Extended Range CT’s

Extended Range CT’sMEA Electric Operations Summit

May 2015

Presented by:

Dennis Krause

General Electric

Extended Range CT’s for Transformer-Rated Revenue Metering

600V Current Transformer

Secondary

Winding

Core

No Base

The challenge with CT’s … VARIATION!

50:5

200:5

400:5

300:5

500:5

600:5

800:5

1000:5

1200:5

1500:52000:5

3000:5

4000:5

Low Base

High Base

Wide Base

Primary Bar

No Bar

2” Window

3.06” Window

3.5x4.5” Window

5” Window

30°C

Single Ratio

B0.5

B0.2

B0.1

0.3

0.15

55°CDual Ratio

Multi Ratio

RF 4

RF 3

RF 2

RF 1

RF 1.5

Solution … SIMPLIFY!With Extended Range CT’s

What can

they do?Simplify meter shop operations

& reduce costs for utilities

How do

they do it?A single “one-size-fits-all” CT

can operate accurately over a

wide range of current

Where are

they used?Revenue metering in commercial

and industrial applications

Product Feature Benefit

Features & Benefits

Same mounting construction Easy substitution & retrofitting

Reduces Inventory & Part NumbersReduce inventory holding costs, less risk

of stock out

Simplifies CT Selection Save engineering time

Simplifies Billing MultipliersSignificant reduced risk of meter

programming error or billing error

Equal to or better accuracy, over a wider

range

One extended rnage unit can functional

replace multiple standard CT ratios

Agenda

• Instrument Transformer Fundamentals

• Selection Characteristics: “BRAVER”

• Next Generation of CT

• CT Selection Quiz

Instrument Transformer Selection Characteristics

IT Selection

B – Burden

R – Ratio

A – Accuracy

V – Voltage Class

E – Etc.

R – Rating Factor

IT Selection

Load on the secondary

side of the transformer

CT

E-0.2

B-0.1

B-0.2

B-0.5

B-0.9

B-1.8

VT

W

X

M

Y

Z

ZZ

B – Burden

R – Ratio

A – Accuracy

V – Voltage Class

E – Etc.

R – Rating Factor

IT Selection

B – Burden

R – Ratio

A – Accuracy

V – Voltage Class

E – Etc.

R – Rating Factor

Primary (Input)

24,000 Volts

Secondary (Output)

120 Volts

H1

X2X1

H2

24000:120V or 200:1 75:5

Primary (Input)

75A Volts

Secondary (Output)

5 Amps

H1

X2X1

H2

IT Selection

B – Burden

R – Ratio

A – Accuracy

V – Voltage Class

E – Etc.

R – Rating Factor

Class Description

0.6 Indicating

0.3 Standard Revenue Metering

0.15 High Accuracy Metering

0.15S Special High Accuracy

(Accubute™)

0.3 B-0.9

IT Selection

B – Burden

R – Ratio

A – Accuracy

V – Voltage Class

E – Etc.

R – Rating Factor

IT Selection

B – Burden

R – Ratio

A – Accuracy

V – Voltage Class

E – Etc.

R – Rating Factor

Window Size (CT)

Indoor vs. Outdoor

Insulation Type

1 Bushing or 2 Bushing

Hardware (Fuse, Baseplates)

IT Selection

B – Burden

R – Ratio

A – Accuracy

V – Voltage Class

E – Etc.

R – Rating Factor

RF

1.0

1.33

1.5

2.0

3.0

4.0

Rated current x (RF) =

Maximum continuous operating

current, without:

• Exceeding temperature limits

• Loss of published accuracy

Burden

Graph: Bill Hardy – TEC PowerMetrix

CT Accuracy – Burden – Rating Factor

Less Burden = Higher Accuracy More Load = Higher Acc. (until saturated)

Primary

Current

CT

X1X2

Burden of

Devices ()

Burden of

Leads ()

Secondary current

Total

Burden ZT

What creates Burden?Metering/Indication

Standard Burdens per IEEE C57.13

Burden Impedance

(Ohms)

Volt-amps

(at 5

amps)

Power

Factor

B0.1 0.1 2.5 0.9

B0.2 0.2 5.0 0.9

B0.5 0.5 12.5 0.9

B0.9 0.9 22.5 0.9

B1.8 1.8 45.0 0.9

E0.2 0.2 5.0 1.0

E0.04 0.04 1.0 1.0

Leads Resistance Values

Wire Size

(AWG)

