representative meeting / switzerland june 7 2017 · representative meeting / switzerland june 7th....

Non-conventional instrument transformers

and power quality aspects – an overview

Erik P. Sperling

Representative Meeting / Switzerland June 7th. 2017

PFIFFNER Technologie Ltd. R&D / Page 2 / 12/06/2017

Presentation overview

1. History

2. Instrument transformer overview

3. Power quality aspects

4. NCIT’s for voltage measurements

5. NCIT’s for current measurements

History

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• Since 120 years, inductive instrument transformers are used for billing, metering and protection purposes

• British patent from 1887, voltage transformer from 0.1 V up to 10 kV

• Beginning of the 1930s, a changeover from 110 kV to 220 kV system voltage network

• In the 1950s, a second important changeover from 300 kV to 420 kV system voltage network

• Current topics today UHV with voltage levels up to 1.2 MVAC and ±1.1 MVDC

1936 220 kV Cascade voltage transformer of Emil Pfiffner.

Instrument transformer overview

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Conventional type

Inductive voltage transformers Capacitive voltage transformers

Inductive current transformers

AC AC

AC

IEC standard IEC 61869-1 & IEC 61869-2/-3/-5

Non-conventional type

Divider (C/RC/R - type) Pockels/Piezo effect

Zero-flux Rogowski coils Faraday effect Shunts

AC (DC)

DC AC AC DC

AC DC

IEC standard IEC 61869-1 & IEC 61869-6 IEC 61869-7/-10/-11/-14/-15

AC

AC DC

System requirements – frequency content in a network

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• Rated frequency

• Sweeps, dips, swells, flicker, ferro-resonance

• Power quality ranges

• Transient impulses LIWL, SIWL, chopped, chopped under SF6

• DC components

| Defined as measuring range in standard

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Definition:

It is the comparison between current existing values, measured in the power network, and agreed characteristics of the energy by the supplier.

Main quality criteria are:

1. Voltage/current magnitude

2. Fundamental frequency

3. Wave shape (voltage/current)

4. availability

Definition of power quality criteria in:

Standard EN 50160

System requirements – Power quality

EMC – standards: (HV- and UHV networks)

(Limits)

IEC 61000–3–6 harmonics

IEC 61000–3–7 Flicker

IEC 61000–3–13 Unbalance

(Test technics)

IEC 61000–4–7 General Guide

IEC 61000–4–30 PQ measuring methods

IEEE 519-2014 ” IEEE Recommended Practices and Requirements for Harmonic Control in Electric Power Systems”

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System requirements – PQ examples

Range of frequency DC (0 Hz) up to < fr

DC offset in a AC network

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System requirements – PQ examples

Voltage dips

0 0.02 0.04 0.06 0.08 0.1 0.12-150

-100

-50

0

50

100

150test signal: dip 60 %, 2.5 cycles

Range of frequency DC (0 Hz) up to < fr

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System requirements – PQ examples

Swells in voltage systems

0 0.02 0.04 0.06 0.08 0.1 0.12-300

-200

-100

0

100

200

300test signal: swell 200 %, 2.5 cycles

Range of frequency DC (0 Hz) up to < fr

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System requirements – PQ examples

Range of frequency DC (0 Hz) up to < fr Unbalance in voltage systems

Flicker 1 Hz to 70 Hz

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System requirements – PQ examples

Range of frequency DC (0 Hz) up to < fr Single phase ferro-resonance oscillations Characteristic: sub-harmonics 1/3; 1/5; 1/7 of fr

Three-phase ferro-resonance oscillations Characteristic: sub-harmonics 1/2 of fr

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System requirements – PQ examples

Range of frequency fHF > fr

f = h fr; h: even-whole-numbered f = h fr; h: uneven-whole-numbered

f h fr; inter-harmonics

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System requirements – PQ examples

Range of frequency fHF > fr

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System requirements – PQ examples

Range of frequency fHF > fr Voltage sag with 400 Hz superimposed signal

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System requirements – PQ examples

Range of frequency: transient Phenomena >> fr

Voltage interuption

Switching operation in parallel switchyard

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System requirements – PQ examples

Range of frequency: transient Phenomena >> fr

Few impulses Very fast du/dt Duration: approx. 0.3ms

Many impulses High-frequency content Duration: approx. 1ms

Power Quality – Possible causes

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DC

• No. of DC systems increasing

• Coupling between AC/DC systems (kV up to MV)

• Solar activity (natural phenomenon)

• Earthing strategy

SHR TFR

• Increasing voltage fluctuation due to load variation

• Increasing ferro-resonance oscillations

• Unbalances load

• Fluctuate production of energy because of renewable sources

• Significant increasing of switching operations

• Coupling between AIS/GIS systems

• Increasing of natural phenomenon effects because of AIS area expandings

• Equipment or system failures

HFR

• Electric energy feed-in by power electronics

• Non-linear loads

• Frequency converter for traction and drives

• Coupling between different networks with converters

• Electric-arc furnaces

Power Quality – Possible impact

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increasing of power losses within the network

increasing electric stresses within the HV insulation system

thermal stresses within the connected equipment due to harmonic currents

increased sound noise emission (transformers, coils, capacitors etc.)

incorrect control of equipment.

faulty activation of protection equipment (old protection system)

Question: how suitable are inductive instrument transformers for PQ-measurements ?

