PST 692U Transformer Backup Protection Device

Guodian Nanjing Automation PSM 692U Motor Comprehensive Protection and Control Device

1 Functions
1) Current quick-break protection
2) Definite-time overcurrent protection
3) Two-stage definite-time negative sequence overcurrent protection / inverse-time negative sequence protection
4) Overheat protection
5) Locked-rotor protection
6) Single-phase grounding protection
7) Undervoltage protection
8) Overload protection
9) Non-electrical protection
10) F-C blocking function
11) 4-20mA output
12) 9 fault recordings, 2 startup recordings
13) I, U, P, Q, Cosφ, active energy, reactive energy, 14-channel switch status acquisition
14) GPS time synchronization (minute pulse, second pulse, or IRIG-B mode)

2 Principle Description
2.1 Current Quick-Break Protection
During the startup process of an asynchronous motor, the current is very high, typically reaching 5 to 8 times the rated current (Ie), and the startup time can last up to several tens of seconds. The device is equipped with two quick-break settings. During the startup process, the "startup quick-break setting" is used, which is set to avoid the motor starting current. After the motor startup process is completed, the "post-startup quick-break setting" is automatically adopted. This value is determined based on the motor's self-starting current and the larger feedback current during an external outlet short circuit, taking the larger of the two currents.
a) The startup time tst is set to avoid the longer startup time, tst > tstx.
b) The setting value during startup 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 self-starting current and the larger feedback short-circuit current during an external outlet short circuit. The magnitude of the self-starting current is related to factors such as the delay of backup power automatic switching. When the plant power fast switching is successful, the motor almost does not undergo a self-starting process because the speed has not significantly decreased. Only during residual voltage switching or synchronous capture switching, when the motor speed has significantly decreased, the self-starting current can be large. According to traditional calculation methods, the self-starting current Iast = 5Ie, Iop.l = krel × Iast × Ie = 1.3 × 5 × Ie = 6.5Ie.
For an external outlet three-phase short circuit, considering the inherent delay of the protection (40～60)ms, the feedback current Ifb = 6Ie.
Iop.l = krel × Ifb = 1.3 × 6Ie = 7.8Ie.
d) The short delay of the quick-break protection is used to coordinate with the F-C circuit.