Electrical Power Systems Protection Lab in PTUK

Faculty of Engineering and Technology
Department of Electrical Engineering
Electrical Power Systems Protection Lab Manual
(12120204)
First Edition
Student Manual
Prepared by:
Eng. TareQ FoQha
2021

Palestine Technical University-Kadoorie
Faculty of Engineering and Technology | Electrical Engineering Department
Electrical Power Systems Protection Lab || Eng. TareQ FoQha
II | Page Electrical Power Systems Lab
Abstract
The power systems protection laboratory is designed to directly apply theory learned in
lectures to devices that will be studied in the laboratory. Power system protection is concerned
with protecting electrical power systems from faults within the network by isolating the
faulted components so as to leave as much of the remaining the electrical network operational
as possible. Moreover, by properly protecting the system components from overloading, the
probability of fires and other catastrophic and expensive system failures can be minimized.
In understanding power protection, it is necessary to understand what is actually being
protected. Providing superior protection is essential in mitigating the effects of disruptions on
system stability. As such, it is essential for power engineers to understand the concepts and
practices underlying power protection.
The creation of a Power System Protection Lab at Palestine Technical University gives
students the opportunity to gain some real world experience in protection. Moreover, a
laboratory of this type facilitates educational opportunities. It also provides numerous
additional benefits such as research.
Objectives
The laboratory course is intended to provide practical understanding of power system
protection. The main goal is to enable students to apply and test theoretical knowledge
they mastered in previous years of studies. The laboratory course enables them to develop
practical skills in various fields of power engineering in a controlled environment.
The Laboratory covers all phases for the Protection devices specific of this field.
All protection and control devices of the electrical machines are exactly equal to those
installed in the industrial units. So, the sequences of control maneuvers in the control
stations are exactly equal to those necessary in the industrial units.

III | Page Electrical Power Systems Lab

3 | Page Electrical PS Protection Lab
For the static equipments, the term relay can be used when it carries out a specific elementary
logic function while the term relay device is applied to equipment including a total logic
function corresponding to the combination of more elementary logic functions.
Protection Device or Automatic Relay Device:
Relay device performing a specific protection or automatism function as it results from the
qualification of the same device.
Relay Protection System:
These are among plant engineering systems designed for a specific purpose, in which a
determinant part is played by the electrical relays which are sets with the purpose of
protection. A protection system includes the measurement transformers, the transmission
channels, the cables or conductors, the release circuits, etc. necessary to achieve the
purpose. The designer qualifies the protection system specifying the job it must perform and
describing in details the characteristics of the elements composing the same system.
Electrical Relay:
Equipment to be used to cause predetermined changes of state in its output electrical circuits
when particular power supply conditions occur across its input electrical circuits.
Relay Device:
Set of relays connected between them so that they fulfill the purpose the device is supposed to
perform and with which the manufacturer qualifies the same device. The terms relay and relay
device are usually applied equipments of electromechanical kind, while for those of static kind
it is sometimes difficult to find the border between the relay and relay device.
Characteristic Variable of a Measurement Relay:
Electrical variable which passage across a specified value, which is associated to a given
accuracy, determines the relay operation; the characteristic variable characterizes the name of
the relay. In the relays with one input power supply variable the names of the characteristic
variable and the input power supply ones usually coincide; however there are exceptions: e.g.
those relays in which the characteristic variable is the frequency, that are generally powered
with a voltage.

6. Adjust the voltage of the variable power line and the load rheostat to obtain a current
lower than 0.5-A.
Condition Relay operation
Normal
Load Current Tripping Time Notes
7. Overload Condition: Increase the test current over 0.5-A, record the load current and
the tripping time and check the operation of the relay.
8. This condition is kept stored in memory even after the current drops below the preset
value; therefore the device will be reset with the corresponding button, resetting
manually the device by pressing the RESET button.
Overload
Overload Current Tripping Time Notes
9. Short Circuit Condition: Increase the test current over 1-A, record the load current
and the tripping time and check the operation of the relay.
10. This condition is kept stored in memory even after the current drops below the preset
value; therefore the device will be reset with the corresponding button, resetting
manually the device by pressing the RESET button.
Short Circuit
Short Circuit Current Tripping Time Notes

Questions:
1. Suppose you have to protect a three–phase induction motor from an overload condition,
the nameplate of the motor is shown in figure 1.
(A) Sketch the connection needed to connect three-phase induction motor with:
(1) 3-phase supply
(2) Contactor
(3) SR1: Overcurrent relay
(B) Explain how to put the settings of the relay?
(C) Explain how to reset the relay after removing the cause of overload?
(D) Explain the operation of the relay in this case?
Hints:
1) Motors with a service factor (SF) of 1.15 or more, the settings of the overload relay
should be 125% of the full load current.
2) Motors with a service factor (SF) less than 1.15, the settings of the overload relay should
be 115% of the full load current.

Objectives:
1. Connection and study of a maximum and minimum voltage relay in a 3-phase network.
2. To measure the tripping time of maximum/minimum in a three-phase network with
different voltage values;
Theory and concepts:
Code CEI: 59 Maximum voltage relay
27 Minimum voltage relay
The purpose of the maximum and/or minimum voltage relays is to detect anomalous voltage
rising or dropping near the production or usage centers so to prevent damages of machines or
OFF parallel situations.
The three-phase voltage relay detects the limits of
the triad of voltage generated in ordinary service of
the alternator or distributed by the transmission
line. Usually, the relay acts on the main switch to
set the controlled object out of service (alternator
or user connected to the line) when a rise or drop
of voltage can cause malfunctions or damages.
The characteristic equation is: V = KV1 / VN
Experiment (2) Max/Min 3-phase voltage Relay (SR3)

Characteristic Threshold Limit Lines:
In a measurement relay with characteristic threshold line, the lines located on the two sides of
the theoretical line, delimiting the maximum and minimum values, within which the relay, in
specified conditions, could not intervene.
Maximum or Minimum Relay:
Measurement relay with characteristic variable in which the prescriptions related to the
accuracy refer to the achievement of the operation value of the same characteristic variable
when its values rise or drop.

