Non-conventional instrument transformers and power quality aspects an overview

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1 Representative Meeting / Switzerland June 7 th Non-conventional instrument transformers and power quality aspects an overview Erik P. Sperling

2 Presentation overview 1. History 2. Instrument transformer overview 3. Power quality aspects 4. NCIT s for voltage measurements 5. NCIT s for current measurements PFIFFNER Technologie Ltd. R&D / Page 2 / 12/06/2017

History Since 120 years, inductive instrument transformers are used for billing, metering and protection purposes British patent from 1887, voltage transformer from 0.

3 History 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 kv Cascade voltage transformer of Emil Pfiffner. Pfiffner R&D / Page 3 /

4 Instrument transformer overview Conventional type Non-conventional type Inductive voltage transformers Capacitive voltage transformers AC AC Divider (C/RC/R - type) Pockels/Piezo effect AC (DC) AC DC Inductive current transformers AC Zero-flux Rogowski coils Faraday effect Shunts AC AC AC AC DC DC DC IEC standard IEC & IEC /-3/-5 IEC standard IEC & IEC IEC /-10/-11/-14/-15 PFIFFNER Technologie Ltd. R&D / Page 4 / 12/06/2017

5 System requirements frequency content in a network 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 PFIFFNER Technologie Ltd. R&D / Page 5 / 12/06/2017

6 Definition: System requirements Power quality It is the comparison between current existing values, measured in the power network, and agreed characteristics of the energy by the supplier. EMC standards: (HV- and UHV networks) Main quality criteria are: (Limits) 1. Voltage/current magnitude 2. Fundamental frequency IEC harmonics 3. Wave shape (voltage/current) IEC Flicker IEC Unbalance 4. availability (Test technics) Definition of power quality criteria in: Standard EN IEC General Guide IEC PQ measuring methods IEEE IEEE Recommended Practices and Requirements for Harmonic Control in Electric Power Systems Pfiffner R&D / Page 6 / 12/06/2017

7 System requirements PQ examples Range of frequency DC (0 Hz) up to < f r DC offset in a AC network Pfiffner R&D / Page 7 / 12/06/2017

8 System requirements PQ examples Range of frequency DC (0 Hz) up to < f r Voltage dips 150 test signal: dip 60 %, 2.5 cycles Pfiffner R&D / Page 8 / 12/06/2017

9 System requirements PQ examples Range of frequency DC (0 Hz) up to < f r Swells in voltage systems 300 test signal: swell 200 %, 2.5 cycles Pfiffner R&D / Page 9 / 12/06/2017

10 System requirements PQ examples Range of frequency DC (0 Hz) up to < f r Flicker 1 Hz to 70 Hz Unbalance in voltage systems Pfiffner R&D / Page 10 / 12/06/2017

11 System requirements PQ examples Range of frequency DC (0 Hz) up to < f r Three-phase ferro-resonance oscillations Characteristic: sub-harmonics 1 / 2 of f r Single phase ferro-resonance oscillations Characteristic: sub-harmonics 1 / 3 ; 1 / 5 ; 1 / 7 of f r Pfiffner R&D / Page 11 / 12/06/2017

12 System requirements PQ examples Range of frequency f HF > f r f = h f r ; h: even-whole-numbered f = h f r ; h: uneven-whole-numbered f h f r ; inter-harmonics Pfiffner R&D / Page 12 / 12/06/2017

13 System requirements PQ examples Range of frequency f HF > f r Pfiffner R&D / Page 13 / 12/06/2017

14 System requirements PQ examples Range of frequency f HF > f r Voltage sag with 400 Hz superimposed signal Pfiffner R&D / Page 14 / 12/06/2017

15 System requirements PQ examples Range of frequency: transient Phenomena >> f r Switching operation in parallel switchyard Voltage interuption Pfiffner R&D / Page 15 / 12/06/2017

16 System requirements PQ examples Range of frequency: transient Phenomena >> f r Few impulses Very fast du/dt Duration: approx. 0.3ms Many impulses High-frequency content Duration: approx. 1ms Pfiffner R&D / Page 16 / 12/06/2017

17 Power Quality Possible causes DC SHR HFR TFR No. of DC systems increasing Coupling between AC/DC systems (kv up to MV) Solar activity (natural phenomenon) Earthing strategy Increasing voltage fluctuation due to load variation Increasing ferroresonance oscillations Unbalances load Fluctuate production of energy because of renewable sources 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 Significant increasing of switching operations Coupling between AIS/GIS systems Increasing of natural phenomenon effects because of AIS area expandings Equipment or system failures Pfiffner R&D / Page 17 / 12/06/2017

18 Power Quality Possible impact 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) Pfiffner R&D / Page 18 /

19 Question: how suitable are inductive instrument transformers for PQmeasurements? Frequency response measurement Ind. current transformer EJOF 72 Ind. voltage transformer EOF 72 Pfiffner R&D / Page 19 / 12/06/2017

20 How to measure PQ parameters? First resonance peak of conventional VT s depending on the system voltage V m Source: IEC/TR , Pfiffner R&D / Page 20 / 12/06/2017

21 Characteristics and measurement f < f r & f > f r Frequency response measurement 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-RCdivider (yellow); as measured at PFIFFNER Frequency response of ɛ U (f) for 36kV-VT(light green), 72.5kV-VT(dark green), 123kV-VT(blue), 245kV-VT(purple),420kV-CTVT(red) and 420kV-RCdivider (yellow), as measured at PFIFFNER PFIFFNER Technologie Ltd. R&D / Page 21 / 12/06/2017

secondary active part Type ROF/RGF Secondary terminal box AC voltages: 72.

