02-09-2017, 03:18 PM
An electric meter, an electric meter, an electric meter or an energy meter is a device that measures the amount of electrical energy consumed by a residence, business or electrical device. Electric utilities use electric meters installed at customer premises to measure the electrical energy delivered to their customers for billing purposes. Usually calibrated in billing units, the most common is kilowatt hour [kWh]. Usually one billing period is read once.
When energy savings are desired during certain periods, some meters can measure the demand, the maximum use of energy in some interval. The "time of day" measurement allows to change the electric tariffs during a day, to register the use during the periods of greater cost and periods of lower cost and of lower cost. In addition, in some areas, the meters have relays for load shedding to respond to demand during peak load periods.
The most common unit of measure in the electricity meter is kilowatt hour [kWh], which is equal to the amount of energy used by a kilowatt charge in a period of one hour, or 3,600,000 joules. Some power companies use SI megajoule instead.
The demand is normally measured in watts, but averaged over a period, usually a quarter or half hour.
Reactive power is measured in "thousands of volt-amperes-hours reactive", (kvarh). By convention, a "delayed" or inductive load, such as a motor, will have a positive reactive power. A leading, or capacitive, load will have negative reactive power.
Volt-Amperes measures all power passing through a distribution network, including reactive and current. This is equal to the product of the mean volts and quadratic amps.
The distortion of the electric current by charges is measured in several ways. The power factor is the ratio of resistive (or actual) power to volt-amperes. A capacitive load has a leading power factor, and an inductive load has a delay power factor. A purely resistive load (such as a filament lamp, heater or boiler) has a power factor of 1. Current harmonics are a measure of waveform distortion. For example, electronic loads, such as computer power supplies, draw their current at the peak voltage to fill their internal storage elements. This may lead to a significant voltage drop near the peak of the supply voltage which is shown as a flattening of the voltage waveform. This flattening causes odd harmonics that are not permissible if they exceed specific limits, as they are not only wasteful, but may interfere with the operation of other equipment. Harmonic emissions are required by law in the EU and other countries to be within specified limits.
When energy savings are desired during certain periods, some meters can measure the demand, the maximum use of energy in some interval. The "time of day" measurement allows to change the electric tariffs during a day, to register the use during the periods of greater cost and periods of lower cost and of lower cost. In addition, in some areas, the meters have relays for load shedding to respond to demand during peak load periods.
The most common unit of measure in the electricity meter is kilowatt hour [kWh], which is equal to the amount of energy used by a kilowatt charge in a period of one hour, or 3,600,000 joules. Some power companies use SI megajoule instead.
The demand is normally measured in watts, but averaged over a period, usually a quarter or half hour.
Reactive power is measured in "thousands of volt-amperes-hours reactive", (kvarh). By convention, a "delayed" or inductive load, such as a motor, will have a positive reactive power. A leading, or capacitive, load will have negative reactive power.
Volt-Amperes measures all power passing through a distribution network, including reactive and current. This is equal to the product of the mean volts and quadratic amps.
The distortion of the electric current by charges is measured in several ways. The power factor is the ratio of resistive (or actual) power to volt-amperes. A capacitive load has a leading power factor, and an inductive load has a delay power factor. A purely resistive load (such as a filament lamp, heater or boiler) has a power factor of 1. Current harmonics are a measure of waveform distortion. For example, electronic loads, such as computer power supplies, draw their current at the peak voltage to fill their internal storage elements. This may lead to a significant voltage drop near the peak of the supply voltage which is shown as a flattening of the voltage waveform. This flattening causes odd harmonics that are not permissible if they exceed specific limits, as they are not only wasteful, but may interfere with the operation of other equipment. Harmonic emissions are required by law in the EU and other countries to be within specified limits.