Chapter 2
Protection Relays For High And Low Voltage Networks
Contents
Experiment (1) Overcurrent Relay (SR1) 07-11
Experiment (2) Max/Min three-phase voltage Relay (SR3) 12-16
Experiment (3) Directional Relay (SR10) 17-24
Experiment (4) Differential Relay (SR14) 25-38

Objectives:
1. Connection and study of a fixed time maximum current relay and of a 3- phase line
short-circuit one with different currents.
2. To measure the tripping time of maximum-current (over load and short-circuit) in a
three-phase network with different current values;
Code CEI: 50 Instantaneous intervention relays
51 Delayed intervention relays
50N-51N max homopolar current relays.
These are the most famous protection relays. Main purpose is the detection of the phase to
phase or phase to ground faults. In particular the relay 50N or 51N can be used also with
networks with insulated neutral under particular conditions.
 The three-phase amperometric relay set to maximum current (overload) protection
function enables to fix the limit of the current provided by an alternator (its nominal
power) or the current that a power line can usually stand.
 The values of the currents are adjustable and so is the intervention time delay.
 The three-phase amperometric relay set to protection function against short-circuit
intervenes instantly when the controlled current overcomes the set value. The current
values are adjustable, but the time delay is not so as it is instantaneous. Usually the relay
acts on the main switch to set the controlled object out of service (alternator or line).
 The current value (overload, short-circuit) as well as the delay time, must be adjusted and
checked during the test phase and next in the periodical testing to be sure the protection
device operates.
For the fixed time relay: (figure 1)
Iint = K I1 /In for the overload
Iint = K I2 /In for the short-circuit
Experiment (1) Overcurrent Relay (SR1)

Figure (1)
SR1 Max current three-phase relay description:
Three-phase maximum-current (overload and short-circuit) relay
at definite time and three-phase short-circuit.
Overcurrent Relay settings/Current and time settings
(overload and short circuit):
The technical characteristics of the device are shown in appendix A.
SI1 first level regulation range (overload).
SI2 second level regulation range (short-circuit)

Necessary Material:
1. AMT-3/EV: Variable three-phase power supply mod.
2. SR-1/EV: Overcurrent relay.
3. RC3-PT/EV: Three-phase rheostat 3 x 50.
4. Contactor with on-off control.
5. AZ-VIP: Digital instrument.
Experimental Procedures:
1. Connect the circuit as shown in figure 2.
Figure (2)
2. Connect the auxiliary power line of 230 Vac with the relay, without powering it.
3. Connect the relay between the variable power line and the load rheostat (Y-connection).
4. Suppose to adjust the device with the following design data:
 Overload threshold = 0.5-A;
 Tripping delay time = 5-s;
 Short-circuit threshold = 1-A;
 Tripping delay time = 0.1-s.
5. Normal Condition: Power the relay with the auxiliary supply voltage and check
whether which led will goes on in the frontal panel. Check the contacts of the
contactor.

Operation diagram of the relay
Figure (1)
The technical characteristics of the device are presented in appendix A.
Necessary Material:
2. SR-3/EV: Max/min three phase voltage relay.
3. IL-2/EV: Variable inductive load mod.
4. Contactor with on-off control.

Figure (1)
2. Connect the relay to a variable three-phase power supply line.
3. Connect a voltmeter to measure the line voltage.
4. Adjust the device with the following design data:
 Line nominal voltage Ue = 380 V;
 Maximum voltage threshold (MAX VOLTAGE) = 105 %;
 Intervention delay for maximum voltage (DELAY MAX) = 5 s;
 Minimum voltage threshold (MIN VOLTAGE) = 90 %;
 Intervention delay for minimum voltage (DELAY MIN) = 5 s.
5. Normal Condition: Adjust the voltage of the variable power supply line up to 380 V
(with no load condition).
Normal
Voltage Tripping Time Notes
6. Overvoltage Condition: Increase the test voltage over 400 V, record the line voltage
and the tripping time and check the operation of the relay (with no load condition).

7. The relay has a hysteresis of 3% in respect to the set point, take back the voltage to the
nominal value (380 V) and record the reset value.
Overvoltage
Voltage Tripping Time Reset Value Notes
8. Undervoltage Condition: Drop the test voltage under 342 V, record the line voltage
and the tripping time and check the operation of the relay (with no load condition).
9. The relay has a hysteresis of 3% in respect to the set point, take back the voltage to the
nominal value (380 V) and record the reset value.
Undervoltage
Voltage Tripping Time Reset Value Notes
10. Undervoltage Condition: Set the system under load with the insertion of the inductive
load and measure the following:
Inductive
Load
Minimum
voltage
threshold %
Line
voltage
(V)
intervention
delay
Measured
delay
(Sec)
Reset
Value
(V)
B 95% 5 sec
A||B 90% 5 sec

Questions:
1. Suppose you have to protect a three–phase induction motor from an undervoltage
condition, the nameplate of the motor is shown in figure 1.
(A) Sketch the connection needed to connect three-phase induction motor with:
(1) 3-phase power supply;
(2) Contactor;
(3) SR3: Max/Min voltage relay.
(B) Explain how to put the settings of the relay to protect the motor from
undervoltage condition; the voltage applied to the motor should be at least
95% of the nominal voltage?
(C) Explain how to reset the relay after removing the cause of undervoltage?
(D) Explain the operation of the relay in this case?

Objectives:
1. Connection and study of a maximum current directional relay for maximum current.
2. To measure the tripping time with inverse current flow.
Code CEI: 67 Directional relay
32 Directional or power inversion relay
It is a much extended family of equipment sharing the capacity to operate a control on the
power direction. The concept of direction in the alternated currents is not proper; we should
rather talk of angular relation between the voltages and the phase currents. However, by
convention, we have fixed to consider as positive a vector direction resulting from the
composition of a reference vector with another set within ± 90° from the first; as negative the
one resulting from the composition with a superior angle.
The diagram of figure 1 shows straight line “L” called inversion or limit or threshold. One of
the pros of directional relays is just the one to operate, near the inversion straight line, without
operation uncertainties. To fulfill their purpose, the directional relays carry out the
measurement comparing two variables in module and in phase: the voltage and the current.
Generally they are defined on the plane V–I and can be
reproduced by the equation:
Figure (1)
Experiment (3) Directional Relay (SR10)

Part I: SR-14 in a single phase line. Simulation of a fault: current imbalance between
wires.
1. Connect the circuit as shown in figure 1 and 2.
Figure (1)
2. Put the settings of the relay as follows:
With NO power applied to the relay, set the following parameters:
Time adjustment 0.1 Second constant multiplier: tx10
Fault Current adjustment 0.25 A constant multiplier: IΔnx1
AUTO – MAN Reset The Reset is carried out with the Reset pushbutton.
N – FS FS = relay positive safety activated.
3. Give power to the relay (230 VAC). With the DMM (ohmmeter), check the continuity.
Check also the other set of output contacts.

