U.4.66
SEL-421 Relay User’s Guide Date Code 20090715
Basic Relay Operations
Operating the Relay Inputs and Outputs
Setting a Control Input: Circuit Breaker Auxiliary Contacts (52A): Terminal
This is a step-by-step procedure to configure a control input that reflects the
state of the circuit breaker auxiliary (52A) NO (normally open) contact. A
common relay input is from circuit breaker auxiliary contacts; the relay
monitors the 52A contacts to detect the closed/open status of the circuit
breaker. Perform the following steps to connect three-pole circuit breaker
auxiliary contacts to the SEL-421. This example is for a 125 Vdc system; the
open state of the auxiliary contacts is 0 Vdc (circuit breaker open), and the
closed state of the auxiliary contacts is approximately 125 Vdc (circuit
breaker closed). The voltage drop in the connecting wires from the auxiliary
contacts through the station battery to the relay gives a slightly lower voltage
than the station battery at the relay control input terminals. Make the control
input pickup, dropout, and debounce timer settings as explained in Control
Inputs on page U.2.5.
This example assumes that you have successfully established communication
with the relay (see Making an EIA-232 Serial Port Connection on page U.4.5).
In addition, you must be familiar with relay access levels and passwords (see
Changing the Default Passwords: Terminal on page U.4.9 to change the
default access level passwords).
Step 1. Prepare to control the relay at Access Level 2.
a. Using a communications terminal, type ACC <Enter>.
b. Type the Access Level 1 password and press <Enter>.
You will see the => action prompt.
c. Type the 2AC <Enter> command.
d. Type the correct password to go to Access Level 2.
You will see the Access Level 2 =>> prompt.
Step 2. Configure the relay to read the circuit breaker auxiliary contact.
a. Type SET M <Enter> (see Figure 4.57).
These settings are the breaker monitor settings.
b. Type <Enter> to bypass the Breaker 1 Monitoring
enable, and <Enter> again to bypass the Breaker 2
Monitoring enable (NUMBK := 2 in this example).
c. At the BK1TYP setting, type 3 <Enter> for a three-
pole circuit breaker for this particular example.
(Use the setting BK1TYP appropriate for your circuit
breaker(s).)
d. At the BK2TYP setting, type 3 <Enter> for a three-
pole circuit breaker for this example.
The relay displays the 52AA1 SEL
OGIC control
equation action prompt.
e. Type IN101 <Enter> at the
? prompt to specify input
IN101 as the control input that represents the close/
open state of Circuit Breaker 1.
The relay next displays the 52AA2 SEL
OGIC control
equation action prompt.
f. Type IN102 <Enter> at the
? prompt to specify input
IN102 as the control input that represents the close/
open state of Circuit Breaker 2.
Courtesy of NationalSwitchgear.com
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