Background and Motivation
The Lane Department of Computer Science and Electrical Engineering (LCSEE) at West Virginia University (WVU) has utilized a power simulator since the 1970s, originally featuring analog relays This simulator was subsequently enhanced with microprocessor-based relays, thanks to a donation from Schweitzer Engineering Laboratories (SEL).
In July 2018, the department dismantled the power simulator to create an Innovation Lab, relocating the power system equipment to the new Energy Systems Lab located in room 219 of the Engineering Research Building (ERB).
Considering the cost and applications of industrial circuit breakers, VARIAC, switches, resistors, meters, potential transformers, and electromechanical and microprocessor electrical
Figure 1.1 Front view of power simulator that was dismantled, Spencer [1]
Two protection relays were salvaged from the simulator for potential future use, leading to the creation of a mobile test bench to demonstrate the operation of electrical overcurrent protection relays, essential components of electrical protection systems This project utilizes two primary types of overcurrent relays: the electromechanical CO-8 inverse time overcurrent relays and modern microprocessor feeder protection relays The latter not only offers instantaneous and time overcurrent protection across various US and IEC curves but also includes additional features such as over and under voltage protection, frequency variation protection, and power factor lead/lag protection This test bench will effectively showcase the application, functionality, configuration process, and benefits of both relay types.
Scope of Document
Section 2 offers a comprehensive guide on the operation of the Overcurrent Protection Relays Test Bench, making it a valuable resource for users In Section 3, a concise overview of the equipment utilized in the design and implementation of the test bench is presented Section 4 details the step-by-step procedure for configuring the SEL-751A Feeder Protection Relays to establish communication with a PC running the SEL ACSELERATOR QuickSet ® SEL-5030 software.
The 3351 Computing Platform with Substation SERVER.NET enables users to access and modify relay settings through ACSELERATOR QuickSet® SEL-5030 software, which also displays relay data for SEL [2] and SEL [3] Additionally, the article includes appendices featuring circuit schematics, a detailed description of SEL-751A settings, US curves for Inverse Time relays, login passwords, and a comprehensive parts list.
To minimize costs, the design leverages existing equipment at the Energy Systems Lab, specifically repurposing one of the four benches previously used for motor-generator sets Although these sets are no longer in use, the benches serve as valuable resources for students' senior design projects, providing essential electrical connections Given their portability and availability, one bench was selected for modification to accommodate the project However, the panel's dimensions—approximately 41.5 inches in length, 6 inches in width, and 25.5 inches in height—posed challenges in designing a three-phase circuit.
The design of the Overcurrent Protection Relay Test Bench required the integration of six electromechanical overcurrent relays, two microprocessor feeder protection relays, three breakers, and a variable autotransformer The placement of the heavy autotransformer significantly influenced the layout, necessitating its low positioning to maintain stability, as its depth is nearly three times that of the selected connection bench.
Limited information was available regarding the removed power simulator The SEL relays, integrated into the simulator, were linked to the SEL-3351 Computing Platform, capable of supporting various devices However, there was a lack of documentation detailing the communication setup between the relays and the Computing Platform, as well as the connection between the Computing Platform and the lab PC This gap in information posed a challenge that necessitated significant time to resolve.
The design of the Overcurrent Protection Relays Test Bench necessitates two circuit breakers for effective operation by the overcurrent protection relays One circuit breaker is essential for the primary side of the transformer, while the other is needed for the secondary side Currently, only one industrial circuit breaker is available in the lab, which has been allocated to the secondary side of the transformer Unfortunately, ordering a new circuit breaker for the primary side is not feasible at this time.
Figure 1.2 Connection bench that was modified for the overcurrent relay setup
4 an option as that would have raised the cost considerably Instead, a breaker circuit for primary side protection had to be designed
The Overcurrent Protection Relay Test Bench is illustrated in Figure 2.1, showcasing its front view, while Figure 2.2 presents the layout of the front panel Additionally, Figure 2.3 details the functional diagram of the test bench For comprehensive wiring schematics, please refer to Appendix A.
Figure 2.1 Front view of the Overcurrent Protection Relay Test Bench
Change over switch primary side
Change over switch load side
B- Transformer Primary Side Protection Breaker Circuit
F- GE AC Ammeter 0-5A G1, G2- Manual Changeover Switches H- Auto Transformer (VARIAC) I- GE Industrial Circuit Breaker for Transformer Secondary Protection
Figure 2.2 Front layout of the Overcurrent Protection Relay Test Bench
Figure 2.3 Functional diagram of the Overcurrent Protection Relay Test Bench
The Overcurrent Protection Relays Test Bench features a wiring schematic akin to the application example found in SEL [2] (pp 2.28 and 2.29), but it incorporates two distinct types of protection devices: the microprocessor-based SEL-751A and the electromagnetic Westinghouse CO-8 relays The design utilizes changeover switches (G1 and G2) to toggle between these relays Notably, the setup omits the use of current transformers (CTs) for current measurement and potential transformers (PTs) for voltage measurement, opting instead for direct wiring to the devices Additionally, the circuit does not facilitate neutral current measurement through the SEL-751A for neutral overcurrent detection.
The test bench features a 3-phase variable autotransformer (VARIAC) with wye-connected primary and secondary windings It includes a microprocessor-based SEL-751A Feeder Protection Relay, which monitors current across phases A, B, and C, alongside three Westinghouse electromechanical overcurrent protection relays dedicated to each phase The current path can be toggled between the SEL-751A and the electromechanical relays using a cam selector switch Selecting position ‘1’ activates the SEL-751A, which triggers a breaker circuit upon detecting overcurrent conditions based on its settings Conversely, selecting position ‘2’ activates the electromechanical relays, where any relay's closure sends a tripping signal to the breaker circuit In the ‘0’ position, both relays are disconnected, preventing voltage from reaching the autotransformer.
The secondary side of the auto variable transformer (H) features a similar configuration, allowing for the selection of either the SEL-751A (C2) or electromechanical relays (D4, D5, and D6) via the cam switch (G2) Additionally, an AC voltmeter (E) measures the line-to-line voltage between phases A and B, while an AC ammeter (F) monitors the current in phase A The tripping signal is determined based on the selection made on G2.
The industrial breaker (I) is activated when the output contacts of C2 or any of the contacts D4, D5, or D6 are closed This mechanism allows the voltage supply lines to be routed through breaker (I) to the load connection ports (J).