22 Non-conventional measuring devices voltage High voltage terminal Metallic expansion bellows (hermetically sealed) RC-divider primary active part Insulator (Porcelain or composite) RC-divider secondary active part Type ROF/RGF Secondary terminal box AC voltages: kV DC voltages: ±50 ±500kV Oil- or SF 6 -gas impregnated solutions ROF 420, Germany PFIFFNER Technologie Ltd. R&D / Page 22 / 12/06/2017

Switzerland Secondary terminal box Ground terminal AC voltages: 72.

23 Non-conventional measuring devices voltage HV terminal Insulator Type RGK Primary active part R 1 & C 1 Secondary active part R 2 & C 2 RGK 400DC, Switzerland Secondary terminal box Ground terminal AC voltages: kv DC voltages: ±50 ±500kV PFIFFNER Technologie Ltd. R&D / Page 23 / 12/06/2017

24 Non-conventional measuring devices voltage Complex transfer function Frequency dependent ratio U 2 (jω) U 1 (jω) = I Z 2 I Z ges = Z 2 Z ges Z 2 Z ges = R 2 R 2 + R jωc 2 R jωc 1 R 1 f 0 U 2 U 1 = r R = R 2 R 2 + R 1 Equivalent circuit diagram Z 2 Z ges = C 1 C 1 + C jωc 2 R jωc 1 R 1 f U 2 U 1 = r C = C 1 C 1 + C 2 Pfiffner R&D / Page 24 / 12/06/2017

25 Non-conventional measuring devices voltage Frequency response of an RC-divider (NCIT) f 0 f Type ROF 420 U pr : 400 kv U m : 420 kv U T : 630 kv U LIWL : 1425 kvpeak U SIWL : 1050 kvpeak U chop. : kvpeak U sr : 100/ 3 class: 0.2% cable length: 270 m PFIFFNER Technologie Ltd. R&D / Page 25 / 12/06/2017

26 Non-conventional measuring devices voltage ECD secondary terminals connected in series ECD secondary terminals connected in parallel Pfiffner R&D / Page 26 / 12/06/2017

Non-conventional measuring devices voltage RC-Dividers Pockels/Piezo-Effect (electro-optical effect) Basically, no magnetic iron core is used Source:

27 Non-conventional measuring devices voltage RC-Dividers Pockels/Piezo-Effect (electro-optical effect) Basically, no magnetic iron core is used Source: FastPulse Technology, Inc.; Electro-Optic Devices in review, Figure 2, Laser & Applications April 1986 PFIFFNER Technologie Ltd. R&D / Page 27 / 12/06/2017

28 Frequency response performance of NCIT voltage measurement systems Pfiffner R&D / Page 28 /

effect) Source: IEC TR 61869-103, figure 40 u i t ~ di(t) dt

29 Non-conventional measuring devices current Faraday effect (magneto-optic current measurement) Rogowski coil (magnet field effect) Source: IEC TR , figure 40 u i t ~ di(t) dt Basically, no magnetic iron core is used PFIFFNER Technologie Ltd. R&D / Page 29 / 12/06/2017

Non-conventional measuring devices current Shunt (resistance current measurement) Zero flux (magnet field saturation effect) CT Detect residual flux, its direction and value Cancel the oscillator s

30 Non-conventional measuring devices current Shunt (resistance current measurement) Zero flux (magnet field saturation effect) CT Detect residual flux, its direction and value Cancel the oscillator s effect Integrator Amplifier Resistance Amplifier Amplifier Peak detector Amplifier u t = R i(t) Output the polarity and value of the voltage in the case that residual flux is not zero Relay Saturation detector K1 relay operates if Ip become over the limit of amplifier output, Oscillator Energize the cores Electrical circuit Contact of K1 relay PFIFFNER Technologie Ltd. R&D / Page 30 / 12/06/2017

31 Frequency response performance of NCIT current measurement systems Pfiffner R&D / Page 31 /

32 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. Pfiffner R&D / Page 32 /

33 Thank you very much! PFIFFNER Technologie Ltd. R&D / Page 33 / 12/06/2017

Resistive capacitive voltage divider

Resistive capacitive voltage divider Outdoor operation Oil insulated ROF 72 550 kv General description Resistive capacitive voltage dividers type ROF (RC divider) are used in high voltage networks within