In the example mentioned in the last figure 1 –during normal operation– the users coming
from the lines E and F absorb the current I1 + I2 as they are powered by the line as well as the
local generator. In case the national line would be missing, all charge of the sector would rest
on the local generator with logical intervention of the maximum current protections. All this is
regular but in case the point A is to be sectioned for electrical maintenance and with no-load
users D E F or those with weak absorptions, there is a danger situation and the distribution
societies force the generator separation although no actual power inversion occur. The solution
consists in adding a protection device against inverse power in point C provided with high
sensitivity. The completion of the circuit under test sees a further protection against the
inverse power in point D.
The intervention characteristics of a power inversion relay should be the as shown in figure 2.
The directional relays are a very large family of equipment sharing the capacity to control the
power direction. The concept of direction comes from the angular relations between phase
voltages and currents where, by convention, positive is considered the direction of a vector
resulting from the composition of a reference vector with another set within ± 90° from the
first; negative the one resulting from the composition with a superior angle. To fulfill their
purpose, the directional relays carry out the measurement comparing two variables in module
and phase: voltage and current. The adjustment of the intervention current threshold, the delay
time and the characteristic angle α (+/- 30°) enables to use the relay in different applications.
 This protection relay senses the current direction, and consequently, operates the output
contacts.
 According to the relay model, and the selected connection, the relay is able to:
 Block the active power direction of a generator (Reverse Power Relay). Generators
prime movers (Diesel engines or turbines) are designed to develop mechanical power,
not to accept power. Mechanical power is directly related with the generated active
power. When in parallel, it is possible that a generator becomes a motor (“accepting”
power). Then this “motor” drags the prime mover, with eventual danger for the
Diesel or the turbine.

 Control the current increase in an out of step of a synchronous machine.
 Control the current increase in the ph-to ph fault.
Use of the relay to block the reverse current and active power. The following figure shows the
voltages vectors in a 3-ph balanced system.
Vector V12 is the Reference vector in the second figure, with the following parameters:
 E1 is the phase 1 voltage vector
 Ψ= insertion angle; it is the (-30°) angle between the V12 and E1 vectors.
 α = relay characteristic angle. The relay is manufactured with (+/-30°) angle.
 φ = phase shift among R current and voltage vectors.
 φMS= (α – Ψ) phase shift for relay max. sensitivity.
The current I1R is the current active component of I1RL, and its direction coincides with the E1
vector.
I1R = I1RL * cos (φ + Ψ- α)
I1R is max when cos (φ + Ψ- α) = 1 → (φ + Ψ- α); φ = α - Ψ = -30°- (-30°)= 0.
 If I1RL is absolutely inductive cos (φ + Ψ- α) = 0 and I1R = 0.
 Current Isc is the acceptable reverse current, a limit to be set in the relay. When the
active reverse current I1R is greater than Isc, the relay will trip. It is clear that if I1RL is
absolutely inductive and I1R = 0, Isc is never reached, whatever the value of I1RL .

Necessary Material:
2. SR-10/EV: Maximum current directional relay.
3. RL-2/EV: Variable resistive load mod.
SR10 Maximum current directional relay description:
Maximum current directional relay
The installed device is a directional relay (In = 5 A) which, with the current or power direction
following the input one (input in the higher terminals) does not enter alarm state; with current a
little over the threshold set in Is and with the current or power in the reverse direction, it alarms
after the time Ts.
Intervention Current Is = Inominal (5 A) x [Weight of the dip-switches (0-8.5) + 1] x K (0.02)
Intervention time Ts = [Weight of the dip-switches (0-16.5) + 0.1]
The technical characteristics of the device are shown in appendix A.

Figure (1)
2. Connect the terminals (Power Supply) to the 230-Vac auxiliary power supply line, but
do not connect the voltage. Connect the terminal PE to the protection conductor, too.
3. Connect the terminals (Voltage Input) respectively to L1 and L2 of the variable three-
phase power supply source. Connect a voltmeter to measure the relay input alternated
voltage (line voltage).
4. From the same three-phase power supply source mentioned above, by-pass the three-
phase load consisting in the RC rheostat (Y-connection load), the current I1 (also
called R1) must reach the terminals (Current Input).

5. Connect an ammeter to measure the relay input alternated current (load current). In
practice, it is sufficient to insert the load only on the conductor L1 – Neutral.
6. Suppose and adjust the device with the following design data:
- Dip-switch angle α = 30°;
- Delayed intervention dip-switch = ON;
- Inverse current threshold (Is) = 0,7 A (dip-switch a 2 + 4 ON);
- Intervention time (Ts) = 5 s (dip-switch t 0.1 + 0.8 + 4).
7. Some important considerations:
- SR-10/EV senses only one phase current (the L1 phase).
- If the load is balanced, the three currents L1-L2-L3 are equal, so sensing one of them
is enough.
- If the load is not balanced, the relay will trip ONLY if the L1 current is over the
limit.
8. As set, it is a directional relay that, with the current direction (In = 5A) to the input
(input in the higher terminal)
9. Check the correspondence of the output relay contacts (powered device not in alarm
state).
10. The relay reset is manual; it can be done only after the current goes back under the
threshold, with the pushbutton on the front panel or with the insertion of a jumper into
the RESET terminals.
Test (1): Resistive Load Only.
1. Increase the current over 0.7-A, simulating a reverse current over the accepted limit.
(Full line in the last design in figure 1).
Measured With AZ-VIP/EV Calculated
Comments
I1RL (A) PF I1R = I1RL * PF (A)
2. To simulate the direct current invert the SR-10 current input terminals, Modify the load
to increase the current over 0.7 A, and up to 2 A.
(Dotted lines in the last design in figure 1).
Measured With AZ-VIP/EV Calculated
Comments

Test (2): Resistive Inductive Load.
1. In this case, I1R vector direction lags to E1 vector direction. Try to follow the table
below for the tests. (full line in the last design).
Measured With
AZ-VIP/EV
Calculated
Comments
2. Now invert the SR-10 current input terminals, to simulate the direct current. Modify
the load to increase the current I1R over 0.7 A, and up to 2 A.
(Dotted lines in the last design).
Measured With
AZ-VIP/EV
Calculated
Comments

Objectives:
1. Use of the differential relay in a single phase network, control of the tripping current
and the tripping delay time. Simulation of a fault: current imbalance between wires.
2. Use of the differential relay in a 3-phase network, without neutral wire. Simulation of
a fault: current imbalance between wires.
3. Use of the differential relay in a 3-phase network, with neutral wire. Simulation of a
fault: current imbalance between wires.
4. Use of the differential relay in a 3-phase network, TN connection. Simulation of a fault
to ground, use of the Isolation Transformer SR21.
Code CEI: 87 Differential protection relay.
87G Differential ground relay.
87N Residual current differential relay.
We start the study of Differential Protections with the classical example of the single-phase
ELCB (Earth Leakage Circuit Breaker), a device that become common even at home. It will
help to understand the principle of the differential currents and its technical solution. See Fig 1
Figure (1)
Experiment (4) Differential Relay (SR14)

Necessary Material:
1. GCB-3/EV: Control board for the generating set mod.
2. MSG-3/EV: Synchronous generator-motor unit mod.
3. RL-2/EV: Variable resistive load mod.
Part I: Relay for phase sequence, phase failure and voltage asymmetry.
1. Insert three jumpers into the terminals set to power the relay for phase sequence, phase
lacking and voltage asymmetry as indicated in Figure 1.
2. Connect an ohmmeter to check the state of the output relay contact and complete the
wiring involving the step resistive load mod. RL-2/EV, be sure that all switches of the
steps of each phase are in position of excluded load (OFF) as shown in Figure 1.
Test 1: Disconnect one of the three phases and check the intervention of the output relay.
Test 2: Displace one of the three phases with another one and check the intervention of the
output relay.
Figure (1)
………………………………………………………………………………………………………………………………….….
……………………………………………………………………………………………………………………………….…….
………………………………………………………………………………………………………………………………….….
……………………………………………………………………………………………………………………………….…….