The test bench operates without the use of current transformers (CTs) or potential transformers (PTs) for measuring current and voltage It is limited by the autotransformer's maximum rated current of 3.5 A The primary voltage is a three-phase 208 VLL at 60Hz, while the secondary voltage can be adjusted within a range of 0 to 208 VLL using the autotransformer.
2.1 Procedure for Using the Overcurrent Protection Relays Test Bench
The step by step procedure for using the Overcurrent Protection Relays Test Bench is given as follows,
1) Connect the three-phase load at the load connecting ports (J) in either wye or delta configuration
2) Select either microprocessor SEL-751A relay (C1) or the electromechanical relays (D1, D2 and D3) from the selector switch (G1) For the selector switch, the setting options are, ‘0’- Circuit disconnected from the primary side
To select the relays on the secondary side, use the selection switch (G2), which offers options that mirror those available on the primary side (G1) as outlined in step 2.
4) Apply power to the test bench by moving the handle of the isolation breaker (A) up
To activate the breaker protection circuit on the primary side (B), simply move the on/off toggle switch to the highest position and press the reset button on the breaker circuit.
6) Turn on the industrial breaker (I) by moving its handle in the up position
7) Increase the voltage by turning the handle of variable autotransformer (H) in clockwise direction The voltmeter (E) should show the secondary line to line voltage If the load
9 switches are on then phase current will be indicated on the ammeter (F) The current should not exceed 3.5 A at any point
Before adjusting relay settings or using selector switches (G1 and G2), ensure the system is de-energized by turning off the power This can be achieved by moving the handle of the isolation switch (A) to the off position.
Procedure for Using the Overcurrent Protection Relays Test Bench
The step by step procedure for using the Overcurrent Protection Relays Test Bench is given as follows,
1) Connect the three-phase load at the load connecting ports (J) in either wye or delta configuration
2) Select either microprocessor SEL-751A relay (C1) or the electromechanical relays (D1, D2 and D3) from the selector switch (G1) For the selector switch, the setting options are, ‘0’- Circuit disconnected from the primary side
To choose the relays on the secondary side, utilize the selection switch (G2), which offers options comparable to those found on the primary side (G1) as outlined in step 2.
4) Apply power to the test bench by moving the handle of the isolation breaker (A) up
To activate the breaker protection circuit on the primary side (B), simply move the on/off toggle switch to the top position and press the reset button on the breaker circuit.
6) Turn on the industrial breaker (I) by moving its handle in the up position
7) Increase the voltage by turning the handle of variable autotransformer (H) in clockwise direction The voltmeter (E) should show the secondary line to line voltage If the load
9 switches are on then phase current will be indicated on the ammeter (F) The current should not exceed 3.5 A at any point
When selecting or changing relay settings, it is crucial to ensure that the system is de-energized Always turn off the power by moving the isolation switch handle (A) to the off position before adjusting the relays with selector switches (G1 and G2) or modifying any relay settings.
When the industrial breaker (I) trips, its handle shifts to a tripping position between the on and off settings, requiring a reset by first moving the handle to the off position and then back to on If the SEL-751A is selected via the selector switch, the reset must be done by pressing the "Target Reset" button on the relay's keypad panel For a trip caused by the primary side circuit (B), resetting involves pressing the reset push-button If there is no fault present, the relay should automatically reset.
System Limitations
As stated before, the Overcurrent Protection Relays Test Bench does not use CTs or PTs The maximum current is limited to 3.5 A Primary side voltage is fixed at 3 phase 208 VLL
The system has been tested with resistive loads only In case of reactive loads, it is recommended to use inductive load in parallel with a resistive load
The communication configuration for SEL relays on the test bench employs serial communication, allowing only one SEL relay to connect to a PC running ACSELERATOR QuickSet® software at any given time For a detailed discussion on the communication setup, please refer to Chapter 4.
A brief overview of the equipment used in the test bench is provided as follows
A 10A, 3-phase manual breaker is used as the main isolation for the Overcurrent Protection Relays Test Bench This breaker was removed from the power simulator
Transformer Primary Side Protection Breaker Circuit (B)
The Overcurrent Protection Relays Test Bench circuit requires two circuit breakers: one on the primary side and another on the secondary side of the autotransformer (H) Due to the unavailability of a second industrial circuit breaker, the secondary side is equipped with one, while a custom circuit utilizing solid-state relays, a 15 VDC power supply, voltage limiting resistors, and a general-purpose double pole double throw (DPDT) relay has been designed for the primary side The functional diagram of this breaker circuit is illustrated in Figure 3.2, with a detailed wiring schematic available in Appendix A-2.
The S-1 relay is a versatile 12 VDC DPDT relay that controls the breaker circuit, while S-2, S-3, and S-4 are solid-state relays featuring normally open (NO) contacts that act as switches for the three-phase voltages linked to the primary side of the variable autotransformer (H) A 15VDC power supply feeds the supply points of S-2, S-3, and S-4 through a toggle switch that functions as an on/off control for the breaker, along with a normally closed contact from S-1 The coil of S-1 connects to the power supply via a voltage-limiting resistor and a parallel arrangement of the output contacts from the SEL-751A Feeder Protection Relay (C1) and three CO-8 electromechanical overcurrent relays (D1, D2, D3) The voltage supply to S-1 can be chosen from either the SEL-751A (C1) or the CO-8 overcurrent relays (D1, D2, D3) using a cam changeover switch (G1) Additionally, an NO contact of S-1 is connected in parallel with the output contacts of relays C1, D1, D2, and D3, as well as the positive supply to the coil of S-1, completing the circuit through a push-button reset switch.
In normal operation, relays S-2, S-3, and S-4 remain energized via the normally closed (NC) contact of relay S-1, keeping their output contacts closed When a fault is detected by a designated protection relay, its output contacts close, applying voltage to the coil of S-1 This action opens the NC contact of S-1, cutting off the supply to S-2, S-3, and S-4, which then disconnects the AC circuit and triggers a trip As the current decreases, the output contacts of the protection relays, which are non-latching, will open Meanwhile, the supply to the coil of S-1 is sustained through its normally open (NO) contact The breaker can be reset using a push-button reset switch that momentarily disconnects the supply to S-1, causing the NO contact to open and cut off the supply A reset is only possible if no faults are detected by the microprocessor protection relay C1 or the electromechanical relays D1, D2, or D3.
