Digital Logic for Protection & Control

Digital Logic for Protection & Control35th Annual Hands-On Relay SchoolMarch-2018

Kevin Damron, PESr. Protection Engineer – Avista UtilitiesAdjunct Professor – Gonzaga [email protected]

Why?

NERC-wide Misoperations by Cause Code (2011 – 2012)

AgendaFundamentals Logic Gates, Truth Tables, Logic Equations, and Schematics

Positive and Negative LogicLogic PropertiesMore Logic Latches, Edge Triggers, Timers

Examples

OR Gate

XA

B

A B X0 0 00 1 11 0 11 1 1

X = A + B

A B

X X

= A OR B

AND Gate

X = A * B

B

A

X X

XA

B

A B X0 0 00 1 01 0 01 1 1

= A AND B

NOT Gate (Inverter)

X = !A

A

X X

XA

A X0 11 0

= NOT A

Gate Variations

OR

OR +

>1

Inverted Inputs

XA

C

A B C

0 0 00 0 10 1 00 1 1

A B

X X

B

C

X

1011

1 0 01 0 11 1 01 1 1

1111

X = A + B + !C = A OR B OR NOT C

Inverted Outputs

XA

C

A B C

0 0 00 0 10 1 00 1 1

A B

X X

B

C

X0100

1 0 01 0 11 1 01 1 1

0000

X = ! (A + B + !C) = NOT (A OR B OR NOT C)

Positive and Negative Logic

XA

BX

A

B

A B X0 0 10 1 11 0 11 1 0

X = !(A * B)

A B X0 0 10 1 11 0 11 1 0

X = !A + !B

=

= NOT A OR NOT B = NOT (A AND B)


=XA

B

A B

X X

XA

B

B

A

X X


A B X0 0 10 1 01 0 01 1 0

X = !A * !B

A B X0 0 10 1 01 0 01 1 0

X = !(A + B)

XA

BX

A

B =

= NOT A AND NOT B = NOT (A OR B)


XA

B

A B

X X

XA

B

B

A

X X

=

Logic GatesANDORNOTNAND NORXORXNOR

Most common for protection and control

Universal GatesVery important for hardware design

Logic PropertiesCommutative Property: X = A + B = B + A X = A * B = B * A

Associative Property: X = (A + B) +C = A + (B + C) X = (A * B) * C = A * (B * C)

Distributive Property: X = A * (B + C) = A * B + A * C

Logic PrecidenceMath: My Dear Aunt Sally = Multiply -> Divide -> Add -> Subtract

• 2 + 3 x 4 = ??• 2 + 3 x 4 = 2 + (3 x 4) = 14• 2 + 3 x 4 ≠ (2 + 3) x 4 = 20

Logic: NOT -> AND -> OR

• X = A + B * C = A or B and C• X = A + B * C = A + (B * C)• X = A + B * C ≠ (A + B) * C

Combining GatesA

BX

C

A

B X

C

A B C

0 0 00 0 10 1 00 1 1

X0001

1 0 01 0 11 1 01 1 1

0101

X = (A + B) * C = A + B * C

A B C

0 0 00 0 10 1 00 1 1

X0001

1 0 01 0 11 1 01 1 1

1111

X = A + (B * C) = A + B * C

Latches

A (SET)L

B (RST)

L = A + (L * !B)

RESET DOMINANT LATCH SET DOMINANT LATCH

L

SET

RST

A (SET)L

B (RST)

L = (A + L) * !B

Latches

L

SET

RSTA L

SETL = A * !L

RSTL = A * L

Edge Triggers

LSET

RSTA L

SETL = /A * !L

RSTL = /A * L

00

10 0

00

0

Edge Triggers

LSET

RSTA L

SETL = /A * !L

RSTL = /A * L

1

11 1

11

01

Edge Triggers

LSET

RSTA L

SETL = /A * !L

RSTL = /A * L

0

10 0

00

00

Edge Triggers

Timer(drop-out delay)

• Edge triggers can be shown a variety of ways in logic diagrams• Rising-edge or falling-edge not always specified

• Rising-edge = 0 1 transition• Unless otherwise noted, a rising-edge trigger can be assumed

