Guodian Nanzi Computer Integrated Protection PST692U transformer Backup protection device
1、 Features
1. Complex voltage blocking (direction) overcurrent protection
2 Zero sequence current protection
3 Gap zero sequence current protection
4 Zero sequence voltage protection
5 Overload protection
6 Start ventilation
7 Lock on load voltage regulation
8 I，U，P，Q，Cos φ， Active kilowatt hour, reactive kilowatt hour, 14 circuits switch Quantity acquisition
9 GPS time synchronization (minute pulse, second pulse or IRIG-B mode)
2、 Principle description
2.1 Composite voltage blocking (direction) overcurrent protection
This protection reflects phase to phase short circuit fault and serves as backup protection for transformer and adjacent components. A total of three sections of composite voltage blocking overcurrent protection are set, of which section I and II can have directions and three time limits are set respectively, while section III does not have directions and two time limits are set. Each section is equipped with soft pressing plates that can be enabled or disabled.
a) Composite voltage element:
If the transformer has high, medium and low sides, three backup protections shall be installed. The protection on each side adopts the voltage on its own side, so the protection on this side can judge whether the compound voltage element on this side acts, and other Whether the compound voltage element at side A acts or not depends on the switching value input. The HV side backup protection transmits the action of the HV side compound voltage element to the backup protection at the MV side and LV side through the contact; The backup protection at the medium voltage side transmits the action of the compound voltage element at the medium voltage side to the backup protection at the high voltage side and low voltage side through the contact; The low-voltage side backup protection transmits the action of the low-voltage side compound voltage element to the backup protection on the high-voltage side and the medium voltage side through the contact. Action criteria of composite voltage element on this side: when the small value of the three line voltages is less than the low voltage fixed value, or the negative sequence voltage is greater than the negative pressure fixed value, the composite voltage element acts. Considering the no-load closing of the transformer or the withdrawal of one side of the transformer from operation, the auxiliary criterion of switch position is added to the device for the composite voltage element to always act because of the voltage free bus. When the switch on this side is closed, the composite voltage element can act.
b) Direction element:
The positive terminal of TA is on the bus side, and the positive direction of current is considered as flowing from the bus to the transformer.
Ia and Ubc form phase A directional element, Ib and Uca form phase B directional element, and Ic and Uab form phase C directional element. When the current in the directional element is within the range of - 45 °~+135 ° relative to the voltage, it is a positive direction, pointing to the transformer; Otherwise, it is in the opposite direction, pointing to the bus. The directional element has a memory function to eliminate the dead zone of the directional element in case of three-phase short circuit at the near end.
c) Overcurrent element:
If any value of the three-phase current on this side is greater than the fixed value, the overcurrent element will act.
d) PT disconnection:
When the device judges that there is PT disconnection, it will automatically exit the direction element.
2 Zero sequence current protection
This protection reflects single-phase grounding fault and can be used as backup protection of transformer. Zero sequence protection is equipped with hard strap. Action criteria: 3I0>fixed value of zero sequence overcurrent. Wherein, 3I0 is the zero sequence current, which is taken from the zero sequence TA on this side. This protection is configured with two time limits, the time limit jumps to this side, and the second time limit jumps to each side.
2.3 Gap zero sequence current protection
This protection reflects the zero sequence current of transformer gap breakdown, and can be used as backup protection when the transformer is not grounded.
This protection has the function of automatic switching on/off. When the neutral grounding switch of the transformer is opened, the clearance zero sequence current protection will be automatically switched on.
Action criteria: 3I0jx>clearance zero sequence current setting.
