Schweitzer Engineering Laboratories SEL-251 - Ogic; Table 2.1: Trip Circuit Monitor Alarm (TCMA) Truth Table; Figure 2.5: Trip Circuit Monitor Alarm (TCMA) Logic

2-10 Specifications Date Code 20000421
SEL-251, -2, -3 Instruction Manual
Trip circuit monitor logic ensures that the 52A and TCM inputs agree. When the circuit breaker
is closed, inputs 52A and TCM are energized; 52A and 52A
TC
contacts are closed. When the
circuit breaker is open, inputs 52A and TCM are deenergized; 52A and 52A
TC
contacts are open.
If the two inputs disagree for 60 cycles, the trip circuit monitor alarm (TCMA) bit asserts in the
Relay Word. The TCMA bit deasserts 60 cycles after the TCMA condition ends.
Table 2.1: Trip Circuit Monitor Alarm (TCMA) Truth Table
TCM
Input 52A
TCMA
Relay Word Bit Notes
0 0 0
0 1 1 (a)
1 0 1 (b)
1 1 0
(a) Abnormal open circuit in TCM input/lower trip circuit path
or a short circuit exists across the TCM input (e.g., TRIP output is asserted)
or 52A contact short circuited or "stuck closed"
(b) 52A
TC
short circuited or "stuck closed"
or there is an abnormal open circuit in the 52A input circuit path
Figure 2.5: Trip Circuit Monitor Alarm (TCMA) Logic
Besides alarming for an abnormal open circuit in the trip circuit, the TCMA bit provides 52A
input verification. It effectively compares the circuit breaker status input to 52A
TC
.
The TCMA bit can be used to alarm, cancel reclosing, or trigger event reports.
In Figure 2.4, a 52A contact is connected to relay input 52A. You can connect a 52B contact
instead. Wire a 52B contact to a relay input !52A to perform the 52A function. Input options
52AR or !52AR can also be used. (See SEL-251 Relay SELOGIC
TM
Control Equations.)
SEL-251 RELAY SELOGIC CONTROL EQUATIONS
SELOGIC Control Equations put relay logic in the hands of the relay applications engineer.
Assign the inputs to suit your application, logically combine selected relay elements for various
control functions, use non-dedicated timers for special applications, and assign output relays to
your logic functions.
Programming SELOGIC Control Equations consists of assigning functions to the programmable
inputs, designing the internal logic you need, expressing that logic in terms of the relay elements