12a-Case-study-DRM-HV-breaker
1
Static vs. Dynamic Contact Resistance
Qaisar.khan@omicronenergy.com
© OMICRON
© OMICRON Academy
Page 1
01-Introduction-CBR-testing
Page 2
What is a circuit breaker?
Definition of a circuit breaker
 Automatically operated electrical switch designed to protect an electrical circuit from damage caused
by overload or short circuit
 Basic function: immediately discontinues electrical flow
Ideal switch
making
carrying
breaking
© OMICRON
According to IEC 62271-100 and ANSI C37.100-1992 a circuit breaker is a mechanical switching device,
capable of making, carrying and breaking currents under normal circuit conditions and also making, carrying
for a specified time and breaking currents under specified abnormal conditions such as short circuit.
© OMICRON Academy
Page 2
01-Introduction-CBR-testing
Page 3
What is a circuit breaker?
Static behavior
 Carry operational currents
 Insulating HV parts to ground
 Isolating faulted parts to the grid (in case the breaker is open)
Dynamic behavior
 Breaking and making operational currents
 Breaking and making fault currents (fault clearance)
© OMICRON
The main task of a circuit breaker is to interrupt operational + fault currents and to isolate faulty parts such as
overhead lines, cables, transformers, generators, etc. from the system. Hence a circuit breaker has a dynamic
behavior (breaking and making operational and fault currents) and a static behavior (carry operational currents
and insulating HV parts to ground).
In regards to the current the wording "break" and "make" is used whereas in regards to the action "open" and
"close" is used.
A circuit breaker is controlled by the protection device of the corresponding asset and the SCADA system
which allows controlling the grid by remote.
© OMICRON Academy
Page 3
01-Introduction-CBR-testing
Page 4
Overview components
Example: Live-Tank circuit breaker
Interrupter unit(s)

Breaking chamber, interrupter chamber,
interrupter housing, etc.

Contains interrupter, interrupting medium
Support insulator

Line-to-ground insulator

Contains insulated pull-rod,
mechanical linkage, insulating
medium
Operating mechanism & control

Stored energy, secondary wiring
© OMICRON
Depending on location of in the electrical network, network design and region several design of circuit
breakers are common – which is discussed in later more in detail. All of them consist of following three main
components
Interrupter unit(s)
Support insulator
Operating mechanism & control unit
© OMICRON Academy
Page 4
04a-Methods-MV-HV-breakers
Page 5
Circuit breaker components
Mechanical
linkage
Interrupter
 Components
Control
Operating
mechanism
© OMICRON
The trip or close command from any control device is forwarded to the circuit breakers' main contacts via the
functional chain. The functional chain consists of the following parts:
Control: This is the control device of the circuit breaker, e.g. the protection device. For HV circuit breakers this
part is not included directly in the circuit breaker. But some MV breakers are equipped with the protection
device itself.
Operating mechanism: Coils, armatures and the drive itself (spring, hydraulic, pneumatic, magnetic)
Mechanical linkage: Linkage between the drive and the interrupter. In order to obtain synchronicity of the
breaker's main contacts the mechanical linkage can be tuned via screws.
Interrupter: Main contacts of the circuit breaker
© OMICRON Academy
Page 5
04a-Methods-MV-HV-breakers
Page 6
Typical test on circuit breakers?
 Coil current profile analysis
 Under- & overvoltage tests
Mechanical
linkage
 Pick-up tests
Interrupter
Performance of control circuits
Control
Operating
mechanism
© OMICRON
© OMICRON Academy
Page 6
04a-Methods-MV-HV-breakers
Page 7
Typical test on circuit breakers?
 Motor current analysis
 Current trace
 Inrush current
Interrupter
Test performance of charging motor
 Under- & overvoltage tests
Mechanical
linkage
 Charging time
Control
Operating
mechanism
© OMICRON
© OMICRON Academy
Page 7
04a-Methods-MV-HV-breakers
Page 8
Typical test on circuit breakers?
 Timing of main and auxiliary contacts
Mechanical
linkage
 Contact travel (motion) of main contacts
Interrupter
Test performance of kinematic chain
Control
Operating
mechanism
© OMICRON
© OMICRON Academy
Page 8
04a-Methods-MV-HV-breakers
Page 9
Typical test on circuit breakers?
Mechanical
linkage
Static Contact Resistance
Dynamic Contact Resistance
Interrupter
 Identify contact wear and tear of main and arcing contacts
Control
Operating
mechanism
© OMICRON
© OMICRON Academy
Page 9
04a-Methods-MV-HV-breakers
Page 10
Contact wear and tear of main contacts
Static Contact Resistance
Motivation
Measurement done
 Check the status of the main contact/bus bar
junctions
 Using the four-point resistance measurement
method
 The ability to carry the rated current without big
losses
 Injection current level
 50[A] (IEC)
 100[A] (ANSI)
Analysis
 Resistance value
 Typical value between 10 to 100 [µΩ]
 Comparing to previous results
 High variations between phases
© OMICRON
One very common and “simple” test is the static contact resistance test.
It is done to check the status of the main contact (and/or also bus bar junctions)
The test is done when breaker is closed using the four-point resistance measurement method. This is done to
exclude the resistance from test leads in the end value.
For the analysis, the resistance value is checked against the manufacturer specifications, comparing the
values between the phases and with the previous results if available.
© OMICRON Academy
Page 10
04a-Methods-MV-HV-breakers
Contact wear and tear of main contacts
Page 11
Static/contact resistance test (µΩ)
 Micro-ohm (µΩ) meter
 Validates resistance of primary path
 Ensures low losses of load current
 Can be used for circuit breakers,
bus bar joints, etc.
 Measurement method
 Inject a high current
 Measure small voltage in a
noisy environment
 Use 4-wire technique for
connection
 Unique CIBANO 500 features
 Same wiring setup as for the timing test
 Short lightweight high-current cables
 Eliminate capacitive interference
 Allow easy wiring setup
© OMICRON
Principle
The principle of contact resistance measurement (µΩ meter test) is to measure the resistance in static
position: breaker closed.
A high current is injected between the breaking elements (direction of line) and measure the voltage drop
(line-ground). As the contact resistance is in µΩ- range a 4-wire measurement has to be applied, as otherwise
the resistance of the test leads (mΩ- range) falsify the results.
Conventional method
Disadvantage of using conventional units is the confusingly wiring effort for breakers with several interrupting
units. Connection mistakes are highly possible. Furthermore the measurement can be affected due to long
connection leads → inductive loop (antenna).
Method with CIBANO
The usage of contact modules CB MC2 reduces the effort and complexity of wiring. The screened Ethernet
cables for power supply (Power over Ethernet = PoE) and data communication to CIBANO 500 main unit are
not affected by noise.
© OMICRON Academy
Page 11
04a-Methods-MV-HV-breakers
Performance of trip and close components
Page 12
 Dynamic Contact Resistance (DRM)/Timing test
Motivation
Measurement done
 Check the timing to ensure a safe and reliable circuit
breaker operation
 Using four-point resistance measurement method
 Checking the arcing contact wear
 Often together with contact travel
 Check misalignment and/or wrong assembly in the
interrupter
 Different sequences possible
 O, C
 OC (reclose)
 CO (trip-free)
 O-CO (auto-reclosing)
 Analysis
 Operating times & Synchronicity
 per phase and between phases
 Resistance curves
 Comparing to previous results
 Contact wipe
 Arcing contact length
 Comparing to previous results
© OMICRON
© OMICRON Academy
Page 12
04a-Methods-MV-HV-breakers
Page 13
Contact wear and tear of main contacts
Why Dynamic contact resistance (DRM)?
 Static Resistance Measurement = pic 1 + pic 9
 Dynamic Resistance Measurement = pic 1 + pic 2 + ..... + pic 9
6
7
8
9
5
4
3
2
1
© OMICRON
What are arguments for performing a Dynamic Resistance Measurement (DRM) instead of a conventional
Static Contact Resistance measurement? Well it may become quite obvious comparing the sequences of a
circuit breaker operation with the jump of a motocross racer in the picture shown above.
Static Contact Resistance does only provide us an insight of the main contacts condition (resistance) in
defined open and close state. Represented by picture 1 = takeoff (open) and picture 9 = landing (close).
Dynamic Contact Resistance allows us to have a better insight of the main contacts condition (resistance)
during whole process of the movement. This allows us to see the condition of the arcing but also main
contacts providing information of resistance, timing and motion/travel (represented by picture 1+ picture 2 + ...
picture 9).
© OMICRON Academy
Page 13
04a-Methods-MV-HV-breakers
Page 14
Contact wear and tear of main contacts
Dynamic contact resistance (DRM)
 Records contact resistance
during breaker operation
(resistance over time)
 Combination of contact
resistance, timing and
travel measurements
 Use DRM to find out
The arcing contact length
Contact finger problems
Lubrication problems
Main contact
Contact travel
Arcing contact length
Resistance
 Procedure
Inject high current
Start recording current
and voltage
Operate circuit breaker
Calculate resistance
Start of
contact travel
Separation of
main contact
Arcing contact
is seperated
© OMICRON
A dynamic contact resistance measurement is a commonly used method, because it determines the contact
length without having to disassemble the circuit breaker.
When the arcing contact becomes shorter than the minimum requirement specified by the circuit breaker
manufacturer, a safe operation can no longer be guaranteed and the interrupter unit needs to be maintained
properly.
In order to apply that method it is important to know the components of an SF6 circuit breaker interrupter unit
and how the current is interrupted during an open operation
Principle
The principle of Dynamic Resistance measurement (DRM) is to combine all information contact resistance,
timing, coil currents and travel (motion) into one diagram for the different operations. Thereby the whole
operation can be analyzed to find out arcing problems (e.g. bouncing), contact finger problems.
Method with CIBANO
For DRM measurement CIBANO 500 main unit, contact modules CB MC2 and transducer note CB TN3 is
used. No re-wiring needed!
© OMICRON Academy
Page 14
04a-Methods-MV-HV-breakers
Page 15
Contact wear and tear of main contacts
 Dynamic contact resistance (DRM)
Closed position
Arcing
Idc
Open position
R<100μΩ
R>>100μΩ
2 Stationary arcing contact
7 Stationary main contact
3 Moving arcing contact
8 Moving main contact
© OMICRON
Analyze the conductive integrity of the main contacts in closed position.
When the circuit breaker is and stays in the closed position, the current injected flows through the main
contact because it has an ohmic resistance, most of the times, lower than 100μΩ. However the arcing contact
has an ohmic resistance much higher than 100μΩ.
© OMICRON Academy
Page 15
04a-Methods-MV-HV-breakers
Page 16
Contact wear and tear of main contacts
 Dynamic contact resistance (DRM)
Closed position
Arcing
Open position
Idc
R<100μΩ
2 Stationary arcing contact
7 Stationary main contact
3 Moving arcing contact
8 Moving main contact
R>>100μΩ
© OMICRON
When the main contact is already opened but the arcing contact stays closed, the current injected will flow
through the arcing contact.
Tungsten copper (WCu) materials are used for arcing contacts in SF6 circuit breakers for high and medium
voltage applications. At the heart of the switching chamber, WCu arcing contacts are exposed to extreme
mechanical and thermal stresses, with temperatures ≥ 20,000 K being reached during arcing.
Tungsten-copper has unique material properties. A high level of temperature resistance is one of the most
important advantages of tungsten, while the copper content increases the electrical and thermal conductivity.
© OMICRON Academy
Page 16
04a-Methods-MV-HV-breakers
Page 17
Contact wear and tear of main contacts
 Dynamic contact resistance (DRM)
Source: SIEMENS
© OMICRON
Above example shows a Dynamic Resistance Measurement on Open [O] operation. Overlaying the
information of contact resistance and travel (motion) over time allows to refer to the arcing contact length.
© OMICRON Academy
Page 17
04a-Methods-MV-HV-breakers
Contact wear and tear of main contacts
Page 18
 Dynamic contact resistance (DRM)
Source: SIEMENS
© OMICRON
Animated Open [O} sequence
Circuit breaker in closed position. The trip (open) command is send and energizing the coil (black).
Once the energy is enough the latch hits the trigger, releasing the stored energy in the spring and the
armature starts to move. Until here the main contact is still is still carrying the operational currents. In the
same time SF6 is compressed in the puffer volume
Until the main contact is separated and the arcing contacts is taking over. The arcing contacts separate and
arcing is taking place and the arc and the arc extinguishing process starts. The arcing can be easily seen in
the resistance recorded over time as the resistance value is no more stable.
The arcing is taking as long the arc is fully extinguished. The measured resistance is now very high
impendent. The coil current is interrupted by the auxiliary contact and the armature moves until it’s end
position.
© OMICRON Academy
Page 18
04a-Methods-MV-HV-breakers
Contact wear and tear of main contacts
Page 19
 Dynamic contact resistance (DRM)
© OMICRON
Same sequence explained on a cutaway example.
© OMICRON Academy
Page 19
07a-Hardware-CIBANO-500+accessories
Page 20
CIBANO 500: 3-in-1 circuit breaker test system
 Multi-channel timing and travel analyzer
Checks the mechanical performance
Detects problems during coil actuation
Reveals defects of the trip or close coils
 High-accuracy micro-ohm (µ) meter
Assesses the condition of the main and arcing contacts and resistor switches
 Powerful coil and motor supply of 2.4 kW
Applies a stable DC voltage
level to the breaker, even
if a station battery is
not available
Timing and
travel analyzer
Digital
micro-ohm-meter
Coil and
motor supply of 2.4 kW
© OMICRON
With CIBANO 500, OMICRON has introduced the first ever 3-in-1 test system that can be used to test all
types of circuit breakers: medium- and high-voltage breakers with live- or dead-tank design. CIBANO 500
is unique in that it combines a micro-ohmmeter, timing analyzer, and circuit breaker supply in just one system.
This enables both standard tests, such as contact resistance measurement and switching time
analysis, as well as advanced tests, such as motion analysis and dynamic resistance measurement, to be
carried out with ease.
Thanks to the integrated circuit breaker supply, the user is able to freely adjust DC voltage with CIBANO 500
as well as simulate a circuit breaker supply with undervoltage without having to change the cabling. Thus it is
possible to test the circuit breaker during the commissioning of switchgear systems where no station battery is
available.
© OMICRON Academy
Page 20
07a-Hardware-CIBANO-500+accessories
Page 21
CIBANO 500 Hardware Overview
CB MC2
 Functional scheme
CIBANO 500
Digital
transmission
© OMICRON
The accessories main contact module CB MC2 and transducer node CB TN3 are powered via PoE+ (Power
over Ethernet) by the main device CIBANO 500. Over the EtherCAT® interface power supply and data
commination realized where a number of units can be connected as the based on serial bus technology.
© OMICRON Academy
Page 21
07a-Hardware-CIBANO-500+accessories
Main contact module CB MC2
Page 22
 2 high-current outputs and 2 sensitive voltage measurement
channels
 Output power source: powerful “super-capacitor”
 Same wiring set-up for all circuit breaker tests: no timeconsuming rewiring necessary
 Overall wiring minimized and clearly arranged
 Short high-current cables:
easier and faster measuring set-up
 Light-weight digital connection cables between CB MC2
modules and CIBANO 500: transmission of measuring results
without interference
 Powered via PoE+ (Power over Ethernet)
© OMICRON
The idea of main contact module CB MC2 is too minimize the wiring effort by using one module for each
phase of circuit breaker. By having 2 current output and 2 voltage measurement inputs using short cables can
be used to measure contact resistance, dynamic resistance measurement and timing tests.
The main advantage is that for all test no re-wiring is required and all wires are clearly visible arranged.
© OMICRON Academy
Page 22
07a-Hardware-CIBANO-500+accessories
Page 23
Main contact module CB MC2
2x 100 A DC
current output to
interrupting unit
Visualization LED
status indication
2x voltage/
binary input
voltage inputs
EtherCAT® with PoE+
to CIBANO 500 main unit
© OMICRON
Current output 1x 200A in case of a connecting to a CB with one interrupter unit
2x 100A in case of connecting of a connecting to a CB with two interrupter
unit
Voltage input
units
2x voltage input, one for each interrupter unit of a CB with two interrupter
Visualization LED
Indicating the status to identify which unit connected to which phase
EtherCAT® interface
power supply and data communication with CIBANO 500 main device
© OMICRON Academy
Page 23
06a-Performing-MV-HV-breakers
Page 24
Connection concept
Live-Tank circuit breaker
CB MC2
CB MC2
CB MC2
CB MC2
 Grounding on both sides of the interrupter unit
 CIBANO 500 + 3 x CB MC2 : all tests on 3-phase circuit breakers with one or two interrupters
CIBANO 500
© OMICRON
Page 24
Here a standard connection example of 3-phase SF6 Live-Tank Circuit breaker (ganged operation) shown.
Important: first always ground all interrupter units from both sides (to busbar and asset to be protected). For
each phase (with two interrupter units) on CB MC2 is connected. Use one CB TN3 and connect all 3
transducers (rotary/linear).
Connections of trip/close coils, motor and auxiliary has to be done depending on the wiring diagram of the
circuit breaker control.
© OMICRON Academy
Page 24
12a-Case-study-DRM-HV-breaker
Case study – Norway
SF6 Live tank CB, condition assessment
25
Time-optimized circuit breaker diagnostics with CIBANO 500
© OMICRON
© OMICRON Academy
Page 25
12a-Case-study-DRM-HV-breaker
Details about breaker
Page 26
315 kV Live-tank SF6 breaker
 Manufacturing year
1986
 Rated current
3,15 kA
 Rated s.c. current
40,0 kA
 Pole operation
ganged
 Operating mechanismpneumatic
© OMICRON
Inspection was scheduled for this 315kV Live-tank SF6 breaker during maintenance. Both measurement files
are in the chapter 10. Practical exercises:
2014-09-10_DRM-Norway-before-maintenance.ptm
2014-09-15_DRM-Norway-after-maintenance.ptm
© OMICRON Academy
Page 26
12a-Case-study-DRM-HV-breaker
Function principle
Page 27
 Interrupter unit – cutaway view
© OMICRON
© OMICRON Academy
Page 27
12a-Case-study-DRM-HV-breaker
Condition assessment // 2014-09-10
Page 28
 Contact resistance measurement
© OMICRON
The results of contact resistance measurement doesn’t provided much insight in the condition of the main &
arcing contacts. Just a deviation of the resistances in close position observed between the phases L1, L2, L3.
But no further assumptions can be made based on this results.
© OMICRON Academy
Page 28
12a-Case-study-DRM-HV-breaker
Condition assessment // 2014-09-10
Page 29
 Timing Close [C]
© OMICRON
First timing measurement for Close operation doesn’t provide much information so far.
© OMICRON Academy
Page 29
12a-Case-study-DRM-HV-breaker
Condition assessment // 2014-09-10
Page 30
 Timing Open [O]
© OMICRON
Same for timing measurement in open cycle.
© OMICRON Academy
Page 30
12a-Case-study-DRM-HV-breaker
Condition assessment // 2014-09-10
Page 31
 DRM Open [O] – resistances
© OMICRON
Another DRM measurement on open sequence indicates that the second interrupter unit in shows
discontinuity of the arcing contacts which would lead to heavy arcing.
© OMICRON Academy
Page 31
12a-Case-study-DRM-HV-breaker
Before maintenance
Page 32
 Main contacts
© OMICRON
As a result of the DRM results it was decided to take the interrupter unit to the workshop for inspection and
maintenance. Especially on the right picture heavy arcing can be observed on the main contacts at the
location of the contact fingers.
© OMICRON Academy
Page 32
12a-Case-study-DRM-HV-breaker
Before maintenance
Page 33
 Arcing contact
© OMICRON
As well the female arcing contact showed heavy wear.
© OMICRON Academy
Page 33
12a-Case-study-DRM-HV-breaker
After maintenance
Page 34
 Main and arcing contact
© OMICRON
Main contact was completely renewed and the arcing contact polished.
© OMICRON Academy
Page 34
12a-Case-study-DRM-HV-breaker
After maintenance // 2014-09-15
Page 35
 Contact resistance measurement
© OMICRON
After re-building the interrupter units and assembling back the breaker the measurement was repeated. The
contact resistance measurement shows now equal resistance in close positon after maintenance in all 3 poles.
© OMICRON Academy
Page 35
12a-Case-study-DRM-HV-breaker
Page 36
After maintenance // 2014-09-15
 DRM Open [O] – resistances
© OMICRON
Repeating the DRM measurements in open position show proper performance when the arcing contact is
taking over the current flow from the main contact. No interruption any more!
© OMICRON Academy
Page 36
12a-Case-study-DRM-HV-breaker
After maintenance // 2014-09-15
Page 37
 DRM Open [O] – currents
© OMICRON
Same measurement with view of currents over time instead of contact resistance.
© OMICRON Academy
Page 37
09-Assessment-CBR-measurements
38
Assessment examples
Time-optimized circuit breaker diagnostics with CIBANO 500
© OMICRON
© OMICRON Academy
Page 38
09-Assessment-CBR-measurements
Case study 1 – Assessment Timing vs DRM
Page 39
© OMICRON
© OMICRON Academy
Page 39
09-Assessment-CBR-measurements
Case study 1 – Assessment Timing vs DRM
Page 40
© OMICRON
© OMICRON Academy
Page 40
09-Assessment-CBR-measurements
Case study 1 – Assessment Timing vs DRM
Page 41
Start of contact travel
Main contact is separated
© OMICRON
This dynamic resistance measurement during opening of the circuit breaker shows that the main contact could
have something. Normally when the movement starts there will be a small change in the resistance due to
friction and a bigger increase of the resistance when the transaction from main contact to arcing contact takes
place, but in this case the bigger change is taking place immediately when the contact travel starts. This
indicates that there is either a contact problem i.e. loose main contacts (fingers) or the main contact has
contamination on the surface due to wear. But it could also be that the clamps are not correct mounted and
are moving due to the vibration during operation.
© OMICRON Academy
Page 41
09-Assessment-CBR-measurements
Case study 2 – Assessment Timing vs DRM
Page 42
© OMICRON
© OMICRON Academy
Page 42
09-Assessment-CBR-measurements
Case study 2 – Assessment Timing vs DRM
Page 43
© OMICRON
The dynamic resistance measurement during closing of the circuit breaker shows that the contamination of the
main contact surface can be excluded as the behavior is continuing also after that the main contact has reach
it end position. This indicates more in direction loose main contacts (fingers) or badly mounted clamps.
© OMICRON Academy
Page 43
09-Assessment-CBR-measurements
Case study 2 – Assessment with DRM
Page 44
 Phase B: worn out arcing contact?
© OMICRON
This dynamic resistance measurement during opening of the circuit breaker shows that the main contact for
phase LB has something. In this measurement the resistance change is small when the contact travel starts
(due to friction), which is okay, but when the transaction from main contact to arcing contact takes place the
resistance value starts to have high peaks until the arcing contact is opened. This indicates that there is
probably a contact problem e.g. arcing contact in bad condition due to wear. The next slides shows the same
even clearer when the current trace is enabled instead.
© OMICRON Academy
Page 44
09-Assessment-CBR-measurements
Case study 3 – Assessment with DRM
Page 46
Example 1: SF6 MV CB – discontinuity of main contact
discontinuity
on red phase
Source: Schneider Electric
© OMICRON
Above DRM measurement on a SF6 MV Circuit breaker shows a good example of discontinuity of one phase.
For a short moment the main contact losses continuity before the arcing contact is taking over which can lead
to serious arcing and heavy wear off the main contacts.
Measurement of contact resistance in both states open-close would show any problem.
09 - Assessment examples
Page 46
09-Assessment-CBR-measurements
Case study 3 – Assessment with DRM
Page 47
Example 1: SF6 MV CB – discontinuity of main contact
travel (mm)
DRM (Ω)
coil current (A)
Video: Schneider Electric
© OMICRON
Above shows the same before on an Open sequence and corresponding DRM measurement but just
animated.
09 - Assessment examples
Page 47