LAB2.docx - POWER SYSTEM PROTECTION SWITCHGEAR LAB...

POWER SYSTEM
PROTECTION &
SWITCHGEAR
LAB ASSIGNMENT - 02
SURABHI RAMAN
17BEE0029

MICRO-CONTROLLER BASED OVER/UNDER VOLTAGE RELAY
IDMT/DMT RELAY
Ex.No : 02
AIM
i. To study the Micro Controller based over voltage relay.
ii. To study the Micro Controller based Under Voltage relay.
EQUIPMENT REQUIRED
1) VPL – 05 Module
2) 1 φ Auto transformer
3) Connecting wires
Formulae Used:
1. Calculate Relay tripping time for over voltage IDMT Relay
t = TMS
[
K
[
V
V
S
]
α
− 1
]
+ C
2. Calculate Relay tripping time for Under voltage IDMT Relay
t = TMS
[
K
[
V
S
V
]
α
− 1
]
+ C
α = 0.02, K = 0.14, C = 0
Theory
In a power system consisting of generators, transformers, transmission and
distribution circuits, it is inevitable that some failure will occur somewhere in the
system. When a failure occurs on any part of the system, it must be quickly detected
and disconnected from the system. There are two principle reasons for it. Firstly, if
the fault is not cleared quickly, it may cause unnecessary interruption of service to
the customers. Secondly, rapid disconnection of faulted apparatus limits the amount

of damage to it and prevents the effects of fault from spreading into the system.
The detection of a fault and disconnection of a faulty section or apparatus can
be achieved by using fuses or relays in conjunction with circuit breakers. A fuse
performs both detection and interruption functions automatically but its use is limited
for the protection of low-voltage circuits only. For high voltage circuits, relays and
circuit breakers are employed to serve the desired function of automatic protective
gear. The relays detect the fault and supply information to the circuit breaker which
performs the function of circuit interruption.
A Protective relay is a device that detects the fault and initiates the operation
of the circuit breaker to isolate the defective element from the reset system. The
relays detect the abnormal conditions in the electrical circuits by constantly
measuring the electrical quantities which are different under normal and fault
conditions. The electrical quantities which my change under fault conditions are
voltage, current, frequency and phase angle.