Department: ELECTRICAL ENGINEERING
Student Name: LEONARD GWAMULUMBA
Student ID No.: 200003209
EEB 525 – POWER SYSTEMS ANALYSIS
LABORATORY REPORT 2
MAY 2017
TABLE OF CONTECTS
TABLE OF CONTECTS....................................................................................................................................2
OBJECTIVES..................................................................................................................................................3
INTRODUCTION......................................................................................................................................3
THEORY....................................................................................................................................................4
PROCEDURE...........................................................................................................................................6
RESULTS AND ANALYSIS......................................................................................................................8
DISCUSSIONS.........................................................................................................................................9
CONCLUSION..........................................................................................................................................9
REFERENCES........................................................................................................................................10
OBJECTIVES
Investigate the behavior of two inverse definite minimum time (IDMT) relays producing a
radial feeder when discrimination is observed.
1. current
2. time setting
to investigate the behavior of these relay when connected in series in the radial feeder
but with each relay having its own current and time setting and to predict from the relay
characteristics curve which relay will be the first to operate
NOTE: it is preferable if the relay characteristics curves obtained in
demonstration/investigation are used to verify both parts of the object.
INTRODUCTION
Electrical Power System protection is required for protection of both user and the system
equipment itself from fault, hence electrical power system is not allowed to operate
without any protection devices installed.
Power System fault is defined as undesirable condition that occurs in the power system.
These undesirable conditions are short circuit, current leakage, ground short, over
current and over voltage. With the increasing loads, voltages and short-circuit duty in
distribution system, over current protection has become more important role today. The
ability of protection system is demanded not only for economic reason but also
consumers just expect ‘reliable’ service. In a Power System Protection, the system
engineer needs a device that can monitor current, voltage, frequency and in some case
over power in the system. Thus a device called Protective Relay is created to serve the
purpose.
The protective relay is most often relay coupled with Circuit Breaker such that it can
isolate the abnormal condition in the system. In the interest of reliable and effective
protection, some designers of power distribution select relay alternative to electro-
magnetic circuit breakers as a method of circuit protection.
THEORY
Overcurrent Relays in power system are like the hidden solders in the system, they
become active when there is any fault, in order to protect system under its protective
area. Faults may occur in any part of power system. In such condition a heavy fault
current pass through the system. The relay detects intolerable or undesirable
conditions and also can sense how serious the fault is (for faster or slower operation to
trip). Relay must be operated correctly and make the circuit breaker tripped for
disconnecting the faulty portion of the circuit from rest of the healthy system means the
relay gives signal to circuit breakers whether to disconnect or remain silent to ensure
safety and prevent damage to personnel and property in its serving area.
Overcurrent Relay has inverse characteristics with respect to the currents being
monitored. Most mainstream relays utilized on medium-and low-voltage frameworks for
some, and current computerized transfers' attributes are still essentially in light of this
kind of relay, it is advantageous concentrating on the operation of this in point of interest
to comprehend the embraced in the computerized relays.
Whole of the power system can be subdivided in to number of radial feeders fed from
one end. Generally such radial feeders are protected by over current and earth fault
relays used as primary relays for 11 KV and 66 KV lines. For lines of voltage rating
beyond 66 KV, distance protection is applied as a primary protection whereas over
current and earth fault relays are used as back up relays.
A simplified radial feeder network without transformers (in actual practice transformers
do exist at substations) is shown in single line diagram of fig. 1.1 below.
The importance of the coordination of distinct protective device is increasing now since
the equipment are very much expensive in this field. A power system consists of many
number of equipment so eventually more number of circuit breakers and relays are
required to protect the system from faulty situation of over current. A relay must receive
sufficient chance to protect the zone under its primary protection whenever a fault is
seen in the line, thus high current. If the primary protection does not remedy the fault,
the back-up protection installed must initiate tripping, and therefore, overcurrent relay
participation in power distribution network is a major concern of protection power
engineer. The relay coordination in distribution network is highly constrained
optimization problem. The demand for electrical power is increasing at a faster rate in
mainly economically emerging countries as well as developing countries.
Extremely inverse relays are yet better. Very inverse relays are faster in operation for
close-in faults yet maintaining the discrimination with fuse and other relays. Extremely
inverse relays are more meritorious in this aspect too. Instantaneous o/c relays are not
immune to Zest/Zl ratio. Definite time o/c relays are 100 % immune to this ratio [1]. Very
inverse relays can be used with an additional advantage while protecting a machine or a
transformer as they match with the heating characteristic of equipment better than their
normal inverse equivalent. Extremely inverse relays can best co-ordinate with the fuse
characteristic. The aim of this experiment is to reveal these facts experimentally.
Fig: 1.2 normal, very and extremely inverse characteristics
Apparatus required:
Timer
IDMT relay
NC trainer board
1 phase dimmer stat = 230v, 10a
Ammeter ac (0-10a)
Connecting wires
PROCEDURE
The principle of this investigation is shown in figure 1.3 and the distribution trainer circuit
arrangement is shown in figure 1.4.
1. Isolate the circuit by opening the MCB .short circuit the secondary side of the
current transformer my using the CT short links
2. Energies the circuit by closing the MCB .adjusting the load until 5a flows. Isolate
the circuit, i.e. open the MCB and remove the CT shorting links. Adjust the time
multiplier (TM) relay a ( and b . Adjust the current setting of to
3A and the current setting of to 1.5A.Close the MCB thus energizing the
circuit.
