Description of the SEL-751 Relay Logic component in Schematic Editor
The SEL-751 Relay Logic component, shown in Table 1, is a Schematic Editor
library block from the Protection part, of the Microgrid
library. It implements the following protection elements: Overcurrent, Time-Overcurrent,
Overvoltage, and Undervoltage with the Trip/Close and Reclose Supervision Logic. The model
is parametrized using two SEL-751 configuration files (Group settings and Logic
settings). Initially, if the files are not loaded, the SEL-751 Relay Logic component is
parametrized with the SEL-751 Factory Default values. Please refer to the SEL 751's instruction
manual for the Factory Default values.
Table 1. SEL-751 Relay Logic component in the Schematic Editor core library
component
component dialog window
component parameters
Property tabs:
1 - General
2 - Configuration
3 - Extras
Protection functions
The SEL-751 model includes
the following protection elements:
Instantaneous/Definite-Time Overcurrent Elements
Time-Overcurrent Elements
Voltage Elements
Frequency protection
Rate of change of frequency protection
Four levels of Instantaneous/Definite-Time Overcurrent Elements
are available for phase (P), neutral (N), residual (G), and negative-sequence (Q) overcurrent.
Each element can be torque controlled (enabled/disabled) through the use of appropriate
SELogic control equations.
Phase overcurrent protection operates on the maximum phase
current, neutral overcurrent protection operates on the neutral current, ground overcurrent
protection operates on the sum of the three phase currents, and negative-sequence
overcurrent protection operates on three times the negative-sequence current.
The
settings necessary to set the instantaneous overcurrent elements are listed in Table 2. The exact Setting Names,
according to the element and level of interest, could be derived replacing x with
“P”, “N”, “G”, or “Q”, and replacing n with “1”, “2”, “3”, or “4”.
Table 2. Settings of the Instantaneous Overcurrent Elements
Setting
Description
50xnP
Pickup of level n of the function, in secondary amps. If set as “OFF”,
the level is disabled.
50xnD
Intentional delay of the operation of level n of the function, in
seconds.
50xnTC
Torque control SELogic equation.
One level of inverse Time-Overcurrent Elements (TOC) is available for
A-, B-, C-phases and negative-sequence (Q) overcurrent. Two levels of inverse
time-overcurrent elements are available for maximum phase (P), neutral (N), and residual (R)
overcurrent. Five U.S. and five IEC inverse characteristics are supported. Each element can
be torque controlled (enabled/disabled) through the use of appropriate SELogic control
equations (when 51P1TC := IN301 the 51P1 element is operational only if IN401 is asserted).
The phase elements operate on phase A current, phase B current, and phase C current,
respectively. The maximum phase inverse time-overcurrent protection operates on the maximum
of the three phase currents, neutral inverse time-overcurrent protection operates on neutral
current and ground inverse time-overcurrent protection operates on the sum of the three
phase currents and negative-sequence overcurrent protection operates on three times the
negative-sequence current.
The settings necessary to set the inverse time overcurrent
elements are listed in Table 3.
The exact Setting Names, according to the element and level of interest, could be derived by
replacing x with “A”, “B”, “C”, “P1”, “P2”, “Q”, “N1”, “N2”, “G1”, or “G2”.
Table 3. Settings of the Inverse Time-Overcurrent Elements
Setting
Description
51xP
Pickup of the TOC element, in secondary amps. If set as “OFF”, the level is
disabled.
51xC
Curve selection of the TOC element.
51xTD
Time dial of the TOC element.
51xRS
Electromechanical reset delay of the TOC element. If set as “Y”, the
resetting time is computed using the selected reset curve. If set as “N”, the
reset time is instantaneous.
51xCT
Constant time that is added to the operating time given by the characteristic
curve, in seconds.
51xMR
Minimum response time of the TOC element, in seconds.
51xTC
Torque control SELogic equation.
The current transformer (CT) ratio settings configure the relay to accurately
scale measured current values. The current transformer ratio settings are listed in Table 4.
Table 4. CT configuration settings
Setting
Description
CTR
Phase CT ratio, Parameter that is used for determining the secondary phase
currents.
CTRN
Neutral CT ratio, Parameter that is used for determining the secondary
neutral current.
