Design criteria for instrument transformers

Florian Gegier

PFIFFNER Instrument Transformers Ltd.

Switzerland

The PFIFFNER Group – Organisation, Presence, Product Range

Instrument Transformers – History and outlook

Overview and types

Design criteria for instrument transformers

Modern Challenges/What’s happening in the grid?

Measurement Technology for the 21st Century

Table of Contents

www.pmw.ch / page 2 / 27.08.2017

PFIFFNER Group – Organisation

PFIFFNER Holding Ltd.

Hirschthal, Switzerland

MGC Moser-Glaser AG

Kaiseraugst, Switzerland

PFIFFNER Instrument

Transformers Ltd.

Hirschthal, Switzerland

ALPHA Elektrotechnik AG

Nidau, Switzerland

PFIFFNER Transformatör A.S.

Ankara, Turkey

PFIFFNER do Brasil Ltda

Itajaí, Brazil

PFIFFNER Deutschland GmbH

Itzehoe, Germany

PFIFFNER Technology Ltd.

Est. 1927 by Emil PFIFFNER

Present on all continents, in all climate zones IEC, BS, IEEE, ANSI, ABNT…

…new to the UK!

PFIFFNER Group – Global Presence

www.pmw.ch / page 4 / 27.08.2017

PFIFFNER Group – Product Range

www.pmw.ch / page 5 / 27.08.2017

Bushing type

current transformers

400V

Transformer station

Substation

Substation

Cable current

transformers

Medium voltage

12 – 72 kV

Low voltage

current and voltage

transformers

Support type

current and voltage

transformers

Power plant, generators Generator current

transformers

Transformer Combined transformers,

outdoor operation

High voltage

72 - 550 kV

GIS

substation

GIS current and

voltage transformers

Medium voltage

12 – 72 kV

PFIFFNER Group – Product Range

www.pmw.ch / page 6 / 27.08.2017

Current transformer

JOF 24 – 550 kV

Combined transformer

EJOF 24 – 170 kV

Inductive VT

EOF 24 – 245 kV

PFIFFNER Group – Product Range

www.pmw.ch / page 7 / 27.08.2017

Capacitive VT

ECF 72 – 550 kV

RC Divider

ROF 72 – 550 kV

PFIFFNER Group – Product Range

www.pmw.ch / page 8 / 27.08.2017

Current transformer

JGF 245 – 550 kV Combined transformer

EJGF 245 – 550 kV

Inductive VT

EGF 245 – 550 kV

PFIFFNER Group – Product Range

www.pmw.ch / page 9 / 27.08.2017

High voltage

GIS CT & VT

Medium voltage

Support type CT

Low voltage

CT & VT

Medium voltage

Ring core CT

History and outlook

1936 220 kV Cascade

voltage transformer of Emil

Pfiffner.

Since 120 years inductive ITs for billing, metering and protection

purpose

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

1930s: 110kV to 220kV systems

1950s: 300kV to 420kV systems

Current topics today UHV with voltage levels up to

1.2 MVAC and ±800 kVDC

Future:

Non-conventional types

New challenges for grid operators and IT manufacturers

Overview and types

Conventional types

Inductive voltage transformer

Capacitive voltage transformer

Inductive current transformer

Divider (C/RC/R - type)

Pockels/Piezo effect

Zero-flux

Rogowski coil

Faraday effect

Shunt

AC

AC

AC

AC (DC)

DC

AC

AC DC

AC DC

AC

AC DC

Non-Conventional types

Criterion 1: Transformation Ratio

N

A

1a

1n

Prim

Sec

Sec

PrimCT

N

N

I

Iratio

ISec

P1

P2

S1

S2

burden NSec

NPrim

Θ=Σ I

Φ

Voltage transformer (VT) Current transformer (CT)