Figure (3)
Figure (4)
Differential protection of devices with two or more wounds
Fig. 5 shows the currents in case of an internal fault. Observe the use of CTs. The analysis is
done on the currents through the differential protection: a fault over i3, produces an imbalance
in the relay that will cause it to trip. A similar situation (imbalance) could occur even when
there is no fault; it is the case when there is a load imbalance or when a breaker is open for any
reason. The differential protection will “see” these cases, as only one of the sides of the
differential protection is affected.
Figure (5)

Percentage Differential Relays
The disadvantage of the current differential protection is that the CTs must be identical,
otherwise there will be current flowing through the CTs for faults outside of the protected
zone or even under normal conditions. Briefly, it is a problem on the CTs sensitivity and their
errors; the protection device could trip even with no fault. The technique named percentage
differential relays reduces the CTs’ sensitivity so to avoid the above mentioned problem.
Fig. 6 shows the circuit, where the difference with the previous ones are the restraint coils, in
series with the secondary currents of the CTs. The purpose of the restraint coil is to prevent
undesired relay operation due to CTs errors. The operating relay current |i1 - i2| required for
tripping is a percentage of the average current through the restraint coils, given by:
| i1 - i2 | ≥ k | i1 + i2 | / 2
K is the proportion of the operating coil current to the restraint coil current.
The restraint coils collect the currents relative to the machines, increasing the currents through
the operating coil. By so doing, the error sensitivity of the CTs is lowered.
Figure (6)
Differential Protection of Three Phase Power Transformers
Differential protection of 3- phase transformers should take into account the change in
magnitude and phase angle between primary and secondary currents.

Transformers Connected Y-Y or Δ-Δ
In these two connections, the primary and secondary currents are in phase, but their
magnitudes are different. The difference in the current magnitude must be balanced out by the
current transformer ratios. It can be demonstrated that:
CTR1 / CTR2 = a
Where:
- a = N1 /N2; transformer ratio; N1 = number of coils of the primary; N2 = number of
coils of the secondary.
- CTR1, CTR2: the current transformers ratio of primary and secondary.
Transformers Connected Y-Δ or Δ-Y.
In these power transformer connections, primary and secondary currents have different
magnitudes and also 30° phase shift. Both, the magnitude and the phase shift must be balanced
by appropriate ratio and connection of the current transformers. The phase shift on a Y-Δ bank
is corrected by connecting the CTs on the Δ in Y, and on the Y side in Δ . See Fig. 7. Relations
among currents are quite complex in this case.
Figure (7)

Objectives:
1. Protection against overcurrent in a power transmission line using overcurrent relay
SR1/EV.
2. Protection against Single line to ground fault in a power transmission line with insulated
neutral conductor using differential relay SR14/EV.
Sometimes the current crossing the conductors of a power transmission line may be higher than
the rated current. These situations occur when the line is overloaded, because too many users
are connected with the line or some users require greater power at the same time, and when
there are short circuits due to breaks in the supports of bare conductors or to insulation losses
between active conductors. An overload occurs when the line is crossed by a current exceeding
the rated current (generally it is approximately 10 times as high); this provokes the
overheating of conductors and devices, and it can be borne for a certain time. The current/time
relation may be fixed: when a certain current value is exceeded, after a certain time of tolerance
the protection relay will control the power device (switch) to put the line out of commission.
But this protection ratio may also be of inverse time/current type where a shorter intervention
time corresponds to a higher current. Short circuits generate a very strong current with thermal
and mechanical phenomena and destructive electric arcs, therefore the reaction time of the
protection relay must be instantaneous.
Necessary Material:
1. SEL-1/EV: Simulator of electric lines mod.
2. P14A/EV: Three-phase transformer mod.
3. Contactor with On-Off control
5. SR-1/EV: Overcurrent relay.
6. SR-14/EV: Differential relay.
7. IL-2/EV: Variable Inductive load mod.
8. RL-2K/EV: Variable Resistive load mod.
Experiment (1)
Protection of Transmission lines using
Electromechanical Relays

Figure (2)
4. Normal Condition: Apply balance load (switch A) to the circuit with the switches
of RL-2A/EV (1);
Normal
IΔ Tripping Time Notes
5. Set RL-2A/EV (2) as indicated in Test 1 with various value of resistance, and
connect as the dotted line. This connection simulates a “controlled imbalance
load” (the imbalance current is controlled by RL-2A/EV (2)).
Test R-load
Relay operation
Test (1) A
Test (2) B
Test (3) A||B

Objectives:
To configure the protection device SR16/EV with the use of the DIGSI software as:
1. Instantaneous [50] and delayed [51] maximum current relay to protect a no-load power
transmission line against phase-phase faults.
2. Instantaneous [50N] and delayed [51N] maximum homopolar current relay to protect a
no-load power transmission line against phase-ground faults.
3. Max ground directional current relay [67N], to protect a no-load power transmission
line against phase-ground faults.
4. Distance relay [21], protection against phase-ground and phase-phase fault in a no-load
power transmission line.
The Impedance Relay (IR) is one of the most important protection relays against short circuits.
It is mainly used when the current overload relays do not provide adequate protection; these
relays can work even when the short circuit current is low and the overload relays could not
operate safely. Additionally, the speed operation of the IR is independent from the short circuit
current value. Basically, it is a relay that senses the current and voltage of the protected device.
With these values, the IR calculates the impedance Z of the device. The IR compares the real
impedance Z of the protected device against Z0; if Z is equal or less tan Z0, it means that a
failure has occurred (could be a solid or not short-circuit). When the measured impedance of
the protected device Zmed is greater or equal to Z0, it is the normal condition. In the opposite
case, the protected device is in abnormal condition, and the IR will trip.
Necessary Material:
1. SEL-1/EV: Simulator of electric lines mod.
2. PC with DIGSI software installed.
3. SR16/EV: Distance relay mod.
4. SR20/EV: Power transmission line simulator mod.
5. SR21/EV: Isolation transformer mod.
6. UAT/EV: Fixed Power supply mod.
7. RC3-PT/EV: Rheostat mod.
Experiment (2)
Protection of Transmission lines using
Digital Relays

Figure (4)
5. Set RL-2A/EV (2) as indicated in Test 1 with various value of resistance, and connect
as the dotted line. This connection simulates a “controlled imbalance load” (the
imbalance current is controlled by RL-2A/EV (2)).
Test R-load
Relay operation
Test (1) A
Test (2) B
Test (3) A||B

