1. What is a Short Circuit and or Relay Coordination Study?
A. Short Circuit Study is an electrical safety analysis
of a power system, this study determines the faults occurred in an
electrical system. Differentiate these calculations against the ratings
of the equipment. It is the first step to ensuring that the electrical
system is safely protected. After completion of knowing the short
circuit faults, then determine the characteristics of the protective
devices in the power system.
2. What is a breaker coordination study?
A. Breaker coordination study is also known as
Protective Device Coordination study. This study includes checking of
upstream and downstream protective device coordination to avoid the
nuisance, to stop disturbances of tripping and avoid the plant shutdown.
This study helps to the electricians to identify the causes of faults
and make corrections.
3. What is protection and coordination?
A. In Protective Device Coordination studies, the term
protection states that to protect the power system by stopping the
tripping and plant shutdown. At the same time in electrical power
distribution system, the coordination study is mandatory to analyze the
characteristic curves of upstream and downstream breakers to avoid the
tripping of fuses. These studies depend on present electrical safety
standards and regulations like NFPA 70E, NEC, IEEE 1584 and OSHA.
4. What is a coordination study for?
A. As per the Electrical safety standards and
Regulations, Overcurrent Protective Coordination study is very important
to protect the downstream and upstream breakers to avoid the faults in a
circuit breakers. This coordination study is mandatory to minimize the
power system faults and successful fault isolation in a sequential
manner.
5. What is coordination of protective devices?
A. In Electrical Distribution system or Transmission
system commonly use circuit breakers and fuses to protect the equipment
like Motors, Transformers, Conductors and other electrical equipment. If
any kind of faults can occur within this components, this study can help
to protect some portion of the system and minimize the failures within
this system.
6. How to do relay coordination calculation?
A. As per the IEC 60255 report, the equipment safety requirements for
the calculation of relays and protective devices ratings as shown
below:
For A.C voltage up to 1000v with a rated frequency up to 65HZ and For
D.C voltage up to 1500v
Especially, this standard requires electrical safety to minimize the
risks of flashes and Hazards. The calculations of Over current relay
coordination is based on the equations (Relay Characteristic Equation as
per IEC 60255 standard) as follows:
For Standard Inverse Relay Characteristic equation (SI) 𝑡 = TMS×
0.14 I𝑟 0.02 – 1
For Very Inverse Relay Characteristic Equation (VI) 𝑡 = TMS ×
13.5 I𝑟 – 1
For Extremely Inverse Relay Characteristic Equation (EI) 𝑡 = TMS
× 80 𝐼𝑟 2 − 1
The above Relay coordination characteristics equations are used to
do relay coordination calculation.
7. What is fuse coordination?
A. Fuse Coordination is also known as selective
coordination. It is an important system to identify the faults. This
study describes to draw the single line diagram of a power system in
upstream protection system near to the fault area and clear the faults
without affecting the fuses and also circuit breakers (protective
Devices).
8. What is the purpose of selective coordination?
A. The purpose of selective coordination is to identify
the faults in upstream fuses and breakers. It also used to minimize the
effects by using single line diagram. In this study involves
Electronic-trip and ANSI breakers, Molded-case breakers and Ground fault
protection to clear the trappings of the entire upstream system.
9. What is the need of relay coordination?
A. In any distribution system, the relay coordination
study is used to isolate the faults in the protective system within the
short time to stop the fault causing minimum causing of a distribution
system. Mainly protective study protects the upstream protective devices
of the power system.
10. What is the importance of extremely inverse characteristic relay?
A. In Extremely Inverse Relay the Current Transformer saturation later
stage as compared with Inverse Relay. Hence the characteristic remains
inverse up to maximum range of fault current. The Extremely Inverse
Relay equation describes
I2t0=k
Where,
I=Operating current
t=Time Operation of the relay
11. What is protection coordination study?
A. Protective Relay coordination study is used isolate
the faults and fault clearance sequence. This study required to select
the protective devices like fuses and circuit breakers to specify the
necessary settings to fix the faults that's why the intended target will
be achieved. There is so many software to perform Protective
Coordination functions in personal computers.
12. What is protective relay?
A. The relay which protects the upstream protective
devices like fuses and breakers in the Electrical Distribution system is
known as protective relays. The main purpose of the protective relay is
designed to trip a breaker in the circuit to detect the fault. Which
minimize the fault occurring time to save overall distribution system.
13. What is protective relay testing?
A. The Protective Relay Testing depends on the type of
relay and determines by the recommendations of manufacturers and updated
application considerations. First, the testing is starting to inspect of
mechanical problems and recovery on each control element and timing
curve of three points, Overcurrent protection and other control systems
and final testing of the overall functioning system.
14. What is the best practice for testing protective relays?
A. Best practice for testing protective relays is based
on the basic results of a protective device coordination analysis are
the time-current coordination graphs that are plotted to illustrate the
degree of selective coordination achieved in the system. Adjacent to
each Single line diagram TCC curves are plotted. TCC curves show the
device number, description, and settings for each device.
15. How to do relay coordination calculation?
A. Basics of Relay Coordination is as follows:
a) How the protective devices are working so well with each other.
b) The amount of power can be lost during a fault condition.
c) Power system equipment is protected or not.
d) The ratings and settings as we chosen cause nuisance trips or not.