Transcript A method of teaching students the physical modern relay - UNO-EF

A method of teaching students the physical
modern relay programming and operation
ABSTRACT: A microprocessor relay is configured as a portable,
self-contained, low cost learning tool to supplement academic
textbooks and classroom lectures on mainstream power system
protection technology. The presenter’s inspiration to assemble
the demo was the result of the motivation of the students who
would benefit from this educational tool, especially those who
learn best by the “hands-on” 3-D experience. Analogies and
comparisons aid students in understanding new concepts,
especially the merging of logic programming and system
protection engineering. Learning is not just strictly for students
as the presenter is surprised to learn something new about the
behavior of common electrical appliances.
A method of teaching students
the physical modern relay
programming and operation
by Dan L. Glaser, BSEE, MSE, P.E.
Southeast Symposium on Contemporary
Engineering Topics
Electrical and Computer Engineering
September 19, 2014
A method of teaching students the physical
modern relay programming and operation
My INSPIRATION – Local community college with
ABET accredited program in need of industry support
to demonstrate continuous improvement and to
introduce student to modern technology.
The CONSTRAINTS – College’s engineering and
electronics technology curriculum has limited budget
to acquire newer technology.
Their MOTIVATION – Many students who enroll in the
2-year technology program already have employment,
but are seeking better opportunities by dedicating time
In participating 3 hour class sessions each week night.
A method of teaching students the physical
modern relay programming and operation
How to satisfy needs?
INSPIRATION – Volunteer to lecture students on
aspects of the electric utility industry, especially with
emphasis on electrical and computer engineering
applications.
CONSTRAINTS – Seek donations from vendors who
are willing to provide modern technology equipment
for educational purposes.
MOTIVATION – Demonstrate near “real-life”
experience with industry tools used “day-to-day.”
A method of teaching students the physical
modern relay programming and operation
Needs were met.
INSPIRATION – Annual “one evening” lecture on
protective relaying has been offered to students
enrolled in summer session for past 3 years.
CONSTRAINTS – Prominent vendor of relay
protection equipment donated microprocessor relay
to college.
MOTIVATION – “Hands-on” demonstration of
microprocessor relay using simple setup now
included in annual “one evening” lecture.
A method of teaching students the physical
modern relay programming and operation
How do we learn?
Everyday “life experiences” are learning
experiences. Our five senses – seeing, hearing,
touching, tasting, and smelling – are key to
receiving and understanding (learning).
Do each of us have a different way of learning?
Yes, some learn better by seeing – reading or
watching. Others rely on hearing – attending class
or listening to lectures. Some need touching as a
3-D experience or “hands-on” approach for
learning. Tasting and smelling are often learning
approaches to keep us safe from harmful
substances.
A method of teaching students the physical
modern relay programming and operation
So, here’s my solution to appealing to the seeing,
hearing, and touching “learning” senses:
A self-contained demonstration of a microprocessor
relay setup that introduces electrical & computer
engineering technology to the classroom or lab.
A method of teaching students the physical
modern relay programming and operation
I suppose our smelling
sense helps us learn
when too much
current goes through
a resistor.
What about tasting? I would
think that eating a sandwich
at a workbench would not be
a good idea. What do
solder balls and stripped
wire taste like?
A method of teaching students the physical
modern relay programming and operation
Here is the wiring diagram and the programming
assignments for the microprocessor relay demo.
A method of teaching students the physical
modern relay programming and operation
A view of the finished product.
A method of teaching students the physical
modern relay programming and operation
Safety is a vital “learning” concept. Safe work practices
and hazard identification are emphasized during the
demonstration.
Insulating tape over terminal
blocks with “live” AC power.
Use of power strip with
15 amp circuit breaker.
A method of teaching students the physical
modern relay programming and operation
A key method to “learning” is use of analogies. This is
when a similarity is made between a new concept and
something that most people have already encountered.
This is
like this
A method of teaching students the physical
modern relay programming and operation
Another key method to “learning” is use of comparisons. This is
when a difference is emphasized between new concept and
something that most people have already encountered.
SIMILAR
These are both switches.
Both can isolate electricity.
That is how they are similar.
DIFFERENT
The wall switch can break low
voltage & current, but the utility
switch cannot at high voltage.