(depending on which relay is selected), S-1 will remain disconnected NC contact of S-1 will close and provide voltage to S-2, S-3 and S-4 and the AC circuit will be closed
S-2, S-3, S-4 Solid State Relays with one
S-1 NO Normally Open Contact of S-1
S-1 NC Normally Closed Contact of S-1
S-1 NO, S-2 NO, S-3 NO Normally Open
Figure 3.2 Functional diagram of breaker circuit for transformer primary side protection
Figure 3.3 Front and rear view of the breaker circuit used for primary side protection
SEL-751A Feeder Protection Relay (C1 and C2)
Westinghouse CO-8 (Inverse Time) Electromechanical Overcurrent Relay (D1, D2, D3, D4,
The Overcurrent Protection Relays Test Bench features six Westinghouse CO-8 inverse time relays, with three relays installed on the primary side of the autotransformer and one relay designated for each phase Additionally, three relays are installed on the secondary side, ensuring comprehensive phase coverage and effective overcurrent protection.
ABB [4] details the construction, operation, application, and installation of relays, highlighting their use of an electromagnet for overcurrent detection The electromagnet generates out-of-phase fluxes that induce the rotation of a disc, which is influenced by the current tap and time dial settings Based on these configurations, the disc is responsible for closing a contact.
Figure 3.5 Rear view of SEL-751A
The tripping circuit is completed by a tap setting, which indicates the minimum current needed to activate the disc movement The test bench relays feature tap settings of 0.5, 0.6, 0.8, 1.0, 1.5, 2.0, and 2.5, with the tap selected by inserting the tap screw into various options located above the time dial The time dial can be adjusted by rotating it clockwise or counterclockwise, offering settings from 0 to 11 This adjustment alters the distance the tripping contact must travel, with higher settings increasing the distance between the contacts For a visual reference, the tap setting screw and time dial are illustrated in Figure 3.6.
Figure 3.6 CO-8 Electromechanical overcurrent protection relay
The wiring connection used for using the CO-8 electromechanical overcurrent protection relay is detailed in Table 3.2 and shown in Figure 3.7
Table 3.2 Details of CO-8 overcurrent relay Wiring Type Connection Points
Figure 3.7 Rear view of CO-8 electromechanical overcurrent relay
General Electric (GE) AC Voltmeter (E)
A GE 0-300 AC voltmeter has been installed to measure the line to line secondary voltage applied to load connected at connection ports (J).
General Electric (GE) AC Ammeter (F)
An AC ammeter has been installed to indicate the current flow at phase-A on the secondary side of the variable autotransformer
Figure 3.8 AC voltmeter installed in the test bench
Figure 3.9 AC ammeter installed in the test bench
Primary Side and Secondary Side Changeover Switches (G1 and G2)
Cam Changeover switches are installed on both the primary (G1) and secondary (G2) sides of the variable autotransformer, enabling the selection of either SEL-751A or electromechanical Westinghouse CO-8 relays These selector switches feature three positions: setting the knob to position ‘1’ activates the current and circuit breaker tripping paths through the SEL-751A relays, while position ‘2’ routes them through the electromechanical relays Position ‘0’ disconnects both relay types, ensuring flexibility and control in the system.
Variable Autotransformer - VARIAC (H)
The 3-phase variable autotransformer, known as the General Radio Company VARIAC, is designed to supply adjustable voltage to loads connected via its secondary side It operates on a primary supply of 3-phase 208 VLL at 60 Hz, allowing the secondary voltage to be varied from 0 to a maximum of 208 VLL Users can easily adjust the voltage by turning the knob, with clockwise rotation increasing the voltage and counterclockwise rotation decreasing it This transformer is rated for 240 VAC and 4 A, suitable for both 50 and 60 Hz applications.
Figure 3.10 Cam changeover switch front and rear view
The primary and secondary windings are configured in a wye connection, with the primary side linked at connection point '4' and the secondary side at connection point '3' Additionally, a common neutral connection is established at point '2'.
GE Industrial Circuit Breaker for Transformer Secondary Protection (I)
The secondary circuit is linked via a GE Industrial Circuit Breaker, which has been detached from the power simulator This breaker can be activated or deactivated using its handle, and its tripping circuit operates at 125 VDC with a current of 1 A Upon tripping, the handle shifts to a position between the "on" (fully upward) and "off" (fully downward) states To reset the breaker, the handle must be moved from the tripped position to the "off" position and then back to the "on" position.
Figure 3.11 Variable autotransformer front view and rear view Voltage can be adjusted with the knob
Load Connection Ports (J)
The Overcurrent Protection Relays Test Bench allows for the connection of resistive loads via its designated connection port The connectors previously used in this project have been repurposed for this setup This port features male and female connections for phases A, B, and C, as well as a neutral connection, N, as illustrated in Figure 3.13.
Figure 3.12 GE Industrial circuit breaker used in the test bench
Full Wave Bridge Rectifier Circuit
To ensure the proper DC voltage for the tripping mechanism of the industrial breaker (I) connected to the secondary of the variable autotransformer, a bridge rectifier circuit is utilized The schematic representation of this bridge rectifier circuit is illustrated in Figure 3.14.
120 VAC, 60 Hz 100 uF 100 uF 100 uF 100 uF 100 uF 100 uF
Figure 3.14 Schematic of bridge rectifier circuit for the industrial circuit breaker
The circuit utilizes a bridge rectifier diode to achieve full rectification of single-phase AC voltage input To minimize ripple voltage, it incorporates six 100μF electrolytic capacitors A 50Ω resistor is employed to regulate the output voltage to approximately 125 VDC, based on the measured no-load voltage of the rectifier circuit, which is around 175 VDC.
Phase A male and female connectors Phase B male and female connectors Phase C male and female connectors
Neutral male and female connectors
The tripping circuit of the breaker exhibits a resistance of approximately 125 Ω To ensure that the voltage remains within safe limits, a resistance is incorporated, allowing the maximum voltage to stay below 125 VDC during brief applications.
Figure 3.15 Full wave rectifier circuit used in the test bench
SEL Feeder Protection Relay Communication and
The communication setup for the SEL-751-A Feeder Protection Relays in the test bench illustrates the application of microprocessor-based overcurrent relay protection Additionally, the SEL-387A Current Differential Relay showcases microprocessor-based differential current protection The SEL-751A Feeder Protection Relays, integral to the Overcurrent Protection Relays Test Bench, can be easily configured and monitored using ACSELERATOR QuickSet® SEL-5030 software.
QuickSet® SEL-5030 software enables connections via serial, network, or modem options In the test bench setup, SEL-3351 Computing Platform relays are linked through serial ports, while the Computing Platform connects to a Personal Computer (PC) using a crossover Ethernet cable This configuration facilitates communication between SEL relays and ACSELERATOR.
