Download - DA Class About Relays 26122014
-
8/10/2019 DA Class About Relays 26122014
1/45
BASIC
PROTECTION AND
RELAYINGSCHEMES
-
8/10/2019 DA Class About Relays 26122014
2/45
Why protection is needed
Principles and elements of the protection
system
Basic protection schemes
Digital relay advantages and enhancements
THE BASIC QUESTIONS
-
8/10/2019 DA Class About Relays 26122014
3/45
WHY STUDY THIS PROTECTION SCHEME??
Protection scheme plays a vital & important role for
the normal operation or the steady state operation of
different components of power system network, which
must be reliable, fast and efficient.
In order to achieve all these features, it is essential
that these should be proper care in designing and
choosing an appropriate and efficient protection
scheme.
The protective relays functions as the brain behind the
whole schemes
-
8/10/2019 DA Class About Relays 26122014
4/45
DISTURBANCES: WHETHER LIGHT OR SEVERE
The power system must maintain acceptable operation 24
hours a day
Voltage and frequency must stay within certain limits
Small disturbances
The control system can handle these
Example: variation in transformer or generator load
Severe disturbances require a protection system
They can jeopardize the entire power system
They cannot be overcome by a control system
-
8/10/2019 DA Class About Relays 26122014
5/45
TYPICAL SHORT-CIRCUIT TYPE DISTRIBUTION
Single-Phase-Ground: 7080
Phase-Phase-Ground: 1710
Phase-Phase: 108
Three-Phase: 3
2
-
8/10/2019 DA Class About Relays 26122014
6/45
BALANCED VS.
UNBALANCED CONDITIONS
Balanced System Unbalanced System
cI
aI
bI
aI
cI
bI
-
8/10/2019 DA Class About Relays 26122014
7/45
DECOMPOSITION OF AN UNBALANCED SYSTEM
Positive-Sequence
Balanced Balanced
Negative-Sequence
1bI
1cI
1aI
2bI
2aI
2cI
0aI
0bI
0cI
aI
cI
bI
Zero-Sequence
Single-Phase
-
8/10/2019 DA Class About Relays 26122014
8/45
POWER SYSTEM PROTECTION
Operation during severe disturbances:
System element protection
System protection
Automatic reclosing
Automatic transfer to alternate power supplies
Automatic synchronization
-
8/10/2019 DA Class About Relays 26122014
9/45
DAMAGE TO MAIN EQUIPMENT
-
8/10/2019 DA Class About Relays 26122014
10/45
Loss of service in a large
area or population region
Hazard to human life
May result in enormous
economic losses
Overreaction of the
protection system
Bad design of the
protection system
BLACKOUTS
Characteristics Main Causes
-
8/10/2019 DA Class About Relays 26122014
11/45
SHORT CIRCUITS PRODUCE HIGH CURRENTS
FaultSubstation
a
bc
I
IWire
Three-Phase Line
Thousands of Amps
-
8/10/2019 DA Class About Relays 26122014
12/45
MECHANICAL DAMAGE DURING
SHORT CIRCUITS
Very destructive in busbars, isolators, supports, transformers, and machines
Damage is instantaneous
i1
i2
f1 f2
Rigid Conductors f1(t)= ki1(t) i2(t)
Mechanical
Forces
-
8/10/2019 DA Class About Relays 26122014
13/45
ESSENTIAL QUALITIES OF PROTECTION:
Reliability
Selectivity-
Absolute or relative Fastness
Discrimination
-
8/10/2019 DA Class About Relays 26122014
14/45
PROTECTION SYSTEM ELEMENTS
Protective relays
Circuit breakers
Current and voltage transducers
Communications channels
DC supply system
Control cables
-
8/10/2019 DA Class About Relays 26122014
15/45
HOW RELAYS ARE DIFFERENTIATED?
Can be differentiated based on:
* Functional categories
* Input quantities
*Operating Principles
* Performance Characteristics.
