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Introduction to SELOGIC Control Equations

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Introduction to SELOGIC Control Equations

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Introduction to SELOGIC Control Equations

The SEL-710 Motor Protection Relay is equipped with programmable logic so you can customize various relay functions. The SEL-710 Instruction Manual also describes SELOGIC control equations and their various applications within the SEL-710. Use the programmable logic components described in this section to modify the factory-default logic settings. Each relay element is represented internally as a logic point, called a Relay Word bit. Each Relay Word bit exists in one of two states: true or false, picked up or dropped out. The relay uses these results to evaluate fixed logic and the programmable SELOGIC control equations defined in the relay settings. Build SELOGIC control equation settings using logic similar to Boolean algebra logic by combining Relay Word bits together using one or more SELOGIC control equation operators.

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Introduction to SELOGIC Control Equations

The protection and control element results are represented by Relay Word bits. Each Relay Word bit has a label name and can be in one of the following states: 1 (logical 1) or 0 (logical 0) Logical 1 represents an element being picked up or otherwise asserted. Logical 0 represents an element being dropped out or otherwise deasserted. The Relay Word bits are collected into a table of 112 rows, each row containing 8 bits. The SEL-710 Instruction Manual includes a complete listing of Relay Word bits and their descriptions.

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Introduction to SELOGIC Control Equations

Use the rising-edge operator (R_TRIG) with individual Relay Word bits to cause a single processing cycle assertion when the Relay Word bit changes state from logical 0 to logical 1. Use the falling-edge operator (F_TRIG) with individual Relay Word bits to cause a single processing cycle assertion when the Relay Word bit changes state from logical 1 to logical 0. Use parentheses ( ) to logically combine multiple elements. More than one set of parentheses can be used in a SELOGIC control equation setting. Use the NOT operator to invert a single Relay Word bit and also to invert the result of multiple elements combined within parentheses. Use the AND operator to denote logical AND operations. When you use the AND between two Relay Word bits, both must pick up in order for the relay to perform the operation in question. Use the OR operator to denote logical OR operations. When you use the OR between two Relay Word bits, either can pick up to cause the relay to perform the operation in question. To define a condition as always picked up or always dropped out, you can set SELOGIC control equations directly to 1 (logical 1) or 0 (logical 0).

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Introduction to SELOGIC Control Equations

The slide shows the three basic Boolean expressions that allow flexibility within SEL relays.

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Introduction to SELOGIC Control Equations

As explained earlier, the rising- and falling-edge detectors allow you to detect just when a Relay Word element changes state. The rising-edge operator detects the moment in time that a relay element picks up. When a Relay Word element asserts, or changes from a not picked up state to a picked up state, the rising-edge function of that element will logically assert for one processing interval (pulse one time). The opposite is true for the falling-edge detect operator. Latch Bits: Latch bits provide a way to seal-in a relay element operation. When the latch is set, the output of the latch is asserted and stays asserted until the latch is reset. Latch functions, such as lockout conditions, are easy to implement with latch bits and can be used to electrically latch internal elements or output contacts either open or closed. Latches should not be used to create blinking LEDs, etc. Every time a latch is set or reset, this is stored in memory. Memory can be written to only so many times before it’s destroyed. If you need to turn something on and off repeatedly, you should use SV variables. Timers: In SEL relays, all SELOGIC variable timers have a programmable pickup and dropout time. If you want to time delay a pickup of an element, such as in a breaker failure scheme, combine that element with a timer and set the desired pickup delay. Then use the timer in SELOGIC as you would have used the relay element. The timer is logically equivalent to the delayed relay element pickup. If you want to time delay a dropout of an element, combine that element with a timer, set the pickup delay to zero, and set the dropout delay to the desired value. The timer is logically equivalent to the delayed relay element dropout. It is also possible to time delay both the pickup and the dropout of a relay element within the same timer.