QuickSet® utilizes serial to network conversion through SubstationSERVER.NET, which is installed on the SEL-3351 Computing Platform This software supports multiple communication protocols, and for this application, the Port Server functionality provided by SubstationSERVER.NET is essential.
ACSELERATOR QuickSet ® to access the serial ports on the computing platform through Ethernet connection
SEL-387A CURRENT DIFFERENTIAL RELAY (Not part of the Overcurrent Relay Test Bench)
Personal Computer (PC) running SEL
Ethernet Connection (Cross over cable)
Figure 4.1 Communication set up for SEL microprocessor-based relays
The procedure used in this project for configuring and monitoring SEL relays is outlined in figure 4.2
Figure 4.2 Procedure employed for configuring and monitoring SEL relays
Hardware Connections Connect hardware according to figure 4.1
Ethernet Connection Establish Ethernet connection between PC and SEL-3351 Computing Platform
Substation SERVER.NET Configure SubstationSERVER.NET on SEL-3351 Computing Platform for Port Server operation Start Port Server services
AcSELerator QuickSet Setup Run ACSEL ERATOR QuickSet on the PC Configure data base
Access individual relays via QuickSet Terminal and setup each relay according to the application/requirements
Monitor Monitor relay data using HMI in QuickSet
SEL-751A Setup Setup the relay protection settings with
Establishing Ethernet Connection between PC and SEL-3351 Computing Platform
4.2 Establishing Ethernet Connection between PC and SEL-3351 Computing Platform
Once the hardware setup is complete, it's essential to establish an Ethernet connection between the lab PC and the SEL-3351 Computing Platform This requires assigning IP addresses to both devices to ensure proper communication.
To set up the lab PC and Computing Platform, both operating on Windows XP, follow a similar procedure The outlined steps ensure a coherent configuration for optimal performance.
1) From the main desktop of lab PC, access My Network Places by following, Start MenuAll ProgramsMy Network Places
2) Click View network connections (Figure 4.4)
3) Right Click on Local Area Connection and select Properties
4) From the window that appears, select Internet Protocol (TCP/IP) A window will appear Enter IP address as shown
The IP address settings used for Lab PC and SEL-3351 Computing Platform are given in the following Table 4.1
Table 4.1 IP properties used for PC with QuickSet and SEL-3351 Computing Platform
Important- First three fields of the IP address should match The last number in the IP address should be different for PC and Computing Platform
To assign an IP address to the SEL-3351 Computing Platform, follow the outlined procedure After setting the IP address, verify the connection between the PC and the Computing Platform by using the ping command in the command prompt on either device If you are checking the connection from the PC, ensure to ping the Computing Platform's IP address, for example, ping 192.168.56.2.
SubstationSERVER.NET Setup
After establishing the Ethernet connection, it's essential to connect SEL relays with a PC running ACSELERATOR QuickSet software This connection can be achieved through the SubstationSERVER.NET software on the SEL-3351 Computing Platform, which facilitates protocol translation and enhances communication capabilities.
The manufacturer's guide available at SUBNET outlines the software's capabilities, focusing on the relevant features for this project The software can be easily accessed by clicking its icon on the desktop of the SEL-3351 Computing Platform.
Upon launching the software, users will see a screen similar to Figure 4.7 The left pane displays the supported protocols of SubstationSERVER.NET, while the center pane lists the configured devices and ports for each protocol, allowing for new port configurations The right side reveals the properties associated with a selected port, such as Ethernet or serial COM ports, corresponding to the chosen protocol on the left.
Some of the pertinent protocols and applications supported by SubstationSERVER.NET installed on the Computing Platform are listed in the Table 4.2
Table 4.2 Protocols supported by SubstationSERVER.NET installed on the Computing Platform
DNP3 Modbus SEL Fast Messaging (For SEL devices)
Modbus Enterprise Applications Port Server
Event File Collection SEL ASCII
Modbus and DNP3 protocols are essential in industry for connecting field devices, such as relays, to third-party applications In this project, SEL-751A relays are configured to work with SEL ACSELERATOR QuickSet on the Overcurrent Protection Relays Test Bench To facilitate this, the Port Server within Enterprise Applications in SubstationSERVER.NET can be used to connect the SEL relays to ACSELERATOR QuickSet Proper configuration of the COM ports, where the relays are connected, is crucial, involving settings like baud rate, byte size, parity, and stop bits This article details the configuration process for serial port 5, using a spare SEL-751A relay connected to COM5, which is not part of the testing bench Additionally, similar configurations have been applied to COM2, COM3, and COM4 for other SEL relays involved in protection applications.
Double Click on SSNET Explorer icon to launch SubstationSERVER.NET
Figure 4.8 Computing Platform Desktop with SSNET Explorer icon
1) Launch SubstationSERVER.NET from its desktop icon on the Computing Platform
Before configuring a new port, ensure that all services are stopped You can verify this in the right-side pane, as illustrated in figure 4.9 If any services are active, right-click on SubstationSERVER.NET and select "Stop All Services," as demonstrated in figure 4.10 This step is crucial, as the software will not permit port configuration while services are running.
Right click here and select “Stop All
Figure 4.9 Main screen when SSNET Explorer is launched Status of various is indicated as shown
All services should be Stopped This is indicated by “Not Running” against each service
To define a new COM port in the Enterprise Application under Port Server and Terminal Server, it is recommended to use the Online Relay Wizard for SEL devices, which simplifies the process Navigate to Substation SERVER.NET-SELnet.ssnet* in the left pane, then go to Master Protocols and select SEL Fast Messaging To create a new serial connection, right-click in the center pane and choose New followed by Serial Connection, as illustrated in Figure 4.11.
Figure 4.11 Defining new COM port under SEL Fast Messaging
Select SEL Fast Messaging from here
Right Click on the center pane and select NewSerial Connection
When a new COM port is created, it is automatically assigned the default name COM1 To ensure proper identification, this name should be modified to reflect the specific port used for connecting the device to the computing platform In our example, since we are utilizing serial port 5, we rename it to COM5, as illustrated in Figure 4.12.
Newly created serial port has a default name of COM1 The name is changed from here
Figure 4.12 Renaming serial COM port
To access the properties of the newly created COM port, click on its name in the device manager It is essential to verify the baud rate, byte size, parity, and stop bits, which can be compared to the default settings outlined in SEL device manuals or checked directly on the device using the front panel keys In this example, the SEL-751A is configured with specific properties that need to be noted.