Resistance

Ohms / 1000 FT

@ 20 deg C

10 0.9989

11 1.260

12 1.588

13 2.003

14 2.525

15 3.184

16 4.016

For reference only

CT Burden Calculation

100ft. of #10 = 100* (0.999/1000) = 0.10

Ω

100ft. of #12 = 100* (1.588/1000) = 0.16

Ω

With classic rotating style meter w/25’ #12 leads:

Ammeter = 0.75VA pf 0.9

WHr meter = 0.50VA pf 0.6

Leads = 50’ total * 1.588/1000’ = 0.080 Ω

Convert Meter VA to an impedance:

Z = 0.75 / (5A)2 = 0.03 ohms = .027 + j 0.013

Z = 0.50 / (5A)2 = 0.02 ohms = .012 + j 0.016

Total Meter = 0.039 Ω + j0.029

Total Burden on CT = 0.119 + j0.029 = 0.122 Ω

Minimum requirement of CT = B0.2

Burden Example #1

Burden Impedance

(Ω)

B0.1 0.1

B0.2 0.2

B0.5 0.5

B0.9 0.9

B1.8 1.8

E0.2 0.2

E0.04 0.04

Burden Example #2

Burden Impedance

(Ω)

B0.1 0.1

B0.2 0.2

B0.5 0.5

B0.9 0.9

B1.8 1.8

E0.2 0.2

E0.04 0.04

*or* E0.2

With electronic meters w/25’ #12 leads:

Ammeter = 0.2VA pf 1.0

WHr meter = 0.0125VA pf 1.0

Leads = 50’ * 1.588/1000’ = 0.08 Ω

Convert Meter VA to an impedance:

Z = 0.2 / (5A)2 = 0.008 ohms

Z = 0.0125 / (5A)2 = 0.0005 ohms

Total Meter = 0.008 + 0.0005 = 0.0085 Ω

Total Burden on CT = 0.08 + 0.0085 = 0.0885 Ω

Minimum requirement of CT = B0.1

Electronic meter burdens are very small

Therefore:

Actual field burdens < 0.1 ohm

Burden Power Factor can approach 1.0

CT burden length of connecting leads

Per IEEE C57.13.6

Accuracy

Actual secondary

currentRated secondary

Current (5A)=

Difference in % is known as

the “Accuracy”

of the CT

CT Accuracy

Sample CT Test Card

The Ratio Correction Factor (RCF) has

been defined as the factor by which the

marked ratio must be multiplied in order to

obtain the true ratio.

Example:

Current Transformer ratio is 150:5

The tested RCF is .9981

The true ratio is 150 x .9981 = 149.7:5

Ratio Correction Factor (RCF)

The Phase Angle of an instrument

transformer (PA) is the phase

displacement in minutes between the

primary and secondary values.

Phase Angle (PA)

The Ratio Correction Factor (RCF) and

the Phase Angle (PA) are combined to

determine whether or not the transformer

meets accuracy requirements.

CT Accuracy

What causes

ratio error

and

phase error?

Relative factors that DECREASE CT accuracy:

Operating current <100% of rated current

Operating at higher burden

Design Factors:

Larger Window

Low Ratios (less primary or secondary turns)

Smaller Core

Relative factors that INCREASE CT accuracy:

Operating current near rated current or within rating factor

Operating at low burden

High Ratios (more primary or secondary turns)

Higher grade core steel (higher accuracy class)

CT Accuracy Factors

Medium Voltage Extended Range & High Accuracy CT’sPer IEEE C57.13.6

Class Description

0.6 Indicating Instruments

0.3 Standard Revenue Metering

0.15 High Accuracy Metering

0.15S Special High Accuracy (Accubute™)

-- Extended Range

CT Accuracy Parallelogram per IEEE

0.9940

0.9970

1.0000

1.0030

1.0060

-40.0 -30.0 -20.0 -10.0 0.0 10.0 20.0 30.0

RC

F

Phase Angle, minutes

100%

10%

0.3 Metering Accuracy Class

0.9940

0.9970

1.0000

1.0030

1.0060

-40.0 -30.0 -20.0 -10.0 0.0 10.0 20.0 30.0

RC

F


100%

10%

0.3 Metering Accuracy Class

By their physics, a CT

accuracy must always

be here … unless…Fa

vo

rs

Cu

sto

me

r

Fa

vo

rs

Utilit

y

Compensation

A true 200:5 has 40 Turns

200 Amps / 40 Turns = 5 Amps

5 Amps * 0.997 = 4.985 Amps

A “compensated” 200:5 (or 199.4:5)