Part III: SR-14 in a Three phase line with neutral wire. Simulation of a fault: current
imbalance between wires.
Figure (5)
4. Normal Condition: Apply a balance load (switch A) to the circuit with the switches of
RL-2A/EV (1);
Normal

Figure (6)
as the dotted line. This connection simulates a “controlled imbalance load” (the
Test R-load
Relay operation
Test (1) A
Test (2) B
Test (3) A||B

Part IV: SR-14 in a Three phase line with neutral wire. Simulation of a fault: current
imbalance between wires.
Figure (7)
4. Normal Condition: Apply a balance load (switch A) to the circuit with the switches of
RL-2A/EV (1);
Normal

Figure (8)
as the dotted line. This connection simulates a “controlled phase to ground fault” (the
Test R-load
Relay operation
Test (1) A
Test (2) B
Test (3) A||B

Chapter 3
Synchronous Generator Protection
Contents
Part (1) Relay for phase sequence, phase failure and voltage asymmetry.
Part (2) Relay for Max/min three-phase voltage.
Part (3) Relay for Max/min frequency of a power production plant.
Part (4) Relay for Maximum current (overcurrent) to a three-phase line

Objectives:
Studying and applying a relay for:
1. Phase sequence, phase failure and voltage asymmetry to a three-phase circuit.
2. Max/min three-phase voltage.
3. Max/min frequency of a power production plant.
4. Maximum current (overcurrent) to a three-phase line.
1. Relay for phase sequence, phase failure and voltage asymmetry.
It detects that the triad of voltages is in the set direction and detects the voltage
asymmetries, occurring, for instance, for too unbalanced load. Its action prevents
dangerous overvoltages to the synchronous generator.
SR6 Phase sequence and voltage asymmetry relay description:
- Asymmetry adjustment with rotary potentiometer from the 5 to the 15 % with intervention
after DELAY time and automatic reset when the unbalance drops under the 1% of the set
point.
- Adjustment of the intervention time with DELAY potentiometer from 0.1 to 10 s.
- Instant intervention for phase lack or wrong phase sequence.
- Intervention for line frequency variation over the 5%
Experiment (1) Synchronous Generator Protection

The electrical and the operation diagram of this relay are shown in the following
figures:
2. Relay for Max/min three-phase voltage.
It detects the limit of the voltage triad produced in normal operation by the
synchronous generator, or distributed to the transmission line. Usually, the relay,
acts on the main switch to set the controlled object out of service (synchronous
generator or user connected with the line) when a voltage rise or drop can cause
malfunctions or damages.

3. Relay for Max/min frequency of a power production plant.
The relay enables the max/min
frequency control of the alternating
power output by the synchronous
generator in normal operation. As
protection device, it acts on the main
switch of the synchronous generator. It
is used to protect the synchronous
generator in case of over or under
speed of the prime mover.
The electrical and the operation
diagram of this relay are shown in the
following figures:
SR5 Max/min frequency Relay description:
Max/min frequency Relay settings:
- Adjustment of the intervention threshold for maximum frequency with rotary switch from
0.5 to 10 Hz.
- Adjustment of the intervention time for maximum frequency with potentiometer Delay
max from 0.1 to 30 s.
- Adjustment of the intervention threshold for minimum frequency with rotary switch from
0.5 to 10 Hz.
- Adjustment of the intervention time for minimum frequency with potentiometer Delay min
from 0.1 to 30 s.

(B) Setting Group A – distance zones (quadrilateral)-:
1. Zone Z1:
(a) Operating mode Z1[No. 1301] = Forward
(b) R(Z1), Resistance for PH-PH faults [No. 1302] = 42.000 ohm
(c) X(Z1), Reactance [No. 1303] = 49.000 ohm
(d) RE(Z1), Resistance for PH-E faults [No. 1304] = 42.000 ohm
(C) Configuration matrix (Masking I/O):
1. Dis. General
(a) Dis.Gen. Trip [No. 03801]  Led (3) : L (latched)
3. Turn ON the power supply mod. UAT/EV
4. Push the NO button 1I on panel mod. SR16/EV.
Part III-1: Phase – Phase Fault
1. Connect a 20 Ω resistor in series to the T.M.C.B between two phases as shown in Figure. 8.
2. Turn ON the switch to perform a phase-phase fault, respectively at 25, 50, 75 and 100 km.
3. Measure the fault current with SIGRA program.
Figure (8)

3. Set the synchronous generator under load with the insertion of the resistive load.
Test 3: Put unbalanced load and record the value of phase voltages and currents (using power
analyzer) and delay time (using chronometer), fill the following table.
Asymmetry
%
Line voltages (V) Line currents (mA) Operation
delay in
asymmetry
Measured
delay
(Sec)Va Vb Vc Ia Ib Ic
5%
(AB,A,A)
10 sec
7.5%
(C,A,A)
10 sec
10%
(AC,A,A)
10 sec
Part II: Max/min three-phase voltage Relay.
1. Remove jumpers of the symmetry relay and insert four jumpers into the terminals set to
power the max/min three-phase voltage relay as indicated in Figure 2.
wiring of the GCB-3/EV panel as shown in Figure 2.
Figure (2)

Test 1: Max voltage relay.
Increase the voltage supplied by the synchronous generator by increasing the excitation current
and record the time between the “overvoltage” moment and the same output relay tripping one.
Reduce the voltage again to its rated value (400 V) and check the alarm suppression (the
maximum voltage output relays is reset). Consider that the relay has a hysteresis of 3% with
respect to the set point. Determine at which value of voltage will the relay reset?
Maximum
voltage threshold
%
Line voltage
(V)
Maximum voltage
intervention delay
Measured delay
(Sec)
Reset Value
(V)
105% 5 sec
110% 5 sec
Test 2: Min voltage relay.
Way 1: Decrease the voltage supplied by the synchronous generator by decreasing the excitation
current and record the time between the “undervoltage” moment and the same output relay
tripping one. Increase the voltage again to its rated value (400 V) and check the alarm suppression
(the minimum voltage output relays is reset). Consider that the relay has a hysteresis of 3% with
respect to the set point. Determine at which value of voltage will the relay reset?
Minimum
voltage threshold
%
Line voltage
(V)
Minimum voltage
intervention delay
Measured delay
(Sec)
Reset Value
(V)
95% 5 sec
90% 5 sec
Way 2: Complete the wiring including the step resistive load mod. RL-2/EV. Be sure that all
step switches of each phase are in position of load excluded (OFF). Set the synchronous
generator under load with the insertion of the resistive load (with different values of the
resistive load) and measure the following:
Resistive
Load in Ω
Minimum
voltage
threshold %
Line
voltage (V)
Minimum voltage
intervention delay
Measured
delay
(Sec)
Reset
Value
(V)
A 95% 5 sec
A||B 90% 5 sec