Table 4.3 Serial Properties for SEL-751A
Property Description Value/Setting used in this example
This is usually number of the serial port on the Computing Platform We are configuring COM 5
Baud Rate This is baud of the device (relay) being connected 9600
Byte Size Byte size selected for the relay 8
Parity Parity being used by the device for serial communication none
Byte Size Byte Size being used by the device for serial communication 1
RTS Line Request to Send Constant
CTS Line Clear to Send Check
1 Click on the name of newly created
COM port 2 Enter the serial port properties here
To initiate the connection after configuring the serial COM properties, launch the Online Relay Wizard located in the lower right pane This action will bring up a new window, as illustrated in Figure 4.14 Input the level 1 password for the connected relay and click on the Connect button.
Once autoconfiguration is complete, click Finish
Figure 4.15 Successful completion of auto configuration
Figure 4.14 Starting the Online Relay Wizard
Click on Online Relay Wizard
Enter Level 1 Password of relay being connected
7) Access Terminal Server from the left pane by selecting,
Substation SERVER.NET-SELnet.ssnet* Enterprise Applications Port Server Terminal Server
Right click on the center pane and select New Serial Port
Figure 4.16 Defining serial COM port under Terminal Server
8) Rename the newly created COM port to COM5 (same name as given in step 4) See Figure 4.17
When a COM port is created, it is initially assigned the default name COM1 To ensure proper identification, it is essential to rename the port according to the physical connection on the computing platform In this example, we will rename the port to COM5 to correspond with port 5.
Figure 4.17 Changing the name of newly defined COM port
9) Under COM properties (right pane), following parameters are set These are indicated in Figure 4.18 and 4.19 The properties not described in the Table 4.4, are left at default settings
Table 4.4 Configuration of COM properties
COM Properties Settings Description Setting/Value
This feature allows for the direct import of serial port settings, eliminating the need for manual entry After previously importing device settings by specifying COM5 under SEL Fast Messaging, we can easily share these serial port settings by selecting COM5 This action creates a connection between COM5 defined under the Terminal Server and COM5 established under SEL Fast Messaging.
Address Enter the IP address of Computing
Transport Given by default TCP/IP
To disable SEL Maintenance, set the port value to zero (0) For TCP direct port settings, use the format 100xx, where 'xx' denotes the specific port number.
43 Figure 4.18 Selecting COM port from Shared drop-down menu
After configuring the settings, start the Port Server services by right-clicking on Port Server (Substation SERVER.NET-SELnet.ssnet* under Enterprise Applications) or by selecting "Start" in the right-side pane For added convenience, enable the "Start this server automatically when system starts up" option, as illustrated in Figure 4.20.
Services can also be started as shown in Figure 4.3.14
Port Server services can be started by right clicking on Port Server and clicking on Start
Port Server services can also be started by clicking Start option on the right-side pane
Figure 4.20 Start Port Server services
Right click on SubstationSERVER.NET- SELnet.ssnet and select Start All Services
Figure 4.21 Another way of starting services
To initiate Port Services, click OK if prompted by any messages The status of the various running services can be viewed in the right-side pane, as illustrated in figure 4.22.
AC SEL ERATOR QuickSet ® Settings
AC SEL ERATOR QuickSet Communication Settings (Direct Communication)
The steps required to configure settings for establishing communication between
AcSELerator QuickSet and relays connected with computing platform are described below
1) Launch ACSELERATOR QuickSet from start All Programs SEL Applications
Click OK on any message appearing after the services are started
2) From the main menu go to Communications Parameters as shown in Figure 4.24
Figure 4.24 Accessing communication parameters from the main menu
3) Use the following setting in the Communication Parameters to configure COM5 port on Computing Platform as shown in Figure 4.25
Figure 4.25 Setting communication parameters in QuickSet
These are Level One and
SEL devices Usually default password are provided and don’t have to be entered For SEL-751A default Level One password is OTTER and
Level Two password is TAIL
The format used for port number is 100xx Since we are configuring COM5 so Port Number is
In Host IP Address enter the IP address of the Computing Platform We have set the IP address of Computing Platform as 192.168.56.2
Select Active Connection Type Network
4) Once the communication between relay and acSELerator QuickSet is successfully established, the lower portion will state the condition Connected and also list the communication parameters To ensure that successful communication open Terminal by clicking on its icon on the main menu When terminal window is opened, and = sign will appear Type ACC If communication is established, the Terminal will prompt for Level One password of device (in this case SEL 751-A relay) This is shown in Figure 4.26
Launch Terminal by clicking this icon
Figure 4.26 Confirming successful communication in QuickSet
AC SEL ERATOR QuickSet ® Communication Settings (Through Database)
Section 4.4.1 described the process of establishing direct communication with a SEL device
Using the ACSELERATOR QuickSet Database simplifies device configuration by allowing users to save individual settings for various devices The default database, Relay.rdb, facilitates easy connection to devices once the settings are stored This streamlined process enhances efficiency in device management.
1) From the main menu select Tools Device Manager Devices The Device Manager option is also available on the main display when ACSELERATOR QuickSet is first launched A window shown in Figure 4.27 will appear In the field where password is required, enter the password of the database The password of the default database in QuickSet installed in the lab PC is aperc
Figure 4.27 Access to ACSELERATOR Database
2) When the database is opened the folders defined in the database are shown on the left pane under Connection Explorer Since a SEL-751A Feeder Protection Relay is being added, the configuration is added in Overcurrent Relay folder This is done by right clicking on the folder name and then selecting Add and then Device as shown in Figure 4.28 A window, shown in figure 4.29, will appear Select SEL-751A
Figure 4.28 Adding a new device in the database
3) Once the device is selected, the name of device is added under folder tree Clicking on the device name will open a new window where properties of the device can be configured This is shown in Figure 4.30 Select Connection and then click on Edit on the lower right corner
1) Click on the device name
4) Enter the communication properties as shown in Figure 4.31
Host IP address: IP address of Computing Platform 192.168.56.2
Port Number: TCP/IP port number Format used is 100xx, where xx is the COM port number 10005 File Transfer Option: Raw TCP
5) Once the communication parameters for the device are set, then the connection with device is made by right clicking on the device name under folder name on the left-pane The first option on the window that appears ‘Connect’ is then selected This is shown in Figure 4.32
Figure 4.32 Connecting a relay with QuickSet
6) Once connection parameters of a device are defined, it becomes easier to connect the device Save any changes if prompted to do so To connect to a defined device requires only to right click on the device name and select ‘Connect’ as described in the previous step A connected device can be disconnected in the same way When a device is connected, the device name will have a green dot Right clicking on the device name will give the option of ‘Disconnect’ A disconnected device will have a grey dot followed by the device name When the device name is selected the dot turns blue
When the device is connected the device name will have a green dot
4.5 SEL 751-A Feeder Protection Relay Settings
SEL-751A device settings can be read and modified either by accessing a device with QuickSet, or by accessing the settings directly using a terminal emulator QuickSet has a
“Terminal” option available which can be used for this purpose
The following describes how device settings can be accessed and modified with the above- mentioned options
4.5.1 Accessing and Modifying SEL Relays Settings with QuickSet
AcSELerator QuickSet allows users to read data from connected relays, enabling modifications to the retrieved data before sending it back to the device.