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Introduction to SELOGIC Control Equations

Effective documentation is very important to understanding and troubleshooting SELOGIC. Documenting internal relay logic presents some challenges to the relay engineer. One way to perceive and document SELOGIC equations is shown on the slide—by representing Relay Word elements as discrete relay components inside the relay. These relay elements can be expressed as contacts within a contact diagram. Externally, tripping functions are performed by the relay contacts. Relay wiring diagrams tend to oversimplify relay functionality and not give a detailed explanation of relay contact functionality. Referencing a control circuit diagram will also show what physical relay contacts are being used and their purposes. However, typical control circuit diagrams do not indicate internal element functionality. Additional documentation is helpful to indicate complete relay contact functionality. Drawing an internal relay element contact diagram is one method of providing this additional source. On the slide, SELOGIC has been used to develop a simple trip scheme.

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Introduction to SELOGIC Control Equations

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Use display points to view either the state of internal relay elements (Boolean information) or analog information on the LCD display. Although the LCD screen displays a maximum of 16 characters at a time, you can enter as many as 60 valid characters. Valid characters are 0–9, A–Z, –, /, “”, {, }, and a space. For text exceeding 16 characters, the LCD displays the first 16 characters and then scrolls through the remaining text not initially displayed on the screen.

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Any or all of Alias, Set String, or Clear String can be empty. Although the relay accepts an empty name setting as valid, a display point with an empty name setting is always hidden. Commas are significant in identifying and separating the four strings. Use quotation marks only if the text you enter for Alias, Set String, or Clear String contains commas or spaces. For example, DP01 = Name, Text is valid, but Name, Text is not valid (contains a space). Correct the Alias name by using the quotation marks: Name, “Text 3”. You can customize the data display format by entering data in selected strings only.

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In this example, if Latch 1 asserts, then the SEL-710 rotating display will show “ALARM1 = CHECK FILTER”.

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In general, the legal syntax for analog display points consists of the following two fields or strings: Name and “User Text and Formatting.” Unlike binary quantities, the relay displays analog quantities on both display lines. Name = Analog quantity. All analog quantities occupy two lines on the front-panel display. User text and numerical formatting = Display the user text, replacing the numerical formatting (width.dec,scale) with the value of Name, scaled by “scale”, formatted with total width “width” and “dec” decimal places. Name can be either an analog quantity or a Relay Word bit. The width value includes the decimal point and sign character, if applicable. The scale value is optional; if omitted, the scale factor is 1. If the numeric value is smaller than the string size requested, then the string is padded with spaces to the left of the number. If the numeric value does not fit within the string width given, the string grows (to the left of the decimal point) to accommodate the number.

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Introduction to SELOGIC Control Equations

In this example, Counter 1 is counting the number of hours since the last motor maintenance was done. SC01 is the current count of the number of hours. The statement allows for 4 digits of the current count to be displayed. The pretext is “MAINT” and the post-text is “HOURS” since we are counting the maintenance hours. The SEL-710 rotating display will show “MAINT = XXXX HOURS”.

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Introduction to SELOGIC Control Equations

The operators shown on this slide and the next slide are listed in order of precedence with parentheses being the highest precedence and OR being the lowest precedence. Use parentheses to logically combine multiple elements or override the precedence shown on the slide in both math and logic equations. You can use more than one set of parentheses in a SELOGIC control equation setting. Use the negation operator, –, to change the sign on a numeric value. Use an asterisk, *, to multiply two numeric quantities together and a forward slash, /, to divide one number by another. Note that math variables and analog quantities available in the relay can also be used in SELOGIC math equations.

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Introduction to SELOGIC Control Equations

Use a plus symbol (+) to add two numeric quantities together and a hyphen (-) to subtract one number from another. Note that math variables and analog quantities available in the relay can also be used in SELOGIC math equations. Use the comparison and equality/inequality operators to compare the magnitude of a math variable or analog quantity to a number or another math variable/analog quantity. To define a condition always picked up or always dropped out, you can set SELOGIC control equations directly to 1 (logical 1) or 0 (logical 0).

