Single Phase Meter Components - uploads.westernenergy.org · 8/3/2018 3...

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EXCHANGING EXPERTISE SINCE 1893

NWEMS

Single Phase Meter ComponentsAugust 21, 2017| Track A | Scott Sutton, Snohomish County PUD


PURPOSE of this class:

» What is an electro‐mechanical Watt‐hour meter

» The basic parts of the meter

– The function of these parts

» Adjustments for calibrations

» Compensations

» Electronic vs Electromechanical meters

» Meter types – Examples – Q & A

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The Watt‐hour meter

» Measures energy used ‐

» Power is a rate at which energy flows

– Power X Time = Energy


Relate the Watt‐hour meter to the speedometer and odometer of an automobile

–Miles per hour = Watts being used ‐

Disk speed

–Miles driven = Kilowatt hours –

Register Read

» 30 MPH for 2 hours = 60 miles driven

» 30 kW for 2 hours = 60 kWh

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Today’s Electromechanical kWh meter’s are basically the same design as the ones manufactured 105 years ago.

» Much less expensive

» Light weight

» Highly accurate

» Maintenance free device

» Provide many years of reliable service


Today's meters are vastly improved:

» They are highly accurate and have a very flat

accuracy curve over extreme loads and

environmental conditions. Single phase self

contained meter’s are so well calibrated from the

manufacture that many utilities do not test new

meters . They may perform a BAR‐X,(sigma) or

Sample Test

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Basic Parts:

» Name Plate

» Base

» Cover

» Frame & magnets

» Stator ‐ potential coil and current coil

» Rotor(disk) and bearings

» Register


Basic Parts: Nameplate

» The most important part of meter

» Form Number ‐ Indicates the internal connections of

the meter. ANSI Stds.

» Voltage ‐ Design or test voltage of potential coil

» CL or Class ‐ Maximum current capacity.

– CL10, CL20, CL100, CL200, CL320‐

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Basic Parts: Nameplate (continued)

» T.A. ‐ Test Amps, (100% Full Load – 10% Light Load)

» Wire ‐ (2w, 3w, 4w, 5w)

» Kh ‐ Watt‐hour Constant

» Multiplier (CT’s, VT’s, internal meter multi)

» Number of stators or potential coils

» Company ID number and MFR. Type

EXCHANGING EXPERTISE SINCE 1893 10

Meter Nameplates

Service Application Manufacture

Frequency HZ

Voltage

# of Stators Class

Company Name and Number

Manufacturer’s Serial #

Register Ratio

Manufacturer Type

Form

Wires

Test Amps

Disk Constant or Kh

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Basic Parts: Base

» Earlier meter bases were made of cast iron, metal alloys and cast aluminum

» Today’s bases are made of high impact strength plastic

» Base configurations ‐ Socket type, A base type & Bolt In type (K base)


Basic Parts: Base (continued)

» Test Link ‐ used to disconnect or isolate one side of the potential circuit from the current circuit when testing

» Screened vents ‐ To prevent insects and dust from getting into meter and allows ventilation to minimize condensation

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Basic Parts:Base (continued)

» Lightening Arrestor ‐ To protect meter from High

Surge Currents

– an air gap between the current coil and ground that will “Flash Over” between 5000 & 6500 volts

» Gasket ‐ Provides a seal between the base & cover

» Hanger ‐ Storage

» Sealing Provision ‐ Security


Basic Parts: Cover

» Purpose ‐ To protect the meter components from weather and dust while providing a means to read the register and inspect meter

» Security ‐ Makes it difficult to tamper with or to conceal tampering

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Basic Parts: Cover (continued)

» Glass ‐ Special stress relieved glass

» Rim ‐ Aluminum or stainless steel

» Plastic ‐ Lexan® (Poly‐Carbonate)

» Special metal Covers protection from vandals

» Demand Resets, Optical ports


Basic Parts: Frame

» Composition ‐ Iron for older meters, Die cast aluminum for new

» Purpose ‐ Mounting & supporting of meter

components in an accurate and stable

relationship. All meter components are

machined to a tolerance of +/‐ 0.002 inch for

precise fit & positioning.

