MICROPROCESSOR PROTECTION FOR SINGLE WINDING SHORT CIRCUITS IN COILS PZC3f.
Purpose
PZC3f type protection is designed to protect all three-phase symmetrically loaded electrical equipment, with a particular focus on three-phase electric motors. The PZC3f protects electrical devices in LV and MV networks of any power(using current transformers) against the effects of single winding coils short circuits. It protects electrical equipment in critical and costly applications for customers.
The PZC3f does not replace the existing basic protections but complements the protection efficiency of three-phase electrical equipment.
PZC3f is the answer to…
One of the main causes of electric motor failure is damage to the windings due to a decrease in the insulation value of the windings and the occurrence of a winding short circuit.
Currently, electric motors are equipped with short-circuit and overload protection based on a thermal model and the measurement of phase current RMS values. Such protection does not safeguard the stator windings in the event of single winding coil short circuits. If a short circuit occurs while the motor is under load, the phase current may not exceed the nominal value, and the basic protection will not shut down the motor in an emergency state. Moreover, in a shorted winding coil, the current will exceed the nominal value by several times. The motor can be damaged due to the rapid increase in temperature in the shorted portion of the winding.
Benefits of using
The use of the PZC3f reduces the risk of fire that may arise from uncontrolled temperature increases in the windings and significantly minimizes the extent of damage and associated repair costs for the protected equipment. Upon detecting a winding short circuit, the extent of repairs is limited to fixing the damaged coil, rather than rewinding the entire winding.
Operation
The advancement in electronics has enabled OPA S.A. in Zabrze to develop a microprocessor-based single winding coil short-circuit protection, known as the PZC3f type. The method and circuit of PZC3f protection is covered by a patent application.
The PZC3f performs rapid identification of winding short circuits based on the measurement of the phase angle displacement of currents. By comparing the current phases with pre-failure values, the protection detects even a single winding coil short circuit with high precision and enables immediate disconnection of the device.
Additionally, the PZC3f allows for temperature monitoring at critical points of the device using two PT1000 temperature sensors (thermistors). An increase in temperature above the set temperature, triggers the protection and shuts down the device.
Areas of application
The PZC3f is a universal protection relay for three-phase equipment of any power rating, compatible with three external current transformers (x/5) connected to a terminal block and with two external temperature sensors. The user, through the relay’s output and input contacts, can easily connect the PZC3f to the control circuits of pumps, fans, compressors, conveyors or use it to protect other devices in industrial or domestic applications.