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Use the setting ELAT to enable up to 32 latch variables. Each variable has a set and reset SELOGIC equation. Note that if both SETn and RSTn are asserted simultaneously, RSTn has priority and LTn = 0.

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Introduction to SELOGIC Control Equations

In this example, the latch is set once the counter output SC01Q asserts after 2160 hours. The latch output (LT01) is used in the display message “ALARM1 = CHECK FILTER” that was introduced earlier. The latch is reset when both Pushbutton 1 ({AUX 1}) and the {TARGET RESET} pushbutton are pressed at the same time.

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Introduction to SELOGIC Control Equations

Use the setting ESV to enable up to 32 logic variables. Each variable has settable pickup and dropout timers in addition to a SELOGIC input (SVn).

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Introduction to SELOGIC Control Equations

In this example, variables SV01 and SV02 are combined to make an hour timer. SV01 makes up the first 30 minutes while SV02 makes up the last 30 minutes. Combined together they produce a 1-hour timer. The timer starts when the motor is in running mode and the timer is reset. Once the first timer (SV01) times out, the second timer (SV02) starts to time the last 30-minute interval. The motor must continue to run for an hour for the timer to continue timing.

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Introduction to SELOGIC Control Equations

Use the setting ESC to enable up to 32 counter variables. Each variable has multiple inputs and outputs. When SCnnLD (SELOGIC equation) asserts, the preset value (SCnnPV) is loaded into the counter. The output SCnnQU asserts when the present value of the counter (SCnn) equals the preset value (SCnnPV). The counter increments its present value (SCnn) on the rising edge of the count-up input (SCnnCU). Reset the counter with the reset input (SCnnR). The counter is also capable of counting down. It begins at the preset value (SCnnPV) and decrements the present count (SCnn) on the rising edge of the countdown input (SCnnCD). When SCnn reaches zero, the SCnnQD output asserts. The countdown counter is reset when the load input (SCnnLD) asserts, loading the preset value (SCnnPV) into the counter. Setting

Type

SCnnLD

SELOGIC input

Load preset value

SCnnPV

Numeric setting

Preset value

SCnnCU

SELOGIC input

Count-up trigger input

SCnnCD

SELOGIC input

Countdown trigger input

SCnnR

SELOGIC input

Reset counter to zero

SCnnQU

Relay Word bit

Counter at preset value

SCnnQD

Relay Word bit

Counter at zero

SCnn

Analog quantity

Present counter value

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Introduction to SELOGIC Control Equations

The figure shows the operation of the counters in the SEL-710. Note the order of precedence of the inputs.

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Order

Input

1

SCnnR

2

SCnnLD

3

SCnnCU

4

SCnnCD

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Introduction to SELOGIC Control Equations

In this example, the counter is counting up each time the SEL variable timer SV02T times out after each hour. The counter is thus counting hours. The counter is reset when both Pushbutton 1 ({AUX 1}) and the {TARGET RESET} pushbutton are pressed at the same time. This pushbutton action also loads the preload value of 2160 hours into the counter. Once the counter reaches 2160, the counter output SC01Q asserts. The number 2160 hours represents 90 days or three months.

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Introduction to SELOGIC Control Equations

Use the setting EMV to enable up to 32 math variables. Assign either a real number or an analog quantity (including another math variable) to any given math variable. You can also use a combination of real numbers and analog quantities with the mathematical operators discussed earlier in this section.

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Introduction to SELOGIC Control Equations

In this example, the rotor resistance is calculated by multiplying the measured rotor frequency by 0.01648 and adding the constant 0.0112 to it. This produces a value of 1.0 ohms at 60 Hz and 0.34 ohms at 20 Hz. The math variable can be set up to calculate the changing resistance, which is dependent on measured rotor frequency. The relay is connected to the rotor current transformers in this wound rotor machine. Thus the relay is measuring the rotor current frequency.

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Introduction to SELOGIC Control Equations

You can assign any control input to the SELOGIC control equation BLKPROT. During certain operational phases, when the level (e.g., motor current) differs from normal values, selected functions are completely disabled as long as the control input is asserted. For operational phases such as those listed below, you could have no warning, no trip or reset, and tripping delays that begin to run only after the function is reenabled: •

During starting (earth fault and short-circuit protection)

•

At no load (protection against asymmetry and underload)

•

During brief overload phases (high overload/jam)

•

During commissioning and fault location (localizing the source of the trouble)

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Introduction to SELOGIC Control Equations

TDURD, minimum trip time: This timer establishes the minimum time duration for which the TRIP Relay Word bit asserts. This is a rising-edge-initiated timer. TR, trip conditions SELOGIC equation: The SEL-710 trip logic offers two ways to stop the protected motor—conditions mapped to TR and the front panel or the serial port STOP command. Either of the two conditions will trigger an event report. The relay controls the TRIP output contacts. Set the TR SELOGIC control equation to include an OR combination of all the enabled protection element Relay Word bits that you want to cause the relay to trip. Use the factory-default settings as a guideline. REMTRIP, remote trip conditions SELOGIC equation: You can map a control input contact to REMTRIP to stop the motor by a contact input to the relay. REMTRIP needs to be added to the trip equation (TR) if you wish to use it. If the relay is tripped by REMTRIP, the display will show “REMOTE TRIP”. ULTRIP, unlatch trip conditions SELOGIC equation: Following a fault, the trip signal is maintained until all of the following conditions are true: •

Minimum trip duration time (TDURD) passes

•

The TR SELOGIC control equation result deasserts to logical 0

•

All the motor lockout functions deassert to 0

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Introduction to SELOGIC Control Equations

TRGTR = Target reset command, front panel or serial ports RSTTRGT = Target reset SELOGIC control equation STOP = Motor stop command, front panel or serial ports TR = Trip SELOGIC control equation ULTRIP = Unlatch trip SELOGIC control equation EMRSTR = Emergency start command, front-panel or Modbus®/DeviceNet™ command STOPPED = Motor stopped Relay Word bit ABSLO = Antibackspin lockout TBSLO = Minimum time between starts lockout NOSLO = Starts-per-hour lockout THERMLO = Thermal element lockout TDURD = Minimum trip time setting

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If the TRIP Relay Word bit is not asserted, the relay asserts the START Relay Word bit in response to any of the following conditions: •

Start motor signal received from the SELOGIC control equation STREQ

•

Emergency restart signal received from the SELOGIC control equation EMRSTR, the front panel, or the serial ports

•

Start motor signal is received from the front panel or the serial ports

The START Relay Word bit remains asserted for 0.5 seconds unless the relay trips. If the relay trips before the 0.5-second timer expires, the relay resets the timer, clearing the START Relay Word bit. In an emergency, you may need to quickly start the motor even though a protection lockout condition exists and is holding the TRIP output asserted. The lockout could be a result of the thermal element or another protection function. You can override all of the lockout conditions by using the emergency restart function. You can assign any control input to the SELOGIC control equations SPEED2 and SPEEDSW. When the SPEED2 control input is asserted and the two-speed enable setting E2SPEED is Y, the SEL-710 selects second values for the settings. Use the SPEED2 input for two-speed motor applications. You can also use this input to change the settings in applications where ambient temperature varies appreciably (e.g., exposed water pumps with different capacities during the daytime and at nighttime). The SPEEDSW control input provides an indication of the rotor speed to the speed switch logic.

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Note: Set 52A := 0 if you do not connect the contactor/breaker auxiliary contact to the relay input. FLAn = Effective full-load current (n is 1 or 2 for Speed 1 or Speed 2) FLAmin = Lowest full-load current setting allowed I1, I2 = Positive-/negative-sequence motor current T1 and T2 are timers with pickup time A of 300 ms L1, L2, and L3 are latches / indicates reset on the rising edge of the reset input 50S and 52A are Relay Word bits

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