200 Amps / 39.88 Turns = 5.015 Amps

5.128 Amps * 0.997 = 5.0 Amps (!!)

0.3

0.6

0.3

0.6

B0.1

B1.8

Fa

vo

rs

Cu

sto

me

r

Fa

vo

rs

Utilit

y

0.9970

0.9985

1.0000

1.0015

1.0030

-16.0 -12.0 -8.0 -4.0 0.0 4.0 8.0 12.0 16.0

RC

F


0.15

Accuracy

Parallelogra

m100%

5%0.3 Accuracy

Parallelogra

m

High Accuracy Class

0.9970

0.9985

1.0000

1.0015

1.0030

-16.0 -12.0 -8.0 -4.0 0.0 4.0 8.0 12.0 16.0

RC

F


New

0.15s

Accuracy

100%

5%

Special High Accuracy Class

0.30

0.30

0.60

0.60

Rating Factor

Accu

racy C

lass -

%

10%

1.0 RF

IEEE C57.13 Accuracy

0.3 @ BX.X; RF = X.X±0.3% Accuracy

from 100% rated

current up to RF

100%

Standard 0.3 Accuracy Class±0.6% Accuracy

from 10% to 100%

of rated current

No accuracy guaranteed at

current levels less than 10%

Typical 0.3 CT

Performance Curve

0.30

0.30

0.60

0.60

Accu

racy C

lass -

%

5%

1.0

±0.15% Accuracy

from 100% up to

RF

100%

0.15 High Accuracy Class

±0.3% Acc.

from 5% -

100%

0.15

0.15

IEEE C57.13.6 Accuracy

0.15 @ BX.X; RF = X.X

Typical 0.15 CT

Performance Curve



RFRating Factor

0.30

0.30

0.60

0.60

Accu

racy C

lass -

%

100%

1.0

0.15

0.15

0.15S Special High Accuracy(Accubute) IEEE C57.13.6 Accuracy

0.15 @ E0.04, E0.20; 0.15 @ BX.X;

RFX.X

5%

±0.15% Accuracy

from 5% up to RF

Typical CT

Accubute™

Performance Curve



RFRating Factor

Accuracies are stated at a BurdenJKW-5A RCF Curve

0.3 B1.8 *OR* 0.15 B0.9 *OR* 0.15S B0.5

Higher Accuracy means Higher Revenue……Generally.

In a typical installation:

1. The load a CT sees will be below the

Rated Primary Current, for a majority of

the time

2. CT error is almost always negative, and

becomes exponentially more negative as

the current load decreases.

3. Negative error means that the CT under

reports current into the meter, meaning

the power being measured is increasingly

lower than what is actually on the line

4. Therefore, less CT error means more

current being metered, meaning more

revenue recorded

Example, a 40A input load on a 100:5 CT, metered as

0.00 Error: 40A ÷ 100/(5 * 1.0000) * 20 multiplier =

40.00A


39.94A


39.88A


39.76A

Some Considerations with High Acc.

• A more “accurate” description would be “tighter tolerance CT”

• A specially compensated CT could have error favoring the utility and therefore increasing accuracy *decreases* total customer bill

• At B-0.1, many standard CT designs will be extremely accurate, especially within Rating Factor.

• The more extreme the conditions, the more potential benefit from high accuracy class (i.e. high voltage, high burden, high variation in operating voltage)

• IEEE standards for Instrument Transformers are written with consideration for Metering standards (ANSI C12.20)

Reason why 5% of Inom is minimum current

ANSI C12.20 Standard for Electricity Meters Class 0.2 - having ± 0.2% accuracy

1% 3% 5%

9S - C20, 120V

Rating Factor

CT Sizing (Rating Factor)

Example:

200:5 CT with RF4.0

May be operated up to:

4.0 x 200A = 800A Primary Current

Note: Secondary current = 4.0 x 5A = 20A

CT Rating Factor

0.25A or 0.5A to 20A = CL20 Meter Op.

Range

0.30

0.30

0.60

0.60

Rating Factor

Accu

racy C

lass -

%

10%

1.0 RF

100%

CT Rating Factor

For optimal performance with a

standard CT, size to operate CT

within Rating Factor

High Accuracy vs. Rating FactorScenario:

• You use a 200:5 ratio with a RF of 3.0.

• Accuracy performance is ± 0.3% from 200A to 600A, and ± 0.6% from 20A to 200A

Suppose you want to increased accuracy. You may be disappointed to learn the higher accuracy option only has an RF of 1.5, and therefore the maximum guaranteed current is only 300A…

Solution:

• Choose a 400:5 high accuracy guaranteed at ±0.15% from 5% to 150%.

• ± 0.15% accuracy from 20amps to 600amps.

• Despite a lower RF, you have improved accuracy over the entire range you had before!