-
8/10/2019 DA Class About Relays 26122014
16/45
WHAT ARE VARIOUS TECHNIQUE USED?
* Electromechanical
*Solid state/Static
* Microprocessor/Numerical
-
8/10/2019 DA Class About Relays 26122014
17/45
NON-UNIT OR UNRESTRICTED PROTECTION :
No specific point downstream up to which protection will
protect
Will operate for faults on the protected equipment;
May also operate for faults on downstream equipment, which
has its own protection;
Need for discrimination with downstream protection, usually
by means of time grading.
-
8/10/2019 DA Class About Relays 26122014
18/45
UNIT OR RESTRICTED PROTECTION :
Has an accurately defined zone of
protection
An item of power system plant is protected
as a unit;
Will not operate for out of zone faults, thus
no back-up protection for downstream
faults.
-
8/10/2019 DA Class About Relays 26122014
19/45
TYPES OF RELAYS
As per function:
Main
Auxiliary
Signal
As per actuating quantity
Over relays
Under relays
-
8/10/2019 DA Class About Relays 26122014
20/45
METHODS OF DISCIMINATIONS:
To locate fault
by time
by current grading
by time and direction
by distance
by time, current and distance
by current balance
by power direction comparison
Type of fault
THREE PHASE DIAGRAM OF THE PROTECTION
-
8/10/2019 DA Class About Relays 26122014
21/45
THREE-PHASE DIAGRAM OF THE PROTECTION
TEAMCTs
VTs
Relay
CB
Control
ProtectedEquipment
-
8/10/2019 DA Class About Relays 26122014
22/45
DC TRIPPING CIRCUIT
SI
52
TC
DC Station
BatterySI
Relay
Contact
Relay
Circuit
Breaker
52a
+
Red
Lamp
-
8/10/2019 DA Class About Relays 26122014
23/45
HOW DO RELAYS DETECT FAULTS?
When a fault takes place, the current, voltage, frequency, and
other electrical variables behave in a peculiar way. For example:
Current suddenly increases
Voltage suddenly decreases
Relays can measure the currents and the voltages and detect
that there is an overcurrent, or an under volt ge, or a
combination of both
Many other detection principles determine the design of
protective relays
-
8/10/2019 DA Class About Relays 26122014
24/45
PRIMARY PROTECTION
-
8/10/2019 DA Class About Relays 26122014
25/45
PRIMARY PROTECTION ZONE OVERLAPPING
Protection
Zone B
Protection
Zone A
To Zone BRelays
To Zone A
Relays
52 Protection
Zone B
Protection
Zone A
To Zone B
Relays
To Zone A
Relays
52
-
8/10/2019 DA Class About Relays 26122014
26/45
BACKUP PROTECTION
AC D
E
Breaker 5
Fails
1 2 5 6 11 12
T
3 4 7 8 9 10
B F
-
8/10/2019 DA Class About Relays 26122014
27/45
POWER LINE PROTECTION PRINCIPLES
Overcurrent (50, 51, 50N, 51N)
Directional Overcurrent (67, 67N)
Distance (21, 21N)
Differential (87)
-
8/10/2019 DA Class About Relays 26122014
28/45
CHARACTERISTICS OF OVERCURRENT RELAYS:
Definite time
IDMT- inverse definite minimum
time
Very inverse
Extremely inverse
-
8/10/2019 DA Class About Relays 26122014
29/45
APPLICATION OF INVERSE-TYPE RELAYS
tRelay
Operation
Time
I
Fault Load
Radial Line
-
8/10/2019 DA Class About Relays 26122014
30/45
Distance
Distance
t
I
T
INVERSE-TIME RELAY COORDINATION
T T
-