Part III: Max/min frequency Relay.
1. Remove jumpers of the max/min voltage relay and Insert two jumpers into the terminals
set to power the max/min frequency relay as indicated in Figure 3.
wiring of the GCB-3/EV panel as shown in Figure 3.
Figure (3)
Test 1: Max frequency relay.
Increase the test frequency using RPM potentiometer and record the time between the
overfrequency and the same output relay tripping one.
Maximum frequency
threshold
Frequency
(Hz)
Maximum frequency
intervention delay
Measured delay
(Sec)
50.2 Hz (+10%) 3 sec
50.4 Hz (+20%) 3 sec

Test 2: Min frequency relay.
Decrease the test frequency using RPM potentiometer and record the time between the under
frequency and the same output relay tripping one.
Minimum frequency
threshold
Frequency
(Hz)
Maximum frequency
intervention delay
Measured delay
(Sec)
49.8 Hz (-10%) 3 sec
49.6 Hz (-20%) 3 sec
Part IV: Overcurrent and Short circuit Relay.
1. Remove jumpers of the max/min frequency relay and connect the 3-Phase Overload and
the Short-Circuit relay with the proper terminals via six jumpers as indicated in
Figure 4.
wiring of the GCB-3/EV panel and complete the wiring including the step resistive load
mod. RL-2/EV to obtain the current regulation in the ammetric relay as shown in
Figure 4.
Figure (4)

Part III: Checking the operation of a differential selective switch [S] with operating
differential rated current Idn = 0.3 A - type A (Q2).
1. Connect the circuit as shown in Figure 3.
Figure (3)
2. Assemble a system in configuration of TT distribution system as indicated in the fig. 1
where the output of the measuring instrument is connected with the differential
protection under test (switch Q2), according to the method explained previously.
3. Insert the jumpers RE1 of 1 Ω, RE2 of 2 Ω.
4. Power the system (panel) and turn all the protection switches involved in this
experiment to ON.
5. Turn the selector EQUIPMENT to the position ~, the warning light on indicates that the
power-absorbing equipment is powered correctly.
6. Use the “combination” of two earth faults to obtain various current values and to check
the operation of the differential protections.

Questions:
1. Describe the effect of the following Abnormal operating conditions on the
synchrouns generator?
(a) Voltage Asymmetry;
(b) Over and under voltage;
(c) Over and under frequency;
(d) Over load.
2. Based on the overload relay experiment answer the following questions:
(a) Sketch the connection needed to connect synchrouns generator with:
1. Relay;
2. Variable three-phase resistive load.
(b) If the load attached on the synchronous generator is (B||C = 120Ω) and the
load current measured is 889mA, if the settings of the overload relay are:
overload current = 0.7A with intervention delay of 5 second.
1) Explain how to put the settings of the relay, and explain how to reset the
relay after removing the cause of overload?
2) Explain the operation of the relay after the load attached?

Part IV: Checking the operation of a delayed differential switch with adjustable
operating differential rated current Idn and time t, type A (RCCB coupled with the
switch Q1 via the CRC coil).
Figure (4)
where the output of the measuring instrument is connected the differential protection
under test (output of RCCB device), according to the method explained previously.
4. Set a current Idn = 0.3A and a time t = 500 ms in the adjustable differential RCCB.
experiment to ON.

8. Change the combination of the two earth faults as shown in table (7) and measure the
fault current with describing the operation of the differential switch Q12.
Differential switch with operating differential rated current Idn = 30 mA - type AC (Q12).
Combination of two faults
Current (mA) Comments
Fault (1) Left (Ω) Fault (2) Right (Ω)
15k 15k
5k 5k
1.5k 1.5k
0.5k 0
0.5k 0.5k
Table (7)
9. Then turn the selector EQUIPMENT to the position =, the earth fault current crossing
the power-absorbing equipment will be of unidirectional pulsating type.
10. Repeat the test changing the value of the earth fault and check how the differential
protection behaves with a unidirectional fault, then tabulate your result in the following
table.
15k 15k
5k 5k
1.5k 1.5k
0.5k 0
0.5k 0.5k
Table (8)

Notes:
Remember that an (adjustable) delayed differential relay must always be coupled with a power
device such as a magnetothermal switch, to provoke the opening of the controlled circuit. This
device consists of a current transformer and of an electronic control circuit. The current
transformer with through hole will detect any “difference” of the current of all the live leads of
the electric system; the electronic control circuit compares the current detected by the
transformer to the selected threshold and it enables the output relay after a possible adjusted
delay time.
The output relay of the differential switch will be connected with an enabling/disabling device
of the power switch. As explained above, the current transformer of the differential relay
could be installed indifferently after or before the power switch. The only expedient concerns
the direction of the live leads running through it; all these must have the same direction.

Objectives:
1. Verification of selectivity among devices against overcurrents
2. Verification of selectivity between differential devices connected in parallel (horizontal
selectivity)
3. Verification of selectivity among differential devices connected in series (vertical,
amperometric and time selectivity)
Standard CEI 64-8536.1 Selectivity among protection devices against overcurrents
When more protection devices are connected in series and service needs require this solution,
the operating characteristics of these devices must be chosen so that only the part of the system
suffering the fault can be disconnected from the power supply. The operational situation
requiring selectivity must be defined by the principal and designer of the system.
Standard CEI 64-8536.3 Selectivity among differential devices
A selectivity among differential devices connected in series can be ordered for operational
reasons, in particular when safety is involved, so that the parts of the system not touched by the
possible fault are anyway powered. This selectivity can be obtained with the choice and
installation of differential devices: in fact, although ensuring the necessary protection to the
various parts of the system, these devices disconnect the supply voltage only from the parts of
the system positioned after the device installed before, and near the point of the fault. The
selectivity of the two differential devices connected in series is ensured when these devices
simultaneously comply with the following conditions:
1) The time-vs-current curve of non-operation of the upstream device must be positioned
above the time-vs-current disconnection curve of the downstream device;
2) The rated differential current of the upstream device must be properly higher than that of
the downstream device.
Experiment (2) Selectivity among Protection Devices

Load Settings of the overload relay
Line current
(mA)
Tripping time
(sec)
R-(Ω) Isetting (A) T (sec) Iline T
A 0.5 5
B 0.5 5
A || B 0.6 5
Part II: Protection against single line to ground fault in a power transmission line with
insulated neutral conductor using differential relay SR14.
1. Start this experiment considering the LINE 2 with the following constants: R= 18 Ω;
L = 72 mH C = 0.2 µF (with Y connection); Length = 50 km.
Figure (2)

3. With no power supply adjust the relay settings as required
4. Enable and adjust the voltage of the power supply at 380 V.
5. Turn the breaking-control switches at the origin and at the end of the LINE 2 to ON.
6. At normal condition with balanced resistive load (A) measure the fault current and
tripping time for this case.
7. Perform a single line to ground fault at the receiving end point by connecting between
the phase 1 and ground then measure the fault current and tripping time.
Load
Condition
Settings of the
differential relay
Fault current
(mA)
Tripping time
(sec)
R-(Ω) IΔn T (sec) IΔn T
(A,A,A) Normal 0.025 2
(A,A,A) SLG (L1-G) 0.025 2