3. Measure the time taken for the circuit to be broken ,i.e. tripped and note the relay
that trips .Record all observations in the tables
4. Reset the relay which is tripped
5. Repeat the investigation but with the relay settings being current settings of
adjusted to 1.5A current setting of adjusted to 3A
6. The time multiplier (TM) of and remains set at 1.0. Record all observations.
7. Repeat investigation (i) but with the following alterations current settings of relay
b adjusted to 2.5a
8. Time multiplier (tm) of relay a adjusted to 0.9, time multiplier (tm) of relay b
adjusted to 0.6. Load adjusted until until current of 4 A flow. Measure the time
taken for the circuit to be broken.
9. Record all observations in the results table. Rest all the relay which tripped the
following settings. Time multiplier (tm) of the relay b adjusted to 0.9
10. The current settings (psm) of both relays and remain at 2.5 A. The load
current remains at 4 A
11. Time multiplier (tm) of relay b adjusted to 0.6 Load adjusted until until current
of 4a flow. Measure the time taken for the circuit to be broken.
12. Record all observations in the results table. Rest all the relay which tripped the
following settings. Time multiplier (tm) of the relay b adjusted to 0.9
13. The current settings (PSM) of both relays and remain at 2.5A.The load
current remains at 4 A
RESULTS AND ANALYSIS
RELAY A RELAY B FAULT RELAY TIME (s)
CURRENT OPERATING
TICK
CURRENT CURRENT predicted Actual
TM TM from curve
SETTING SETTING
WHEN LOAD WAS ADJUSTED TO 4.2 A MAXIMUM CURRENT
2.0A 1.0 1.5A 1 .0 12.58s 21.58
1.5A 1.0 2.0A 1.0 12.60s 21.90
WHEN THE LOAD WAS ADJUSTED TO 4.0 A
1.5A 0.9 1.5A 0.6 13.73
1.5A 0.6 1.5A 0.9 20.72
WHEN THE LOAD WAS ADJUSTED TO 4.2 A MAXIMIMUM
1.75A 0.8 1.5A 0.9 20.09
20.70
TABLE 1.5: Results
In table 1.5 shows the result obtained in the laboratory during the experiment
Standard Inverse (SI)
TMS = Time multiplier Setting
TD = Time Dial setting
Sample of calculation
DISCUSSIONS
According to the results collected, shown in table 1, should a fault occur at maximum
current which is 4.2A relay A was observed to trip first at 21.58s before relay B at
21.90s.The discrimination time between relay A and B is less than 0.4s. Such results
imply that Relay A was used as the primary protection while B was the secondary or
back-up relay. The entire relay coordination curve is investigated to check the prediction
time. Therefore, in the table it shows that the discrimination time interval between each
relay level will be correlated with the setting current value and time multiplier setting
value. The lowest downstream relay should be valued lower than the next upstream
level relay in order to satisfy the overcurrent relay discrimination and to ensure that the
relay at each level will response trip in correct sequence.
CONCLUSION
There is a need for sub-structures and modern networks. In addition, investment should
take place to run intelligent networks. Due to increase in electrical energy consumption,
load compression, and electricity generator sources as well as the need for quick and
safe work of control and productive equipment’s, using digital protective equipment’s
especially digital relays is both necessary and essential in protecting power systems.
These relays have proven from the experiment that they are reliable devices in
protecting equipment’s and electrical systems because they are able to early detect
change in currents and prevent their extension. Each of the two methods described so
far has a fundamental disadvantage. Discrimination by time alone proved that
disadvantageous since depending on severity of faults are cleared in the longest
operating time.
Discrimination by current can only be applied where there is appreciable impedance
between the two circuit breakers con-corned. This is so because of the limitations
imposed by the independent use of either time or current coordination that the inverse
time over current relay characteristic. Based on these attributes, I conclude that the
objectives have been met.
REFERENCES
1. Switchgear Protection And Power Systems By Sunil S. Rao
1. . L. Hewitson, M. Brown, B. Ramesh, Practical Power Systems Protection,
Elsevier 5. Availablehttp://www.gedigitalenergy.com/multilin/manuals12-12-15
6. Science & Technology Books, 2004.
6. J. L. Blackburn and T. J. Domin, Protective Relaying Principles and
Applications, 3rd ed., H. L. Willis, Ed., New York: CRC Press, 2007,pp. 63, 175,
340, 453.
7. [2] GE JBC51M Phase Directional Overcurrent Relays, Instruction ManualGEK-
49848C, GE Digital Energy Multiline..
8. [3] J. Roberts and A. Guzmán, “Directional Element Design and Evaluation,”
proceedings of the 21st Annual Western Protective Relay Conference,
Spokane, WA, October 1994.
9. [4] B. Fleming, “Negative-Sequence Impedance Directional Element,”
proceedings of the
10th Annual Doble Pro Test User Group Meeting, Pasadena, CA, February
1998.
10. [5] N. Fischer, D. Haas, and D. Costello, “Analysis of an Auto transformer
Restricted Earth Fault Application,” proceedings of the 61st Annual Conference
for Protective
Relay Engineers, College Station, TX, April 2008 .