1) Connect a relay with QuickSet as described in 4.4.1 or 4.4.2
2) Click on the “Read Settings From Device” option from the main menu as shown in Figure 4.5.1.1
Figure 4.34 Reading data from a connected device
Device data can also be read from this option
3) If the device is connected through the database as described in section 4.4.2, then device data can also be read as shown in Figure 4.35
A window as shown in Figure 4.36 will appear indicating that device data is being read
Right click on the connected device
Select Device Tasks and then Read
Figure 4.35 Reading device data of a relay configured in database
Figure 4.36 Device data being read from relay
4) When the reading process is complete, user can access the settings of the device Clicking on a particular setting will open details for each setting option New values can be entered as shown in Figure 4.37 Relay protection settings are under Group1 Set1 Logic settings are under Group 1 Once new settings have been entered, the new values can be sent to the relay by clicking on the “Send Active Settings” option on the main menu
Relay settings options can be seen under Group1 on this pane When a particular category is selected, the details menu under it appears on the right
Values for a selected setting can be changed
In this case new settings for overcurrent can be entered here
Once the new settings are entered, these can be sent to the device by “Send Active
Figure 4.37 Detailed device settings Settings can be read, modified and sent to device
5) The software asks the user which settings have to be sent If any changes in the protection are made, then only “Set 1” has to be sent If any changes in the logic settings are made under “Logic 1” then only “Logic 1” can be sent The software offers an option of saving new settings Saving settings can be convenient as the same settings can be used later on without the need of reading the relay data
Figure 4.39 Relay data can be saved in PC and loaded and sent to relay latter on
Figure 4.38 Selecting settings to send to the device
Accessing and Modifying SEL Relays Through Terminal
SEL relays' settings can be accessed and modified using a terminal emulator and ASCII commands through ACSELERATOR QuickSet® 5030 software By connecting a device, such as the SEL-751-A, to the software, users can easily launch the Terminal from the main menu icon, as illustrated in figure 4.40.
The SEL-751A relay offers three access levels for users to communicate and modify its settings, as detailed in section 7 of the SEL documentation However, the two most relevant levels are 'level 1' and 'level 2' At level 1, users can only view the settings, while level 2 allows for modifications to be made For detailed information on these access levels, refer to Table 4.5.
Figure 4.40 Launching Terminal from ACSELERATOR QuickSet
Terminal is launched by clicking on its icon
= sign with blinking cursor indicates that device is communicating
To access level 1 of relay settings in the Terminal, begin by typing ACC after the = sign Upon entering the password for level 1, the prompt will change from = to =>, confirming access At this level, users can view relay settings by typing the SHO or SHOW command Relevant relay settings are detailed in Table 4.6, while comprehensive information can be found in SEL [2] Section 6 “Settings”.
Figure 4.42 Level 1 of SEL-751A SHO is entered to show relay settings
Enter ACC to access level 1
When prompted enter level 1 password
Typing SHO or SHOW will show Group 1 setting
Table 4.6 SEL-751A Settings categories pertinent to this project
Category Description View Settings SEL
Modifying Setting SEL Command Date Show/modify the date configured in the device SHO D SET D
Show/modify device’s front panel settings SHO F SET F
Global Settings Show/modify Global settings SHO G SET G
Show/modify settings under GROUP This category lists the protection settings of the relay
Show/modify settings under LOGIC This category is important as it lists the relay output assignments
Port Show/modify the settings of relay ports
SHO P x, Where ‘x’ is the port on the relay x= 1, 3 or F
SET P x Where ‘x’ is the port on the relay x= 1, 3 or F Report Settings Show/modify Report settings SHO R SET R
Time Show/modify the relay time settings SHO T SET T
To view the settings in each category, you can use the SEL command followed by the specific setting, as outlined in Table 4.6 For instance, entering "SHO L" will display the Logic settings, while simply typing "SHO" will reveal the relay's protection settings.
To modify a setting, users must reach level 2 by entering "2AC" at level 1, after which they will be prompted for a level 2 password, indicated by the prompt ">>" At this level, users can change settings within a category by using commands from Table 4.6 For example, to modify relay protection settings, users can issue the "SET" command The device will display the current value of each setting followed by a '?', allowing users to enter a new value and press "Enter" to proceed to the next setting If no changes are needed, simply pressing "Enter" after the '?' will continue the process.
After completing all the settings, the device prompts you to save any modifications made Press ‘Y’ to save the changes or ‘N’ to discard them and retain the original settings.
The relay settings, accessible via the SHO command and adjustable through the SET command, encompass configuration parameters, various protection settings, and trip logic equations essential for issuing alarms and controlling the output contacts to operate connected breakers Key configuration settings include CT and PT ratios, nominal line-to-line voltage, and transformer connection details The relay provides a range of protection features such as instantaneous and time-phase overcurrent protection, neutral, negative sequence, and residual overcurrent protection, as well as over and undervoltage protection, power factor (pf) lead-lag protection, and frequency variation protection These versatile protection features can be tailored with different trip levels and include customizable trip variables and word bits for optimized relay operation.
1) TR-which assigns a word bit TR to a logical equation that incorporates the protection features of the relay The logical equation uses AND, OR and NOT combinational logic elements to combine various protection elements The default TR equation is given by,
ORED50T= OR output of all instantaneous current protection elements (50)
ORED51T= OR output of all time current protection elements (51)
TR: = ORED50T OR ORED51T OR 81D1T OR 81D2T OR 81D3T OR 81D4T OR 59P1T
OR 59P2T OR 55T OR REMTRIP OR SV01 OR OC OR SV04T
SV04T= SEL logic variable 4 timer output
2) ULTRIP- which assigns a variable ULTRIP to a logical equation that incorporates unlatching feature
3) REMTRIP- this variable takes into account remote trip options This is done by assigning SEL logical equation to REMTRIP variable It usually involves assigning an input contact to REMTRIP.