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Basic Parts: Magnets

» Composition ‐ ALNICO alloy: Aluminum, nickel,

cobalt & iron

» Purpose ‐ to control the speed of the disk

» The magnet can withstand a surge of 20,000 amps

with only 1/2 of 1% change in meter accuracy. Older

meters with chrome steel magnets can only

withstand 10,000 amps resulting in a change in

meter accuracy of 4% or greater.


Basic Parts: Stator

» Electromagnetic element

» The potential coil is connected across the line

terminals

– 2400 turns of #29AWG for 120v



» Fine wire wound on a silicone laminated plate steel

core

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Basic Parts: Stator

» The potential coil is compensated so that the meter

is accurate from 50% to 120% of the rated or

nominal voltage (name plate)

» The potential coil is highly reactive (inductive) in

relation to the current coils & use only about 2

watts of power

» Purpose: to convert applied voltage into a magnetic

field or flux which is proportional to the line voltage


Basic Parts: Stator

» The stator also facilitates or provides

– Light load adjustment

– Power factor adjustment

– Compensations

• Overload

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Basic Parts: Current coil

» The current coils of a meter are always connected in series with the load

» Purpose: Converts the load current into a magnetic field or flux which is proportional to the load current


Basic Parts: Current coil (continued)

» Self contained 200A meter coils are 2 or 4 turns of 30,000 Circular Mils wire (#6AWG)

» Insulated with epoxy resin

» In a form 2S meter two current coils are located beneath the disk and one of the current coils is wound in reverse of the other

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Basic Parts: Rotor or Disk

» Two parts ‐ Disk and the shaft

» Composition ‐ Pure aluminum

– Good conductivity

– Light weight

» Disk is stippled for mechanical strength or stiffness


Basic Parts: Rotor or Disk (continued)

» Graduations painted on the disk for testing

» Edge is serrated for testing at the factory

» Two holes in disk are called Anti‐Creep holes

– these prevent disk rotation when only potential is applied ‐ no load current

» On the shaft a worm gear is cut

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Basic Parts: Bearings

» Two types of bearings ‐ Mechanical and

Magnetic

» Mechanical Bearings – no longer used

– Pivot type: Hardened tip which rides on a sapphire cup

– Ball type: Ball bearing rides between two sapphire cups


Basic Parts: Bearings (continued)

» Magnetic Bearings

–Mutual attraction at top of disk shaft or

– Repulsion at bottom of disk shaft

– Vertical alignment by stainless steel guide pins in the magnets to the top and bottom of the disk shaft

» Mechanical bearing required much more maintenance than magnetic bearings

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Break Time

» 10 minutes


Basic Parts: Register

» A system of gears, dials and pointers designed to count or accumulate the number revolutions of the disk

» The disk rotates at a design speed proportional to the load watts

» Each revolution represents a definite number of watts delivered to the load during the time required for that revolution

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Basic Parts: Register (continued)

» Revolutions made by the disk are communicated to

the register by a set of gears

– Worm gear on the disk shaft

– First gear ‐ gear at the back of the register

» The register reads in kWh so there must be a

relationship between the disk revolutions and the

register ratio and watt‐hours used


Kh or Watt‐Hour Constant

» The number of watt‐hours represented by one

revolution of the disk

– Symbol Kh

– also known as the Disk Constant

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How do we determine Kh?

» The design speed Kh of the meter is determined by

engineers based on different factors

– Minimum Light load speed

– Damping magnet cost

– performance characteristics

– Bearing wear


» Nominal values are 7.2, 1.8, 0.6, 21.6

» For example, a single phase 2S house meter is designed to turn 1000 revolutions per hour with 240 volts and 30 amps applied.

– 240 x 30 = 7200 watts

– 7200/1000 revs p/hour = 7.2 watthours p/rev

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Kh continued

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For Modern 1 ø meters the Design Speed is 16 2/3 RPM

» With this we can figure the Kh & Register

ratio of a meter designed for 240V & 30A

» Rated Voltage X Test Amps = Test Watts

240V X 30A = 7200 watts

» 7200 watts for 1 hour =

7200w X 1 Hr = 7200 watt‐hours

» At design speed, test amps & rated voltage

the disk rotational speed is 16 2/3 RPM


» At 16 2/3 RPM = 50/3 RPM X 60 min

= 1000 Revolutions

» Therefore the number of watt‐hours per disk revolution is:

– 7200 watt‐hours/ 1000 Rev = 7.2 watt‐hours/rev

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Basic Parts: Register: Shaft Reduction

» Definition ‐ The number of revolutions of the disk for one revolution of the first gear on the register which meshes with the worm gear of the disk shaft

» Typical shaft reductions are 50 or 100 teeth on the First Gear

» Symbol ‐ Rs


Basic Parts: Register: Register Ratio

» Definition ‐ The number of revolutions of the first gear for one revolution of the first or right dial pointer

» Symbol – RR

» Basic Register Ratio Formula ‐

10,000 = Kh X RR X RS

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Register Ratio


Basic Parts: Register: Register Ratio (continued)

» We know that one disk revolution = 7.2 watt‐hours ‐ Rs ‐ Shaft reduction = 100

» With 100 revolutions of the disk we have 100 rev X 7.2 watt‐hours/rev = 720 watt‐hours

» We want 10,000 watt‐hours on our register: 10,000 watt‐hours/720watt‐hours = 125/9 =13 8/9 = RR

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Basic Parts: Register: Gear Ratio

» Definition ‐ The number of revolutions of the disk needed to cause the first pointer to make one complete revolution

» Symbol ‐ RG

» Gear Ratio Formula ‐ RR X RS = RG

13 8/9 X 100Revs = 1388 8/9 Revs


Basic Parts: Register: Register Constant

» Definition ‐ The factor by which the register reading is multiplied to obtain total registration or KWH used

» Also know as ‐ Dial constant, Dial Multiplier or Reading Multiplier

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» When considering register constant we have to consider instrument constants:

– CTR Current Transformer Ratio

• Most metering current transformers (CT’s) are labeled :5, reflecting the amount of current in the primary that will produce 5 amps in the secondary. Examples: 400:5 or 80:1

– VTR Voltage Transformer Ratio

• Most metering voltage transformers are labeled as to the primary and secondary

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Basic Parts: Register: Register Constant (continued)

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• cont‐ voltages reflecting the turns ratio of the transformer. Examples would be 7200:60 or 60:1 or 480:120 or 4:1

» By definition, one revolution of the right hand dial on the register is equal to 10 kilowatt hours or 10,000 watt hours

Therefore,

Kr = Kh x Rr x Rs x CTR x VTR

10,000

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Find the Kr

– A single phase meter, form 1S, 120v, Class 100 has a Kh of 1.8, Rr of 55 5/9, Rs of 100. No instrument transformers are used.

» Kr = Kh x Rr x Rs x CTR x VTR / 10,000

» Kr = 1.8 x 55 5/9 x 100 x 1 x 1 / 10,000

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Find the Rr

– You want the Kr to be 1, Kh = 1.8, Rs = 50,

Kr = Kh x Rr x Rs x CTR x VTR / 10,000

1= 1.8 x Rr x 50 x 1 x 1 / 10,000

Rr = 10,000

1.8 x 50

Rr = 111.1111111111 or 111 1/9

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Last one – Find the Kr

– Kh = 1.8, Rr = 166 2/3, Rs = 50, CTR = 50:5, VTR = 7200:120

Kr = Kh x Rr x Rs x CTR x VTR / 10,000

Kr = 1.8 x 166 2/3 x 50 x 10 x 60 / 10,000

Kr = ?????

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Meter Calibration and Adjustments

» Disk Adjustment

» Register Mesh

» Full Load Adjustment

» Light Load Adjustment

» Lag Adjustment


Meter Calibration ‐Disk Adjustment and Register Mesh

» Disk Adjustment

– Using upper and lower bearings center disk in air gap

» Register Mesh

– If equipped adjust gear/shaft mesh for a 30% to 50% mesh between first gear of the register and worm gear of disk shaft

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TOPPED GEARS


Meter Calibration ‐Full Load Adjustment

» Purpose ‐ Adjusts speed of the disk @ rated voltage and Test Amps

» Description ‐ An adjusting screw moves a shunt across the permanent magnet which lets more or less rotation flux to cut across the disk and the disk slows down or speeds up

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Meter Calibration ‐Light Load Adjustment

» Purpose ‐ Adjusts speed of the disk @ rated

voltage and at 10 % of Test Amps

» Description ‐A rectangular plate (brass or copper)

is mounted so that its adjusting motion is at a

right angle to the disk radius. The main air gap

potential flux passes through the plate and

adjusts for shading and to overcome low load

friction.


