Provide innovative and reliable testing solutions to the - - PowerPoint PPT Presentation

• Provide innovative and reliable testing

solutions to the electrical industry. Build strong bonds with our customers and listen to their needs so that using continuous improvement methods we can achieve total satisfaction.

in Melbourne, in 1976 by Richard Dowling (CEO) to supply the local Victoria state utility with instruments. to deliver to the whole Australian market. to satisfy global markets. (80%

• f the production is now sold overseas)

• CEO

Technical Mngr. Operations Mngr. Sales Mngr. Financial/Admin. Mngr.

is a medium sized company with 20 employees. This size and structure give us the advantage of a great flexibility not found on any other competitor in the market. We are able to easily double our actual production capacity without mayor investments of capital or time.

Service & Calibrations R&D Quality Control Production Personnel Purchases Warehouse Personnel Local Sales Internatio nal Sales Accountab ility Accounts Payables & Administration

CT testing :

590G CT Tester 590F Live CT Tester 661 Protection CT Tester

PT (VT) testing

590D-1 PT Full Load Tester

• 661 Protection CT Tester

505B Admittance Tester 594 CT Batch Tester 820 CT Test Bridge Reference CTs

CVT testing

590K CVT Tester

Burden testing

704 CT Burden Tester

Primary winding The winding through which flows the current to be transformed. Secondary winding The winding which supplies the current circuits of measuring instruments, meters, relays, etc. Rated primary current The value of the primary current on which the performance of the transformer is based. Rated transformation ratio

• Rated transformation ratio

The ratio of the rated primary current to the rated secondary current. Current error (ratio error) （ （ （ （CT） ） ） ） The error which a transformer introduces into the measurement of a current and which arises from the fact that the real transformation ratio is not equal to the rated transformation ratio. Phase displacement (CT&PT) The difference in phase between the primary and secondary current vectors. Burden / Secondary circuit The external circuit supplied by the secondary winding of a transformer. Burden The impedance of the secondary circuit in VA and power-factor. Rated burden The value of the burden in VA on which the accuracy requirements of this specification are based. Polarity The way a CT has to be marked or connected so that the secondary current is in phase with the secondary. (Primary current INTO “polarity”; Secondary current OUT OF “polarity”)

• Usually only the meter is tested.

Meter measures only what reaches its terminals

• Even if the meter has zero error, and it is perfect, the billing may not be correct.

Sources of billing errors include: CTs: Incorrect accuracy class Incorrect accuracy class Over-burdened Faulty Wrong Polarity Shorted PTs: Incorrect accuracy class Over-burdened Faulty Wrong Polarity Faulty or incorrect wiring. Loose connections.

Shorted CT Open CT Produces wrong readings, NOT no readings

• Causes of metering errors.

Administrative Error 14% PT problem Theft of Service 6% PT problem 8% Faulty Meter 12% CT Problem 22% Wiring Error 38%

• Basic Theory

CTs should maintain current ratio from zero to full rated current. CT ALWAYS has some errors. Real output is less than the turns ratio. Error is due to magnetizing current in the core. (Output current) = (Current due to turns ratio) – (Magnetizing current). Magnetizing Current depends: Magnetizing Current depends: Voltage of the output (secondary) terminals of the CT Admittance of the core.

Non compensated CT error characteristic curve. (due to magnetizing current) CT Equivalent Circuit.

CT Compensation In order to increase the output current CT manufacturers will slightly change the turns ratio. For example: In a 200/5 CT. with 40 turns, if instead of using 40 turns, to compensate the magnetization loss error, using 39 turns, will mean 200/5.13A (2.5% more current), this is a very big error, so CT manufacturer could connect 2 windings in paralell of different cable gauges, to minimize the extra error and try to compensate for the different cable gauges, to minimize the extra error and try to compensate for the magnetizing current.

Compensated CT error characteristic curve. (error due to magnetizing current + ratio compensation)

CT DESIGN FOR MINIMUM MAGNETISING CURRENT ERROR Magnetizing current = Voltage / Core impedance The Output of a CT always has a large in phase component and a small leading component (caused by the lagging component subtracted from what the output current should be.) To minimize the error, the core admittance can be made smaller: Increase the section size of the core Increase permeability of the core material Increase permeability of the core material Core cost is high so CT manufacturers try to use the smallest possible core. THE EFFECT OF CT BURDEN Affects the voltage on the secondary terminals (higher burden, higher voltage) Small amount of this voltage depends on the CT winding. This voltage increases magnetizing current TO ACHIEVE MINUMUM ERRORS Use CTs with maximum number of turns on the core (Minimizes magnetizing current errors) Parallel turn compensation increases current output (Makes the ratio error more positive)

• Primary Injection

Full primary current injected into the CT (Variac + Transformer). CT output is connected to a Burden box Reference CT to do Nulling test Good Points: Good Points: Theoretically good accuracy Bad Points: Accuracy depends on many components Not practical for field testing Heavy and bulky to carry Large testing times Expensive Difficult to connect (needs specialized personnel) Limited selection of Power Factors Limited testing ratios

