Power System Protection ECE 456
Power System Protection ECE 456
Power System Protection ECE 456
Relay Technology
Protection Relay Functional Block Diagram
I or/and V Trip and Alarm Decision Making Scheme logic and output
The voltage and/or current signal is first reduced to measurable quantities and necessary conditioning done The decision making stage does the actual protection as per the set value The output stage implements the necessary logic before issuing trip and alarm commands.
2005. T.S. Sidhu
Relay Technology
Protection Relay Technology Evolution
PROTECTION RELAY
Relay Technology
Protection Relay Technology Evolution
PROTECTION RELAY
Electromechanical
Static
Electromechanical : A protection relay design which uses magnetomotive force in its decision making stage and has moving parts in it. Static : A protection relay design which does not have any moving part in the decision making stage
2005. T.S. Sidhu
Relay Technology
Protection Relay Technology Evolution
PROTECTION RELAY
Static
Relay Technology
Protection Relay Technology Evolution
PROTECTION RELAY
Relay Technology
Protection Relay Technology Evolution
PROTECTION RELAY
Relay Technology
Protection Relay Technology Evolution
PROTECTION RELAY
hardware
software
2005. T.S. Sidhu
DSPs
Relay Technology
Block diagram of a Modern Numerical relay
Crystal Clock
VTA
Filtering & Buffer Filtering & Buffer Filtering & Buffer Filtering & Buffer Filtering & Buffer Filtering & Buffer
S/H
ADC
from VT
VTB
S/H
ADC
VTC
S/H
ADC
CTA
S/H
ADC
D I G I T A L MUX
from CT
D A T A B U S
CTB
S/H
ADC
Data acquisition Digital Filtering Protection Algorithm Scheme logic DR, ER, FR, etc. Comm. & HMI
CTC
S/H
ADC
Communication Interface
Digital Output (Relays)
Power Supply
Electromechanical Relays
Constructions
Plunger-type relays Balanced beam relays Induction disc relays Induction cup relays
A simple over voltage relay is shown The coil impedance and turns decide the operating torque The spring provides the restraining force The relay operating value (setting) is thus controlled by both the coil and spring
2005. T.S. Sidhu
Beam is balanced for normal conditions During fault, the operating torque exceeds the restraining torque causing the beam to tilt and close the contacts
2005. T.S. Sidhu
Flux produced by both voltage and current coils. The interaction of these two fluxes produces a rotational torque (like induction motors) Disc rotates and closes contact during fault
2005. T.S. Sidhu
IZr1-V
+
V-IZr2
Similar to disc, but the freedom of rotation is restricted. Cannot provide additional time delay in operation..
The above circuits are realised using transistors, Op-Amps, ICs etc. A combination of the above circuits are used to implement a particular protection in static technology
2005. T.S. Sidhu
POWER SYSTEM
PROCESSOR
PROCESSOR
Inputs (3-Window Algorithm) Current : 0009 Previous : -0500, -1230 Processing 1. Calculate Phasors Apply logics (Algorithms) Give Trip Signal
2. 3.
All these processing should be done within T seconds (1 sampling interval), before the next sample arrives
2005. T.S. Sidhu
PROCESSOR
Inputs (3-Window Algorithm) Current : 0378 Previous : 0009, -0500 Processing 1. Calculate Phasors Apply logics (Algorithms) Give Trip Signal
2. 3.
All these processing should be done within T seconds (1 sampling interval), before the next sample arrives
2005. T.S. Sidhu
PROCESSOR
Inputs (3-Window Algorithm) Current : 0969 Previous : 0378, 0009 Processing 1. Calculate Phasors Apply logics (Algorithms) Give Trip Signal
2. 3.
All these processing should be done within T seconds (1 sampling interval), before the next sample arrives
2005. T.S. Sidhu
PROCESSOR
Inputs (3-Window Algorithm) Current : 0598 Previous : 0969, 0378 Processing 1. Calculate Phasors Apply logics (Algorithms) Give Trip Signal
2. 3.