Logic settings encompass various elements such as logic enables, latch bit equations, SEL logic variables, and crucially, output contact assignments These settings can be viewed using the SHO L command and modified with the SET L command The output contacts of the relays are designated for use in signaling alarm devices or tripping breakers, all of which fall under the Logic settings The TRIP word bit is linked to the trip logic TR, as detailed previously, allowing trip settings in TR to be assigned to a contact by designating the word TRIP By default, the TRIP assignment is made to the OUT103 output contact coil.
Using the Terminal to view and modify relay settings has a notable drawback: it only displays SEL names without providing complete descriptions of the settings For comprehensive definitions of these options, refer to section 4 and the SEL-751A settings sheets in SEL [2] Additionally, Appendix B includes definitions for the relay settings available in the relays installed on the test bench.
Monitoring
The relay readings can be monitored with Human Machine Interface (HMI) in QuickSet This can be done with the following steps
1) Connect relay with QuickSet as described in 4.4.1 or 4.4.2
2) Click on the HMI icon on the main menu
Click on the HMI icon on the menu
Figure 4.43 Accessing the HMI in QuickSet
3) The software reads the relay data Once the data is read, the screen shown in Figure 4.44 will appear
Figure 4.44 Device Overview on HMI
To view the phasor representation of live currents and voltages, select the "Phasor" option from the left menu The buttons located on the right side of the plot allow you to display the phasor representation for current and voltage quantities Clicking a button will activate it, revealing the corresponding phasor representation on the plot, while clicking an activated button will deactivate it, removing the phasor representation.
Figure 4.45 Viewing phasor representation of live current and voltage values.
Clicking the buttons will toggle the visibility of the corresponding phasors on the plot When a button is pressed, the phasor is displayed; clicking it again will release the button and remove the phasor from view.
IN= Current through neutral As neutral is not connected through the relay, this should be zero
IG= Phasor sum of IA, IB and IC
VA= Phase voltage of phase A
VB= Phase voltage of phase B
VC= Phase voltage of phase C
VG= Phasor sum of VA, VB and VC
5) Fundamental metering values can be viewed by clicking on “Fundamental” option on the right pane
6) Events can be saved and viewed by going to Tools Events Get Events Files, as shown in Figure 4.47
7) The software shows a list of events Event of interest can be selected After this “Get Selected Events” button is clicked
After selecting the events listed on the left click this button
8) Once the software gets the event data, a window to save the Events will open Select the folder to event file
9) From start menu select All Programs SEL Applications AcSELerator Analytic Assistant
10) From the file menu select the location of the event file
Figure 4.50 Opening AcSELerator Analytic Assistant in the lab PC
Figure 4.51 Opening event file in in AcSELerator Analytic Assistant
The event file will show the waveforms of currents and voltage User can also see the phasor representation of the voltages and currents
Metering data can be accessed via the Terminal by using the MET command in either level 1 or level 2 It is important to note that the metering values are not updated in real-time, so the MET command must be reissued each time new readings are needed.
Figure 4.52 Graphs of currents and voltages from the event file Phasor representation can also be obtained from the options.
The success of the current project has led to plans for constructing a similar bench to demonstrate differential current protection, utilizing the SEL-387A Current Differential Relay A comparable breaker circuit, designed and implemented in this project, will facilitate tripping The proposed schematic for the Differential Current Protection Relay Test Bench is available in appendix A3 This circuit has been tested for both line-to-line and line-to-neutral faults, successfully detecting current imbalances between the primary and secondary sides of a variable autotransformer Additionally, the SEL-387A Current Differential Relay has been configured using ACSELERATOR QuickSet®.
The proposed design closely resembles the example provided in SEL [6] (figure 2.7 pp 2.10) and incorporates the SEL-387A relay along with a variable autotransformer However, this design features a single breaker circuit, specifically developed for this project, positioned on the primary side of the transformer Additionally, load connection points will be integrated on the primary side to facilitate the introduction of both line-to-line and line-to-neutral faults Notably, the proposed design will not connect its neutral to the SEL-387A relay.
The proposed design features a differential system with primary (IAW1, IBW1, ICW1) and secondary (IAW2, IBW2, ICW2) pickup elements connected through a transformer Three-phase loads can be linked via a load connection port, while fault-inducing loads are connected to the primary side of the autotransformer after IAW1, IBW1, and ICW1 Upon introducing a fault, an imbalance occurs between the currents in the primary and secondary pickup elements, prompting the relay to activate contact OUT103 This action trips the breaker circuit, severing the connection between the incoming AC supply and the primary side of the variable autotransformer.
The setup used to test the suggested circuit for the differential current protection is shown in Figure 5.1
Live readings from the current differential relay were observed using HMI in
The AcSELerator QuickSet® provides a comprehensive overview of device operation, illustrated in Figures 5.2, 5.3, and 5.4 These figures depict the device's normal operating conditions, the differential current phasors, and the device status when a fault is detected, prompting the relay to initiate a trip.
Figure 5.1 Differential current protection circuit test setup
Figure 5.2 Device Overview of SEL-387A during normal operation.
75 Figure 5.3 Phasor representation of differential currents.
Figure 5.3 Device Overview of SEL-387A when relay trips.
Appendix A- Overcurrent Protection Relays Test Bench Circuit Schematics Appendix B- SEL -751A Settings Definitions
Appendix C- US Inverse Time Relay Operating Time vs Multiples of Pick-up Current
Breaker Circuit with 15VDC operating and 12VDC control (Detailed schematic in sheet 2)
External Load connected in Wye.
