Basler BE1-27, Инструкция по эксплуатации, Страница: 6 / 43

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 which 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 which 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 flashover 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 throwover 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 line is energized by
the cogenerator.
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.