All these processing should be done within T seconds (1 sampling interval), before the next sample arrives
2005. T.S. Sidhu
Relay Technology
Implementation of a single phase impedance relay in different relay technologies
Electrometrical Static Analgue Numerical
Input signals
Voltage Current
Setting
Impedance setting
2005. T.S. Sidhu
| Z || Z r1 | z z r1
Zr2
Zr2
| Z || Z r1 |
Multiplying both sides by I, we get
IZ is equal to V, the voltage at the relay location if Z is the impedance from the relay location to the fault
| V || IZr1 |
This can be implemented by comparing flux
| IZ || IZr1 |
Im Zr1 Z Operate C Re Restrain
IZr1
Zr2
2005. T.S. Sidhu
Now substituting IZ by V, we get V-IZr2 and IZr1-V. The characteristic can now be defined by (V-IZr2)(IZr1-V) cos ()>0
Zr2
V-IZr2
*Z r1
*(-1)
| V || IZr1 |
0 | IZr1 | | V |
Im Zr1 Z Operate C Re Restrain
Convert to dc voltage
Convert to dc voltage
ADD
Trip
2005. T.S. Sidhu
Zr2
V-IZr2 IZr1-V
Integrator
Zr2
Squaring circuit
Squaring circuit
AND
Level detector
Trip
Trip
2005. T.S. Sidhu
from VT from CT
VT
S/H
ADC
CT
S/H
ADC
D I G I T A L MUX
D A T A B U S
To CB From Plant
Communication Interface
Power Supply
from VT from CT
VT
S/H
ADC
CT
S/H
ADC
D I G I T A l MUX
D A T A B U S
To CB From Plant
Communication Interface
Power Supply
The input current and voltage is reduced to electronics measurable range. Typical 1 to 5V full scale.
2005. T.S. Sidhu
from VT from CT
VT
S/H
ADC
CT
S/H
ADC
D I G I T A l MUX
D A T A B U S
To CB From Plant
Communication Interface
Power Supply
from VT from CT
VT
S/H
ADC
CT
S/H
ADC
D I G I T A l MUX
D A T A B U S
To CB From Plant
Communication Interface
Power Supply
Sampling - Converting the continuous time analog signal to discrete time analog signal Holds the signal at the sampled value for digitizing
2005. T.S. Sidhu
from VT from CT
VT
S/H
ADC
CT
S/H
ADC
D I G I T A l MUX
D A T A B U S
To CB From Plant
Communication Interface
Power Supply
Converts the instantaneous current and voltage to equivalent digital value (0s and 1s) No. of bits representing each value depends on resolution of ADC
2005. T.S. Sidhu
from VT from CT
VT
S/H
ADC
CT
S/H
ADC
D I G I T A L MUX
D A T A B U S
To CB From Plant
Communication Interface
Power Supply
Sends digitized current and voltage in turns to the data bus. Controlled from DSP
2005. T.S. Sidhu
from VT from CT
VT
S/H
ADC
CT
S/H
ADC
D I G I T A l MUX
D A T A B U S
To CB From Plant
Communication Interface
Power Supply
Implements distance protection (magnitude, phase comparison, etc) more in next lecture
Find phasor from digital samples Calculate Impedance
2005. T.S. Sidhu
from VT from CT
VT
S/H
ADC
CT
S/H
ADC
D I G I T A l MUX
D A T A B U S
To CB From Plant
Communication Interface
Power Supply
Digital I/O to issue trip/alarm commands and receive plant status Communication for local and remote communication / SCADA, DCS
2005. T.S. Sidhu
from VT from CT
VT
S/H
ADC
CT
S/H
ADC
D I G I T A l MUX
D A T A B U S
To CB From Plant
Communication Interface
Power Supply
DC/AC to DC converter to provide power to circuit comments at different rail voltage Crystal to provide reference clock for digital processing
2005. T.S. Sidhu
Relay Technology
Any protection can be implemented in all technology Though technology has evolved from electromechanical to numerical, each has its own strength However the flexibility and series of extra features offered by numerical relays combined with advancements in DSP and communication has made numerical relays very popular in recent times