Furthermore, your biggest improvement in accuracy will come at the 20-200amp range.

20

0.30

0.60

0.15

0.30

0.15

0.60

200 400 600

Primary Current Range (Amps)

ACCUBUTE™

400:5 RF=1.5

Conventional CT

200:5, RF = 3

Accu

racy C

lass -

%

Next Generation of CT’s

Redefining CT Performance

Many manufacturers offer performance beyond the current IEEE definition

Standard Accuracy (IEEE vs. Wide

Range)

High Accuracy (IEEE vs. Extended

Range)

Wide Range: How it worksExtending the test limits

Standard CT Wide Range CT

Standard CT Extended Range

Extended Range: How it worksWider range plus tighter test tolerances

Features & Benefits

System Current 6A 20A 40A 60A 80A 100A 200A 400A 600A 800A 1000A 1200A 1400A 1600A 1800A

200:5 JAK-0C

(Rating Factor 4.0)±0.6% Accuracy ±0.3% Accuracy

400:5 JAK-0C

(Rating Factor 4.0)_ ±0.6% Accuracy ±0.3% Accuracy

1200:5 JAK-0C

(Rating Factor 1.5)±0.6% Accuracy ±0.3% Accuracy

600:5 JAK-0S

(1% to 300%)±0.15% Accuracy

…Plus higher accuracy, which translates to higher revenue

• CT error becomes exponentially more

negative at light loads

• Negative error means that the CT under

reports current into the meter

• Less CT error means an increase in kWh

measured

Sample Business Case

Scenario

• Commercial customer, open M-F, 9am-5pm

• 480/277V system with 200A nominal current

• Load is 100% on weekdays, 10% on weeknights, and 5% on weekends

With these conservative assumptions - less than an 18 month payback!

CT Type Ratio kWh Metered Annual Bill Additional Revenue Price Adder

JAK-0C Standard CT 200:5 217,211 $19,549 --- ---

JAK-0S RevenueSense™ 600:5 217,665 $19,590 +$41$20/unit * 3

CT’s

The RevenueSense CT, with its premium accuracy increases billing revenue by $41 annually versus the

standard CT. The additional cost to use (3) high accuracy CT’s is roughly $60, in this example.

Result & Benefits

Sizing CT’s

Nameplate

Majority of revenue loss in most utility systems come from CT-metered installations

because

Installations are larger customers such that an error will create obviously a

much larger loss

CT installations are more complex and comprise more components resulting

in a higher probability of failures.

Most CT-metered installation errors favor the customer resulting in under-billing of the

customer.CT - Basics of Operation & Testing

Norm Ackermann - SpinLab

Why is the correct selection of CT’s important?

Estimated annual impact at US Utility is $450M

Example #1

Secondary Metering Cabinet, Bar-type CT

Need burden of B0.2

Normal operating current of 400A

Maximum operating current of 800A

Minimum operating current near 0

Choices

• 200:5 rated 0.3 B0.5, RF=4.0

• 400:5 rated 0.3 B0.5, RF=4.0

• 600:5 rated 0.3 B0.5, RF=2.0

Example #2


Need burden of B0.2



Minimum operating current near 0

Choices

• 200:5 rated 0.3 B0.5, RF=4.0

• 400:5 rated 0.3 B0.5, RF=4.0

• 600:5 rated 0.15S B0.2, RF=2.0

Example #3

Primary Metering Cabinet, Wound CT

Need burden of B0.5



Choices

• 300:5 rated 0.3 B0.5, RF=1.5

• 400:5 rated 0.3 B0.5, RF=1.5

• 600:5 rated 0.3 B0.5, RF=1.5

• 800:5 rated 0.3 B0.5, RF=1.5

Example #4

Primary Metering Cabinet, Wound CT

Need burden of B0.5



Choices

• 600:5 rated 0.3 B0.5, RF=1.5

• 600:5 rated 0.15S B0.5, RF=1.5

Example #5


Need burden of E0.2


Max operating current near 200A

Choices

• 200:5 rated 0.3 B0.2, RF=2.0

• 600:5 rated 0.15S B0.2, RF=2.0

Example #6


Need burden of E0.2



Minimum operating current near 200A

Choices

• 200:5 rated 0.3 B0.2, RF=2.0

• 600:5 rated 0.15S B0.2, RF=2.0

Should I use lowest ratio possible and

operate within rating factor for extended

range CT’s?

Ratio (RF=3) Standard CT Extended Range

200:5 20A to 600A 2A to 600A

400:5 40A to 1200A 4A to 1200A

600:5 60A to 1800A 6A to 1800A

Documents

Extended Range CT’s