A method of teaching students the physical
modern relay programming and operation
SIMILAR
A better “analogy” or “similarity” is that the house circuit breaker
panel (left) and the high voltage substation circuit breaker (right)
both can isolate and interrupt normal load or short circuit current.
A method of teaching students the physical
modern relay programming and operation
MOTOR OP
SWITCH
CURRENT
TRANSFORMER
CIRCUIT BREAKER
Here’s the
analogy of a
“real” station
layout to the
demo relay.
A method of teaching students the physical
modern relay programming and operation
Now it’s time to define attributes of the demo relay
physical I/O mapping and programming
AUX1 PB toggles OUT103 & OUT105 contact (close/open)
AUX2 PB toggles OUT104 & OUT106 contact (close/open)
AUX3 PB enables 50 instantaneous overcurrent TRIP
AUX4 PB enables 51 inverse time overcurrent TRIP
AUX3 & AUX4 PB enables definite time overcurrent TRIP
Vb energized causes AUX1 LED to illuminate
Vc energized causes AUX2 LED to illuminate
50 instantaneous overcurrent element enabled causes AUX3 LED to illuminate
51 inverse time overcurrent element enabled causes AUX4 LED to illuminate
Definite time overcurrent element enabled causes AUX3 & AUX4 LED to illuminate
A method of teaching students the physical
modern relay programming and operation
Unless default settings and logic are used, the microprocessor
relay is dumb. It needs to be programmed. This includes the
pushbuttons, the LED lamps, and input/output behavior.
TR
= 50P1 * LT10 * !LT11 + 51P1T * !LT10 * LT11 + 67P1T * LT10 * LT11
SET8
RST8
SET9
RST9
= !LT8 * PB7
= LT8 * PB7
= !LT9 * PB8
= LT9 * PB8 + /TRIP
SET10 = !LT10 * PB9
RST10 = LT10 * PB9
SET11 = !LT11 * PB10
RST11 = LT11 * PB10
67P1TC = 1
51P1TC = 1
OUT103 = LT8
OUT105 = LT8
OUT104 = LT9 * !TRIP
OUT106 = LT9 * !TRIP
LED7
LED8
LED9
LED10
= 59B1
= 59C1
= LT10
= LT11
A method of teaching students the physical
modern relay programming and operation
The microprocessor relay uses some fundamental logic
expressions which offer the user flexibility in applying the relay.
LOGIC TERMINOLOGY:
Assert – Logical 1, energized, true, closed contact
Deassert – Logical 0, de-energized, false, open contact
! – Inverted logic, output state opposite of input state
* - AND function, all inputs must be Logical 1 for output to be Logical 1
+ - OR function, any input (at least one) is Logical 1 for output to be 1
/ - Rising edge trigger, asserts when Logical 0 changes to Logical 1
\ - Falling edge trigger, asserts when Logical 1 changes to Logical 0
A method of teaching students the physical
modern relay programming and operation
Let’s follow the programming for pushbutton 7 (PB7):
Since we want PB7 to latch “on” or “off” each time we depress PB7, we will need
a latch bit to retain a continuous “on” or “off” state. Since latch bit 7 (LT7) has
already been used elsewhere by default logic, we will use latch bit (LT8) to hold
the “on” or “off” status that toggles each time we depress PB7.
SET8 = !LT8 * PB7
So, when PB7 is depressed and if LT8 is NOT “on” (but “off”), then latch bit 8
(LT8) will turn “on” by making SET8 logic “1” (asserted). Conversely, the next
logic statement will turn “off” LT8 if it is already “on” and PB7 is depressed.
RST8 = LT8 * PB7
When LT8 is “on” (asserted), output contacts 103 and 105 will close on the relay
as defined in the next two logic statements.
OUT103 = LT8
OUT105 = LT8
A method of teaching students the physical
modern relay programming and operation
Be aware that the LED lamps adjacent to the pushbuttons
are not automatically illuminated when a pushbutton is
depressed. The behavior of the LED must be programmed!
Recall how LT8 is programmed from the following statements.
SET8 = !LT8 * PB7
RST8 = LT8 * PB7
Remember that LT8 controls the position of OUT103 and OUT105 contacts.
