.

VOLTAGE IMBALANCE

is defined as a deviation in the magnitude and/or phase of one or more of the phases, of a three-phase supply, with respect to the magnitude of the other phases and the normal phase angle (l200).

FREQUENCY DEVIATION

is a variation in frequency from the nominal supply frequency above/below a predetermined level, normally plus minus 0.1 percent.

TRANSIENT INTERRUPTION

is defined as a reduction in the supply voltage, or load current, to a level less than 0.1 pu for a time of not more than 1 minute. Interruptions can be caused by system faults, system equipment failures or control and protection malfunctions. Interruptions are considered to be measurable events coining under the field of ‘quality of supply’.

OUTAGE

is defined as an interruption that has duration lasting in excess of one minute.

Popular posts from this blog

ADVANTAGES AND DISADVANTAGES OF CORONA

Corona has many advantages and disadvantages. In the correct design of a high voltage overhead line, a balance should be struck between the advantages and disadvantages. ADVANTAGES (i) Due to corona formation, the air surrounding the conductor becomes conducting and hence virtual diameter of the conductor is increased. The increased diameter reduces the electrostatic stresses between the conductors. (ii) Corona reduces the effects of transients produced by surges. DIS-ADVANTAGES (i) Corona is accompanied by a loss of energy. This affects the transmission efficiency of the line. (ii) Ozone is produced by corona and may cause corrosion of the conductor due to chemical action. (iii) The current drawn by the line due to corona is non-sinusoidal and hence non-sinusoidal voltage drop occurs in the line. This may cause inductive interference with neighboring communication lines.
Read more

ADVANTAGES OF PER UNIT SYSTEM

PER UNIT SYSTEM The per-unit system expressed the voltages, currents, powers, impedances, and other electrical quantities basis by the equation: Quantity per unit (pu) = Actual value/ Base value of quantity ADVANTAGES OF PER UNIT SYSTEM While performing calculations, referring quantities from one side of the transformer to the other side serious errors may be committed. This can be avoided by using per unit system. Voltages, currents and impedances expressed in per unit do not change when they are referred from one side of transformer to the other side. This is a great advantage. Per unit impedances of electrical equipment of similar type usually lie within a narrow range, when the equipment ratings are used as base values. Transformer connections do not affect the per unit values. Manufacturers usually specify the impedances of machines and transformers in per unit or percent of name plate ratings. Transformers can be replaced by their equivalent series impedances. ...
1 comment
Read more

ABSOLUTE AND SECONDARY INSTRUMENTS

The various electrical instruments may, in a very broad sense, be divided into (i) Absolute Instruments (ii) Secondary Instruments. Absolute Instruments are those which give the value of the quantity to be measured, in terms of the constants of the instrument and their deflection only. No previous calibration or comparison is necessary in their case. The example of such an instrument is tangent galvanometer, which gives the value of current, in terms of the tangent of deflection produced by the current, the radius and number of turns of wire used and the horizontal component of earth’s field.  Secondary Instruments  are those, in which the value of electrical quantity to be measured can be determined from the deflection of the instruments, only when they have been pre-calibrated by comparison with an absolute instrument. Without calibration, the deflection of such instruments is meaningless. It is the secondary instruments, which are most generally used in ev...
Post a Comment
Read more