Siemens GMI Series User manual

SIEMENS
5kVand 15kV
Vacuum Circuit Breakers
TypeGMI
Instruction
Installation
Operation
Maintenance
SGIM-3268E
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•••••••
Hazardous uni+ ... ,,.,,.,
Will cause death, serious personal injury or
Always de-energize and ground the equipment before
maintenance.
Maintenance should be
performed only by qualified personnel. The use of
unauthorized oarts in the repair of the equipment or tampering by unqualified
personnel will result
in dangerous conditions which will cause severe personal
injury or equipment damage. Follow
all safety instructions contained herein.
IMPORTANT
The information contained herein
is general in nature and not intended for specific
application purposes. It does not relieve the user
of responsibility to use sound
practices
in application, installation, operation, and maintenance of the equipment
purchased. Siemens reserves the right to make changes
in the specifications
shown herein or to make improvements at any time
without notice or obligations.
Should a
conflict arise between the general information contained in this
publication and the contents of drawings or supplementary material or both, the
latter shall take precedence.
QUALIFIED PERSON
For the purpose
of this manual a quaiified person is one who is familiar with the
installation, construction or operation
of the equipment and the hazards involved.
In addition, this person has the following qualifications:
(a) is trained and authorized to de-energize, clear, ground, and tag circuits and
equipment
in accordance with established safety practices.
(b) is trained in the proper care and use of protective equipment such as rubber
gloves,
hard hat, safety glasses or face shields, flash clothing, etc., in accordance
with established safety practices.
(c) is trained in rendering first aid.
SUMMARY
These instructions do not purport to cover all details or variations in equipment, nor to provide for every possible
contingency to be
met in connection with installation, operation, or maintenance. Should further information be
desired or should particular problems arise which are not covered sufficiently for the purchaser's purposes, the
matter should be referred to the local sales office, listed on back
of this instruction guide.
The contents
of this instruction manuai shall not become part of or modify any prior or existing agreement,
commitment or relationship.
The sales contract contains the entire obligation of Siemens Power Transmission &
Distribution Inc. The warranty contained in the contract between the parties is the sole warranty of Siemens Power
Transmission & Distribution Inc. Any statements contained herein do not create newwarranties or modify the existing warranty.
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kV and 1 uum
Circu1 B
Introduction and Safety
Introduction
Qualified Person
Signal Words
Dangerous Procedures
Field Service Operation
Receiving, Handling and Storage
Introduction
Receiving Procedure
Shipping Damage Claims
Handling Procedure
Storage Procedure
Indoor Storage
Outdoor Storage
Soace Heating
Installation Checks and Initial Functional Tests
Introduction
Inspections,
Checks and Tests without Control Power
De-Energizing Contra: Power
Spring
Discharge Check
Removal from Lower Cell
Removal from
Upper Celi
Removal in Outdoor Non-Walk In Enclosures
Physical Inspections
Manual Spring Charging
Check
As-Found and Vacuum Check Tests
Automatic Spring Charging
Check
Final Mechanical Inspections without Control Power
Interrupter/Operator Description
Introduction
Vacuum Interrupters
and Primary Disconnects
Primary Disconnects
Phase Barriers
Stored Energy Operating Mechanism
Modes of Operation -Mid-1991 and After
Modes of Operation -Discussion
Spring Charging
Mode
Closing Mode
Trip Free Mode
Opening Mode
Rapid Auto-Reclosing Mode
Modes of Operation -UP to Mid-1991
Modes of Operation -Discussion
Spring Charging
Mode
Closing Mode
Trip Free Mode
Opening Mode
Rapid Auto-Reclosing Mode
Closing and Opening Springs
Trip Free Operation
Damper
Manual Spring Charging
Spring Charging Motor
Close Solenoid, Trip Solenoid
and Anti-Pump Relay
Secondary Disconnect
Auxiliary Switch
MOC (Mechanism Operated Ceil) Switch
TOC (Truck Operated Cell) Switch
Limit Switches
Standard Schematic Diagrams
Capacitor Trip Device
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
4-7
4
4
4
4
4
5
6
6
6
6
6
7
8-20
8
8
9
9
9
10
10
10
11
11
11
11
12
12
12
12
13
13
13
14
14
14
14
15
15
15
16
16
16
17
17
17
Undervoltage Release
Interlocks
Trio Free Interlock
Rating Interlock
Circuit Breaker Frame
Ground Disconnect
Circuit Breaker
Handling Wheeis
Racking Mechanism
Maintenance
Introduction and Maintenance Intervals
Recommended Hand Toois
Recommended Maintenance and Lubrication
Removal from Switchgear
Checks of the Primary Power Path
Cleanliness
Check
Inspection of Primary Disconnects
Checks of the Stored Energy Operator Mechanism
Maintenance
and Lubr!cation
Fastener
Check
Manual Spring Charging and Contact Erosion Checks
Damper Assembly Check
Electrical Control Checks
Check of the Wiring and Terminals
Check of the Secondary Disconnect
Automatic Spring Charging
Check
E'ectrical Close and Trip Check
Checks of the Spring Charging Motor
High-Potential Tests
Vacuum Integrity
Check
High Potential Test Voitages
Vacuum Integrity Test Procedure
As-Found Insulation
and Contact Resistance Tests
Insulation and
Contact Resistance Test Equipment
lnsuiation and Contact Resistance Test Procedure
Inspection and C!eaning of Breaker Insulation
Functional Tests
Overhaul
Introduction
Circuit Breaker Overhaul
Rep!acement at Overhaul
Rep!acement
of Closing Springs
Replacement of
Opening Spring
Replacement of Closing
and Tr!pping Solenoids
Replacement
of Anti-Pump Relay
Replacement of the Auxiliary Switch
Replacement of Motor Cut-Off Switch
Replacement of Trip Latch Reset
Check Switch
Replacement
of LS3 -Mid-1991 and After
Replacement
of LS3 Up to Mid-1991
Replacement
of Spring Dump Switch
Replacement
of Damper Assembly
Replacement of Spring Charging Motor
Replacement of Primary Disconnect Fingers
Replacement of Vacuum Interrupters
Preparation
Vacuum Tube Removal
Vacuum Tube Replacement
Periodic Maintenance and Lubrication Tasks
Troubleshooting
Appendix
19
19
20
20
20
20
20
20
21-26
21
21
21
21
22
22
22
23
23
23
23
24
24
24
24
24
25
25
25
25
25
25
25
25
25
26
26
27-35
27
27
27
27
27
28
28
28
28
28
28
29
30
30
30
30
31
31
31
32
36
37
39
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Introduction and Safety
Introduction
The GMI family of vacuum circuit breakers is designed to meet
all the applicable ANSI, NEMA and
IEEE standards. Success-
ful application and operation of this equipment depends
as
much upon proper installation and maintenance bythe user as
it does upon the careful design and fabrication by Siemens.
The purpose of this Instruction Manual
is to assist the user in
developing safe and efficient procedures for the installation,
maintenance and use
of the equipment.
Contact the nearest Siemens representative
if any additional
information
is desired.
Qualified Person
Powercircuitbreakersoperateathighvoltages
and have
spring-loaded mechanical parts
which operate at high speed.
When operated improperly,
this equipment
will causedeath,personal
injury and property
damage.
To avoid electrica: shock. bumsano entang:ement
in moving parts this equipment must be installed,
operated and maintained only by qualified
persons thoroughly familiar with the equipment.
instruction manuals and mawings.
Forthe purpose ofthis manual and product labels, a"Qualified
Person"
is one who is familiar with the installation, construction
and operation
of this equipment, and the hazards involved. In
addition, this person has the following qualifications:
• Training and authorization to energize, de-energize, clear,
ground and tag circuits and equipment
in accordance with
established safety practices.
• Training
in the proper care and use of protective equipment
such
as rubbergloves, hard hat, safetyglasses, face shields,
flash clothing, etc.,
in accordance with established safety
procedures.
• Training
1n rendering first aid.
2
Signal Words
The signal words "Danger", "Warning" and "Caution" used in
this manual ·indicate the degree of hazard that may be encoun-
tered by the user. These words are defined
as
Indicates an imminentlyhazardoussituation which,
if not avoided, will result in death or serious injury.
Warning-Indicates apotentiallyhazardoussituation which,
if not avoided, could result in death or serious injury.
Caution -Indicates a potentially hazardous situation which,
if not avoided, may result in minor or moderate injury.
Dangerous Procedures
In addition to other procedures described in this manual as
dangerous, user personnel must adhere to the following:
1. Always work on a de-energized breaker. Always de-ener-
gizeabreaker, and remove
it from the metal-clad switchgear
before performing any tests, maintenance or repair.
2. Always perform maintenance on the breakerafterthespring-
charged mechanisms are discharged (exceptfor test of the
charging mechanisms).
3. Always let an interlock device or safety mechanism perform
its function without forcing or defeating the device.
Field
Service
Siemens can provide competent, well-trained Field Service
Representatives
to provide technical guidance and advisory
assistance for the installation, overhaul, repair and mainte-
nance of Siemens equipment, processes and systems. Con-
tact regional service centers, sales offices or the factory for
details.
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IVI g, Handlin and Sto
Introduction
Type GM! Vacuum Interrupter Circuit Breakers are normally
installed
in assembled metal-clad switchgear, and the Switch-
gear Instruction Manual (SG-3258) contains the Receiving,
Handling and Storage instructions for assembled metal-clad
switchgear.
This manual covers the Receiving, Handling and Storage
instructions for Type GM! circuit breakers shipped separately
from the switchgear. This section of the manual
is intended to
help the user identify, inspect and protect the circuit breaker
prior to its installation.
Receiving Procedure
Make a physical inspection of the shipping container before
removing orunpacking thecircuitbreaker. Checkfor shipment
damageor indicationsofrough handling bythe carrier. Check
each item against the manifest to identify any shortages.
Accessories such as the manual charging lever, the racking
crank and the plug jumper are shipped separately.
Shipping Claims (When Applicable) -Follow nor-
mal shipment damage procedures, which should include:
1. Check for visible damage upon arrival.
2. Visible damage must be noted on delivery receipt. and
acknowledged with driver's signature. Notation, "Possible
internal damage, subject to inspection" must be
on delivery
receipt.
3. Notify Siemens Sales office immediately of any shipment
damage.
4. Arrange for carrier's inspection. Do not move the unit from
its unloading point.
Handling Procedure
1. Carefullyremovethe shipping cartonfromthecircuitbreaker.
Keep the shipping pallet for later use if the breaker
is to be
stored prior to its installation.
2. Inspect for concealed damage. Notification to carrier must
take place within
15 days to assure prompt resolution of
claims.
3. Each circuit breaker should be appropriately lifted to avoid
crushing the side panels of the breaker, or damaging the
primary disconnect subassemblies.
Heavy Weight
Can cause death,
serious injury, or property
damage.
Obtain the services of a qualified rigger prior to
hoisting the circuit breaker to assure adequate
safety margins
1n the hoisting equipment and
procedures to avoid damage.
TypeGM! circuitbreakersweigh between385to 575 pounds
(175to
261 kg). See Table A-4, Technical Data in Appendix.
4. The palleted circuit breaker can also be moved using a
properly rated fork-lift vehicle. The pallets are designed for
movement by a standard fork-lift vehicle.
s""'""'" .. Procedure
1. Whenever possible, install circuit breakers in their assigned
switchgear enclosures for storage. Follow instructions con-
tained
in the Switchgear Instruction Manual.
2. When the breaker will be placed on its pallet for storage, be
surethe unit
is securelybolted to the palletand covered with
polyethylene film at least
10 mils thick.
Indoor -Whenever possible, store the circuit breaker
indoors. The storage environment must be clean, dryand free
of such items as construction dust, corrosive atmosphere,
mechanical abuse and rapid temperature variations.
Outdoor -Outdoor storage is not recommended.
When no other option
is available, the circuit breaker must be
completelycovered and protected from rain, snow, dirtand all
other contaminants.
Space -Space heating must be used for both indoor
and outdoorstorage to prevent condensation and corrosion.
When stored outdoors. between 150 to 200 watts per breaker
of space heating
is recommended. If the circuit breakers are
stored insidethe switchgearenclosures, and the switchgear
is
equipped with space heaters, energize the space heaters.
3
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Installation Checks and Initial Functional Tests
Introduction
Tris sectio.1 providesa description of the inspectio1s, checks
ard tests to be per'ormed or the circ1.;it breaker prior to
operatior.
in tre metal-clad switchgear.
Inspections,
Checks and Tests without Control Power
Vacuurr. circciit breakers are normally sr:pped witr t'"ieir pri-
~ary contacts open anci he;~ spri'.1gs discharged. However,
it:s critical to firstverify
tre discharged coridition of!hespring-
loaded mechanisms afte' de-energizing cortrol power.
De-Energizing
Control Power in Switchgear - Wren tre
circJi'. breaker is mou'lted in switchgear, open t"'ie control
powerciisco.-:nectdevice
in :he!Tietal-cladswitchgearcubicle.
Figure 1
srows the location o: this discon'."lect ir. a standard
GM switchgear assembly.
Tre con:rol power disconnect dev:ce is located or.
the device
panel above
the :ower c:~cuit breaker and below the upper
circuit breaker. Figure 1
srOVl/S a pi.; lout type fJse 'lOlder.
Removal
of the 'use rolder de-ererg·zes cort'OI power to tre
circJi! breaker ir the respec'.!ve switchgea~ cell. In so""ie
sw'.tcrgearassemb
ies, amolded casecircJit breaker is used
in lieu o: the pJll out type fuse raider. Opering this circuit
breaker accomplishes
the same result: control power is dis-
con:iected.
Spring Discharge Check (Figure 2) -Perform t."ie Spring
Discha~ge Check before removing the circuitbreaker ~rom the
paEet or re~ovi:ig it !rom tre switchgear.
Tre
sprj'."lg discr.arge creek consistsof simply performing tre
following :asks in the ordergiven. Thisc1eckassi..:res:hatboth
the tripping and
clos;'."lg springs are fully discharged.
... ,: .-.
.........
Figure 1: Co!ltrol Power Disconnects in Switchgear.
4
A DANGER
Hazardous voltages and high-speed
mechanical parts.
Wiil cause death, severe personal Injury. or
property damage.
Read ir;str;iction manuals, observe safety
1ns:ruct1ors and use
c;ualif1ed persor.rel.
1. Press red Trip pus"'ibutto'."I.
2 Press black Close pushbutton.
3. Again press red Trip pushbutton.
4. Veri'y Spring Cordition l:idicator shows DISCHARGED.
5. Veri'y Mair. Contact StatJs Indicator shows OPEN.
Removal from Lower Cell In Indoor (If not on raised pad)
and Shelter-Clad Outdoor Switchgear -
1. Open the circuit breaker.
2. If the circuit breaker is
in the Connect position, insert the
racking crank on the racking screw on the front
of the
breaker cell, and push
in. This action operates the racking
interlock latch. Figure 3 shows racking
of a circuit breaker
in the upper cell -the process is similar for a breaker in the
lower cell. Rotate the racking crank counterclockwise until
the breaker is
in the Test position. (If the circuit breaker is in
the Disconnect position, turn the racking crankclockwise to
rack the circuit breaker from the Disconnect position to the
Test position). If the racking crank is not of the "Captive"
type, constant inward pressure is required during racking to
maintain engagement with the racking mechanism.
3. With the circuit breaker
in the Test position and OPEN, de-
energize control power to the circuit breaker. Figure 1
shows the location of control power disconnects in a
normal unit.
• •
• +=
c:
~A 1..,f~:o.., D
I
~
I
-
.,
-
--
Manual
ICl ose •
Figure 2: Front Panel of GMI Circuit Breaker.
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Installation Checks and Initial Functional Tests
4. Perform the Spring Discharge Check. and verify that the
circuit breaker is OPEN
and the closing spring indicator
shows DISCHARGED.
5. Insert the racking crank on the racking screw on the front of
thebreakercell, and push in, as described in step2. Rotate
the racking crank counterclockwise until
the breaker is in
the Disconnect position. The breakercan now be removed
from the cubicle.
6. The circuit breaker is now free
to be rolled out on the floor
using the handles
as shown in Figure4. The wheels of the
circuit breakerare virtually
at floorlevel (unles theswitchgear
is installed
on a raised pad}, and one person can easily
handle the unit.
g
.
. • •
' • '
Ill
Q
"" II!
__ I - -
Figure 3: Racking Circuit Breaker in Switchgear.
Figure 4: Removal
of Circuit Breaker.
Removal from Upper Cell (Indoor and Shelter·Clad Out·
doorSwitchgear)·Removaloftheupperbreakerinatwo-high
assembly is similar
to removal of a breaker from a lower cell.
with several additional steps.
Figure 5 shows one of the two breaker extension rails being
inserted into the fixed rails within the upper cell o! two-high
switchgear equipment. The rails engage locking pins in the
fixed rails to secure them in position.
The procedure for removal of an uppercircuit breaker is:
1. Open the circuit breaker.
2. If the circuit breaker is in the Connect position, insert the
racking crank
on the racking screw on the front of the
breaker cell, and push
in. This action operates the racking
interlock latch. Figure3 shows racking
of a circuit breaker
in the uppercell . the process issimilar for a breaker in the
lower cell. Rotate the racking crank counterclockwise until
the breakerisin the
Test posrtion. (If the circuit breaker is in
the Disconnect position, turn theracking crank
clockwise to
rack the circuit breaker from the Disconnect posrtion to the
Test position). If the racking crank is not of the "Captive"
type, constant inward pressure is required during racking
to
maintain engagement with the racking mechanism.
3. With the circuit breaker in the
Test position and OPEN, de·
energize control power to the circuit breaker. Figure 1
shows the location of control power disconnects in a
normal unit.
4. Perform the Spring Discharge Check, and verify that the
circuit breaker is OPEN and the closing spring indicator
shows DISCHARGED.
5. Insert the
two extension rails into thefixed rails. Be sure the
extension rails are properly secured in place. (This can
be
doneat step 7 ifpreferred.)
6. Insert the racking crank on the racking screwon thefront of
the breakercell, and push in, asdescribed in step 2. Rotate
the racking crank counterclockwise until the breaker is in
the Disconnect position.
7. If you have not yet installed the extension rails, do so now.
Note that some difficulty may be experienced installing
the
extension rails if the circuit breaker is in the Disconnect
Figure 5: Use
of Extension Rails for UpperCompartment.
5
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Installation Checks and Initial Functional Tests
position. Ifdifficulty is encountered, rack the circuit breaker
to the
Test position, install the extension rails, and then rack
the circuit breaker to the Disconnect position.
HeavyWeight
Can cause death,
serious Injury, or property
damage.
Always use extension
~ails to rerr.ove or ins:a·1
c'rc:.;it breaker ir :he upper ceil or in ce~ls not
irstalledat floor
~evel.
8. Move the breakerrelease latch to the left and pull thecircuit
breaker
out from the Disconnect position. The breaker is
now free to be rolled out on the twoextension rails using the
handles
on the front of the circuit breaker.
9. Remove the breaker from the two extension rails using the
approved Siemens breaker lifting device.
10. Lift the two extension rails and withdraw them from the
switchgear.
Figure 6: Manual Charging of Closing Springs.
6
Removalfrom UpperandLowerCell in OutdoorNon-Walk
In Enclosures or for Indoor Switchgear Installed on a
Raised Pad -Because the floor level in non-walk in outdoor
enclosures is approximately 6 inches above grade (founda-
tion) level, the lower breaker in either a one-high or two-high
sectior
of switchgear must be removed using the preceding
procedure for upper breaker removal.
The approved breaker lifting device should be used for re-
moval
of both lower and u~per breakers frory-, the extension
rails
of outdoornon-walk in enclosures.
Physical Inspections
1. Verify thatrating of thecircuitbreakeriscompatiblewithboth
the system and the switchgear.
2. Performavisual shippingdamagecheck. Cleanthebreaker
of all shipping dust. dirt and foreign material.
Manual Spring Charging Check
1. Insert the manual spring charging lever into the manual
c'large handle socket as shown in Figure 6. Operate the
leverup and down until the spring corditionindicatorsl-iows
the closing spring isCharged.
2. Repeat the Spring Discharge Check.
3. Verify that the springs are discharged and the breaker
primary contacts are open
by indicator positions.
21659-93
Figure 7: Split Plug JumperConnected to Circuit Breaker.
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Installation Checks and Initial Functional Tests
As·Found and Vacuum Check Tests -Perform and record
theresultsofboththeAs-Found insulation testand thevacuum
check high-potential test. Procedures for these tests are
described in the Maintenance Section
of this manual.
Automatic Spring Charging Check
Note: A temporarysourceof control powerand test leadsmay
be required if the control power source has not been con-
nectedto the switchgear. (Refer
to the specificwiringinforma-
tion and rating label for your circuit breaker to determine the
voltage required and where the control voltage signal should
be applied. Usually, spring charging power is connected to
secondarydisconnectfingers S016andSD15, closingcontrol
powertoSD13and8015,andtripping powertoSD1 andSD2.)
When control power is connected to the GMI circuit breaker,
the closing springs should automatically charge.
The automatic spring charging features
of the circuit breaker
must
be checked. Control power is required for automatic
spring charging to take place.
1. Open control power circuit by removing pullout fuse holder
shown
in Figure 1.
2. Install breaker end of split plug jumper(if furnished) shown
inFigure7tothecircuitbreaker.
The plugjumperissecured
by means of screws, over the circuit breaker's secondary
contacts.
3. Install the switchgear end of the plug iumper shown in
Figure 8 to the secondary disconnect block inside the
switchgearcubicle. The jumperslides into place. The plug
jumper interconnects all control power and signal leads
(e.g., remote trip and close contacts) between the switch-
gearand the circuit breaker.
4. Energize (close) the control power circuit disconnect (Fig-
ure 1
).
Figure 8: Split Plug JumperConnected to Switchgear.
5. Use theClose and Trip controls{Figure 2) to first Close and
then Open the circuit breaker contacts. Verify contact
positions visually
by observing the Open/Closed indicator
on the circuit breaker.
6. De-energizecontrol power by repeatingStep 1. Disconnect
the plug jumper from the switchgear first and next from the
circuit breaker.
7. Perform the Spring Discharge Check again. Verify that the
closing springsare dischargedand the primary contactsof
the GMI circuit breaker are open.
Final Mechanical Inspections without Control Power
1. Make a final mechanical inspection of the circuit breaker.
Verify that the contacts are in the Open position. and the
closing springs are Discharged.
2. Check the upper and lower primary studs and contact
fingers shown in Figure
9. Verify mechanical condition o!
finger springs and the disconnect studs.
3. Coat movable primary contact fingers (Figure 9) and the
secondary disconnect contacts {Figure 9 and 22) with a
lightfilm ofSiemensContactLubricantNo. 15-171-370-002.
4. The GMI vacuumcircuit breakeris ready for installation into
its assigned cubicle
of the metal-clad switchgear. Refer to
removalproceduresandre-installthecircuitbreakerintothe
switchgear.
5. Refer to the Switchgear Instruction Manual for functional
tests
of an installed circuit breaker.
Figure 9: Rear of GMI Breaker with Primary Disconnects.
7
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Interrupt er /Operator Description
Introduction
The Type GMI vaci.;u~ circui1 breaker is o' drawout construc-
tior designed for use
in medi;.im vo!1age. metal-clad switch-
gear.
The GMI circJit breakerconforrrs tothe requirements of
ANSI standards C37.20.2. C37.04, C37.06. C37.09 and
C37.010.
GM! circuit breakers consist of t'lree vacuum interrupters, a
stored energy operati:ig mechanism, necessary electrical
controls and irterlockdevices, disconnec1devices to connect
the breakerto both pri~ary ar.d cortrol power ard an operator
hoJsir.g. On some
circ;.1it breaker ratings insulatirg barriers
are located between the vacJt..m interrupters or along the
sides.
This section describestne operationof eacr. '.:lajorsubassem-
bly as an aid
ir the operation, installation, maintenance and
repair of the GMI vacuum circuit breaker.
Figure 10: Front View ofGMI Breaker.
8
Vacuum Interrupters and Primary Disconnects
The operating principle of the GMI vac:.ium interrupter is
simple. Figure 11 is a cutaway view of a typical vacuum
interrupter. The entire assembly
is sealed after a vacuum is
established. The interrupterstationarycontactisconnectedto
the upper disconnect stud of the circuit breaker. The inter-
rupter movable contact
is conrected to the lower disconnect
stud and driving!'1echanism ofthe circuit breaker. The metal
bellowsassemblyprovidesa secure seal around the movable
contact. preventing loss of vac;.Jum while permitting vertical
motion ofthe movable contact.
I
ll'I Y /JJ------
(' ~ .. ..
~-···
2
~J·;
. r.
s
····---MOVING
CONTACT
CURRENT
CONNECTION
Figure 11: Cutaway View otGMI Vacuum Interrupters.
When the two contacts separate an arc
is initiated which
continues conduction up to the following current zero.
At
current zero, the arc extinguishes and any conductive metal
vapor which has been created by and supported the arc
condenses on the contacts and on the surrounding vapor
shield. Contact materials and configuration are optimized to
achieve arc motion and to minimize switching disturbances.
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