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DC Measuring Instruments

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Page 1: DC Measuring Instruments - USAID SARI/Energy Integration · DC Measuring Instruments. DC Measuring Instruments DC Current Transducer •Hybrid-Optical Measuring Device ... The measuring

DC Measuring Instruments

Page 2: DC Measuring Instruments - USAID SARI/Energy Integration · DC Measuring Instruments. DC Measuring Instruments DC Current Transducer •Hybrid-Optical Measuring Device ... The measuring

DC Measuring Instruments

� DC Current Transducer

• Hybrid-Optical Measuring Device

• Zero Flux CT

� DC Voltage Divider

Page 3: DC Measuring Instruments - USAID SARI/Energy Integration · DC Measuring Instruments. DC Measuring Instruments DC Current Transducer •Hybrid-Optical Measuring Device ... The measuring

DC Current Measuring Device

� Measurement on DC side for control, monitoring and Protection

� AC CTs cannot be used on DC side – saturation

� DC current measuring devices –

� DC shunt – low value resistor

� mV drop from the shunt taken for determining the current

� To solve insulation problems – electrical signals are converted to optical

at the shunt and at control system converted to electrical

� Supply for the conversion process is obtained from the control panels

in the form of optical power

Page 4: DC Measuring Instruments - USAID SARI/Energy Integration · DC Measuring Instruments. DC Measuring Instruments DC Current Transducer •Hybrid-Optical Measuring Device ... The measuring

6

6 UdL 4

Line 1

Pole1

4

UdN

2 4 8

Electrode

lines

2 4 8

UdN 8

4

11Nos (4 HV+7 LV)

Pole2

04 Nos ( 2 HV+2 LV)

Line 2

6 UdL 4

6

Current Measuring Devices

Voltage Dividers

DC Current Measuring Device (OPTODYN) Lay out at HVDC Kolar

IdH

IdN

IdN Idee1

IdL

IdE

Idee2

Idee3

IdE

IdLIdH

DC Current Measuring Device

Page 5: DC Measuring Instruments - USAID SARI/Energy Integration · DC Measuring Instruments. DC Measuring Instruments DC Current Transducer •Hybrid-Optical Measuring Device ... The measuring

DC Current Measuring Device

Page 6: DC Measuring Instruments - USAID SARI/Energy Integration · DC Measuring Instruments. DC Measuring Instruments DC Current Transducer •Hybrid-Optical Measuring Device ... The measuring

Hybrid-Optical Measuring Device

Measuring Shunt

Sensor Head Box

Composite Insulator

incl. Fiber Optics

Connection Box

Measuring Shunt

Sensor Head Box

Composite Insulator

incl. Fiber Optics

Connection Box

Measuring Shunt

Sensor Head Box

Composite Insulator

incl. Fiber Optics

Connection Box

Page 7: DC Measuring Instruments - USAID SARI/Energy Integration · DC Measuring Instruments. DC Measuring Instruments DC Current Transducer •Hybrid-Optical Measuring Device ... The measuring

Functional Concept

Analog/ Digital

Digital/ Optical

Optical Energy

Electrical EnergyId

Shunt

Sensor Head at high voltage level

Optical Energy

Electrical Energy

Power fibre

Signal fibre

Optical

Digital

Power supply

Fibre optical cable

Digital control/ protection systemSIMADYN D

Control/ Protection system at ground level

Page 8: DC Measuring Instruments - USAID SARI/Energy Integration · DC Measuring Instruments. DC Measuring Instruments DC Current Transducer •Hybrid-Optical Measuring Device ... The measuring

Redundancy Concept

Id

Shunt

Sensor Head Pole control System 1

Sensor Head

Sensor Head

Sensor Head

Protection System 1

Protection System 2

Pole control System 2

common composite insulator and fibre optic cable ground level; control buildinghigh voltage level; switchyard

� Complete redundancy from sensor head via FO cable to control/protection equipment