When the SEL-751 model is configured to use phase-to-phase connected voltage
transformers (VT), setting DELTA_Y = DELTA, the relay provides two levels of phase-to-phase
overvoltage and undervoltage elements. When the SEL-751 model is configured to use
phase-to-neutral connected VTs, setting DELTA_Y = WYE, the relay provides two levels of
phase-to-neutral, phase-to-phase overvoltage, and undervoltage elements. Two levels of
negative-sequence overvoltage elements are available regardless of the voltage transformers
connections. Two levels of zero-sequence overvoltage elements are available when the voltage
inputs are connected in wye configuration (DELTA_Y := WYE).
When the setting
“DELTA_Y” is set as “DELTA”, then phase to phase voltages are used as operating voltages.
When this tap is set as “WYE”, then the phase to ground voltages are used as operating
voltages. The phase undervoltage protections operate on the minimum phase operating voltage,
the phase overvoltage protections operate on the maximum phase operating voltage. The
zero-sequence voltage elements operate on zero-sequence voltage, while the negative-sequence
voltage protection operates on three times the negative-sequence voltage.
The
necessary settings for the voltage elements are listed in Table 5. The exact Setting Names,
according to the element and level of interest, could be derived by replacing x with
“P”, “PP”, “G”, or “Q”, and replacing n with “1” or “2”.
Table 5. Settings of the Voltage Elements
Setting
Description
27xnP
Pickup of the undervoltage level 27xn. If set as “OFF”, the level is
disabled.
27xnD
Time delay of the undervoltage 27xn, in seconds.
59xnP
Pickup of the overvoltage level 59xn. If set as “OFF”, the level is
disabled.
59xnD
Time delay of the overvoltage level 59xn, in seconds.
The voltage configuration settings configure the relay voltage inputs to
correctly measure and scale the voltage signals. The supported voltage settings are listed
in Table 6. For additional
information and examples, refer to the SEL-751 instruction
manual.
Table 6. Voltage settings
Setting
Description
PTR
Phase PT ratio, Parameter that is used for determing the secondary phase
voltages.
LEA_R
Phase Low Energy Analog (LEA) ratio, Parameter that defines used voltage
sensor ratio.
DELTA_Y
Connection type
VNOM
Line voltage
The relay provides six levels of over- and underfrequency elements.
Each element has independent trip level and time-delay settings, and can be torque
controlled using appropriate SELogic control equations. Individual elements operate as an
overfrequency protection when the trip level setting is greater than the nominal frequency
setting. When the trip level setting for an element is less than the nominal frequency
setting, it operates as an underfrequency protection.
Note: If the applied
postive-sequence voltage is less than 10V and the applied positive-sequence current is less
than 0.1 * the nominal secondary current, the measured frequency is set to the nominal
frequency, and protections are not applied.
The settings necessary to set over- and
underfrequency elements are listed in Table 7. The exact Setting Names, according to the level of interest, could be
derived by replacing n with a number between "1" and "6".
Table 7. Settings for over- or underfrequency elements
Setting
Description
81DnTP
Pickup of the over- and underfrequency element, in Hz. If set as "OFF", the
level is disabled.
81DnTD
Time delay of the over- and underfrequency element.
81DnTC
Torque control SELogic equation.
Four levels of rate of change of frequency elements (81R) are
available. There are three settings that are common for all four levels of protection: E81R,
81RVSUP, and 81RISUP. E81R is used to enable the number of elements you want to use. Voltage
and current supervision are specified with the 81RVSUP and 81RISUP settings, respectively.
If these settings are specified, a minimum positive-sequence voltage and/or current are
necessary for operation of this protection. If these settings are set to OFF, this
protection can operate without current and/or voltage supervision. The element is also
supervised by the Relay Word FREQTRK, which ensures that the relay is tracking and measuring
the system frequency.
Other settings necessary to set 81R elements are listed in Table 8. The exact
Setting Names, according to the level of interest, could be derived by replacing n
with "1", "2", "3", or "4".
Table 8. Settings for 81R elements
Setting
Description
E81R
Enables the number of elements you want to use. If set to "N", all levels are
disabled.
81RVSUP
Voltage supervision. If set to "OFF", this supervision is disabled.
81RISUP
Current supervision. If set to "OFF", this supervision is disabled.
81RnTP
Pickup of the 81R element, in Hz/s. If set to "OFF", the level is
disabled.