• Indirect Testing

Computer model of a CT to simulate the performance. Low voltage and currents are applied on the secondary of the CT. Voltage and currents are measured on the primary loop. Variety of VA loads, current test points and Power Factors are tested. Good Points: Light and portable equipment. Fast and automatic tests. Can be powered with LV AC source or a 12 V DC car battery. Unlimited range of CT ratios. No limit to the current test points. Wide selection of Power Factors can be used. Bad Points: Not a traditional testing method (this is changing as more countries and utilities are adopting this method for all the advantages that it has)

• Small & Lightweight (12 Kg), yet tough and durable - Perfect for field

testing and convenient for the workshop. Automatic, fast & fool-proof testing - Reduce testing times and personnel thus lower testing costs. Safe testing – Less components and safer voltage levels increase safety compared to traditional (primary injection) methods. compared to traditional (primary injection) methods. Up to 0.2 Class CT testing 5” screen - Easily see the results in any light condition. Inbuilt memory - Store up to 100 test results and download them to your computer. Four terminal test leads - for superior testing accuracy. Automatic CT demagnetizing after testing.

• CT Error Test – Choice between standard test points.

CT Custom Inject – Input a specific testing point. 1.6kHz Admittance test Burden Test VT/PT ratio test Live CT ratio test – (HV or LV) With 590F accessory. Full Load VT/PT error test- with 590D-1 accessory.

• Most important test.
• Utilities around world concentrating in this test.
• Checks If CT accuracy is within limits.
• Direct effect on revenue.
• Governmental Regulations to do periodical checks.
• 99.5% of CT accuracy depends on turns ratio.
• 0.5% depends on 50/60 Hz. Admittance.
• % of

rated VA

% of Primary Current

120% 100% 20% 5% 1% Ratio Error 100% +0.023% +0.017% -0.032%

• 0.078%
• 0.134%

Phase Displacement 100% +3.6' +3.8' +3.7' +4.5' +6.6' Ratio Error 25% +0.178% +0.152% +0.108% -0.006%

• 0.083%

Phase Displacement 25% +2.4' +2.8' +3.2' +4.2' +5.1'

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11.1 Accuracy class designation Highest permissible percentage current error at rated current. 11.2 Limits of current error and phase displacement for measuring CTs.

For classes 0.1 – 0.2 – 0.5 and 1, the current error and phase displacement at rated frequency shall not exceed the values given in table when the secondary burden is any value from 25% to 100% of the rated burden. given in table when the secondary burden is any value from 25% to 100% of the rated burden. Classes 3 and 5, current error shall not exceed the table values for burdens from 50% to 100% of rated value. Power factor of Burden used for test shall be 0.8. When burden is less than 5VA a 1.0 Power Factor should be used.

Accuracy Class ± % ratio error at % of rated current shown below ± Phase displacement (in minutes) at % of rated current shown below 1 5 20 50 100 120 1 5 20 50 100 120

0.1

• 0.4

0.2

• 0.1

0.1

• 15

8

• 5

5

0.2

• 0.75 0.35
• 0.2

0.2

• 30

15

• 10

10

0.2S

0.75 0.35 0.2

• 0.2

0.2 30 15 10

• 10

10

0.5

• 1.5

0.75

• 0.5

0.5

• 90

45

• 30

30

0.5S

1.5 0.75 0.5

• 0.5

0.5 90 45 30

• 30

30

1

• 3

1.5

• 1

1

• 180

90

• 60

60

3

• 3
• 3
• 5
• 5
• 5

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• Similar to 50 or 60 Hz admittance.
• Inherent error of the CT.
• Blueprint of a CT.
• Used for future reference.
• Fast test, easy to see if shorted turn or tampering.
• Compared with same CT past value or same model

averages.

• Can be done Live with every Meter test and model 505B
• Design of the metering circuits different than reality.
• Connections in the measuring circuit can become loose.
• Important to check if the burden connected to the CT is

lower than the rated burden.

() *# Full load inductive PT error test. Up to 0.1% accuracy

• *

On-line ratio check No need to cut supply Easily check CT ratio Easily check CT ratio HV & LV kits Uses customer Load 100 m fiber optic cable for inaccessible areas

• 590G is a safe testing instrument, it uses low voltage levels. And if used adequately it will

not harm to the user. However, some safety measures are very important to comply. Please make sure to ALWAYS follow these basic rules:

#" #" +

• CTs are intended to be proportional current devices. Very high voltages can result from open circuiting

the secondary circuit of an energized CT. Even very small primary currents can cause damage. As a safety measure, ALWAYS connect first the secondary test leads. ," +()

• Damaging currents will result from short circuiting the secondary circuit of an energized VT.

" -"+

• !"

• CT testing connection

Burden testing connection PT testing connection

• LIVE CT testing connection

(590G + 590F) PT full load testing connection (590G + 590D-1)