OUT103 = LT8
OUT105 = LT8
LED7 = 59B1
Notice that LED7 does not “directly” follow PB7 logic state. LED7 follows PB7 logic only
as an “indirect” result LT8 closing OUT103 and OUT105 contact. Closure of these
contacts energize the circuit section connected to “Vb,” the voltage input measuring
element. When “Vb” voltage exceeds 60 volts AC (as per the 59P1P setting, then the
59B1 logic variable “asserts” to cause LED7 to illuminate.
A method of teaching students the physical
modern relay programming and operation
Now that “programming” of the microprocessor relay has been
introduced, how to you get the “program” into the relay?
Communication with
the microprocessor
relay is achieved with a
PC, communications
cable (serial or USB),
and the relay’s
communication port.
The user can either
use “terminal mode”
that supports simple
messaging or use the relay vendor’s communication software.
A method of teaching students the physical
modern relay programming and operation
The “terminal command” interface has a language of its own.
The vendor’s communication software is quite powerful, supports
storing files as a database, and retrieves event reports.
COMMUNICATION TOOLS FOR RELAY:
AcSELerator Quick Set – relay setting data entry tool
SEL-5601 Analytic Assistant – captured event and waveform viewing tool
Quickset Communications – send terminal commands to interrogate relay
NOTABLE TERMINAL COMMANDS:
ACC – Access Level 1 (password is OTTER)
2AC – Access Level 2 (password is TAIL)
BAC = Access Level B
SHO n = Show settings in Group n
SHO n 1 = Show settings in Logic Group n
CON n = Control Remote Bit n, then SRB n (set), CRB n (rest), PRB n (pulse)
MET = Meter command
SET n = View or change individual setting in Group n
SET n 1 = View or change individual logic settings in Group n
END = End editing with option to save, <ctrl> X to abort without saving
A method of teaching students the physical
modern relay programming and operation
Now that we’ve introduced “computer engineering,” now its
time for some “electric engineering” for the demo relay.
The demo relay will illustrate two principles – control and
protection.
The control part is easier to tackle. We just want the ability to
close and open OUT103 & 105 to energize and de-energize the
section between OUT103 to OUT104 (and OUT105 to OUT106).
This is done with pushbutton 7 (PB7), then observe LED7.
A method of teaching students the physical
modern relay programming and operation
Understanding the protection portion of the relay will
require some background information about relaying.
We need to measure the voltage and
current to determine if something is
abnormal about the circuit.
CT
PT
We need to SCALE down the high voltage (as much
as 500 kV) and large current (up to 65,000 amps) to a
lower magnitude we can use in a measuring device.
PTs (potential transformers) and CTs (current
transformers) scale down the voltage and
current to a safe, measurable value.
A method of teaching students the physical
modern relay programming and operation
For the microprocessor relay, PTs would be connected to voltage
inputs Va, Vb, and Vc, whereas CTs would be terminated
to current inputs Ia and Ib. For demo purposes, no PTs or CTs
are used for this simple single phase loop circuit, but instead, the
actual voltage and current from the AC source are directly
measured.
A method of teaching students the physical
modern relay programming and operation
The protective relay must be set such that it can differentiate
normal load from a short circuit – this is Sensitivity. This can be
achieved with an overcurrent setpoint – current below the setpoint
is ignored, but when over, the current must be interrupted.
An improperly set relay can either
fail to detect a short circuit or it
can cause an unwanted outage.
A method of teaching students the physical
modern relay programming and operation
How does a relay decide to operate for a nearby short circuit but
ignore a short circuit beyond its protection zone? Use Selectivity.
What’s the difference
between normal traffic flow
and a fender bender?
Remember the 2-second driving
rule? The “time” cushion between
cars “selectively” avoids collisions.
A method of teaching students the physical
modern relay programming and operation
An overcurrent relay with an
instantaneous element and a
time curve characteristic can
provide both “sensitivity” and
“selectivity,” respectively.
A nearby fault (short circuit)
will exhibit greater current
magnitude than a distant fault.
This also allows a nearby fault
to be cleared faster than a
distant fault by using a time
curve delay characteristic.
The time delay for lower magnitude distant faults should be
selected to permit relays closer to the fault to operate first.
A method of teaching students the physical
modern relay programming and operation
With relay protection theory explained, we’re ready to
demonstrate the overcurrent protection feature on our demo
microprocessor relay.
We have already discussed the
“analogy” of the demo relay to a
“real life” substation switch, CT,
and circuit breaker, but we have
not mentioned how we will
simulate normal load vs. short
circuit current.
