Guodian Nanjing Automation PSM400 Digital Motor Protection and Control Device

1 Functions
 Instantaneous Overcurrent Protection
 Locked Rotor Protection
 Phase Failure Unbalance Protection
 Overload Protection
 Undercurrent Protection
 Overheat Protection
 3I0 Overcurrent Protection
 Ground Fault Protection
 Undervoltage Protection
 Overvoltage Protection
 Motor Starting Protection
 Phase Sequence Protection
 Contactor Break Lockout
 Voltage Loss Restart
 4~20mA Output
 I, U, P, Q, Cosφ, Active Energy, Reactive Energy, 11-channel Switch Status Acquisition
2 Principle Description
2.1 Instantaneous Overcurrent Protection
During the starting process of an asynchronous motor, the current is very high, typically reaching 5 to 8 times the rated current (Ie), and the starting time can last up to several tens of seconds.
The device is equipped with two instantaneous overcurrent setting values. During the starting process, the "starting instantaneous overcurrent setting value" is used, which is set to avoid the motor starting current. After the motor starting process is completed, the "post-starting instantaneous overcurrent setting value" is automatically adopted. This value is determined based on the motor self-starting current and the larger feedback current during an external outlet short-circuit, taking the larger of the two currents.
a) The starting time tst is set to avoid the longer starting time.
b) The setting value during starting Iop.h is set to avoid the motor starting current Ist, i.e., when t ≤ tst, Iop.h = krel × Ist. To avoid the influence of non-periodic components, krel is taken as 1.5, and Ist is (6~8)Ie.
c) The setting value during operation Iop.l is set to avoid the larger feedback short-circuit current of the motor during an external outlet short-circuit.
Considering the inherent delay of the protection (40~60)ms for an external three-phase short-circuit, the feedback current Ifb = 6Ie.
Iop.l = krel × Ifb = 1.3 × 6 Ie = 7.8Ie.
d) The short delay of the instantaneous overcurrent protection is used to coordinate with the F-C circuit.
2.2 Overload Protection
Overload protection can serve as protection for the motor operating under prolonged overload conditions.
When the motor current exceeds the overload setting value, the device will operate after a delay. It can be selected to trip or issue an alarm. The overload setting value should be less than the locked rotor setting value. This protection is disabled during the motor starting process.
2.3 Undercurrent Protection
Undercurrent protection can prevent damage caused by prolonged no-load or underload operation of certain motors with pump-type loads. When all three-phase currents are below the undercurrent protection setting value, the device will operate after a delay. Undercurrent protection can be selected to trip or issue an alarm. This protection is disabled during the motor starting process.
2.4 Overheat Protection
Motor overload, prolonged starting time, locked rotor, etc., can generate significant positive-sequence current; while phase failure, asymmetric short-circuit, and unbalanced input voltage can simultaneously produce large positive-sequence and negative-sequence currents. Based on the heating characteristics caused by the stator positive-sequence and negative-sequence currents, overheat protection can be provided for the aforementioned faults.