Electrical Metering

8/10/2019 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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Documents

Electrical Metering