Our simulated load and short circuit current will use two 150
watt incandescent light bulbs (for resistive load) and a 3-speed
fan (to introduce some reactive load plus represent fault current
when fan operates at high speed). Let’s get ready to measure.
A method of teaching students the physical
modern relay programming and operation
To set demo relay display for better
resolution, depress METER (CANCEL)
button, next push CNTRL (down arrow),
then push EVENTS (SELECT). Now
the up or down arrow scrolls display.
Make sure that AUX3 & AUX4
Push AUX1 button. Read VB LEDs are not illuminated. If so,
voltage and observe AUX 1
push AUX3 & AUX4 to extinguish
LED. VB energizes when
those LEDs. Now push AUX2
OUT103 & OUT105 close.
and observe VB and its LED.
A method of teaching students the physical
modern relay programming and operation
Use the demo microprocessor relay to measure each of our
simulated loads and fault current with the protection disabled.
We could estimate the bulb
current. Using 150 watts
with 120 VAC, the current
should be I = P / V, or
150 W / 120 V = 1.25 Amps
Not too bad. The actual
measured light bulb current
is 1.239 Amps. Take note
that the light bulb has a power
factor (PF) = 1. This implies a
resistive load.
A method of teaching students the physical
modern relay programming and operation
Let’s take more loading measurements with demo relay.
Two 150 watt bulbs measure about
2.5 Amps. Notice that Ib current is
180 degrees relative to Ia current.
This is true since the current input
polarity of Ib is wired opposite of Ia.
Note current for each fan speed:
Low speed
= 0.633 Amps
Medium speed = 1.044 Amps
High speed
= 1.94 Amps
Notice the fan produces
current that lags voltage.
Reactive load introduced.
A method of teaching students the physical
modern relay programming and operation
Pretend that with both 150 watt bulbs
on and the fan set to medium speed
represent maximum normal load.
The load current is 3.29 Amps.
Now pretend that with the two bulbs
on and the fan set at high speed will
represent a short circuit or fault.
The fault current is 4.13 Amps.
So what would be a suggested
setpoint that distinguishes maximum
load and minimum fault current? Let’s choose 3.5 Amps.
A method of teaching students the physical
modern relay programming and operation
We could have used terminal commands or vendor’s software
to capture of measurements using the MET (meter) command.
Notice the Low
speed fan
measurements
that were
captured using
the meter
command.
A method of teaching students the physical
modern relay programming and operation
Now that we know the characteristics of our test load and
identified what we declare as fault current, we are ready
to apply the protection scheme to the demo relay. The
following setpoints and TRIP logic will be applied.
KEY SETTINGS FOR DEMO:
Group 1, Group Settings:
CTR
E50P
E32
EVOLT
=1
=1
=N
=Y
PTR = 1
E51P = 1
50P1P = 3.50
51P1P = 3.50
67P1D = 30.00
51P1C = U1
59P1P = 60.00
67P1TC = 1
51P1TC = 1
51P1TD = 2.00
TR = 50P1 * LT10 * !LT11 + 51P1T * !LT10 * LT11 + 67P1T * LT10 * LT11
A method of teaching students the physical
modern relay programming and operation
Examine the instantaneous & time curve overcurrent setpoints:
CTR = 1
PTR = 1
No CTs or PTs are used in the relay demo because the voltage and
current inputs will be directly measuring the AC waveforms, so
scaling ratios are not needed. Hence, both ratios are 1:1.
E50P = 1 50P1P = 3.50 67P1D = 30.00
Let’s have one instantaneous overcurrent (50P1) element available
to use. It’s pickup values will be 3.5 amps. We may want to have a
definite (fixed) time delay of 30 cycles applied to it.
E51P = 1 51P1P = 3.50 51P1C = U1 51P1TD = 2.00
We also want one time curve delay overcurrent (51P1T) element.
It’s pickup value will also be 3.5 amps. However, this time delay is
specified by a family of curves (or a math formula). We have
selected curve U1 (moderately inverse) and a time dial of 2.
A method of teaching students the physical
modern relay programming and operation
Instantaneous overcurrent vs. Definite (fixed) time overcurrent
Remember how we defined the instantaneous (50P1) overcurrent
element?
E50P = 1
50P1P = 3.50
67P1D = 30.00
We can use an instantaneous overcurrent tripping element if we
want the quickest operate time possible – no intentional time delay.
This is achieved with the 50P1 relay element.
But, we may want to add a definite (fixed) time delay to allow for
temporary higher current due to magnetizing current inrush on
energizing transformers or to locked rotor current during motor
starting. The 67P1D setting defines the amount of delay which is
30 cycles (1/2 second) for the relay demo. The definite (fixed) time
logic element is labeled as 67P1T.
A method of teaching students the physical
modern relay programming and operation
Get operate time for 51P1T time curve overcurrent element:
6.3
sec
2.0
Time Dial
M = 4.13 / 3.5 = 1.18
TD = 2.00
tp = 6.32 sec
* Normally M > 1.5
1.18X
A method of teaching students the physical
modern relay programming and operation
Let’s check out the remaining setpoints:
E32 = N
67P1TC = 1 51P1TC = 1
These three settings deal with torque control, or relay
directionality. Since we not interested in having the overcurrent
element being directional for our demo, we’ll use the settings as
depicted which allow for non-directional operation.
EVOLT = Y
59P1P = 60.00
The next two settings enable the voltage supervision element and
the setpoint for detecting when an overvoltage measurement is
detected. For the demo, we are interested in knowing when the
voltages are 120 VAC nominal, which happens to be above the
threshold of 59P1P setting (of 60 VAC).
A method of teaching students the physical
modern relay programming and operation
And finally, the ultimate purpose of the protective relay – the
establishment of the trip logic which sends signals to open
substation circuit breakers to clear a faulted circuit.
TR = 50P1 * LT10 * !LT11 + 51P1T * !LT10 * LT11 + 67P1T * LT10 * LT11
Notice inclusion of the instantaneous overcurrent element (50P1),
the inverse time curve delay overcurrent element (51P1T),
and the definite (fixed) time delay ovecurrent element (67P1T).
Be aware that there are latch bits that define conditions when
these overcurrent elements become enabled or disabled.
SET10 = !LT10 * PB9
SET11 = !LT11 * PB10
RST10 = LT10 * PB9
RST11 = LT11 * PB10
Essentially, LT10 and LT11 latch bits respond to PB9 & PB10
which are used to enable/disable selected protection elements.
A method of teaching students the physical
modern relay programming and operation
Now that the “textbook” theory is out of the way, let’s do some
“hands-on” learning with the demo microprocessor relay.
STEP 1
Make sure AUX1, AUX2,
AUX3, and AUX4 LEDs
are extinguished. If not,
depress pushbutton near
the illuminated LED.
STEP 2
Enable AUX1, AUX2, and
AUX4 (but not AUX 3).
Turn both 150 watt bulbs
“on” and turn fan “on” to
“Medium” speed.
A method of teaching students the physical
modern relay programming and operation
Now that the “textbook” theory is out of the way, let’s do some
“hands-on” learning with the demo microprocessor relay.
STEP 3
FAN ON
With LEDs illuminated near
HIGH
AUX1, AUX2, and AUX4
SPEED
pushbuttons, increase fan
to “High” speed and start
counting seconds until you
observe the relay “trip”
BOTH
(open) the circuit to deLAMPS ON
energize the light bulbs
and the fan.
If you correctly followed the steps, you have just observed
your first protective “trip” with the demo microprocessor relay.
A method of teaching students the physical
modern relay programming and operation
Examine what happens after the relay “tripped” the circuit.
STEP 4
You should observe
“target” LEDs. The
TRIP, 50, and 51
LEDs should be
illuminated. This is
an immediate visual
indication of whichrelay elements operated. The 51 target is
evidence there was a time delayed trip.
STEP 5
Notice that AUX2 LED is not illuminated. If you depress the
AUX2 pushbutton, nothing should happen since the TRIP
target is still engaged which “locks out” the ability to CLOSE
OUT104 & OUT106 via the AUX2 pushbutton.
A method of teaching students the physical
modern relay programming and operation
Reset the “targets” to disable “lock out” of control to OUT104
And OUT106 to restore and reenergize the circuit.
STEP 6
Press the TARGET RESET
(LAMP TEST) button to
clear the “targets” and
“unlock” control of OUT104
& OUT106.
STEP 7
The AUX4 LED should still
be illuminated. This means
that the protection remains
enabled. Now, depress
AUX2 pushbutton and the
circuit will be restored – temporarily. Why? Fault is still there.
