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Introduction to 3-Phase Meters

Northwest Electric Meter SchoolAugust 2018

Kevin Williams ~ Meter/Relay Tech IIGrant County PUD

16s 3ph self contained service w/lever bypass

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Grant PUD contractor w/PPE

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• Objectives• Provide a brief overview of polyphase meters

• Provide a basic description of electromechanical meter construction and

operation

• Introduce the meter constant calculation for electromechanical meters.

• Provide a short introduction to the meter form and wiring connections.

Introduction

• The 3-phase meter utilizes the same principles as the single phase meter.

• A 3-phase meter is basically 3 single phase meters combined into one meter.

• Can measure kilowatt hour consumption or kilowatt demand or both.

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Blondel’s Theorem

• In a system of N conductors, N-1 elements, properly connected, will measure the power used. All voltage coils must have a common tie to the conductor in which there is no current coil.

Base Design

• A – Base meter– All connections to meter are made on the bottom of the base which

can’t be detached from the meter. Requires no socket or base.

• S – Base meter (Socket) – All connections to the meter are made to the meter socket, which

enables you to change out the meter without rewiring.

• K – Base meter– All connections are made to socket. The meter has bus attached to

the back which has to be bolted into the base.

• Switchboard meter– All connections are made to switchboard meter case, meter simply

slides out and can be replaced very easily.

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A – Base Meter

S(Socket) – Base meter, socket and test switch

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K - Base

Switchboard Meter

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Measuring Capacity

• Self Contained– Class 100– Class 200– Class 320– Class 480(K-base)

• Transformer rated (CT Meter)– Class 10– Class 20

Types

• Electromechanical

• Electronic (Solid State)

• Hybrid– Typically electromechanical meter with an

electronic demand register.

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Get Kh, Rr and Shaft Reduction

Shaft Reductions

Get Rs for the meter

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Prove the meter constant

• (Kh x Rr x Rs) / 10,000 = Meter Constant– Kh = Watthour constant. The number of watthours

represented by one revolution of the disk.

– Rr = Register ratio. The number of revolutions of the gear which meshes with the disk shaft, per complete rotation of the fastest dial pointer.

– Rs = Shaft gear reduction (first reduction). The number of revolutions of the disk rotor shaft per complete revolution of the gear it engages.

Some CommonMeter Forms

andPossible connections.

Meter forms are defined in ANSI standardC12.10

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Form 9S

4WireCT RatedWye

Form 9 wiring example

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Form 5S

3 or 4 wire serviceWye or DeltaCT rated

Form 5S Wye wiring example

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Form 6S

4 WireWyeCT ratedZ-coil

Form 6S wiring example

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Form 8S

4 WireDeltaCT rated

Form 8S wiring example

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Form 12S

3 WireWye or DeltaSelf contained

Form 12S wiring example

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Form 15S

4 WireDeltaSelf contained

Form 15S wiring example

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Form 16S

4 WireWyeSelf contained

Form 16S wiring example

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Form 14S

Two half turns

4 WireWyeSelf containedZ-coil

Electromechanical Basics

• Voltage is passed through a potential coil.

• Current is passed through a current coil.

• Current and voltage fluxes are created and combined to produce torque on the disk and cause rotation.

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Electromechanical Meters

• An aluminum Laminated disk– Rotor– Creep holes– Worm Gear on shaft. (Single cut or double)– Magnetic bearings are on top and bottom, and suspend

the disk, minimizing friction. (or jewel bearings)– The sectored disk restricts eddy currents induced in the

disk from reacting with the flux of other stators.

• Stators (2, 2.5, 3) A stator is formed by a potential coil and a current coil.

Electromechanical Meters cont.

• Magnetic Shields– Placed around the voltage coils prevent leakage flux from reacting

with the wrong eddy currents and causing metering errors.

• Current coil shields– Made of plastic– To isolate technician from voltage during adjustment.

• Potential coil lights– Indicate that voltage is present– Can be incandescent or Led

• Voltage ranges are often narrow.

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Electromechanical Meters cont.

• Mechanical register.– Many intricate gears– Acts like an adding machine and accumulates the

revolutions of the disk.– Pointer style or cyclometer.

• Can be calibrated and repaired in the shop or field.– There are adjustment screws for Full Load, Light Load

and Power Factor.

• Are sometimes heavy due to amount of metal parts.

Magnetic shield

Light Load Adj.

Power Factor Adj.

Full Load Adj.

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Sectored Disk

Current Coil

Potential Coil

Magnetic Bearing

Register

Retarding Magnet

Potential indicatingLight

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Demand Motor

Demand Register

Kilowatt hour Register

Electronic Basics

• Current is passed through a current sensor. (Small CT)• Voltage is measured with the equivalent of a digital multi-

meter.• The voltage, current and angle are mathematically

computed to find kilowatt hour consumption.• The values are then displayed on the LCD screen. Much

more information is available.• Much more accurate then electromechanical meter at very

light loads. (No friction from register or disk)

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Electronic Meters

• Automatic-wide voltage range

• LCD display and register

• Voltage indicators for each phase

• Current sensors

• No moving parts to wear out

• Lightweight and easily handled

Electronic Meters cont.

• Need to be factory calibrated and repaired (some first generation meters had some adjustments)

• Auto detect wye or delta

• Multiple form replacement– Electronic > Mechanical

• 45S = 5S

• 9S = 8S and 9S (6S requires moving C phase potential)

• 16S = 14S, 15S And 16S

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Electronic Meters cont.

• Site survey software– Per phase values for:

• Voltage and voltage angle• Current and current angle• Power factor

– Total harmonic distortion– Much more can be available– Diagnostics for many conditions, with user

adjustable thresholds.

Electronic Meter

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Electronic Meter Brains

Current Sensor

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Switchboard Meters

• Commonly used in substation metering

• With both current transformers and voltage transformers.

• Commonly contain a modem for remote interrogation.

• KYZ outputs for customer or SCADA indication. (Supervisory Control And Data Acquisition)

• Bidirectional (4 Quadrant) metering

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Switchboard Meter

Switchboard Meter Case

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Switchboard Meter

Can you guess which form # ?

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Lightning arrestors

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• Summary

• You should have gained some knowledge of

• Polyphase meters

• Electromechanical meter construction and operation

• The meter constant calculation for electromechanical meters.

• The meter form and wiring connections.