� Only one Analog/ Digital conversion per signal path

� Direct digital signal processing

Page 9: DC Measuring Instruments - USAID SARI/Energy Integration · DC Measuring Instruments. DC Measuring Instruments DC Current Transducer •Hybrid-Optical Measuring Device ... The measuring

Sensor Head Box with Sensors

Page 10: DC Measuring Instruments - USAID SARI/Energy Integration · DC Measuring Instruments. DC Measuring Instruments DC Current Transducer •Hybrid-Optical Measuring Device ... The measuring

Assembly of Shunt

Page 11: DC Measuring Instruments - USAID SARI/Energy Integration · DC Measuring Instruments. DC Measuring Instruments DC Current Transducer •Hybrid-Optical Measuring Device ... The measuring

Sensor OPTODYN

Analog Input Signal from Shunt

Optical Data Link

Optical Power Supply Link

Page 12: DC Measuring Instruments - USAID SARI/Energy Integration · DC Measuring Instruments. DC Measuring Instruments DC Current Transducer •Hybrid-Optical Measuring Device ... The measuring

The Zero-flux current transformer is a contact-free d.c. current measuring system consisting of a core and coil assembly and an electronics module.

The core and coil assembly constitutes the measuring head which is placed around a current-carrying conductor.

The measurement is based on a perfect ampere-turns balance in the measuring head.

The accuracy is determined only by the burden resistor and the output amplifier, both located in the electronics module

Zero-flux current transformer

Page 13: DC Measuring Instruments - USAID SARI/Energy Integration · DC Measuring Instruments. DC Measuring Instruments DC Current Transducer •Hybrid-Optical Measuring Device ... The measuring

DCCT Principle

Magnetic Field H

Flux Density B

� Flux created from excitation, Primary DC current and cancellation add up

� Nonlinearity of BH curve creates distortion of sense current

� Second Harmonic is zero when no DC offset, i.e. cancellation equals Primary DC current

Page 14: DC Measuring Instruments - USAID SARI/Energy Integration · DC Measuring Instruments. DC Measuring Instruments DC Current Transducer •Hybrid-Optical Measuring Device ... The measuring

Ferrite

f=40kHz

Excitation

2*f detector

Harmonic Detector

A

Cancellation

Feedback

DCCT Basic Diagram

Page 15: DC Measuring Instruments - USAID SARI/Energy Integration · DC Measuring Instruments. DC Measuring Instruments DC Current Transducer •Hybrid-Optical Measuring Device ... The measuring

The measuring head comprises three cores, each having an auxiliary winding, N1, N2 and N3. A compensating winding, N4, is wound around all three cores.

Any voltage induced in tertiary winding N3 as a result of a change of flux due to a primary-current variation is immediately compensated for by the power amplifier

The core equipped with the auxiliary winding N1 is used as a detector of the magneto motive-force balance.

By continuously sensing the ampere-turns balance, the drift of the power amplifier is cancelled out.

The burden resistor converts the secondary current into a reference voltage

Zero-flux current transformer

Page 16: DC Measuring Instruments - USAID SARI/Energy Integration · DC Measuring Instruments. DC Measuring Instruments DC Current Transducer •Hybrid-Optical Measuring Device ... The measuring

DC Measuring Devices

� DC voltage divider

� Capacitive & resistor divider circuit

� Drop across the resistor scaled for determining the voltage

� Optical conversion process is same as the current measuring device

Page 17: DC Measuring Instruments - USAID SARI/Energy Integration · DC Measuring Instruments. DC Measuring Instruments DC Current Transducer •Hybrid-Optical Measuring Device ... The measuring

DC Voltage Measurement

Page 18: DC Measuring Instruments - USAID SARI/Energy Integration · DC Measuring Instruments. DC Measuring Instruments DC Current Transducer •Hybrid-Optical Measuring Device ... The measuring

DC Voltage Measurement

Page 19: DC Measuring Instruments - USAID SARI/Energy Integration · DC Measuring Instruments. DC Measuring Instruments DC Current Transducer •Hybrid-Optical Measuring Device ... The measuring

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