8/10/2019 DA Class About Relays 26122014
31/45
50/51 RELAY COORDINATION
Distance
Distance
t
I
T T T
-
8/10/2019 DA Class About Relays 26122014
32/45
DIRECTIONAL OVERCURRENT PROTECTION
BASIC APPLICATIONS
K
L
-
8/10/2019 DA Class About Relays 26122014
33/45
DISTANCE RELAY PRINCIPLE
Three-Phase
Solid Fault
d
L
RadialLine21
Suppose Relay Is Designed to Operate
When:||||)8.0(|| 1 aLa IZV
cba III ,,
cba VVV ,,
-
8/10/2019 DA Class About Relays 26122014
34/45
THE IMPEDANCE RELAY CHARACTERISTIC
21
22rZXR
R
X Plain Impedance Relay
Operation Zone
Zr1
RadiusZr11rZZ
-
8/10/2019 DA Class About Relays 26122014
35/45
NEED FOR DIRECTIONALITY
1 2 3 4 5 6F1F2
R
XRELAY 3Operation Zone
F1
F2Nonselective
Relay Operation
-
8/10/2019 DA Class About Relays 26122014
36/45
THREE-ZONE DISTANCE PROTECTION
1 2 3 4 5 6
Zone 1
Zone 2
Zone 3
Time
Time
Zone 1 Is Instantaneous
-
8/10/2019 DA Class About Relays 26122014
37/45
CIRCULAR DISTANCE RELAY CHARACTERISTICS
MHO
OFFSET
MHO (1)
PLAIN
IMPEDANCE
R
X
R
X
R
X
OFFSET
MHO (2)
R
X
LENS
(RESTRICTED MHO 1)
TOMATO(RESTRICTED MHO 2)
R
X
R
X
-
8/10/2019 DA Class About Relays 26122014
38/45
DIFFERENTIAL PROTECTION PRINCIPLE
No Relay Operation if CTs Are Considered Ideal
ExternalFault
IDIF = 0
CT CT
50
Balanced CT Ratio
Protected
Equipment
-
8/10/2019 DA Class About Relays 26122014
39/45
DIFFERENTIAL PROTECTION PRINCIPLE
InternalFault
IDIF > ISETTING
CTR CTR
50
Relay Operates
Protected
Equipment
-
8/10/2019 DA Class About Relays 26122014
40/45
PROBLEM OF UNEQUAL CT PERFORMANCE
False differential current can occur if a CT saturates during a through-fault
Use some measure of through-current to desensitize the relay when high currents are present
External
Fault
ProtectedEquipment
IDIF 0
CT CT
50
-
8/10/2019 DA Class About Relays 26122014
41/45
POSSIBLE SCHEME PERCENTAGE DIFFERENTIAL
PROTECTION PRINCIPLE
Protected
Equipment
RS
CTR CTR
Compares:
Relay
(87)
OP S RI I I
| | | |
2
S R
RT
I Ik I k
RPSP
-
8/10/2019 DA Class About Relays 26122014
42/45
DIFFERENTIAL PROTECTION APPLICATIONS
Bus protection
Transformer protection
Generator protection
Line protection
Large motor protection
Reactor protection
Capacitor bank protection
Compound equipment protection
-
8/10/2019 DA Class About Relays 26122014
43/45
DIFFERENTIAL PROTECTION
SUMMARY
The overcurrent differential scheme is simple andeconomical, but it does not respond well to unequal current
transformer performance
The percentage differential scheme responds better to CT
saturation
Percentage differential protection can be analyzed in the
relay and the alpha plane
Differential protection is the best alternative
selectivity/speed with present technology
-
8/10/2019 DA Class About Relays 26122014
44/45
ADVANTAGES OF DIGITAL RELAYS
MultifunctionalCompatibility withdigital integrated
systems
Low maintenance
(self-supervision)
Highly sensitive,
secure, andselective
Adaptive
Highly reliable
(self-supervision)
Reduced burden
on
CTs and VTs
Programmable
VersatileLow Cost
THANK YOU
-
8/10/2019 DA Class About Relays 26122014
45/45
THANK YOU