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Ind. voltage transformer EOF 72 Ind. current transformer EJOF 72

Frequency response measurement

How to measure PQ parameters ?

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First resonance peak of conventional VT’s depending on the system voltage Vm

Source: IEC/TR 61869-103, 2012-05

Characteristics and measurement results @ f < fr & f > fr

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Frequency response measurement

Frequency response of ɛU(f) for 36kV-VT(light

green), 72.5kV-VT(dark green), 123kV-VT(blue),

245kV-VT(purple),420kV-CTVT(red) and 420kV-RC-

divider (yellow), as measured at PFIFFNER

Frequency response of Δ(f) for 36kV-VT(light

green), 72.5kV-VT(dark green), 123kV-VT(blue),

245kV-VT(purple),420kV-CTVT(red) and 420kV-RC-

divider (yellow); as measured at PFIFFNER

Non-conventional measuring devices – voltage

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High voltage terminal

Metallic expansion bellows (hermetically sealed)

RC-divider primary active part

RC-divider secondary active part

Secondary terminal box

AC voltages: 72.5 – 800kV DC voltages: ±50 – ±500kV

Insulator (Porcelain or composite)

ROF 420, Germany Type ROF/RGF

Oil- or SF6-gas impregnated solutions

Non-conventional measuring devices – voltage

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HV terminal

Primary active part R1 & C1

Secondary active part R2 & C2

Secondary terminal box

Ground terminal

Insulator

Type RGK

RGK 400DC, Switzerland

AC voltages: 72.5 – 500 kV DC voltages: ±50 – ±500kV

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Non-conventional measuring devices – voltage

Frequency dependent ratio

𝑍2𝑍𝑔𝑒𝑠

=𝑅2

𝑅2 + 𝑅11 + 𝑗𝜔𝐶2𝑅21 + 𝑗𝜔𝐶1𝑅1

𝑓 → 0 𝑈2𝑈1

= 𝑟𝑅 =𝑅2

𝑅2 + 𝑅1

𝑈2𝑈1

= 𝑟𝑅 =𝑅2

𝑅2 + 𝑅1

𝑓 → ∞ 𝑈2𝑈1

= 𝑟𝐶 =𝐶1

𝐶1 + 𝐶2

𝑈2𝑈1

= 𝑟𝐶 =𝐶1

𝐶1 + 𝐶2

𝑈2(𝑗𝜔)

𝑈1(𝑗𝜔)=

𝐼 ∙ 𝑍2𝐼 ∙ 𝑍𝑔𝑒𝑠

=𝑍2𝑍𝑔𝑒𝑠

Complex transfer function

𝑍2𝑍𝑔𝑒𝑠

=𝐶1

𝐶1 + 𝐶21 + 1

𝑗𝜔𝐶2𝑅2

1 + 1𝑗𝜔𝐶1𝑅1

Equivalent circuit diagram

Non-conventional measuring devices – voltage

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Frequency response of an RC-divider (NCIT)

Type ROF 420 Upr: 400 kV Um: 420 kV UT: 630 kV ULIWL: 1425 kVpeak USIWL: 1050 kVpeak Uchop.: -1640 kVpeak Usr: 100/√3 class: 0.2% cable length: 270 m 𝒇 → 𝟎 𝒇 → ∞

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Non-conventional measuring devices – voltage

ECD secondary terminals connected in series

ECD secondary terminals connected in parallel

Non-conventional measuring devices – voltage

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RC-Dividers Pockels/Piezo-Effect (electro-optical effect)

Source: FastPulse Technology, Inc.; Electro-Optic Devices in review , Figure 2, Laser & Applications April 1986

Basically, no magnetic iron core is used

Frequency response performance of NCIT voltage measurement systems

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Non-conventional measuring devices – current Faraday effect

(magneto-optic current measurement) Rogowski coil (magnet field effect)

Source: IEC TR 61869-103, figure 40 𝑢𝑖 𝑡 ~𝑑𝑖(𝑡)

𝑑𝑡

Basically, no magnetic iron core is used

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Non-conventional measuring devices – current

Shunt (resistance current measurement)

Zero flux (magnet field saturation effect)

𝑢 𝑡 = 𝑅 ∙ 𝑖(𝑡)

CT

Integrator

Amplifier

Saturation

detector

Peak

detector

Relay

Oscillator

Amplifier

Amplifier

Amplifier

Contact of

K1 relay

Detect residual flux, its

direction and value

Cancel the oscillator’s effect

Resistance

Output the polarity and value

of the voltage in the case that

residual flux is not zero

K1 relay operates if Ip

become over the limit of

amplifier output,

Electrical circuit

Energize the cores

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Frequency response performance of NCIT current measurement systems

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Conclusions

• Frequency content in a network can be divided into 4 ranges: DC, sub-harmonic, harmonic & transient voltages

• The conventional instrument voltage transformers have a limited bandwidth depending on system voltage level

• For voltage PQ measurement, RC-dividers have the highest potential due to wideband characteristic and direct secondary voltage analysis

• For current PQ measurement, different measuring applications are available.

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Thank you very much !