81RnTRND
Used for limiting operation of the 81R element to INC (increasing) or DEC
(decreasing) frequency. Should be set to ABS if the frequency trend is not
important.
81RnTD
Time delay of the 81R element.
81RnDO
Drop-out time delay of the 81R element.
81RnTC
Torque control SELogic equation.
SEL-751 Relay Logic inputs and outputs
The
SEL-751 Relay Logic componet has 3 inputs - Relay input from the User Interface (ui_out),
Relay analog input (A_in), Relay digital input (D_in) - and 2 outputs
Relay digital output (D_out) and Relay output to the User Interface (ui_in).
ui_out is the vectorized input which consists of the 4 elements which are described
in Table 9 and where signals
orders are given. These signals are used to send basic manual commands to the relay. These
are digital signals implemented in a positive logic, asserted when high and deasserted when
low.
Table 9. Relay inputs from the User Interface
Number
Input
Description
Signal range
0
TARGET RESET_PUSHBUTTON
Target reset command.
0 or 1
1
LOCK_PUSHBUTTON
Relay lock command.
0 or 1
2
CLOSE_PUSHBUTTON
Relay close command.
0 or 1
3
TRIP_PUSHBUTTON
Relay trip command.
0 or 1
A_in is the vectorized input which consists of the 20 elements which are described
in Table 10 and where signal orders are
given. These are analog signals which are equal to the measured voltages or
currents. All these inputs can be easily obtained from the Three-Phase Meter component that is also part of the Microgrid library. Please refer to the SEL-751
Example model.
Table 10. Relay analog inputs
Number
Analog Input
Description
0
VAn
Phase A voltage. [V]
1
VBn
Phase B voltage. [V]
2
VCn
Phase C voltage. [V]
3
VAB
Voltage between phases A and B. [V]
4
VBC
Voltage between phases B and C. [V]
5
VCA
Voltage between phases C and A. [V]
6
IA
Phase A current measurement. [A]
7
IB
Phase B current measurement. [A]
8
IC
Phase C current measurement. [A]
9
IN
Neutral phase current measurement. [A]
10-19
Reserved
Analog inputs that are not used.
D_in is the vectorized input which consists of the 20 elements. Supported
digital inputs are given in Table 11
along with the signal order. These are digital signals which can be used for digital feedback
signals (from contactor for example) or used as external logic that can influence
the internal protection functions. This can be defined from the imported group settings file
using the SELogic equations definition in the desired protection functions.
Table 11. Relay digital inputs
Number
Digital Input
Description
Signal range
0
IN101
Relay digital input 101.
0 or 1
1
IN102
Relay digital input 102.
0 or 1
2
IN301
Relay digital input 301.
0 or 1
3
IN302
Relay digital input 302.
0 or 1
4
IN303
Relay digital input 303.
0 or 1
5
IN304
Relay digital input 304.
0 or 1
6
IN305
Relay digital input 305.
0 or 1
7
IN306
Relay digital input 306.
0 or 1
8
IN307
Relay digital input 307.
0 or 1
9
IN308
Relay digital input 308.
0 or 1
10-19
Reserved
Digital inputs that are not used.
0 or 1
D_out is the vectorized output which consists of the 20 elements. Supported digital
outputs are given in Table 12 along with the signal order.
Realy digital outputs are programmable and their functionality is defined
from the relay logic settings file using SELogic equations for the desired digital
output.
Table 12. Realy digital outputs
Number
Digital output
Description
Signal range
0
OUT101
Relay digital output 101.
0 or 1
1
OUT102
Relay digital output 102.
0 or 1
2
OUT103
Relay digital output 103.
0 or 1
3
OUT301
Relay digital output 301.
0 or 1
4
OUT302
Relay digital output 302.
0 or 1
5
OUT303
Relay digital output 303.
0 or 1
6
OUT304
Relay digital output 304.
0 or 1
7
OUT305
Relay digital output 305.
0 or 1
8
OUT306
Relay digital output 306.
0 or 1
9
OUT307
Relay digital output 307.
0 or 1
10
OUT308
Relay digital output 308.
0 or 1
11-19
Reserved
Digital outputs that are not used.
0 or 1
ui_in is the vectorized output which consists of the 227 elements which are separated
in three parts: digital outputs that control user Target LEDs, analog outputs with
measurements and Relay Word Bits (RWB) digital outputs.
