Power Quality Monitoring and Power Metering Tutorial. National Instruments provides a variety of hardware and software tools for measuring and monitoring power and power quality. Using modular I/O and programmable software, you can customize a system to meet your exact needs. Introduction. Power generation and transmission today use three- phase alternating current (AC). To understand electrical power quality monitoring and electrical power metering, you must first have a basic understanding of three- phase power. Back to Top. 2. Electricity Basics. Power is analogous to a water system. In a water system you have a pipe that can carry water. The larger the pipe the more water it can carry. To move the water through the pipe you need to pressurize the water and when the water has the ability to move from a high pressure area to a low pressure area (like when you open a valve) you get flow. In the electrical analogy you replace the pipe with a wire. Analysis of Power Quality Problems in Solar Power Distribution. Electric utilities and end users of electric. Electric Power Distribution Systems Operations NAVFAC MO-201 April 1990 SN 0525-LP-320-1900. Instead of carrying water the wire carries electrons. The larger the wire the more electrons it can carry. You pressurize the electrons by applying voltage. When the circuit is complete the electrons flow from the high voltage to the lower voltage and you get flow. The flow is known as current. In a direct current (DC) circuit the voltage and current are constant, or with a constant load. However, in an AC circuit the voltage and the current vary in a sinusoidal manner. Mitsubishi Electric Power System Stabilizer (PSS) Generator power PSS OFF PSS ON PSS OFF PSS ON Time (sec) 0.85 0.9 0.95 Generator power 0.85. Electric is ready to respond to the diversified needs of its customers. PROTECTIVE RELAYING AND POWER QUALITY Chairperson. 3.1 Recommended Practice for Monitoring Electric Power Quality. Relaying” prepared by the Power System Relaying Committee of the IEEE Power. Electric Power System Quality Pdf ConverterThe instantaneous voltage and current levels vary over time based on their phase. Phase in an AC circuit indicates the value of the voltage or current measured in degrees with 3. The value of the sine of the phase angle is proportional to the voltage level. Three- phase power refers to three voltages that have an offset from each other by 1. Usually three wires carry these three voltages (and currents). Three- phase power system is the standard throughout the world because three- phase power system uses fewer and smaller conductors than multiple single- phase systems to provide the same power. Three- phase power also has the ability to drive motors with a constant torque instead of the pulsating torque of single- phase motors. Because each of the phases carries an equal voltage (and current through a balanced load) at 1. With AC power, the ideal configuration is to connect each of the three phases to an equal load, which is called a balanced load. Because the three phases are synchronized at 1. This connection is a wye connection because of the way it appears on a phasor diagram. The three phases can also connect together in a delta connection. Whereas a wye connection can tolerate unbalanced loads by sending current through the neutral wire, the loads in a delta connection must be balanced because a delta connection does not have a neutral wire. Electrical power is measured in watts (W) or kilowatts (k. W) and occurs when a current flow accompanies a voltage. A watt is equal to 1 volt of potential voltage and 1 amp of current. When you apply power over a period of time you accomplish work. Work is measured by multiplying the amount of power applied by the period of time and is usually expressed in kilowatt hours (k. Wh). In an AC power system, you can accomplish the maximum amount of work when the voltage and current are exactly in phase and the more out of phase the voltage and current are the less useful work you can accomplish. When the voltage and current signals are 1. The degree to which the voltage and current are in phase is expressed by power factor. One way to understand power factor is to think about a horse pulling a barge along a canal. The horse must pull the barge from the shore; therefore, the horse is pulling the barge at an angle to the direction of travel. Because the horse is pulling at an angle, not all of the horse’s effort is used to move the barge along the canal. The effort of the horse is the total power or apparent power (k. VA); the power used to move the barge is the working power or real power(k. W); and the power that is trying to pull the barge to the side of the canal is the nonworking power or reactive power(k. VAR). The ratio of the real power to the apparent power is known as the power factor. If the horse is led closer to the edge of the canal the angle of the rope decreases and more of the apparent power is used as the real power, increasing the power factor. In the case of electricity the power factor is based on the phase difference between the current and the voltage sine waves. If the phase difference is zero then all the apparent power can be used as real power and the power factor is 1. This is also called unity power factor. As the phase difference increases the power factor decreases and