Basler Electric BE1-27 - Manual (Page 18)

3-2 BE1-27/59 Functional Description 9170600990 Rev L
Step-Down Transformer
The monitored system voltage is applied to the primary of an internal potential transformer and stepped
down to internal circuit levels. The transformer provides a high degree of isolation.
Low-Pass Filter and Full Wave Rectifier
The output of the step-down transformer is low-pass filtered to prevent undesired response to high-
frequency noise. Frequencies above 226 Hz are attenuated. The ac signal is then full-wave rectified to
produce positive-going half-cycles that represent the magnitude of the monitored system voltage.
Pickup Settings
Controlled by front panel single-turn potentiometers, the pickup settings establish reference voltages
representative of the system voltage that will cause the relay to respond. Pickup settings are individually
adjustable for timed under/overvoltage functions and instantaneous under/overvoltage functions. On BE1-
27/59, Under/Overvoltage Relays, the undervoltage function takes precedence over the overvoltage
function.
Pickup Comparators
The output of the rectifier circuit is compared to each pickup setting. When the monitored system voltage
is greater than any pickup setting, the effected comparator’s output goes high. When the monitored
system voltage is less than any pickup setting, the effected comparator’s output goes low. The effects of
these outputs are shown below.
Comparator
Relevant Pickup Setting
Timed Instantaneous
Undervoltage Overvoltage Undervoltage Overvoltage
High
No effect Lights OV pickup
indicator; initiates
timer
No effect Energizes output
relay
Low
Lights UV pickup
indicator; initiates
timer
No effect Energizes output
relay
No effect
Timer Circuit
Once initiated, the timer circuit measures the interval from pickup. If the adverse condition continues
through the programmed delay, the timer circuit energizes the appropriate output relay. In relay styles
with inverse timing, the extent to which the monitored system voltage exceeds the pickup setting
influences the actual time delay such that a greater voltage difference from pickup produces a more rapid
response. This response is illustrated in the characteristic curves as shown in Figures 3-2 through 3-7.