A method of teaching students the physical
modern relay programming and operation
That was a trick. The fault current was still present upon
restoring the circuit. We need to remove the fault.
STEP 8
FAN ON
Reset the targets. With lamps
MEDIUM
“on,” change the fan speed to
SPEED
“Medium” before depressing
AUX2 pushbutton.
Protection should remain
BOTH
enabled, i.e., AUX4 is “on.”
LAMPS ON
STEP 9
With the fault current removed,
depress the pushbutton for
AUX2. The circuit should
return to normal even while
AUX4 remains enabled.
A method of teaching students the physical
modern relay programming and operation
Let’s try the instantaneous overcurrent “trip” element.
STEP 10
With the circuit energized
(AUX2 LED still illuminated),
depress AUX4 pushbutton to
disable the inverse time curve
overcurrent protection
element. The AUX4 LED will
be extinguished.
STEP 11
Immediately after disabling
AUX4, depress AUX3
pushbutton to enable the
“instantaneous” overcurrent
tripping element.
A method of teaching students the physical
modern relay programming and operation
The no-delay “instantaneous overcurrent trip.
STEP 12
With the circuit energized
(AUX2 LED still illuminated)
and the “instantaneous”
protection enabled (AUX3
LED illuminated), increase
fan speed to “High” to
simulate a fault.
STEP 13
The circuit should “trip” or deenergize without any delay.
You should observe the 50
target plus some other targets.
FAN ON
HIGH
SPEED
BOTH
LAMPS ON
A method of teaching students the physical
modern relay programming and operation
Watch what happens when “instantaneous” element is
enabled during motor starting.
FAN ON
STEP 14
Press the TARGET RESET
(LAMP TEST) button to clear
the “targets.” Keep both lamps
“on.” Put fan on “Low” speed.
LOW SPEED
BOTH
LAMPS ON
STEP 15
The AUX3 LED should remain
illuminated to retain “instantaneous” overcurrent protection
during reenergization of the circuit. Now depress AUX2
pushbutton to close OUT104 & OUT106 to energize the fan.
What happened? The motor start may have caused a current
higher than the 3.5 amp pickup of the “instantaneous” element.
A method of teaching students the physical
modern relay programming and operation
Let’s try the definite (fixed) time overcurrent “trip” element.
STEP 16
Press the TARGET RESET
(LAMP TEST) button to clear
the “targets” and “unlock”
control of OUT104 & OUT106.
FAN ON
LOW SPEED
BOTH
LAMPS ON
STEP 17
The AUX3 LED should remain
illuminated, but now depress AUX4 pushbutton such that both
AUX3 and AUX4 LEDs are illuminated. This combination
enables a definite (fixed) time delay overcurrent element. If the
current exceeds 3.5 amps (as per our setpoint), a “trip” will be
delayed by 30 cycles (or ½ second). Now depress AUX2
pushbutton to close OUT104 & OUT106 to energize the fan.
A method of teaching students the physical
modern relay programming and operation
The definite (fixed) time overcurrent “trip” element can ride
through a motor start.
SLOWLY
STEP 18
If all went well, nothing should
have happened other than the
fan starting and the circuit
remaining energized.
INCREASE
FAN SPEED
LAMPS OFF,
THEN ON
STEP 19
Keep the fan on “Low” speed.
Turn “on” both lamps. The circuit should continue to remain
energized. We’re still below the 3.5 amp “trip” setpoint.
STEP 20
Keep both lamps “on.” Increase the fan speed to “Medium.”
Wait 10 seconds. Then, increase the fan to “High.”
A method of teaching students the physical
modern relay programming and operation
The definite (fixed) time overcurrent “trip” element also
operates for short circuits.
SLOWLY
STEP 21
With both lamps “on” and the
fan at “Medium” speed, the
circuit should have remained
energized. But once the fan
was increased to “High” speed,
the simulated fault current was
interrupted within ½ second.
INCREASE
FAN SPEED
LAMPS OFF,
THEN ON
STEP 22
Turn “off” both lamps and turn “off” the fan in preparation for the
last experiment. Depress the TARGET RESET (LAMP TEST)
button. Depress AUX4 pushbutton to disable “time delay” trip.
A method of teaching students the physical
modern relay programming and operation
Check impact of resistive load upon circuit energization with
“instantaneous” overcurrent protection enabled.