Part I: Configuration of SR16 as maximum current relay [50], [51], [50N] and [51N]
Protections [50N] and [51N] are fed by the amperometric transformer I4 (inside SIPROTEC
7SA610 device). The transformer reproduces the short-circuit current to the secondary in case
of a phase-ground fault. During normal operation, the currents vectorial sum in the three phases
is 0; the magnetic flux produced by the currents is consequently 0. During a ground fault, the
vectorial sum of the three phase currents is different from 0. This means that the resultant
magnetic flux concatenates with the secondary coil of the current transformer, resulting in a
non-zero current. The protection senses the generated homopolar current and intervenes.
1. Perform the electrical connections following the electrical diagram of figures 1 and 2.
Figure (1)

The device installed downstream is a device of general type with differential rated current of
30 mA; the device available in intermediate position is of S type with differential rated current
of 100 mA, and the device installed downstream is of delayed type with definite time and
differential rated current of 300 mA.
The selectivity between two differential devices connected in series (one of S type and the
other of general type) is reached when the ratio between the respective differential rated
currents is at least equal to 3.A system without any differential device at its origin becomes
selective when all the starting circuits are protected by differential devices, separately or in
group. As soon as a fault occurs, only the differential switch protecting the relevant circuit is
enabled.
Standard CEI 64-8536.2 Combining differential devices with protection
devices against overcurrents
When a differential device is built-in or combined with a protection device against
overcurrents, this assembly must comply with the prescriptions of all the separate functions,
besides having a suitable breaking power, operating characteristics versus the rated current,
differential rated current coordinated with the protection earth electrode, in TT systems, or
with the fault loop impedance, in TN systems.
When a differential device is not built-in or combined with any protection device against
overcurrents:
- The protection against overcurrents must be ensured by protection devices against
overloads and short circuits;
- The differential device must be able to bear the thermal and mechanical stresses it can
undergo in case of short circuit occurring after the place of its installation, without
damages;
- The differential device must not be damaged in these conditions of short circuit even
when the same differential device tends to open, for the unbalanced current or for the
earth current.
The stresses mentioned above depend on the estimated short-circuit current in the point where
the differential device is installed and on the characteristics of the protection device against
short circuits.
Protection devises description:
- Quadripolar automatic magnetothermal switch, with rated current In = 2 A, curve C,
including Coil Remote Release;

(B) Setting Group A – Power System Data 2:
1. Measurement: Full Scale Voltage (100%) [No. 1103] = 1 kV
2. Measurement: Full Scale Current (100%) [No. 1104] = 100 A
3. Line Angle [No. 1105] = 85o
4. X’-Line reactance per length unit [No. 1110] = 0.4522
5. Line length [No. 1111] = 100 km
(C)Setting Group A – Backup Overcurrent:
(a) General :
1. Operating mode [No. 2601] = ON, Always Active
(b) Setup the protection parameters [50]:
1. Click on I>> ;
2. Pick up current [No. 2610: Iph>>Pickup] = 0.3 A
3. Time delay [No. 2611: T Iph>>Time delay] = 0 Sec (Instantaneous intervention).
(c) Setup the protection parameters [50N]:
1. Click on I>>;
2. Pick up current [No. 2612: 3I0>>Pickup] = 0.1 A
3. Time delay [No. 2613: T 3I0>>Time delay] = 0 Sec (Instantaneous intervention).
(d) Setup the protection parameters [51]:
1. Click on I>;
2. Pick up current [No. 2620: Iph >>Pickup] = 0.1 A
3. Time delay [No. 2621: T Iph>>Time delay] = 2 Sec.
(e) Setup the protection parameters [51N]:
1. Click on I>;
2. Pick up current [No. 2622: 3I0>>Pickup] = 0.07 A
3. Time delay [No. 2623: T 3I0>>Time delay] = 2 Sec.
(D)Configuration matrix (Masking I/O):
1. P. System Data 2
(a) CB 3p Closed [No. 00379]  BI1 (Binary input 1)  H (High) Led (1) : U (Unlatched)
(b) CB 3p Open [No. 00380]  BI2 (Binary input 2)  H (High)  Led (2) : U (Unlatched)
(c) Relay TRIP [No. 00511]  BO6 (Binary output 6)  U (Unlatched)
2. Back-Up O/C
(a) O/C TRIP I>> [No. 07221]  Led (4) : L (latched)
(b) O/C TRIP I> [No. 07222]  Led (5) : L (latched)

6. Put the proper settings of the Q1,Q11 and Q12 switches.
Protection devices settings
Comments
Q1 Q11 Q12
Current Time Current Time Current Time
7. Simulate a short circuit across the output terminals of Q11 and Q12, on the panel, to
obtain an overcurrent and to study its effects on the protection devices.
8. Measure the short-circuit current with the ammeter tongs and tabulate your results in the
following table.
Condition
Short circuit
current
Protection devices stauts
Comments
Q1 Q11 Q12
Short circuit

Part I-2: Phase – Ground Fault
1. Connect the T.M.C.B. between the phase and ground, as shown in figure 4.
2. Turn ON the switch to perform a phase-ground fault, respectively at 25, 50, 75 and 100 km.
Figure (4)
4. Insert the data obtained with the measurements in the following table:
Phase – Ground Fault
PH-E fault Line (km) T start (ms) T trip (ms)
Fault Current
(A)
Protection
intervetion
L1 – E 100
L2 – E 75
L3 – E 50
L1 – E 25

Part II: Configuration of SR16 as maximum ground directional current relay [67N]
This protection also has the I4 homopolar amperometric transformer (inside the SIPROTEC
7SA610 device). The protection [67N], besides measuring the homopolar residual current in a
ground fault, measures the homopolar voltage V0. That’s why we use three voltmetric
transformers (n=1000/100) without open Delta connection of the secondaries, because
calculation of the homopolar voltage V0 is internally calculated. During a normal operation the
vectorial sum of the three voltages over the secondaries of the VT is zero. In case of a phase-
ground fault, the sum of the three voltages is different from zero. Once the homopolar current
vector I0, the homopolar voltage vector V0 and their phase shift φ are measured, the protection
will be able to estimate the real power, that is equal to P0= V0*I0*cos φ.
The power sign (positive or negative) allows the relay [67N] to determine the fault current
direction, and then to establish if the fault is upstream or downstream.
Due to this property the protection [67N] is called ground directional relay. Since the
protections are selective, the directional relay [67N] controls the breaker opening only in case
of a downstream ground fault.
1. Perform the electrical connections following the electrical diagram of figures 1 and 5.
Figure (5)