The first 20 elements are
digital outputs that control the Target LEDs. All Target LEDs are fixed pre-programmed with
a SEL-751 Default settings. Supported LED digital outputs are given in Table 13 with the corresponding signals' position in
the ui_in vectorized output.
Table 13. User Target LEDs settings
Number
LED Signal
Pre-programmed functionality
0
ENABLED
1
1
TRIP
TRIP
2
INST OC
ORED50T
3
PHASE OC
51AT OR 51BT OR 51CT OR 51P1T OR 51P2T
4
GND/NEU OC
51N1T OR 51G1T OR 51N2T OR 51G2T
5
NEG SEQ OC
51QT
6
O/U FREQ
81D1T or 81D2T or 81D3T or 81D4T
7
BRKR FAIL
0 (functionallity not supported)
8-19
Reserved
Digital outputs that are not used.
The next 40 elements are reserved for analog signals of measured voltages and
currents. Supported analog measurements are given in Table 14 with the corresponding signals' position in
the ui_in vectorized output.
Table 14. Supported measurements
Number
Signal
Description
20
|VPmax|
Maximum Phase Voltage Magnitude [V]
21
|VPmin|
Minimum Phase Voltage Magnitude [V]
22
|VPPmax|
Maximum Phase to Phase Voltage Magnitude [V]
23
|VPPmin|
Minimum Phase to Phase Voltage Magnitude [V]
24
|3V2|
Negative Sequence Voltage Magnitude [V]
25
|3V0|
Zero-Sequence Voltage Magnitude [V]
26
|VA|
A-Phase Voltage Magnitude [V]
27
|VB|
B-Phase Voltage Magnitude [V]
28
|VC|
C-Phase Voltage Magnitude [V]
29
|VAB|
AB Phase to Phase Voltage Magnitude [V]
30
|VBC|
BC Phase to Phase Voltage Magnitude [V]
31
|VCA|
CA Phase to Phase Voltage Magnitude [V]
32
|IA|
A-Phase Current Magnitude [A]
33
|IB|
B-Phase Current Magnitude [A]
34
|IC|
C-Phase Current Magnitude [A]
35
|IP|
Maximum Phase Current Magnitude [A]
36
|IN|
Core-Balance Current Magnitude [A]
37
|IG|
Residual Current Magnitude [A]
38
|3I2|
Negative-Sequence Current Magnitude [A]
39
IA_ang
Phase angle of the A-Phase current [Deg]
40
IB_ang
Phase angle of the B-Phase current [Deg]
41
IC_ang
Phase angle of the C-Phase current [Deg]
42
VA_ang
Phase angle of the A-Phase voltage [Deg]
43
VB_ang
Phase angle of the B-Phase voltage [Deg]
44
VC_ang
Phase angle of the C-Phase voltage [Deg]
45
VAB_ang
Phase angle of the AB voltage [Deg]
46
VBC_ang
Phase angle of the BC voltage [Deg]
47
VCA_ang
Phase angle of the CA voltage [Deg]
48
Frequency-meas
Frequency [Hz]
49-59
Reserved
Outputs that are not used.
The final 167 elements of the ui_in output are Relay Word Bits (RWB) digital
outputs. These RWBs are calculated from the implemented protection functions and also can be
used for defining the SELogic equations in the input configuration files. If some RWB is used
but is not supported in the model, it will be automatically replaced with 0 and reported in
the message log of Schematic Editor. Supported RWBs are given in Table 15 with their position in the
ui_in vectorized output.
Table 15. Relay Word Bits list
Number
RWB output
Description
60
50A1P
Level 1 A-phase instantaneous overcurrent element pickup.
61
50B1P
Level 1 B-phase instantaneous overcurrent element pickup.
62
50C1P
Level 1 C-phase instantaneous overcurrent element pickup.
63
50P1P
Level 1 phase instantaneous overcurrent element pickup.
64
67P1P
Level 1 phase directional overcurrent pickup.
65
50P1T
Level 1 phase instantaneous overcurrent element trip.
66
67P1T
Level 1 phase directional overcurrent trip.
67
50N1P
Level 1 neutral-ground instantaneous overcurrent element pickup.
68
67N1P
Level 1 neutral directional overcurrent pickup.
69
50N1T
Level 1 neutral-ground instantaneous overcurrent element trip.
70
67N1T
Level 1 neutral directional overcurrent trip.
