Discrimination of protection devices on installations

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Discrimination of protection devices on
installations

• Janet Roadway
• Product Manager, Power Breakers

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Topics of Discussion

• Explaining the terminology
• Degrees of discrimination
• Different techniques to achieve discrimination
• Backup protection
• Protection devices
• Any Questions?

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Protection - Basics

• Lets go back to basics

• Question Why do we use protection devices????
• Common Ans To prevent Faults

Wrong! Protection whether by fuse, circuit
breaker or relay cannot prevent faults from
happening. Only good design, high quality
components, careful installation, preventative
maintenance along with good working practices can
prevent major faults However, protection devices
can limit the damage and inconvenience caused if
faults occur.
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Protection - Overload

• What do we mean by a fault?
• Overload
• Operating condition in an electrically undamaged
  circuit which causes an current to flow in excess
  of the full load current
• Example Starting condition during DOL start
• If this type of fault continues indefinitely
  because of an anomolous operating condition.,
  damage begins to occur creating.

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Protection Short Circuit

• What do we mean by a fault?
• Short Circuit
• Operating condition in an electrically damaged
  circuit where there is an accidental or
  intentional connection by a relatively low
  resistance between two points of a circuit which
  are normally at different voltages
• This type of fault can generate high current
  flows, arcing and fire if not cleared quickly

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Discrimination

• Coordinate devices to
• Guarantee safety for people and installations
• Identify and exclude only the zone affected by a
  problem
• Limiting the effects of a malfunction
• Reducing the stress on components in the affected
  zone
• Ensuring service continuity with good quality
  supply voltage
• Achieving a valid compromise between reliability,
  simplicity and cost effectiveness

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Explaining the terminology

• Discrimination or Selectivity
• To make it possible to isolate a part of an
  installation involved in a fault condition from
  the overall system such that only the device
  located immediately on the supply side of the
  fault intervenes

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Discrimination

• Needs
• Fast Fault Detection
• Fast Fault Elimination
• Let-Through Energy Reduction
• High Fault Current Withstanding

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Explaining the terminology
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Degrees of discrimination

• Total Discrimination
• This means that the isolation described occurs
  for all fault levels possible at each point of
  the circuit

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Degrees of discrimination
t
A
B
Prospective Fault Current Icc
I
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Degrees of discrimination

• Partial Discrimination
• This means that above certain current levels
  there is simultaneous operation of more than one
  protection device

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Degrees of discrimination
t
A
B
Prospective Fault Current Icc
I
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Discrimination

• Traditional solutions
• Current discrimination
• Time discrimination
• Energy discrimination
• Zone (logical) discrimination

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Discrimination

• Current discrimination
• Discrimination among devices with different trip
  threshold setting in order to avoid overlapping
  areas.
• Setting different device trip thresholds for
  different hierarchical levels.

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Discrimination

• Current discrimination
• An example

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Discrimination

• Current discrimination
• Applications
• final distribution network with low
• rated current and low short-circuit current
• ACB chains
• Fault area short circuit and overload
• Discrimination limit current low
• Discrimination levels low
• Devices ACBs, MCCBs and devices with
  time/current curves
  (contactors with thermal relays, fuses )
• Feasibility discrimination study easy
• Customer cost low

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Discrimination

• Time discrimination
• Discrimination among devices with different trip
  time settings in order to avoid overlapping areas
• Setting different device trip delays for
  different hierarchical levels

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Discrimination
Electronic release
L (Long delay)
S (Short delay)
I (IST)
Setting 0.9 Curve B Setting 1 Curve
A Setting 1 Curve A
Setting 8 Curve D Setting 10 Curve C

• Time discrimination
• An example

E4S 4000 PR111-LSI R4000 E3N 2500 PR111-LSI
R2500 S7H 1600 PR211-LSI R1600
Off Off Setting 10
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Discrimination

• Time discrimination
• Applications low complexity plant
• Fault area short circuit and overload
• Discrimination limit current low, depending
  on the Icw of the upstream device
• Discrimination levels low, depending on the
  network
• Devices ACBs, MCCBs and devices with adjustable
  time curves
• Feasibility discrimination study easy
• Customer cost medium

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Types of Discrimination

• Energy Discrimination
• Many Low Voltage protection devices such as
  Circuit breakers and Fuses have the ability to
  limit the peak of the current let through them to
  a value lower than the prospective short circuit
  peak.
• Any protective device which clears short circuits
  in less than 1/2 cycle of the sinusoidal wave
  (i.e 10mS for 50Hz) will current limit to a
  certain degree
• Energy based discrimination is the only way to
  determine true discrimination between
  current-limiting devices

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Discrimination

• Energy discrimination
• Discrimination among devices with different
  mechanical and electrical behaviour depending on
  energy level
• It is necessary to verify that the let-through
  energy of the circuit-breaker upstream is lower
  than the energy value needed to complete the
  opening of the CB downstream

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Discrimination

• Energy discrimination
• An example

Time-currents Curve
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Discrimination

• Energy discrimination
• Applications medium complexity networks
• Fault area Short circuit only
• Discrimination limit current medium/high
• Discrimination levels medium, CBs size
  dependent
• Devices ACBs, MCCBs, MCBs Fuses
• Feasibility discrimination study medium
  complexity
• Customer cost medium

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Discrimination

• Zone discrimination
• Discrimination among devices in order to isolate
  the fault zone keeping unchanged feeding
  conditions of maximum number of devices
• Zone discrimination is implemented by means of an
  electrical interlock between devices

Zone 1
Zone 2
Zone 3
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Discrimination

• Zone discrimination
• Applications high complexity plant
• Fault area short circuit, overload, ground fault
• Discrimination limit current medium,
  depending on
  Icw
• Discrimination levels high
• Devices ACBs, MCCBs with dialogue and control
  features
• Feasibility discrimination study complex
• Customer cost high

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Explaining the terminology

• Cascading or Backup protection
• Uses supply circuit breakers or fuses with
  current limitation effects to protect downstream
  devices from damage
• The amount of energy let through (i2t) by the
  supply device needs to be lower than that which
  can be withstood without damage by the device on
  the load side
• By using this effect it is possible to install
  devices downstream that have short circuit
  breaking capacities lower than the prospective
  short circuit current

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Back-up protection/Cascading

• Back-up protection or Cascading is recognised and
  permitted by the 16th Edition of the IEE Wiring
  Regulations 434-03-01 and is covered by IEC
  364-4-437 standard

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Why Use Back-up Protection?

• Substantial savings can be made on downstream
  switchgear and enclosures by using lower short
  circuit ratings
• Substantial reductions in switchgear volumes can
  also result

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What about Discrimination?

• Backup protection should not be confused with
  discrimination.
• Backup protection does not infer discrimination
  can be achieved but in practice, discrimination
  is normally achieved up to the maximum breaking
  capacity of the downstream device

BACKUP
Discrimination
GO!
WAIT!
CONTINUITY OF SERVICE
FAULT
FAULT DAMAGE
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Practical Example

• Problem
• Installation requires the use of Busbar rather
  than cable to distribute electrical power.
• Fault level calculations reveal 25kA prospective
  fault level at the point of installation of
  standard MCB distribution board

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Practical Example

• Solution -
• Using a standard Isolator as the distribution
  board incoming device - all the MCBs would need
  to be 25kA or above
• Using an MCCB as the incoming device such as an
  ABB Tmax T3N250TMD100, 6kA S200 MCBs could be
  safely used

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A word of caution ...

• Back-up protection can only be checked by
  laboratory tests and so only device combinations
  specified by the manufacturer can be guaranteed
  to provide co-ordination of this type.

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Types of protection available

• Fuses
• Miniature Circuit Breakers
• Moulded Case Circuit breakers
• Air Circuit breakers

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Typical fuse

• Ultra Reliable
• Standard Characteristic
• High current limitation effects
• High threshold on low overloads ( clears
  overloads at approx 1.45x rated FLC)

Time (s)
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Fuseless technology

• Two main types-
• Thermomagnetic protection- MCB and lower rated
  MCCB plus older type protection relays
• Electronic protection Microprocessor based
  relays fed from CTs either external to switches
  or integral within a circuit breaker

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Thermomagnetic

• Offer thermal longtime overcurrent protection
  using Bi-metal technology ( operates at 1.3x FLC)
• Uses the magnetic effect of short circuit
  currents to offer shorttime short circuit
  protection

Thermal curve
Magnetic curve
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Electronic Relays

• Overcurrent functions such as-
• Long time overcurrent
• Short time instantaneous protection
• Short time time delayed protection
• Ground fault or Earth fault protection

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Electronic Relays

• Overcurrent functions such as-
• Long time overcurrent
• Short time instantaneous protection
• Short time time delayed protection
• Ground fault or Earth fault protection

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Protection releases general features
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Data logger a professional built-in fault
recorder.

• Data logger a professional built-in
  fault recorder.
• Standard in PR122 and PR123
• Recording of 8 measurements (currents and
  voltages)
• Configurable trigger (i.e. During a fault)
• Sampling frequency up to 4.800kHz
• Sampling time up to 27s
• Output data through SD-Pocket or TestBus2.
• Exclusive from ABB SACE.

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Conclusion

• So what is the secret to achieving a successful
  discrimination study
• The secret is to be aware of the capability of
  the technology you are using and to design your
  installation within the limits of the protection
  you have chosen

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Protection releases news on standard protection
functions

• Double S
• Used to obtain discrimination in critical
  conditions
• Double G
• Two different protection curves, one with the
  signal coming from internal CTs and the other
  from an external toroid
• Dual Setting
• Two different set of protection parameters in
  order to protect in the best way, two different
  network configurations (e.g. normal supply and
  emergency supply)

These features are available on PR123/P
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Protection releases news on standard protection
functions

• Double S
• low setting on S protection function due to the
  settings on MV circuit-breaker
• The circuit-breaker on LV side of the LV-LV trafo
  needs high settings due to the inrush current

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Protection releases news on standard protection
functions
Without double S
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Protection releases news on standard protection
functions
With double S
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Protection releases news on standard protection
functions

• Double G
• Its possible to protect the network, with the
  same protection release, against earth fault both
  upstream and downstream the circuit-breaker
• Restricted Earth Fault the fault is upstream the
  LV circuit-breaker

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Protection releases news on standard protection
functions

• Double G
• Its possible to protect the network, with the
  same protection release, against earth fault both
  upstream and downstream the circuit-breaker
• Restricted Earth Fault the fault is upstream the
  LV circuit-breaker
• Unrestricted Earth Fault the fault is downstream
  the LV circuit-breaker

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Protection releases news on standard protection
functions

• Double G
• The combination of both Unrestricted and
  Restricted Earth Fault protection is named
  Source Ground Return. The new PR123/P is able
  to detect and to discriminate both earth faults
• If the fault is downstream the LV circuit-breaker
  the PR123/P will trip Emax circuit-breaker

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Protection releases news on standard protection
functions

• Double G
• The combination of both Unrestricted and
  Restricted Earth Fault protection is named
  Source Ground Return. The new PR123/P is able
  to detect and to discriminate both earth faults
• If the fault is downstream the LV circuit-breaker
  the PR123/P will trip Emax circuit-breaker
• If the fault is upstream the LV circuit-breaker
  the PR123/P will trip the MV circuit-breaker

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Protection releases news on standard protection
functions

• Dual setting
• It allows to program two different protection
  parameter sets in order to adapt them to the
  different network configurations
• The most representative example is a network with
  supply by the utility and by emergency generator
• With dual setting the discrimination between CBs
  is guaranteed in both network conditions

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Protection releases news on standard protection
functions

• Dual setting
• Normal network condition
• CB A gtgtgt closed
• CB B gtgtgt open
• Discrimination is guaranteed between A and C

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Protection releases news on standard protection
functions

• Dual setting
• Emergency network condition
• CB A gtgtgt open
• CB B gtgtgt closed
• Discrimination is not guaranteed between B and C,
  due to the low settings (protection of the
  generator) of C protection functions

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Protection releases news on standard protection
functions

• Dual setting
• Emergency network condition
• CB A gtgtgt open
• CB B gtgtgt closed
• Discrimination is guaranteed between B and C
  thanks to the second set of protection parameters

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Protection releases advanced protection functions

Residual current
RC
D
Protection against directional short-circuit with
adjustable time-delay
Protection against phase unbalance
U
Protection against overtemperature (check)
OT
Protection against undervoltage
UV
Protection against overvoltage
OV
Protection against residual voltage
RV
Protection against reverse active power
RP
Thermal memory for functions L and S
M
Underfrequency
UF
Overfrequency
OF
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Protection releases measurements functions
Current (phases, neutral, earth fault).
Accuracy 1,5

Voltage (phase-phase, phase-neutral, residual).
Accuracy 1
Power (active, reactive, apparent) Accuracy
2,5
Power factor Accuracy 2,5
Frequency and peak factor Accuracy 0,1Hz
Energy (active, reactive, apparent,
meter) Accuracy 2,5
Harmonics calculation (display of waveforms and
RMS spectrum up to 40th _at_50Hz)
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Protection releases measurements functions
Current (phases, neutral, earth fault).
Accuracy 1,5

Voltage (phase-phase, phase-neutral, residual).
Accuracy 1
Power (active, reactive, apparent) Accuracy
2,5
Power factor Accuracy 2,5
Frequency and peak factor Accuracy 0,1Hz
Energy (active, reactive, apparent,
meter) Accuracy 2,5
Harmonics calculation (display of waveforms and
RMS spectrum up to 40th _at_50Hz)