Basler BE1-27 Manual - page 2
BE1-27, 59, 27/59
APPLICATION
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 to operate with
relatively constant voltage. 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, ground fault detection, and
supervision of automatic transfer switching schemes.
Motor Protection
When selecting the type of protection for motor applica
tions, 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 unneces
sary tripping during low voltage dips. If the undervoltage
condition persists for the established time delay, the relay
output contacts are used to either trip the unit off line or
sound an alarm at the 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 manu
facturer 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 Tr ansfer 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 accept
able time period, automatic transfer switching can be
applied to initiate the throwover from primary power to the
2
alternate power source. The BE1-27 Undervoltage Relay
can initiate switching after a given time delay to avoid
transfer switching during temporary low voltage condi
tions. 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.
Cogener ation
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 condi
tion, the utility requires the cogenerator to be discon
nected from the system before reclosing the utility
breaker. If the cogenerator remains connected to the
system, the utility may attempt to reclose onto an ener
gized line. This could result in reconnecting two systems
out of synchronism. The BE1-27 undervoltage relay
monitoring the line voltage at the substation will inhibit
reclosing of the utility circuit breaker if the line remains
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 over
voltage conditions that may result when power factor
correction capacitors are located on the feeder.
Tr ansformer Protection
Voltage relays can be applied to protect large transform
ers from damage as a result of overexcitation. The
concern for transformer overvoltage may be minimized in
many power system applications where proper voltage
control of the generating unit is provided. However, where
a tap changing regulating transformer is located between
the generating source and the load, some form of voltage
protection may be required to supplement the tap
changing control and to prevent equipment damage due
to over, as well as undervoltages resulting from a failure of
the tap changing control. The BE1-27/59 Under/Overvolt
age Relay is well suited for these applications.
Ground Faul t D etection
In a three-phase, three-wire system, a single conductor
may break or the insulation may deteriorate resulting in a
high resistance ground fault which may be sensed by an
overvoltage relay connected to a grounded wye, broken
delta set of voltage transformers (VT's).
www
. ElectricalPartManuals
. com