1MRS751802-MUM
REX 521
235
Protection Relay
Technical Reference Manual, Standard Configurations
11.7.2.
Measurements
The following measurements are supported in this application example:
• True RMS measurement of phase currents
• True RMS measurement of phase-to-phase voltages
• True RMS measurement of neutral current
• True RMS measurement of residual voltage
• Fundamental frequency active power [kW]
• Fundamental frequency reactive power [kVAr]
• Fundamental frequency displacement power factor cos (
φ
)
• Power factor PF including the harmonics
• Fundamental frequency active energy [kWh]
• Fundamental frequency reactive energy [kvarh]
• System frequency measurement
11.7.3.
Protection
All the necessary settings for the protection functions can be set via Relay Setting
Tool or the local HMI. The settings can be found in
Main menu\Protection\
.
11.7.3.1.
Thermal overload protection
Thermal Overload Protection (3Ithdev>) constitutes a full three-phase thermal
overload protection. When applied to motor protection, the thermal unit forms an
overload protection with two time-constants, separately for both the stator and the
rotor.
Two setting groups (basic settings and advanced settings) are available. Normally,
the user sets the motor data only to the basic settings, and the relay automatically
calculates the advanced settings.
• The type of the motor to be protected is selected by means of the Device type
setting.
• The Starting current setting is the ratio of the motor starting current to full load
current.
• The Starting time setting is the maximum permitted starting time for motor.
• No of starts setting specifies how many times the motor is allowed to be started
from cold condition state (assuming the motor has the ambient temperature).
• Cooling factor setting determines how slowly (compared to running condition)
the motor cools down in case the motor is stopped. It can be defined also as a
ratio of cooling constant (for a stopped motor) to heating constant.
A normal, totally enclosed motor cooled by a fan on the
rotor shaft generally has the setting of 4...6.
• By means of Ambient temp. setting, the thermal protection can be given a
standard temperature reference level (typically 40°C).
Cooling
τ
Heating
τ
⁄
=
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