NEED FOR PHASE ANGLE MEASUREMENT

 Phase angle meters are used to verify the correct connection of three-phase

transformer banks which must be paralleled with an existing electrical bus or

high voltage line. The process of making these measurements is known as

“phasing-out” and is performed before the tie-in is made.

 Phase angle measurement is also employed to analyze the operation of AC

synchronous generators and synchronous motors to verify the proper operation

of field regulators and synchronizing equipment.

 The Phase angle measurement is used for verifying the proper installation of

medium and high-voltage primary metering equipment and sophisticated

protective relays that receive input from Potential and Current Transformers (PTs

& CTs).

 Phase Angle Measurement for Power Factor Determination:

The most important application of the equipment which measures phase angle is

the determination of power factor for conducting electrical system load studies

and power factor correction studies.

The system power factor is equal to the cosine of the phase angle that exists between

the system voltage and current. In the ideal AC electrical system the voltage and current

are in phase. This condition only occurs on systems where the entire load is resistive,

such as electric heat, incandescent lighting, or fluorescent lighting with power factor

corrected ballasts. Electrical utilization equipment such as motors and welders has a

considerable amount of inductance and the inductive reactance (XL which is measured in

International Journal of Emerging trends in Engineering and Development Issue 2, Vol.6 (September 2012)

Available online on http://www.rspublication.com/ijeted/ijeted_index.htm ISSN 2249-6149

Page 475 Measurement of Phase Angle using a PLL ohms) causes the circuit current to lag

the applied voltage. The actual amount, or

number of degrees of lag, depends on the ratio of the Inductive Reactance (XL) in ohms

to the ohmic value of Resistance (R) of the system. Once the system power factor is

known, power factor correction, if desired, can be applied to the system using power

factor correction capacitors or by using synchronous motors, either of which can supply

leading Volt Amperes Reactive (VARs) to the system to compensate for the lagging

power factor. Most electric utilities charge a penalty for poor system power factor, so

keeping the power factor above the required minimum value will result in a lower utility

bill and will also improve the voltage drop on the system.

Although both the current and the voltage oscillate sinusoidally in an AC circuit

they will not necessarily rise and fall simultaneously with each other in each circuit

element or the circuit as a whole. The current and voltage will oscillate with the same

frequency but they will (in general) be out of phase with each other,exception being

when the circuit is in resonance or if there is only resistor in the circuit.

The phase difference between two sinusoidal waveforms that have the same

frequency and are free of a dc component can be conveniently described as shown in

figure 1. It can be seen that the phase angle can be considered as a measure of the time

delay between two periodic signals expressed as a fraction of the wave period. This

fraction is normally expressed in units of angle, with a full cycle corresponding to 360°.

For example, in figure 1, where the voltage v1 passes through zero one-eighth cycles

before a second voltage v2, it leads v2 by (360°/8) or 45°.

Поиск по сайту: