Download seminar - Voltimum

Janet Roadway
Product Manager, Power
Breakers
Curva Tempo-Corrente FFF
1E4s
1E3s
100s
10s
1s
0.1s
1E-2s
0.1kA
1kA
10kA
Discrimination of
protection devices
on installations
Topics of Discussion

Explaining the terminology

Degrees of discrimination

Different techniques to achieve discrimination

Backup protection

Protection devices

Any Questions?
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.
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……….
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
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
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
Discrimination
Needs
 Fast
Fault Detection
 Fast
Fault Elimination
 Let-Through
 High
Energy Reduction
Fault Current Withstanding
WAIT!
CONTINUITY OF
SERVICE
GO!
FAULT
FAULT DAMAGE
Explaining the terminology
X
A
XB
Fault occurs here
XC
Degrees of discrimination

Total Discrimination

This means that the isolation described occurs for all fault
levels possible at each point of the circuit
Degrees of discrimination
t
B
A
Prospective Fault
Current Icc
I
Degrees of discrimination

Partial Discrimination

This means that above certain current levels there is
simultaneous operation of more than one protection device
Degrees of discrimination
t
B
A
Prospective Fault
Current Icc
I
Discrimination
Traditional solutions
 Current
 Time
discrimination
 Energy
 Zone
discrimination
discrimination
(logical) discrimination
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.
Discrimination
Current discrimination

An example:
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
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
Discrimination
Electronic release
Time discrimination

An example:
L (Long delay)
S (Short delay)
I (IST)
E4S 4000 PR111-LSI R4000
Setting: 0.9
Curve: B
Setting: 8
Curve: D
Off
E3N 2500 PR111-LSI R2500
Setting: 1
Curve: A
Setting: 10
Curve: C
Off
S7H 1600 PR211-LSI R1600
Setting: 1
Curve: A
Setting: 10
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
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
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 circuitbreaker upstream is lower than the energy value needed to complete
the opening of the CB downstream
Discrimination
Energy discrimination

An example:
Energy
discrimination
up to 24 kA
Time-currents Curve
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
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 3
Zone 2
Zone 1

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
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
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
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
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
WAIT!
CONTINUITY OF
SERVICE
GO!
FAULT
FAULT DAMAGE
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
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
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 coordination of this type.
Types of protection available

Fuses

Miniature Circuit Breakers

Moulded Case Circuit breakers

Air Circuit breakers
Typical fuse
Ultra
Reliable
Standard
Time (s)
High
Characteristic
current limitation
effects
High
threshold on low
overloads ( clears overloads
at approx 1.45x rated FLC)
Current (A)
Fuseless technology

Two main types:-

Thermomagnetic protectionMCB 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
Thermomagnetic
Offer
thermal longtime
overcurrent protection using Bimetal technology ( operates at
1.3x FLC)
Time (s)
Thermal
curve
Uses
the magnetic effect of
short circuit currents to offer
shorttime short circuit
protection
Magnetic curve
Current (A)
Electronic Relays

Overcurrent functions such as:Long
Time (s)
time overcurrent
Short
time instantaneous
protection
Short
time time delayed
protection
Ground
fault or Earth fault
protection
Current (A)
Electronic Relays

Overcurrent functions such as:Long
Time (s)
time overcurrent
Short
time instantaneous
protection
Short
time time delayed
protection
Ground
fault or Earth fault
protection
Current (A)
Protection releases: general features
 Complete set of standard protection functions
MORE
Rc
D
U
RV
OT
UV
OV
RP
 Complete set of advanced protection functions
MORE
A
V
Hz

 Complete set of measurements functions
W
VA
VAR
E
THD
MORE
Data logger: a professional built-in fault recorder.
500
Voltage L1-L2
400
Neutral
Current phase 1
300
Current phase 2
200
Current phase 3
100
-100
time
0
-200
-300
-400
-500
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.
BACK
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
Protection releases: news on standard protection functions

Double S*

Used to obtain discrimination in “critical” conditions
MORE

Double G*

Two different protection curves, one with the signal coming from
internal CTs and the other from an external toroid
MORE

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)
MORE
BACK
* = These features are available on PR123/P
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
Protection releases: news on standard protection functions
Without double S
Protection releases: news on standard protection functions
BACK
With double S
Protection releases: news on standard protection functions

Double G

It’s 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 circuitbreaker
MV
LV
Restricted Earth Fault
Protection releases: news on standard protection functions

Double G

It’s 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 circuitbreaker

Unrestricted Earth Fault: the fault is downstream the LV circuitbreaker
MV
LV
Unrestricted Earth Fault
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
L1
Trafo secondary windings
Emax internal CTs
L2
L3
External toroid
N
PE
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
L1
Trafo secondary
windings
Emax internal CTs
L2
L3
BACK
External
toroid
N
PE
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
Protection releases: news on standard protection functions

Dual setting


“Normal” network condition

CB “A” >>> closed

CB “B” >>> open
Discrimination is guaranteed
between A and C
Protection releases: news on standard protection functions

Dual setting


“Emergency” network
condition

CB “A” >>> open

CB “B” >>> closed
Discrimination is not
guaranteed between B and
C, due to the “low” settings
(protection of the generator)
of C protection functions
Protection releases: news on standard protection functions

Dual setting


“Emergency” network
condition

CB “A” >>> open

CB “B” >>> closed
Discrimination is
guaranteed between B
and C thanks to the
second set of
protection parameters
BACK
Protection releases: advanced protection functions
RC
Residual current
D
Protection against directional short-circuit with adjustable time-delay
U
Protection against phase unbalance
OT
Protection against overtemperature (check)
UV
Protection against undervoltage
OV
Protection against overvoltage
RV
Protection against residual voltage
RP
Protection against reverse active power
M
Thermal memory for functions L and S
UF
Underfrequency
OF
Overfrequency
BACK
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 @50Hz)
BACK
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 @50Hz)
BACK