this documents will help to under stand relay and indications occurs after fault.

1. IN THE NAME OF ALLAH WHO IS THE MOST
BENEFICENT AND THE MOST MERCIFUL

2. Measurement and Relay
Indications
National Transmission and Despatch Company Ltd
PRESENT
ED BY:
ENGR: SYED GHULAM MUSTAFA
Deputy Manager (T
echnical)
o/o Chief Engineer T
SG (South) NT
DC HYderabad
PCC-OG-140

3. CONTENTS
INTRODUCTION
FUNCTIONS OF PROTECTION SCHEMES
CLASSIFICATION OF PROTECTIVE RELAYS BASED ON
TECHNOLOGY
INDICATIONS
Q&A

4. FUNCTIONS OF
PROTECTION SCHEMES
T
o sense/detect the fault occurrence and other abnormal conditions
at the protected equipment/area/section.
T
o operate the correct circuit breakers so as to disconnect only the
faulty equipment/area/section as quickly as possible, thus
minimizing the damage caused by the faults.
T
o operate the correct circuit breakers to isolate the faulty
equipment/area/section from the healthy system in the case of
abnormalities like overloads, unbalance, undervoltage, etc.
T
o clear the fault before the system becomesunstable.
T
o identify distinctly where the fault hasoccurred.

5. CLASSIFICATION OF PROTECTIVE
RELAYS BASED ON TECHNOLOGY
Protective relays can be broadly classified into the following three
categories, depending on the technology they use for their
construction and operation.
1. Electromechanical relays
2. Solid state (static) relays
3. Digital / numerical relays

6. CLASSIFICATION OF PROTECTIVE
RELAYS BASED ON TECHNOLOGY
1. Electromechanical relays
 The oldest type of relay.
 First generation of electromechanical relay which came in 1901.
 Operate based on the regulation of mechanical force generated
through the flow of current in windings wounded on magnetic
core.

7. CLASSIFICATION OF PROTECTIVE
RELAYS BASED ON TECHNOLOGY
1. Electromechanical relays – thermal relay
- Operates on the principle of
heating effect of electrical
current.
- When the overload condition is
detected, the bimetal strips
bend and allow the trip contact
to energize the trip circuit.
THERMAL RELAY

8. CLASSIFICATION OF PROTECTIVE RELAYS
BASED ON TECHNOLOGY
1. Electromechanical relays – attracted armature relay
- Operates on the principle of
electromagnetic force produced
which attracts the plunger or
hinged armature.
- When the electromagnetic force
exceeds the restraining force, the
moving contact closes due to the
movement of the armature.
Hinged type Plunger type
ATTRACTED ARMATURE RELAY

9. CLASSIFICATION OF PROTECTIVE
RELAYS BASED ON TECHNOLOGY
1. Electromechanical relays – induction relay
- Operates on the principle of
electromagnetic induction.
- Operating force is developed
due to the interaction of two
AC flux displaced in time and
space in movable element
(rotor).
INDUCTION RELAY
Induction disc relay Induction cup relay

10. CLASSIFICATION OF PROTECTIVE
RELAYS BASED ON TECHNOLOGY
1. Electromechanical relays – balance beam relay
- Operating coil produces operating
torque, whereas restraining coil
produces restraining torque.
- The electromagnetic force of both
coils are in opposition.
- When operating torque exceeds
restraining torque, the movement of
armature closes the contact.
BALANCE BEAM RELAY

11. CLASSIFICATION OF PROTECTIVE
RELAYS BASED ON TECHNOLOGY
1. Electromechanical relays
Alstom IDMT earth fault relay Alstom Check Synchronising Relay
EXAMPLES OF ELECTROMECHANICAL RELAY

12. CLASSIFICATION OF PROTECTIVE
RELAYS BASED ON TECHNOLOGY
1. Electromechanical relays
ADVANTAGES DISADVANTAGES
 Fast operation and can be reset fast.
 Simple construction.
 Reliable and rugged.
 The values can be easily set
and no programming is
required.
 People can be trained on these relays
easily.
 Have high VAburden thus require high
burden CTs and VTs to operate them.
 Do not have directional feature.
 Affected by the ageing of
components, dust and pollution
resulting in spurious trips.
 Operation speed is limited by the
mechanical inertia of the component.
 One relay can only perform one
function (multifunctioning not
possible).