71
50G1P
Level 1 residual-ground instantaneous overcurrent element pickup.
Logical OR of all the instantaneous overcurrent elements tripped
outputs.
128
51AP
A-phase time-overcurrent element pickup.
129
51AT
A-phase time-overcurrent element trip.
130
51AR
A-phase time-overcurrent element reset.
131
51BP
B-phase time-overcurrent element pickup.
132
51BT
B-phase time-overcurrent element trip.
133
51BR
B-phase time-overcurrent element reset.
134
51CP
C-phase time-overcurrent element pickup.
135
51CT
C-phase time-overcurrent element trip.
136
51CR
C-phase time-overcurrent element reset.
137
51P1P
Level 1 maximum phase time-overcurrent element pickup.
138
51P1T
Level 1 maximum phase time-overcurrent element trip.
139
51P1R
Level 1 maximum phase time-overcurrent element reset.
140
51P2P
Level 2 maximum phase time-overcurrent element pickup.
141
51P2T
Level 2 maximum phase time-overcurrent element trip.
142
51P2R
Level 2 maximum phase time-overcurrent element reset.
143
51QP
Negative-sequence time-overcurrent element pickup.
144
51QT
Negative-sequence time-overcurrent element trip.
145
51QR
Negative-sequence time-overcurrent element reset.
146
51N1P
Level 1 neutral-ground time-overcurrent element pickup.
147
51N1T
Level 1 neutral-ground time-overcurrent element trip.
148
51N1R
Level 1 neutral-ground time-overcurrent element reset.
149
51N2P
Level 2 neutral-ground time-overcurrent element pickup.
150
51N2T
Level 2 neutral-ground time-overcurrent element trip.
151
51N2R
Level 2 neutral-ground time-overcurrent element reset.
152
51G1P
Level 1 residual-ground time-overcurrent element pickup.
153
51G1T
Level 1 residual-ground time-overcurrent element trip.
154
51G1R
Level 1 residual-ground time-overcurrent element reset.
155
51G2P
Level 2 residual-ground time-overcurrent element pickup.
156
51G2T
Level 2 residual-ground time-overcurrent element trip.
157
51G2R
Level 2 residual-ground time-overcurrent element reset.
158
ORED51T
Logical OR of all the time overcurrent elements tripped outputs.
159
27P1
Level 1 phase undervoltage element pickup.
160
27P1T
Level 1 phase undervoltage element trip.
161
27P2
Level 2 phase undervoltage element pickup.
162
27P2T
Level 2 phase undervoltage element trip.
163
3P27
Three-phase undervoltage pickup when all three phases are below 27P1P.
164
27PP1
Level 1 phase-to-phase undervoltage element pickup.
165
27PP1T
Level 1 phase-to-phase undervoltage element trip.
166
27PP2
Level 2 phase-to-phase undervoltage element pickup.
167
27PP2T
Level 2 phase-to-phase undervoltage element trip.
168-172
Reserved
Not used.
173
59P1
Level 1 phase overvoltage element pickup.
174
59P1T
Level 1 phase overvoltage element trip.
175
59P2
Level 2 phase overvoltage element pickup.
176
59P2T
Level 2 phase overvoltage element trip.
177
59G1
Level 1 zero-sequence instantaneous overvoltage element pickup.
178
59G1T
Level 1 zero-sequence instantaneous overvoltage element trip.
179
59G2
Level 2 zero-sequence instantaneous overvoltage element pickup.
180
59G2T
Level 2 zero-sequence instantaneous overvoltage element trip.
181
3P59
Three-phase overvoltage pickup when all three phases are above 59P1P.
182
59PP1
Level 1 phase-to-phase overvoltage element pickup.
183
59PP1T
Level 1 phase-to-phase overvoltage element trip.
184
59PP2
Level 2 phase-to-phase overvoltage element pickup.
185
59PP2T
Level 2 phase-to-phase overvoltage element trip.
186
59Q1
Level 1 negative-sequence instantaneous overvoltage element pickup.
187
59Q1T
Level 1 negative-sequence instantaneous overvoltage element trip.
188
59Q2
Level 2 negative-sequence instantaneous overvoltage element pickup.
189
59Q2T
Level 2 negative-sequence instantaneous overvoltage element trip.
190-193
Reserved
Not used.
194
TR
Trip SELOGIC control equation (also has been referred to as TRIPEQ).
