Basler Electric BE1-47N - Manual (Page 9)

9170400990 Rev J BE1-47N General Information 1-1
SECTION 1 • GENERAL INFORMATION
Purpose
BE1-47N Voltage Phase Sequence Relays respond to negative sequence voltage (V
2
) which results from
a fault or misconnection on a balanced, three-phase system.
Application
BE1-47N relays are designed to protect equipment from damage caused by phase failure, reverse phase
sequence, phase unbalance, undervoltage, or overvoltage.
The relay detects reverse phase connection of lines, transformers, motors, generators, and synchronous
condensers and is often applied in automatic transfer schemes to assure connection of proper phase
rotation as well as voltage conditions. When used in a motor application, the relay provides protection by
preventing motor startup during open-phase or reverse-phase conditions and by tripping the motor off line
for phase unbalance, undervoltage, or overvoltage conditions.
Negative sequence voltage is the result of any unequal phase condition on the source. This can be due to
unequal single-phase loads on the system or unequal transformer impedances between phases. A 1 to
2% level can normally be expected in an industrial supply. Any significant increase above this level can
indicate a power service problem and could lead to serious plant problems. The BE1-47N has the ability
to detect negative sequence voltage levels of this magnitude.
Undervoltage and voltage balance relays have traditionally been applied to protect induction motors from
operating with one phase open. These relays may not reliably detect this condition due to the back-EMF
of the motor on the open phase. However, an induction motor with a starting current of 6 per-unit will
generate a negative sequence voltage of 16% if fully loaded when a fuse opens. The negative sequence
voltage will be somewhat reduced if the motor is not fully loaded. The sensitivity of the BE1-47N and its
insensitivity to frequency allow reliable protection to be applied to motors.
Motor losses and current unbalance increase with the negative-sequence voltage level. The increased
loss due to negative sequence voltage is not a function of motor load but is independent. A machine
operating with 3.5% negative sequence voltage will have its losses increased by 25%. An open fuse on a
power factor correction capacitor bank can result in a significant increase in negative sequence voltage.
The effect of this condition can be costly.
BE1-47N relays can be applied to protect motor buses from an open phase. It can also be applied to
protect critical individual motors, static, and non-rotating loads from the effects of negative sequence
voltage.
A choice of time delay characteristics allows the relay to respond in the desired manner for a wide variety
of transient and fault conditions.
BE1-47N relays may also be used to provide overvoltage and undervoltage protection. A separate time
delay is utilized to prevent shutdown of equipment during minor voltage dips and to permit sequential
operation when the relay is being used in a supervisory capacity.
Phase Rotation Sensitivity
Relays that use phase-to-phase voltage to determine negative sequence are sensitive to phase rotation.
BE1-47N relays are phase rotation sensitive. Unless otherwise noted, all connections shown in this
manual assume ABC rotation.
Model and Style Number
BE1-47N electrical characteristics and operational features are defined by a combination of letters and
numbers that make up the style number. Model number BE1-47N designates the relay as a Basler
Electric Voltage Phase Sequence Relay. The model number, together with the style number, describes
the options included in a specific device and appears on the front panel, draw-out cradle, and inside the
case assembly.
The style number identification chart for the BE1-47N relay is illustrated in Figure 1-1.