2. Set the Parameters of the protection device SR16/EV and power system data using DIGSI
software as follows:
(A)Setting Group A – Earth Fault Overcurrent:
(a) General :
1. Earth Fault Overcurrent function [No. 3103] = ON
(b) 3I0>>>:
1. Operating mode [No. 3110] = Forward
2. Pick up current [No. 3111: 3I0>>> Pickup] = 0.07A
3. Time delay [No. 3112: T 3I0>>Time delay] = 0 Sec (Instantaneous Intervention).
(c) Direction:
1. Polarization [No. 2611]: With U0 +IY or U2
2. ALPHA, Lower angle for forward direction [No. 3612A]= 338o
3. BETA, Upper angle for forward direction [No. 3613A]= 122o
4. Min. zero seq. voltage 3U0 for polarizing [No. 3164]= 0.5 V
(B) Configuration matrix (Masking I/O):
1. Earth Fault O/C
(a) EF Trip [No. 01361]  Led (6) : L (latched)
3.Turn ON the power supply mod. UAT/EV
4.Push the NO button 1I on panel mod. SR16/EV.
5.Connect the T.M.C.B. between the phase and ground, as shown in figure 6.
6.Turn ON the switch to perform a phase-phase fault, respectively at 25, 50, 75 and 100 km.
7.Measure the fault current with SIGRA program.

Figure (6)
Phase – Ground Fault
PH-E fault Line (km) T start (ms) T trip (ms)
Fault Current
(A)
Protection
intervetion
L1 – E 100
L2 – E 75
L3 – E 50
L1 – E 25

Maximum and minimum three-phase voltage relay (SR3).
- Maximum and minimum three-phase voltage relay
- Switch for the nominal voltage of the three-phase line to be controlled 380 V, 400 V or 415
Vac + 10% / -15%.
- Adjustment of the intervention threshold for overvoltage with Max Voltage potentiometer
from the 102 to the 110%.
- Adjustment of the intervention time for overvoltage with Delay Max potentiometer from
0.1 to 10 s.
- Adjustment of the intervention threshold for undervoltage with Min Voltage potentiometer
from the 85 to the 98%.
- Adjustment of the intervention time for undervoltage with Delay MIN potentiometer from
0.1 to 10 s.
- Power supply from measurement circuit.
- Automatic reset when the current goes back to fixed parameters.
- State of the normally energized relays, de-energized at the intervention
- Led ON: indicating the presence of power supply.
- Led MAX indicating the maximum voltage intervention.
- Led MIN: indicating the minimum voltage intervention.

Phase – Phase Fault
PH-PH
fault
Line
(km)
Measured line
distance (km)
T start
(ms)
T trip
(ms)
Fault Current
(A)
Protection
intervetion
L1 – L2 100
L2 – L3 75
L1 – L3 50
L1 – L2 25
Part III-2: Phase – Ground Fault
1. Connect a 20 Ω resistor in series to the T.M.C.B between the phase and ground as shown
in Figure 9.
2. Turn ON the switch to perform a phase-phase fault, respectively at 25, 50, 75 and 100 km.
Figure (9)

Current directional relay with fixed time (SR10).
- Electronic directional current relay with fixed time.
- Direct measurement or via CT and VT.
- Nominal current 5 A
- Nominal voltage 400 V
- Adjustment of the inverse current intervention threshold (In / Is) con dip-switch from 0.1 to
0.95 la In.
- Selection of the characteristic angle α= 30° or -30°
- Adjustment of the overload intervention time with dip-switch from 0.1 to 16.6 s.
- Auxiliary power supply of 230 Vac 50-60 Hz.
- Manual reset with pushbutton on the front panel or with external Reset contact.
- Normally energized state of relay, de-energized at the intervention.
- Normal green led indicating the auxiliary power supply presence and regular operation.
- Trip red led indicating the intervention for inverse current.
- Memory yellow led indicating the relay intervention.
- Test switch for relay intervention.
- Local reset with Reset pushbutton and /or remote with a NO pushbutton connected to the
proper Reset terminals.
Electrical Diagram

Objectives:
1. Checking the operation of a differential switch with operating differential rated current
Idn = 30 mA - type A (Q11).
2. Checking the operation of a differential switch with operating differential rated current
Idn = 30 mA - type AC (Q12).
3. Checking the operation of a differential selective switch [S] with operating differential
rated current Idn = 0.3 A - type A (Q2).
4. Checking the operation of a delayed differential switch with adjustable operating
differential rated current Idn and time t, type A.
Checking the operation of a differential switch
By reducing the value of the variable resistance Rp will
provoke an increase of the current. Then the voltage is
measured between the exposed-conductive-parts (UT touch
voltage) and an independent auxiliary earth electrode
(voltage probe). Also the operating current Id of the
differential device is measured: this current must never be
higher than the rated current Idn of the switch under test.
The following condition: UT > UL * (Id / Idn); where UL
is the conventional limit of touch voltage, must be
complied with.
This method uses an auxiliary earth electrode.
Experiment (1)
Checking the Operation of the Protection
Devices with Differential Current

Necessary Material:
1. PDG-R/EV: Neutral Point Connection panel mod.
2. Multimeter for a.c. voltages.
3. Ammeter tongs for alternating currents.
Part I: Checking the operation of a differential switch with operating differential rated
current Idn = 30 mA - type A (Q11).
Figure (1)

experiment to ON.
Differential switch with operating differential rated current Idn = 30 mA - type A (Q11).
50k 50k
15k 50k
15k 15k
5k 0
5k 5k
9. Repeat the test changing the value of the earth fault and make sure that the differential
protection of class A is immediately enabled, like in the case of the sinusoidal fault
(EQUIPMENT in the position ∼), then tabulate your results in table (2).
Differential switch with operating differential rated current Idn = 30 mA - type A (Q11).
50k 50k
15k 50k
15k 15k
5k 0
5k 5k

Part II: Checking the operation of a differential switch with operating differential rated
current Idn = 30 mA - type AC (Q12).
experiment to ON.
Figure (2)

50k 50k
15k 50k
15k 15k
5k 0
5k 5k
Table (3)
9. Repeat the test changing the value of the earth fault and check how a differential
protection of class AC behaves with a unidirectional fault. then tabulate your results in
table (4).
50k 50k
15k 50k
15k 15k
5k 0
5k 5k
Table (4)

fault current with describing the operation of the differential selective switch Q2.
Differential selective switch with operating Idn = 0.3 A - type A (Q2).
15k 15k
5k 5k
1.5k 1.5k
0.5k 0
0.5k 0.5k
Table (5)
9. Repeat the test changing the value of the earth fault and check how the differential
protection behaves with a unidirectional fault, then tabulate your results in the following
table.
Differential selective switch with operating Idn = 0.3 A - type A (Q2).
15k 15k
5k 5k
1.5k 1.5k
0.5k 0
0.5k 0.5k
Table (6)

Electrical Power Systems Protection Lab in PTUK

Electrical Power Systems Protection Lab in PTUK

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