Electrical Metering
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Transcript of Electrical Metering
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Definition: Instrument: A device for measuring value of unit. Meter: Measures & registers the integral value over an
integral of time
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1. Ammeter
2. Voltmeter
3. Wattmeter
4. VARmeter
5. Power Factor Meter
6. Kilowatthour (KWH) Meter
7. Frequency Meter
8. Synchroscope
9. Analog / Digital
Metering
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Measure the current that flow in the circuit. Direct ammeter are employed for values 60A or
below. Above 60A, a CT operated ammeter wherethe CT step down the value to 5 or 1A.
3 ammeters are used for generator sets where itis important to monitor the three phases to verifythat the gen. set supply is balanced.
Metering1. Ammeter
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Ammeters are connected in seriesand not parallel. For DCoperation, the priority must becorrect otherwise the meter willdeflection backwards
Metering1. Ammeter - Connection
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Measuring the potential difference between twophases or conductors.
For 415V, direct connection is normal done at thesupply source of the main switchboard or incomer toa distribution board.
Metering2. Voltmeter
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Voltmeter are connected in parallel. For DCoperation, the priority must be correct otherwise themeter will deflection backwards.
Metering2. Voltmeter - Connection
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Measure the magnitude of the actual power delivered tothe load: single phase
3 phase 3w balanced or unbalanced load.
3 phase 4w for balanced or unbalanced load.
Metering3. Wattmeter
Unbalance meter more expansive
Balanced vs Unbalanced ?
Balanced 1 CT
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The polarity and phasing must be correct for accuratereadings
Metering3. Wattmeter - Connection
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Metering
3. Wattmeter - ConnectionThe polarity and phasing must be correct for accuratereadings
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Metering
3. Wattmeter - ConnectionThe polarity and phasing must be correct for accuratereadings
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Metering
4. VARmeter - ConnectionMeasure the magnitude of the reactive power delivered to the
load. The polarity and phasing must be correct for accuratereadings
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Metering
4. VARmeter - ConnectionThe priority and phasing must be correct for accuratereadings
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Can be read directly from the power factor meter. Read accurately when adequately loaded. Be careful of l ight ly loaded condi t ions n o t
accurate (com mo n pro blem !) Power factor meter are required to verify that the
consumer dos not exceed the limit set by TNB.
Metering
5. Power Factor Meter
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Balanced power factors measure only one phase while unbalanced oneall 3 phases for 3ph 4w & 2 phases for 3ph 3w. Current and voltage mustbe connected. If only voltage is connected, pointer rotates clockwise. Ifonly current, counterclockwise.
Metering
5. Power Factor Meter - Connection
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Metering
5. Power Factor Meter - ConnectionBalanced power factors measure only one phase while unbalanced oneall 3 phases for 3ph 4w & 2 phases for 3ph 3w. Current and voltage mustbe connected. If only voltage is connected, pointer rotates clockwise. Ifonly current, counterclockwise.
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Metering
5. Power Factor Meter - ConnectionBalanced power factors measure only one phase while unbalanced oneall 3 phases for 3ph 4w & 2 phases for 3ph 3w. Current and voltage mustbe connected. If only voltage is connected, pointer rotates clockwise. Ifonly current, counterclockwise.
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Measures the amount of energy consumed by aload.
The accuracy for TNB metering purpose is CL 0.2whereas if private consumer require to monitor
power consumption of her tenants, the accuracyis CL 1. If the consumption is substantial, themeter used may be CL 0.2.
Metering
6. Kilowatthour (kWH) Meter
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For low voltage, unbalanced kWH meter is used. The
connection is 3ph 4w. It is important to connect the CT &voltage wires correctly otherwise the meter will operate in thereverse direction. A demand meter can be attached to thekWH meter to register the average power demand during aspecified interval of the maximum demand,
Metering
6. Kilowatthour (kWH)Meter -Connection
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The frequency of an ac power supply can bemeasured directly.
2 type :
I) vibrating redii) Pointer indicating
Usually used in generator boards
Metering
7. Frequency Meter
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Measure the difference between phase angle of the twosystem.
If the frequency of the system < target system
it revolves in one direction If the frequency of the system > target system
it revolves in the opposite direction If the frequency of the system = target system
stops revolving ( the sys tem c an be paral lel )
Metering
8. Synchroscope
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SYNCHROSCOPE
- 145 G
- 146 G
Single or 3-phase
systems
The synchroscope is used when two generator or
systems are to be paralleled
Metering
8. Synchroscope - Connection
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Example
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Example
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Example
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Example
Protection Relay & DPM
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Example
Semi-Conductor Plant
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Example
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Power Quali ty Moni tor ing Utili ty Check M eter
M ax Demand Control
Example
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Large Steel Plant - Retrofit 11kV
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