13. CLASSIFICATION OF PROTECTIVE
RELAYS BASED ON TECHNOLOGY
2. Solid state (static) relays
 Due to the advent of electronic devices such as diode,
transistor, ICs, chips etc.
 Second generation of relays.
 Came into operation in 1950s.
 More accurate and higher reliability compared with
electromechanical relays.

14. CLASSIFICATION OF PROTECTIVE
RELAYS BASED ON TECHNOLOGY
2. Solid state (static) relays
 The static means the relay has no moving part.
 The semiconductor devices are used for data processing and also
to create relay characteristic.
 Lower relay burden due to no moving parts thus further reduces
the CT/VT requirement.
 Require separate DC power supply.

15. CLASSIFICATION OF PROTECTIVE
RELAYS
BASED ON TECHNOLOGY
2. Solid state (static) relays
EXAMPLE OF STATIC RELAY BLOCK DIAGRAM
Generalized block diagram of static time overcurrent relay
- The secondary current from CT is
rectified, filtered and fed to timing and
curve shaping circuit.
- The output of timing circuit is then
given to level detector which compares
between relay and reference
quantities.
- When the magnitude of relay quantity
exceeds the magnitude of reference
quantity, it generates a voltage signal.
- The voltage signal is then amplified by
amplifier block and fed to tripping
circuit.
- Finally, the tripping circuit generates a
tripping command and send to trip coil
of circuit breaker.

16. CLASSIFICATION OF PROTECTIVE
RELAYS BASED ON TECHNOLOGY
GEC Alstom Static Distance Protection Relay GEC Static Differential Protection Relay
EXAMPLES OF STATIC RELAY
2. Solid state (static) relays

17. 2. Solid state (static) relays
CLASSIFICATION OF PROTECTIVE
RELAYS BASED ON TECHNOLOGY
ADVANTAGES DISADVANTAGES
 Do not contain moving parts – thus free
from problems such as contact
bouncing, arcing, erosion and friction.
 Significantly less burden on
instrument transformers
(CT/VT).
 Can incorporate variety of functions in a
single unit.
 Quick response and reset action.
 Greater sensitivity can be obtained by using
amplification block.
 Superior characteristic and accuracy.
 Electronic devices are more sensitive
to voltage spike and other transients
that can cause malfunction.
 Require auxiliary DC to operate.
 Has low short time overload capacity.
 The characteristic of electronic devices
are affected by temperature and
ageing of semiconductor devices.
 Costlier compared to electromechanical
relay.
 Require highly trained persons to service
static relay which has complex protective
functions.

18. 3. Digital / numerical relays
 Entered the market around 1980s.
 Based on microprocessors and microcontrollers.
 Instead of using analog signals, this relay
analogue quantities into digital signals.
converts all measured
 Microcontrollers are used in replacement of analogue circuits used in
static relays.
 Digital / numerical relays introduce Analogue to Digital Convertor (A/D
conversion) of all measured analogue quantities and use a
microprocessor to implement the protection algorithm.
CLASSIFICATION OF PROTECTIVE
RELAYS BASED ON TECHNOLOGY

19. 3. Digital / numerical relays
CLASSIFICATION OF PROTECTIVE
RELAYS BASED ON TECHNOLOGY
BASIC BLOK DIAGRAM OF
A DIGITAL / NUMERICALRELAY
Anti aliasing
filter

20. 3. Digital / numerical relays
CLASSIFICATION OF PROTECTIVE
RELAYS BASED ON TECHNOLOGY
ABB digital distance protection relay SEL Transmission Protection System
Siemens Transformer differential
protection
EXAMPLES OF DIGITAL OR NUMERICAL RELAY

21. 3. Digital / numerical relays
CLASSIFICATION OF PROTECTIVE
RELAYS BASED ON TECHNOLOGY
ADVANTAGES DISADVANTAGES
 Various functions such as multiple setting
groups, programmable logic, events
recording and oscillography.
 Has the ability of self monitoring and self
testing.
 Ability to communicate with other
relays and control computers.
 Cost per function is lower.
 User can develop their own logic schemes.
 Less burden on instrument transformers.
 Less panel space because it can provide
many functions in a single relay.
 Short life cycles due to fast advancement in
microprocessor and microcontroller technology.
 Because it can provide many functions in a
single relay, all the functions will share a
common failure. For example, failure of a
power supply or an input signal processor
may disable the entire relay functions.
 Not immune to electrical transients
such as electromagnetic interference
(EMI) and radio frequency interference
(RFI).
 The increased number of settings may
pose problems in managing the
settings and in conducting functional
tests.

26. Q & A
Session