you need to supply more currents to give the same amount of real power. Back to Top. 3. Power Quality Events. Many facilities today have sensitive computerized equipment or telecommunication equipment that use ground as the reference for all the internal operations in facilities and connect throughout the plant. Using ground as the reference makes the facilities susceptible to ground differences and to power quality problems. Whereas many people believe that most power quality problems come from power suppliers, the majority of power quality problems are introduced inside the plant. Leading/Lagging Power. Because electrical utilities must supply additional currents to compensate for lower power factors, the electrical utilities must increase their infrastructure to generate and handle higher currents. The utilities pass this additional cost to customers as a charge based on power factor. In a plant, the power factor, or difference in the phase of the voltage and current waves, is the result of inductive and capacitive loads. An inductive load, like a motor, causes the current to lag behind the voltage. A capacitor has the opposite effect and causes the current to lead the voltage. Because average industrial sites use 8. To help compensate for the “lagging power factor”, many sites install capacitor banks to help correct the power factor and save on utility company charges. RMS Voltage Variations. RMS, or root mean squared, is the standard way to measure the level of a sinusoidal wave. The RMS value of a sine wave is equal to the equivalent value had the wave been a DC signal. To calculate power, you measure the voltage (and current) levels in RMS. There are three types of RMS voltage variations: a sag, a swell, and an interruption. A sag occurs when the RMS voltage level drops to below 9. RMS level, but is greater than 1. A swell occurs when the voltage increases to greater than 1. RMS voltage. An interruption occurs when the RMS voltage falls to below 1. Sags are the most common power quality disturbance and are usually the result of problems within the facility as opposed to supply problems from electric utilities. Sags caused within the facility often come from load variations or improper wiring. One common cause of sags is starting an electrical motor. Starting a motor produces a very high inrush current (sometimes 6- 1. Interruptions in a facility typically come from fault protection from a circuit breaker or a fuse. A loose wiring connection sometimes can also cause interruptions. Swells typically come from a rapid decrease in load such as shutting off an electric heater. Sags and swells that last longer than three minutes are called sustained undervoltage or overvoltage conditions. A sustained undervoltage condition (also called a brownout) is the result of improper transformer tap settings or supply problems from electric utilities. Sags and interruptions can cause problems in a facility by shutting down sensitive electronics, computers, and process equipment. Waveform Harmonics. Whereas you can think of power as a clean 6. Hz sine wave, in practice the waveform may contain harmonics. Harmonics occur at an integer multiple of the base frequency (6. Hz, 1. 20 Hz, 1. 80 Hz. Power quality problems related to waveform harmonic usually come from equipment with a nonlinear current draw. Modern electrical equipment such as computerized equipment and telecommunication equipment often use switching power supplies to step up or step down the voltage. Using switching power supplies introduces a non- sinusoidal load that pulls current in short pulses during every cycle. Other nonlinear devices such as digital/electronic components and arching devices (for example, fluorescent lamps) can cause abnormal waveforms and serious decreases in power quality. Pulling power in a nonlinear manner introduces harmonics in an electrical system and can overheat plant distribution transformers. These harmonics can cause current transmission over a neutral power conductor in a wye power system. In an ideal balanced three- phase power system without harmonics no current transmits along the neutral conductor. When nonlinear devices induce harmonics, the current from each of the three phases no longer cancels and the current is forced through the neutral conductor. Electrical systems are especially susceptible to triplen harmonics (3rd, 6th, 9th, etc) because in a three- phase system the triplen harmonics are additive. This high current that transmits along the neutral conductor can overload circuits, breakers, and transformers. In some instances, plants have been forced to install power conditioning equipment or a second neutral conductor. Back to Top. 4. NI Lab. VIEW Electrical Power Suite. The NI Lab. VIEW Electrical Power Suite helps you develop a custom three- phase power monitoring, metering, or quality analysis application. The following analysis functions are included with the Full version of the NI Lab. VIEW Electrical Power Suite and conform to the IEC 6. Power frequency. Magnitude of the supply voltage. Flicker. Supply voltage dips and swells. Voltage interruptions. Supply voltage unbalance. Voltage harmonics. Mains signaling voltage on the supply voltage. Rapid voltage changes (RVC)Measurement of underdeviation and overdeviation parameters.
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