Edge Triggers


Rising-Edge Trigger Timing Diagram

Edge Triggers


Falling-Edge Trigger Timing Diagram

Timers

2

0

X

A XT

X = AXPU = 2XDO = 0

A

XT

10 2 3 4 5 6 7 8 9 10

Timers

2

0

X

A XT

X = AXPU = 2XDO = 0

A

XT

10 2 3 4 5 6 7 8 9 10

Timers

0

3

X

A XT

X = AXPU = 0XDO = 3

A

XT

10 2 3 4 5 6 7 8 9 10

Timers

2

3

X

A XT

X = AXPU = 2XDO = 3

A

XT

10 2 3 4 5 6 7 8 9 10

Timers

2

3

X

A XT

3

2

Timers

0

9

X

TRIP

OUT1 = XT OR TRIP

OUT1

0

9

X

TRIP

X = TRIPOUT1 = XTXPU = 0 cyclesXDO = 9 cycles

OUT1

Timers

0

9

X

TRIP OUT1

52a

X = TRIPOUT1 = TRIP + XT + 52a * OUT1XPU = 0XDO = 9

Comparator

Output = 1 if (+) Input > (-) Input

Complete Logic

A L

X=AXPU = 3 secondsXDO = 0 secondsSETL = /XT * !LRSTL = /XT * L

3

0

X LSET

RST

Example #1 – 43 Switch Enable on Close

LT03 = F_TRIG SV17T AND NOT LT05 AND NOT 52A3P= 1 * NOT (0) * NOT (1)= 1 * 1 * 0= 0

Example #1 – 43 Switch Enable on Close

LT03 = F_TRIG SV17T AND NOT LT05 AND NOT 52A3P= 1 * NOT (0) * NOT (0)= 1 * 1 * 1= 1

Example #2

IN1

43PSAUX

IN2

43PS12F1

IN3

43PS12F2

IN4

43PS12F3

IN5

43PS12F4

IN6

43PS12F5

IN7

43PS12F6

IN8

43PS12F7

48VDC

Example #2 cont.

Example #2 cont.

32216282422212

5

4

3

2

1

0

=

=

=

=

=

=

2048210242512225621282642

11

10

9

8

7

6

=

=

=

=

=

=Binary (Base 2)

Slide Credit to Stephen Marx, BPA

Example #2 cont.

953 expressed in Decimal (Base 10)

=953

953350900131051009103105109 012

=++++++

xxxxxx


Example #2 cont.

11120811214081

21212021 0123

=++++++

+++xxxx

xxxx

Convert 1011 binary (base 2) to Decimal (base 10)

102 111011 =

=1011


Example #2 cont.

Courtesy of Electroswitch

Example #2 cont.

Courtesy of Electroswitch

IN1

43PS

IN2

43PS

IN3

43PS

48VDC

11

12

11

13

11

14

Example #3 – Breaker Failure “Blinking” LED

Breaker Failure

Reset (0)

Latch

00

LED

0 11

Timer 1 Timer 2

10A

B

CD E F

State A B C D E F Timer 1 Timer 21 0 0 1 0 0 1 - -2 1 1 1 1 0 1 Timing -3 1 1 0 0 1 0 Time-Out Drop-Out4 1 0 0 0 0 0 Drop-Out Timing5 1 1 1 1 0 1 Timing -


Breaker Failure

Reset (0)

Latch

11

LED

0 11

Timer 1 Timer 2

11

Timing

AB

D E F


C


Breaker Failure

Reset (0)

Latch

10

LED

1 00

• After Timer #1 input asserted for ½ second

Timer 1 Timer 21*

1

T/O D/O

AB

D E F

* = 1-processing interval


C


Breaker Failure

Reset (0)

Latch

00

LED

0 01

• After Timer #2 input asserted for ½ second

Timer 1 Timer 21

D/O Timing

AB

D E F0


C


Breaker Failure

Reset (0)

Latch

11

LED

0 11

Timer 1 Timer 21

D/O Timing

AB

D E F


C

Recommendations on Testing

• Both positive and negative logic tests

• Understand state of return from power cycle/reset

• Always use the as-left relay settings to test output logic

• All setting changes must be completed first.

• Use end-devices (breaker/disconnect switch staus) whenever possible.

• Question the design engineer!

• Ask for/compare against an Operating Description (if it exists)

Questions?

Kevin Damron, PESr. Protection Engineer – Avista UtilitiesAdjunct Professor – Gonzaga [email protected]

Documents

Digital Logic for Protection & Control