Basler Electric BE1-27 - Manual (Page 9)

9170600990 Rev L BE1-27/59 General Information 1-1
SECTION 1 • GENERAL INFORMATION
Purpose
The BE1-27 Undervoltage, BE1-59 Overvoltage and the BE1-27/59 Under/Overvoltage Relays are solid-
state devices that provide reliable protection for generators, motors, and transformers against adverse
system voltage conditions.
Application
Electric power systems are designed for constant voltage operation. Loads utilizing commercial electric
power are designed to operate at a constant input voltage level with some tolerance. Radical voltage
variations on a power system are indicative of a system malfunction. Protective relays that monitor
system voltage and provide an output signal when the voltage goes outside predetermined limits, find a
variety of applications. Some of these applications include motor and transformer protection, interface
protection for cogeneration systems, and supervision of automatic transfer switching schemes.
Motor Protection
When selecting the type of protection for motor applications, the motor type, voltage rating, horsepower,
thermal capability during start-up, and exposure to automatic transfer restarting following a voltage
interruption need to be considered. During motor start-up, a low terminal voltage condition will inhibit the
motor from reaching rated speed. The BE1-27 Undervoltage Relay will detect this low voltage condition
and trip. Critical applications requiring continuous motor operation and applications where overloads
during start-up may be maintained for a given time period, usually have a definite time or inverse time
delay characteristic incorporated to avoid unnecessary tripping during low voltage dips. If the
undervoltage condition persists for the established time delay, the relay output contacts are connected to
the station alarm annunciator panel, allowing the station operator to take corrective action. The BE1-59
Overvoltage Relay is applied to insure the voltage does not exceed the limits established by the machine
manufacturer for proper operation. Overvoltage conditions stress the insulation level of the equipment and
may cause a dielectric breakdown resulting in a flash over to ground.
Automatic Transfer Switching
Distribution substations are sometimes designed with duplicate supply circuits and transformers to
eliminate service interruptions due to faults located on the primary feeder. In order to restore service
within a given acceptable time period, automatic transfer switching can be applied to initiate the throw
over from primary power to the alternate power source. The BE1-27 Undervoltage Relay can initiate
switching after a given time delay to void transfer switching during temporary low voltage conditions. To
return the substation to normal service upon the restoration of primary voltage, the BE1-59 Overvoltage
Relay supervises the transition to its normal operating condition.
Cogeneration
Utilities employ the use of a voltage check scheme to supervise reclosing at the substation when
cogenerators are connected to a radial distribution feeder and the cogenerator is capable of supplying the
entire load when the utility circuit breaker is open. During a faulted condition, the utility requires the
cogenerator to be disconnected from the system before reclosing the utility breaker. If the cogenerator is
connected to the system, the utility will reclose to an energized line.
This could result in reconnecting two systems out of synchronism with each other. A BE1-27
Undervoltage Relay monitoring the line voltage will inhibit reclosing of the utility circuit breaker if the
cogenerator energizes the line.
At the interface between the utility and the cogenerator, overvoltage and undervoltage relays are installed
as minimum protection to provide an operating voltage window for the cogenerator. During faulted
conditions, when the cogenerator may become overloaded, the BE1-27 Undervoltage Relay will detect
the decline in voltage and remove the cogenerator from the system. The BE1-59 Overvoltage Relay will
protect the system from overvoltage conditions that occur when power factor correction capacitors are
located on the feeder.