A-1 Main Wiring Schematic of Over Current Protection Relays Test
Manual Changeover Switch Primary Side
Toggle ON/OFF Switch Push Button Reset
Phase-A Primary Side of VARIAC
Phase-B Primary Side of VARIAC
Phase-C Primary Side of VARIAC
A-2 Wiring Schematic of Beaker Circuit for Primary Side Protection
120 VAC Single Phase Connection from Main Isolation Breaker
IAW1 IBW1 ICW1 IAW2 IBW2 ICW2
15VDC operating and 12VDC control
Fault Connection Point External Load
A-3 Proposed Schematic for Differential Current Protection Setup
B- SEL-751A Relay Settings Definitions Pertinent to This Project from SEL [2]
SEl-751A Relay Protection Settings SHO and SET
ID RID Relay ID settings SEL-751A
TID Relay ID settings FEEDR RELAY
CTR Phase CT Ratio Value between 1-5000 can be set This should set to ‘1’ because in this project no CTs have been used
CTRN Neutral CT Ratio Value between 1-5000 can be set This should set to ‘1’ because in this project no CTs have been used 1-5000
PTR Phase PT Ratio Value between 1.00-10000.00 can be set
This should be set to ‘1’ because the test bench does not use PTs
1.00-10000.00 DELTA_Y Transformer Connection This should be set at WYE WYE, DELTA VNOM Line to Line Voltage This is set at 208 V
=WYE) SINGLEV Single V Input This is set at N because we have three phase voltage Y, N
50P1P Maximum Phase Overcurrent Trip Level 1 Trip current level is in Amps This should not exceed 3.5 A OFF, 0.50–100.00 50P1D Maximum Phase Overcurrent Trip Delay 1 Time in seconds 0.00–5.00
Maximum Phase Overcurrent Torque Control (50P1P) operates based on the truth of a SELogic expression assigned to it When the expression evaluates to true, 50P1P becomes functional; for instance, assigning 50P1TC=IN101 activates 50P1TC when the digital input IN101 is true If no logic expression is assigned, a value of 1 (true) must be set to ensure the functionality of 50P1P.
Default value used, if no logical or external control is required, is 1
50P2P Maximum Phase Overcurrent Trip Level 2 Trip current level is in Amps This should not exceed 3.5 A
OFF, 0.50–100.00 50P2D Maximum Phase Overcurrent Trip Delay 2 Time in seconds 0.00–5.00
50P2TC Maximum Phase Overcurrent Torque Control 2 Same applies to this setting as explained for 50P1TC
The default value is set to 1 when no logical or external control is needed The 50P3P Maximum Phase Overcurrent Trip Level 3 indicates that the trip current, measured in Amps, must not exceed 3.5 A, with an OFF range of 0.50 to 100.00 Additionally, the 50P3D Maximum Phase Overcurrent Trip Delay 3 specifies a time delay in seconds, ranging from 0.00 to 5.00.
50P3TC Maximum Phase Overcurrent Torque Control 3 Same applies to this setting as explained for 50P1TC
The default value is set to 1 when no logical or external control is necessary The maximum phase overcurrent trip level (50P4P) is 4, with a trip current in Amps that must not exceed 3.5 A, and can be adjusted between OFF and 100.00 Additionally, the maximum phase overcurrent trip delay (50P4D) is 4 seconds, with a time range from 0.00 to 5.00 seconds.
50P4TC Maximum Phase Overcurrent Torque Control 4 Same applies to this setting as explained for 50P1TC
Default value used, if no logical or external control is required, is 1
The 50N1P, 50N2P, 50N3P, and 50N4P Neutral Overcurrent Levels can all be set to OFF since we are not utilizing a neutral connection Each level allows for settings ranging from 0.50 to 100.00.
Residual Overcurrent Level 1 This should not exceed 3.5 A
The residual current IG is the phasor sum of phase currents
50G2P Residual Overcurrent Level 2 This should not exceed 3.5 A OFF, 0.50–100.00 50G3P Residual Overcurrent Level 3 This should not exceed 3.5 A OFF, 0.50–100.00 50G4P Residual Overcurrent Level 4 This should not exceed 3.5 A OFF, 0.50–100.00
The 50Q1P, 50Q2P, 50Q3P, and 50Q4P negative sequence overcurrent levels are all crucial settings that should not exceed a maximum current of 3.5 A Each level can be adjusted between OFF and a range of 0.50 to 100.00 A, ensuring optimal performance and safety in electrical systems.
51AP Phase A - Phase Current Trip Level This should be set so that maximum current through a phase does not exceed 3.5A OFF, 0.50-16
Phase A - Phase Current Curve The relay has options for various US and IEC curves,
US: U1 (Moderately Inverse), U2 (Inverse), U3 (Very Inverse), U4 (Extremely Inverse), U5 (Short-time Inverse) IEC: C1 (Standard Inverse), C2 (Very Inverse), C3 (Extremely Inverse), C4 (Long-time Inverse), C5 (Short-time Inverse)
51ATD Phase A - Time Dial 0.50-15.00 for US curves 0.05-1.00 for
0.50 - 15.00 0.05 - 1.00 51ARS Phase A - EM Reset Delay Setting this to ‘Y’ will introduce a reset delay which is a characteristic of electromechanical relays
51ACT Phase A - Constant Time Adder Raises the curve by a constant time 0.00-1.00
51AMR Phase A - Minimum Response Time of Curve 0.00-1.00
Phase A - Torque Control activates when a SELogic expression is assigned to the bit, making it true only when the expression evaluates to true, thus enabling the functionality of 51AP For instance, assigning 51ATC=IN101 will ensure that 51ATC is true when IN101 is true If no logic expression is assigned, a value of 1 (true) must be set to ensure that 51AP remains functional.
Default value used, if no logical or external control is required, is 1
The 51BP Phase B settings should ensure that the maximum current through a phase remains below 3.5A when turned off, with a range of 0.50 to 16A Additionally, the 51BC Phase B current curve options are identical to those provided for the 51AC model, including U1, U2, U3, U4, and U5 configurations.
C1, C2, C3, C4, C5 51BTD Phase B - Time Dial 0.50-15.00 for US curves 0.05-1.00 for
51BRS Phase B - EM Reset Delay Y or N
(default N) 51BCT Phase B - Constant Time Adder Raises the curve by a constant time 0.00-1.00
51BMR Phase B - Minimum Response Time of Curve 0.00-1.00
51BTC Phase B - Torque Control Same applies to this setting as explained for 51ATC
The default value is set to 1 when no logical or external control is necessary For the 51CP Phase C, the phase current trip level must be configured to ensure that the maximum current does not surpass 3.5A, with options ranging from OFF to 0.50-16 Additionally, the 51CC Phase C phase current curve offers the same curve options as those available for 51AC, including U1, U2, U3, U4, and U5.
C1, C2, C3, C4, C5 51CTD Phase C - Time Dial 0.50-15.00 for US curves 0.05-1.00 for
51CRS Phase C - EM Reset Delay Y or N
(default N) 51CCT Phase C - Constant Time Adder Raises the curve by a constant time 0.00-1.00
51CMR Phase C - Minimum Response Time of Curve 0.00-1.00
51CTC Phase C - Torque Control Same applies to this setting as explained for 51ATC
Default value used, if no logical or external control is required, is 1 51P1P