STEP 23
Turn only one lamp with 150 watt bulb
“on” prior to energizing the circuit.
STEP 24
With AUX3 illuminated (enabled) and
AUX4 extinguished (disabled), this
allows only the “instantaneous” (no time
delay) overcurrent element to be active.
STEP 25
Depress pushbutton for AUX2 to close
OUT104 & OUT106. What happens?
A method of teaching students the physical
modern relay programming and operation
Result of resistive “light bulb” load upon circuit energization
with “instantaneous” overcurrent protection enabled.
WHAT???
We measured
earlier that the
150 W bulbs
exhibited 1.0 PF
(Power Factor)
which is a purely
resistive load.
Why is “instantaneous” overcurrent operating for resistive load?
There should not be “inrush” current for resistive load, or maybe?
A method of teaching students the physical
modern relay programming and operation
The demo microprocessor relay records events and fault
traces to help diagnose protection “misoperations.”
A method of teaching students the physical
modern relay programming and operation
Why did “instantaneous” overcurrent element trip upon
energizing an incandescent light bulb?
ANSWER: Even though a light bulb has a “resistive”
characteristic, its resistance increases as its tungsten element
increase in temperature. All resistors exhibit some change in
resistance with temperature, but most stay within a fixed
ranged. The resistance of tungsten changes significantly as
the temperature of the bulb goes from ambient air
temperature (cool) to its operating temperature (hot).
Whereas the event report did not explain the reason why the
current went dramatically high upon the light bulbs
energization, it demonstrated that the current was high
(implying low resistance) until the bulb reached its stable
operating temperature (and operating resistance and current).
A method of teaching students the physical
modern relay programming and operation
Wait a minute! We’re not done. Remember the setup for the
motor start experiment?
FAN ON
In STEP 14, we were directed
to keep both lamps “on” and
put fan on “Low” speed.
LOW SPEED
BOTH
LAMPS ON
LAMPS OFF
With AUX3 the “instantaneous”
overcurrent element enabled,
the circuit tripped without
delay. We “assumed” that the trip was caused by a motor start
characteristic of the fan. That may have been a “false” inference
since we now know that the light bulbs cause a current surge.
Hence, the motor start test needs to be redone, but this time we
need to make sure both lamps are “off” and only the fan is “on.”
A method of teaching students the physical
modern relay programming and operation
Let’s do the motor start experiment again – the correct way.
What will happen?
FAN ON
So we repeat STEP 14 with
both lamps “off” and the fan
on “Low” speed.
LOW,
MEDIUM, &
HIGH SPEED
With AUX3 the “instantaneous”
BOTH
overcurrent element enabled,
LAMPS OFF
the circuit surprisingly remains
energized. Try this again with the fan on “Medium” speed, and
then on “High” speed with both lamps remaining “off.”
There is no current surge for the fan. With the fan “off,” insert a
yard stick through the fan’s front and rear grill. Then turn “on”
the fan to check for “locked rotor” current. The fan motor may
use a split winding exhibiting the same start and run current.
A method of teaching students the physical
modern relay programming and operation
In conclusion, let’s see what the demo microprocessor relay
has done for us.
1. We learn through our five senses. Everyone has a
preferred sense for learning.
2. New concepts are easily introduced using “analogies” to
show “similarities” and “comparisons” to illustrate
“differences.”
3. “Hands-on” experimentation adds “3-D” to learning.
4. The demo microprocessor relay introduces the merger of
logic programming and power system protection which is
the mainstay of the power industry.
5. The “self-contained” demo relay uses common household
items to illustrate protection concepts. It’s a low cost tool.
6. Even the teacher can be the student and learn something
new – you can teach an old dog new tricks!
A method of teaching students the physical
modern relay programming and operation
“Their motivation was my inspiration - thanks.”
I thank the students of Delgado Community College’s ELET
(Electrical and Electronics Technology) program for inspiring
me to pursue acquisition of the demo microprocessor relay
and make it a useful training tool that introduces students to
modern system protection technology.
I appreciate the generosity of SEL Engineering Laboratories
for donating the SEL-351S relay to Delgado College with
special thanks to Sal Jadid for making this happen.
I also thank ELET faculty members Ramon Ariza and Mike
Nixon for giving me the opportunity to support and improve
Delgado’s ELET “ABET” accredited program.