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TOPIC 5 : POWER METER RAJKUMAR A/L RAJENDARAN LEENA A/P MUNIANDY
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Measurement ee101

Nov 17, 2014

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Page 1: Measurement ee101

TOPIC 5 : POWER METER

RAJKUMAR A/L RAJENDARAN

LEENA A/P MUNIANDY

Page 2: Measurement ee101

INTRODUCTION…POWER METER may refer to :

Electricity meter - measures electrical energy (electrical power supplied to a residence, business or machine over time)

Wattmeter - measures the electrical power circulating in any electric circuit

Optical power meter - measures energy in an optical signal

Google Power Meter – is a tool to track a household’s energy usage

A cycling power meter – measures the power output of a bicycle rider

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ELECTRIC POWER• Electric power is the rate at which electric energy

is transferred by an electric circuit.• The SI unit of power is the watt.• When electric current flows in a circuit, it can

transfer energy to do mechanical or thermodynamic work.

• Device convert electrical energy into many useful forms such as, heat (electric heaters), light (light bulbs), motion (electric motors), sound (loudspeaker), information technological processes (computer), or even chemical changes.

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POWER METER• A meter for measuring the amount of electric

power used.• Some examples of power meter are:

Wattmeter KWH meter Clamp meter

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ANALOGUE WATTMETER• Symbol of analogue wattmeter

• Basic Principle of Analogue WattmeterA wattmeter has two coils that multiply volts times amps.

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• One coil is wired as an ammeter with a shunt, the other as a voltmeter with a multiplier.

• This instrument is of the electrodynamic type.• It consist of a pair of fixed coils, known as current coils

and movable coil known as the potential coil.• The voltage is measured across (parallel) the load and

charges the pointer magnet.

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• The current is measured in series with the load and charges the field magnets.

• The movable coil carries a needle which moves over a suitable marked scale.

• Spiral coil springs hold the needle to a zero position.

Fig1: A simplified electrodynamic wattmeter circuit

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KWH METER• An electric meter or energy meter is a device that

measures the amount of electrical energy consumed by a residence, business, or an electrically powered device.

• Electric meters are typically calibrated in billing units, the most common one being the kilowatt hour.

• The most common type of electricity meter is the electromechanical induction watt-hour meter.

• The electromechanical induction meter operates by counting the revolutions of an aluminium disc which is made to rotate at a speed proportional to the power.

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• The metallic disc is acted upon by two coils.

• One coil is connected in such a way that is produces a magnetic flux in proportion to the voltage and the other produces a magnetic flux in proportion to the current.

• This produces eddy currents in the disc and the effect is such that a force is exerted on the disc.

• A permanent magnet exerts an opposing force proportional to the speed of rotation of the disc. The equilibrium between these two opposing forces results in the disc rotating at a speed proportional to the power being used.

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CLAMP METER• An electrical meter with integral AC current clamp.• This allows properties of the electric current in the

conductor to be measured, without having to make physical contact with it.

• Clamp meters are often sold with a device that is plugged in between the power outlet and the device to be tested. The device is essentially a short extension cord with the two conductors separated.

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CLAMP METER CONSTRUCTION FOR ALTERNATING CURRENT….Leakage current measurement basics

Leakage current most commonly flows in the insulation surrounding conductors and in the filters protecting electronic equipment around the home or office. So what's the problem? On circuits protected by GFCIs (Ground Fault Current Interrupters), leakage current can cause unnecessary and intermittent tripping. In extreme cases, it can cause a rise in voltage on accessible conductive parts.

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THE CAUSES OF LEAKAGE CURRENT

• Insulation has both electrical resistance and capacitance – and it conducts current through both paths. Given the high resistance of insulation, very little current should actually leak. But -- if the insulation is old or damaged, the resistance is lower and substantial current may flow. Additionally, longer conductors have a higher capacitance, causing more leakage current. That's why GFCI breaker manufacturers recommend one-way feeder length be limited to 250 feet, maximum.

• Electronic equipment, meanwhile, contains filters designed to protect against voltage surges and other disruptions. These filters typically have capacitors on the input, which adds to the overall capacitance of the wiring system and the overall level of leakage current.

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Measurement of Leakage Current to Ground

• When the load is connected (switched on), the leakage current measured includes leakage in load equipment. If the leakage is acceptably low with the load connected, then circuit wiring leakage is even lower. If circuit wiring leakage alone is required, disconnect (switch off) the load.

• Test single-phase circuits by clamping the phase and neutral conductor. The measured value will be any current flowing to ground.

• Test three-phase circuits by clamping around all three-phase conductors. If a neutral is present, it should be clamped along with the phase conductors. The measured value will be any current flowing to ground. 

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Measuring leakage current through the ground conductor• To measure the total leakage flowing to the intended ground connection, place the

clamp around the ground conductor.

Measuring leakage current to ground via unintentional paths to ground.• Clamping phase/neutral/ground together identifies imbalance current that represents

leakage at an outlet or electrical panel via unintentional paths to ground (such as the panel sitting on a concrete base). If other electrical bonding connections exist (such as a connection to a water pipe), a similar imbalance may result. 

 

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Tracing the source of leakage current• This series of measurements identifies the overall

leakage and the source. The first measurement can be made on the main conductor to the panel. Measurements 2, 3, 4 and 5 are made subsequently to identify circuits carrying the larger amounts of leakage current. j k l m n 

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• SummaryLeakage current can be an indicator of the effectiveness of insulation on conductors. High levels of leakage current may be present in circuits where electronic equipment with filters is used, and can cause voltages that disrupt normal operation of equipment. It is possible to locate the source of leakage current by using a low current leakage current clamp to take methodical measurements as described above. If necessary, this enables you to re-distribute loads around the installation in a more balanced way.

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HOW TO USE CLAMP METER?• Step 1Turn on the clamp meter and set the function for measuring current. A selection knob or button to select whether we are measuring alternating current (AC) or direct current (DC) flow. Most household electric devices use household voltage from an outlet, which will be AC current.• Step 2Clamp the meter onto the power cord. The ends of the clamp meter arms, which resemble pinchers, will have a recessed area through which the power cord should be placed. Ensure that the clamp meter arms are stable with the cord between them.

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• Step 3Read the current flow on the clamp meter display. Most clamp meters have automatic range finders, but if it does not, increase the range of the meter until get a reading. Write down the reading, which will be numbers that represent the amount of amperes, or amps, flowing through the cable.• Step 4Measure the amount of current flow through an appliance (washing machine) by turning it on and having it perform its functions. The current flow will be much higher when the appliance motor is turning. For a refrigerator, turn down the thermostat to turn on the cooling action, which will increase current flow.• Step 5 Adjust the position of the clamp meter to ensure we are getting accurate current flow readings.• Step 6Remove the clamp meter from the power cord

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Optical power meter Cycling power meter

A cycling power meter is a device on a bicycle that measures the power output of the rider. Most cycling power meters use strain gauges to measure torque applied,and, combined with angular velocity,calculate power. The technology was adapted to cycling in the late 1980s and was tested in professional bicycle racing

An optical power meter (OPM) is a device used to measure the power in an optical signal.

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Google power meter

• Google PowerMeter was a software project of Google's philanthropic arm, Google.org, to help consumers track their home electricity usage. The development of the software was part of an effort by Google to invest in renewable energy, electricity grid upgrades, and other measures that would reduce greenhouse gas emissions. It was launched on October 5, 2009 and ended on September 16, 2011.

• The software was designed to record the user's electricity usage in near real-time. According to the company, if half of America's homes' energy use was cut by ten percent, it would equal the average energy used by eight million cars.

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