195
REMTRIP
Remote trip.
196
ULTRIP
Unlatch Trip SELOGIC control equation state.
197
52A
Circuit breaker N/O contact.
198
52B
Circuit breaker N/C contact.
199
CL
CL Close SELOGIC equation.
200
ULCL
Unlatch Close SELOGIC control equation state.
201
TRGTR
Target reset.
202
CLOSE
Initiates closing action when asserted.
203
RCSF
Reclose supervision failure (asserts for Tslow time period).
204
TRIP
Breaker trip.
205
TRIPLEDRST
Reset the trip led.
206-210
Reserved
Not used.
211
IN101
Contact Input IN101.
212
IN102
Contact Input IN102.
213
IN301
Contact Input IN301.
214
IN302
Contact Input IN302.
215
IN303
Contact Input IN303.
216
IN304
Contact Input IN304.
217
IN305
Contact Input IN305.
218
IN306
Contact Input IN306.
219
IN307
Contact Input IN307.
220
IN308
Contact Input IN308.
221-225
Reserved
Not used.
226
RSTTRGT
SELOGIC control equation: reset trip logic and targets when asserted.
227
81D1T
Level 1 definite-time over- and underfrequency trip.
228
81D2T
Level 2 definite-time over- and underfrequency trip.
229
81D3T
Level 3 definite-time over- and underfrequency trip.
230
81D4T
Level 4 definite-time over- and underfrequency trip.
231
81D5T
Level 5 definite-time over- and underfrequency trip.
232
81D6T
Level 6 definite-time over- and underfrequency trip.
233
ORED81T
ORed, over- and underfrequency element.
234
FREQTRK
Frequency tracking enable bit - tracking enabled when bit is asserted.
235
81R1T
Level 1 rate of change of frequency element trip.
236
81R2T
Level 2 rate of change of frequency element trip.
237
81R3T
Level 3 rate of change of frequency element trip.
238
81R4T
Level 4 rate of change of frequency element trip.
239
ORED81RT
ORed frequency rate of change element.
In the Example,
the SEL-751 Relay Logic component is surrounded by helping subsystems where inputs and
outputs are also defined. This is shown in Figure 1. The UI subsystem contains just a small and representative part of the
available SEL-751 Relay Logic signals. The selection is done using Bus Selector components and numbers from the upper tables.
These subsystems can be freely changed according to the specific application or reused in the
other models. This whole structure is located in the wrapping SEL-751 Subsystem in order to
keep everything in one place. For the more information, please refer to the provided SEL-751
Example model. Figure 1. SEL-751 Relay Logic helping subsystems
Component dialogue box and parameters
The SEL-751 Relay Logic component dialogue box consists of four tabs for specifying parameters
of the component.
Tab: "1 - General"
In this component tab, general parameters of the SEL-751 Relay Logic component can be
specified. Figure 2. SEL-751 Relay Logic "1 - General" parameters.
The secondary voltage input configuration is the parameter that defines what type of
voltage inputs are used for the relay. When Standard is selected, 300V rated inputs are
presented on the relay; if LEA is selected, 8V inputs are presented instead. This setting
influences how the measured voltages are scaled internally. The PTR parameter is valid for
the standard input. For LEA inputs, the LEA_R parameter is used instead of the PTR (see
Table 6). Please refer to the
SEL-751 instruction manual for additional information.
Tab: "2 - Configuration"
In this component tab, parameters that are related to the Configuration of the SEL-751 can
be specified.Figure 3. SEL-751 Relay Logic "2 - Configuration" parameters
The faster execution rate is the rate at which RMS values are calculated using a one-cycle
cosine filter. By default this value is set to 625us, which implies 32 samples per power system
cycle (50Hz) and it matches the real SEL-751 Relay. In this model, the Faster execution rate
value can be changed in order to adapt the component to the other execution rates in the
model if necessary. The cosine filter will work with a different number of samples
depending on the execution rate. The minimum Faster execution rate is 500us. The Slower execution
rate is the rate at which protection functions are executed, which is set to four
times faster than the power system cycle by default. The Slower execution rate can also be changed and adapted to other execution
rates in the model. Changing the execution rates of the SEL-751 Relay Logic can produce
small differences in dynamic responses relative to the default values.
Example
Overall behavior and control methodologies can be better understood with the use of the
given example:
