Power supply to electric furnaces

Switch/circuit-breaker
for the control of
heavy duty furnaces

ISF2 :

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Merlin Gerin

■

Square D

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Telemecanique

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2

ISF2 switch/circuit-breaker

Description

Application

The ideal technology for electric furnace
control

The ISF2 is a three-phase switch/circuit-breaker for
indoor use based on SF6 technology.
It carries out control of electric furnaces up to 40.5 kV
and complies with IEC standard publications 56 and
694.

Safety

The SF6 breaking technique is especially well suited to making and breaking furnace
currents while avoiding any overvoltages likely to damage equipment on the furnace
supply line.
The ratings, rated current breaking under rated voltage, are held at 0 relative bars.
Each pole-unit, filled to a pressure of 0.15 MPa (i.e. 1.5 relative bars), is fitted with a
safety disk and diagnostic system for continuous monitoring of the SF6 pressure.

Durability suitable for heavy duty

The mechanical durability of the ISF2 is 50,000 mechanical switching operations
with maintenance every 10,000 operations.

Reliability

The mechanical operating mechanism, based on energy storing springs, is a key
feature of the device’s reliability: Schneider has 25 years of experience in these
types of mechanism.
Because Schneider fully masters the design and monitoring of sealing systems,
the device will give you lasting performances throughout its service life.

Environmentally friendly

The ISF2 furnace switch has been designed for environmental protection:

c

the materials used, insulators and conductors, are identified, easy to separate

and recyclable,

c

the SF6 can be recovered at the end of the device service life and reused after

being treated.

Quality

Each switch undergoes systematic routine tests for checking quality and conformity:

c

pole-unit sealing tested,

c

correct mechanical operation of the device tested together with associated locking

systems,

c

simultaneous contact closing tested,

c

power frequency insulation level tested,

c

main circuit resistance tested,

c

auxiliary circuit insulation tested,

c

switching operation speed tested,

c

switching cycle tested,

c

switching operation times tested.

The results obtained are recorded on each device’s test certificate.
The entire switch creation and manufacturing process is quality controlled in
compliance with the French association for quality assurance (AFAQ): ISO 9002
certification. The ISF2 switch has passed type tests in compliance with IEC 56 and
265 standards.

ISF2

ISF2 switch/circuit-breaker

3

Device description

The ISF2 is a disconnectable fixed device made up of:

c

3 separate pole-units, each being built into a “sealed pressure system” type

insulating enclosure; each pole-unit is filled with SF6 at low pressure (0.15 MPa,
i.e. 1.5 bars),

c

a Gmh type spring stored energy operating mechanism,

c

a front panel with the manual operating mechanism and position indicators,

c

upstream and downstream terminals for power circuit connection,

c

a multipin socket for auxiliary circuit connection,

c

un dispositif d’auto-diagnostic, pour le contrôle permanent du gaz SF6 sur chacun

des 3 pôles, équipé de :

v

1 “low threshold” contact, for possible pressure drop indication,

v

1 “high threshold” contact, for indication of a rise in pressure due to abnormal

overheating of the pole-unit or the arcing contact wear limit being reached.

Principle of the breaking technique
auto-compression

This breaking technique has been widely tried and tested and produces high
performances.
The arc is blown and thus extinguished by forced convection.

Fig 1: The circuit-breaker is closed.

Fig 2: When the main contacts open (a), the current is sent into the breaking circuit (b).

Fig 3: When the arcing contacts separate an electric arc appears: this is controlled
by the insulating nozzle; a piston (c) attached to the moving contact moves
downwards and compresses the gas in (d); the gas then escapes via the holes in the
piston into the tubular arcing contact zone, cools down and deionizes the electric arc
zone, thus extinguishing the arc when the current reaches 0 point.

Fig 4: The circuit-breaker is open.

a

b

d

c

Fig 1

Fig 2

Fig 3

Fig 4

Ratings

(1) For voltage of 36 to 40.5 kV, suitable inter-phase barriers supplied with the device must be
installed by the contractor.

CEI 56

rated voltage

kV, 50/60 Hz

24

40.5

(1)

insulation level

r.m.s. kV, 50 Hz - 1 mn

50

85

kV, 1.2/50

µ

s impulse

125

185

(1)

rated current

A

2500

2500

Isc breaking capacity

r.m.s. kA

31.5

25

making capacity

peak kA

79

62.5

allowable short time

r.m.s. kA, 3 s

31.5

25

with stand current

peak kA

79

62.5

rated switching cycle

O - 3 mn - CO - 3 mn - CO

c

c

operating time

ms

opening

45 to 65

45 to 65

breaking

60 to 80

60 to 80

closing

70 to 90

70 to 90

electrical durability

number

time

10

10

total

see curve p.5

see curve p.5

4

ISF2 switch/circuit-breaker

Application example

Simplified diagram

1

2

3

4

5

6

8

7

9

5

11

12

10

13

1

HV circuit-breaker

2

HV/MV step-down transformer

3

Power factor correction device

4

Protective circuit-breaker

5

Earthing switch

6

Isolation switch

7

ISF2 for furnace control

8

Voltage transformer

9

Current transformer

10

Surge arrester

11

RC circuit

12

Furnace MV/LV transformer

13

Furnace electrodes

Schneider offers complete solutions for the power supply to your furnaces:
consult us.

ISF2 mounting in a cubicle

8

9

7

HV MV

MV LV

ISF2 switch/circuit-breaker

5

Maintenance

Life expectancy of pole-units

The stress that the device has to withstand is variable depending on the type of
installation and the operating rules. The life expectancy of the poles is essentially
proportional:

c

to the number of load current making and breaking cycles,

c

to the value of the furnace supply transformer rated current.

Example: for an arc furnace fed by a 100 MVA transformer at 30 kV (or 67 MVA
at 20 kV) with a load cycle of 2000 A, the life expectancy of an ISF2 is 28,000
CO cycles (or 50,000 CO cycles when the set of pole-units is replaced).

Electrical durability

This depends on:

c

the furnace load current,

c

the circuit configuration when the device switches:

v

opening

v

closing

c

the rating of the furnace transformer and in particular of the inrush current during

no-load energization,

c

the elements inserted in the furnace supply line, saturable reactor, non-saturable

reactor, etc.

The electrical durability can be estimated using the graph in figure 1 based on the
following operating hypotheses:
1- Protection of overload currents above 2 In is carried out by the circuit-breaker
located upstream.
2 - Switching operations are carried out with the electrodes out of the bath.
3 - The no-load inrush current of the furnace transformers is below 4 In.

cycles

I (A)

0

10000

20000

30000

40000

50000

0

500

1000

1500

2000

2500

Fig 1 - Life expectancy of a set of pole-units (number of
CO cycles) depending on the furnace load current I.

Maintenance

SF6 breaking devices do not generally require special maintenance.
However, since the furnace operating mechanism undergoes heavy stress, it is
advisable to carry out basic maintenace involving the following operations:

c

depending on the ambient environment, clean the surface of the insulating

enclosures;

c

every 10,000 switching operations:

v

measure the wear on the arcing contacts without removing the pole-units during

inspection and maintenance operations (the auto-diagnostic system monitors wear
on the pole-units throughout the device service life);

v

clean the operating mechanism, grease it and check the nuts and bolts.

6

ISF2 switch/circuit-breaker

Gmh stored energy operating mechanism

Operating mechanism

The ISF2 is fitted with a Gmh type operating mechanism based on stored energy
which gives the device a closing and opening speed which is not dependent on the
operator.
The GMh operating mechanism is made up of:

c

a stored energy mechanism which stores the energy required for device closing

and then opening in springs;

c

a manual charging mechanism using a removable lever;

c

an electrical charging mechanism with a motor which automatically recharges the

operating mechanism as soon as the device is closed;

c

a mechanical “opening-closing” mechanism actuated by 2 pushbuttons located on

the front panel;

c

an electrical “closing” mechanism including:

v

1 closing release for remote control,

v

1 anti-pumping relay;

c

an electrical “opening”system, including 1 shunt opening release; an optional

undervoltage release can be added to this device;

c

a mechanical position indicator with “white-black” or “red-green” mechanical

indicators;

c

a switching operations counter.

c

A 14 strong auxiliary contact block including:

v

2 contacts for the electrical operating mechanism,

v

1 contact for the shunt release,

v

11 available contacts;

c

1 closing contact for “operating mechanism charged” indication;

c

1 “open” position key-lock support (lock supplied);

c

a multipin connector (male and female) with 36 pins and a 2 metre lead.

Gmh operating mechanism

Operating mechanism low voltage auxiliaries

charging motor

closing release

(1)

opening release

M

YF

YO1, YO2

YM

supply voltages

AC (V)

50 - 110 - 127 - 220

50 - 110 - 127 - 220

50 - 110 - 127 - 220

50 HZ

AC (V)

120 - 240

120 - 240

120 - 240

60 HZ

DC (V)

(2)

24 - 48 - 60 - 110 - 127 - 230

24 - 48 - 60 - 110 - 127 - 230

24 - 48 - 60 - 110 - 127 - 230

consumption

AC

700 VA

120 VA

120 VA

100 VA

DC

570 W

70 W

70 W

10 W

Auxiliary contacts

rated current

10 A

breaking capacity

CA

10 A at 220 V (cos

ϕ

<i 0.3)

CC

3 A at 110 ou 220 V (L/R <i 0.01 s)

(1) With anti-pumping relay.
(2) For other values, please consult us.

ISF2 switch/circuit-breaker

7

Operating mechanism wiring diagram

J

Circuit-breaker.

KN

Anti-pumping relay.

M

Charging motor.

M1-M2

End-of-charging limit switches.

M3

“Operating mechanism charged” contact.

QF

Circuit-breaker auxiliary contacts.

SE

Trip hold contact.

Sm1

Closing pushbutton (external).

Sm2-Sm4

Opening pushbuton for shunt
release(external).

Sm3

Opening pushbutton for undervoltage
release (external).

Sn

Closing disable contact (external).

SP1-SP2

Pressure switch contacts.

YF

Closing release.

Y01-Y02

Shunt opening release.

YM

Undervoltage release.

Sm2

Sm3

M3

KN

Y01

YM

SP1

SP2

Sm1

Sn

M2

SE

YF

J

M1

M1

M

QF

Y02

Sm4

Dimensions and weights

a: fixing lugs supplied on the frame are used to anchor the device to the ground;
b: the device is fitted with rollers to facilitate handling and installation;
c: multipin connector;
d: inter-phase barriers delivered with the 40.5 kV version;
e: removable charging lever.

Approximate weight: 194 kg

300

300

1108

630

736

190

300

1010

644

910

322

35

690

1060

a

e

c

d

b

Connection pad:

2 Ø 14

Ø 60

30

30

20

78

ISF2 switch/circuit-breaker

1

A few furnace switch references

c

Cockerill Sambre - 156 MVA - Belgium

c

Baotou - 150 MVA - China

c

Betasteel - 100 MVA - United States

c

Ascometal - 90 MVA - France

c

Usinor - 55 MVA - France

c

Sollac - 85 MVA - France

c

United Steel Mill - 85 MVA - Israel

c

ILSA - 120 MVA - Mexico

c

Taleras - 38 MVA - Mexico

c

Aceros DMSA de CV - 35 MVA - Mexico

c

Huta Batory - 156 MVA - Poland

c

Yamato - 96 MVA - Thailand

Schneider Electric SA

Postal address
F-38050 Grenoble cedex 9
tel : [phone]
telex : merge 320842 F

As standards, specifications and designs change from time to
time, please ask for confirmation of the information given in this
publication.

Design and production: AXESS (07)
Printing:

AMTED397053EN
ART.78659

02 / 1998

This document has been
printed on ecological paper.