Meter Calibration ‐Lag or Power Factor Adjustment

» Purpose ‐ Adjusts the phase angle of the potential coil flux to lag the applied voltage by 90 degrees

» Description ‐ The Lag adjustment is a metal plate attached to the potential coil core. The resistance of the plate adjusts the power factor. This adjustment is set at the factory and normally does not need any further adjustment

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Break Time

» 10 minutes


Meter Compensations

» Voltage

» Overload

» Temperature Class I

» Temperature Class II

» Frequency

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Meter Compensations‐ Voltage

» Modern electromechanical watt‐hour meters will

operate accurately between 50% & 120% of

rated voltage

» A section of the potential coil core cross

sectional area is reduced and shunted. At rated

voltage the iron is operating at saturation, as the

applied voltage increases the increased flux is

shunted across the air‐gap and does not affect

the meters accuracy.


Meter Compensations‐Overload

» Modern watt‐hour meters will operate accurately between .33% & 667% of Test Amperes or (once starting watts are overcome; about 24 watts)

» A current shunt is across the current poles, when there is a overload the shunt saturates and allows more flux on the disk

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Meter Compensations‐Temperature Class I

» Class I compensations effect all loads and power factor

equally, it is considered equivalent to changes in the

strength of the retarding magnet affected by ambient

temperatures.

» A shunt across the permanent magnet carries a large

amount of flux at low temperature and very little flux at

high temperatures. This characteristic is opposite of the

permanent magnet which gets stronger as the

temperature decreases and weaker as the temperature

increases thus compensating for changes in temperature


Meter Compensations‐Temperature Class II

» This compensation corrects changes in the

resistance of the potential coil and lag plate as

the temperature varies. Class II compensation

consists of a reactor attached to the lag plate .

As the temperature varies the resistance of the

reactor changes opposite to the resistance of

the lag plate

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Meter Compensations‐Frequency

» Because of frequency stability of modern

electrical systems, variations in meter accuracy

due to frequency variations are negligible


» Benefits

– Weight

– Cost

– Accuracy

– Programmability and additional functions

» Drawbacks

– Customer concerns

– Half life

– Adjustability

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Solid State VS Electromechanical

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» Current Sensing (CT)

– GE ‐ KV2C and I‐210

– Landis and Gyr ‐ Alf

– ABB ‐ A1D

» Hall Effect

– Itron ‐ C1S

– Icon Sensus ‐ iSO1

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Types of Solid State Meters


» Perhaps the easiest to understand in terms of

an electronic meter. Current sensing meters

work on the same principle as a transformer

rated service. Current passed through the

current coil or primary side is reduced based on

the multiplier relationship established by the

manufacturer to the output or secondary side

of the CT.

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Current Sensing (CT) Meters

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» This measured (secondary) current is then sent

to the microprocessor to be calculated with

the voltage and service type. The

corresponding load, KW, KWh, and any other

requested measurements are produced and

sent to the readout for display.

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Current Sensing (CT) Meters (continued)


Current Sensing (CT) Meter Internal Example

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» A Hall‐effect meter is an electronic device that provides a digital readout of the magnetic field strength in gauss or tesla units. The meters use a very small conductor or semiconductor element at the tip of the probe. Electric current is passed through the conductor. In a magnetic field, a force is exerted on the moving electrons which tends to push them to one side of the conductor.

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Hall Effect


» A buildup of charge at the sides of the conductors will balance this magnetic influence, producing a measurable voltage between the two sides of the conductor. The presence of this measurable transverse voltage is called the Hall‐effect after Edwin H. Hall, who discovered it in 1879

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Hall Effect (continued)

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Hall Effect


» Vh = I B Rh / b

» Where:Vh is the voltage generated.I is the applied direct current.B is the component of the magnetic field that is at a right angle to the direct current in the Hall element.Rh is the Hall Coefficient of the Hall element.b is the thickness of the Hall element.

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Hall Effect Meter Internal Example

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Hall Effect Meter Internal Example


Solid State VS Electromechanical Types

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Solid State Examples


Electromechanical Types

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Questions & Answers

» Hands on

» Thank You for your time!

Single Phase Meter Components - uploads.westernenergy.org · 8/3/2018 3...

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