IPrim

Sec

Prim

Sec

PrimVT

N

N

U

Uratio

USec

UPrim

NPrim

NSec

Criterion 2: Magnetisation Curve

VT

CT

Transformer formula

FEPrim ANf2π

U2B

ˆ

Criterion 3: Accuracy Requirements

CT VT

Equivalent Circuit Diagram Vector Diagram

Criterion 3: Accuracy Requirements

CVT

Equivalent Circuit Diagram Vector Diagram

• Rated frequency

• Sweeps, flicker, ferro-

resonance, dips

• Power quality ranges

• Transient impulses

BIL, SIL, chopped,

chopped under SF6

• DC components

| Defined as measuring

range in standard

based on TC38/WG47

Modern Challenges – Frequency Content

Transient phenomena

Continuous phenomena

Compact system installation combined

with GIS-type or conventional SF6 types

- within MHz range (very fast switching operation)

Reduction of secondary loading (3 pol. ferro-

resonance)

- 2nd. sub-harmonics of fundamental frequency fR

High numbers of switching operations

- frequency range from kHz up to MHz

Harmonic waves (keyword „power quality“)

- demands within a frequency range of kHz

Compact network systems

- demands because of proximity effects,

heating, shielding

Reduction of secondary loading (single phase ferro-

resonance)

- demands because of 3rd. or 5th. sub-harmonics of fR

AC/DC or DC/AC converters

Modern Challenges – New phenomena

Modern Challenges – New phenomena

Relevance example: Wind Power in the UK

Wind power boom in the UK, 6th largest producer in the world

Currently 6579 turbines providing over 13 GW, around 10% of UK power

Further growth expected: 2009 Low Carbon Transition Plan (Brown

Ministry) to generate 30% out of renewables by 2020, wind power fastest

growing

Further stress on and increased aging of substation components

What is happening in the grid?

West of Duddon Sands Wind Farm Harestanes Wind Farm

Distortion by harmonic signals

Modern Challenges – New phenomena

U

t

Disconnector operation:

Voltage at the primary terminal of a

voltage transformer 245 kV

Modern Challenges – New phenomena

U

t

Circuit breaker operation: Voltage at the primary terminal of a voltage transformer 245 kV

Source: Smeets at all; Recent standardization developments and test-experiences in switching inductive load current; CIGRE Nagoya Japan 2015

Modern Challenges – New phenomena

Measurement Technology for the 21st C.

Limitations of conventional instrument transformers

Frequency response of ɛU(f)

Measurement Technology for the 21st C.

Performance of RC Divider

Measurement Technology for the 21st C.

PFIFFNER Resistive Capacitive Divider ROF (72-550 kV)

Oil/Paper or SF6 (For GIS)

Protection/Measurement in HV transmission

Measurement of power quality

Highest accuracy from DC up to 10 kHz

Ferroresonance-free and no saturation

effects

Measurement of harmonics up to 1MHz

Florian Gegier

PFIFFNER Instrument Transformers Ltd.

Switzerland

+41 62 739 28 90

Florian.Gegier@pmw.ch

www.pmw.ch

Design of Conventional IT – CT

High voltage terminal

Metallic expension bellows

Composite insulator

Voltage grading

fine-grade low-grade

Current tranformer active part

(sec. windings)

Secondary terminal box

Ground terminal

High voltage terminal

Metallic expansion bellows

Composite insulator

Voltage grading

fine-grade low-grade

Voltage tranformer active part

(prim. and sec. windings)

Secondary terminal box

Ground terminal

Design of Conventional IT – Ind. VT

Design of Conventional IT – Combined

High voltage terminal

Metallic expension bellows

Composite insulator

Voltage grading

fine-grade low-grade

Current tranformer active part

(sec. windings)

Secondary terminal box

Ground terminal

Voltage tranformer active part

(prim. and sec. windings)

Voltage tranformer active part

(prim. and sec. windings)

Design of (Non-)Conventional IT – CVT

High voltage terminal

Metallic expension bellows

Composite insulator

Secondary terminal box

Ground terminal

Resistive capacitive divider

active part

Capacitive divider

active part

Electro magnetic

unit (EMU)