PRESENTED BY:
Sibasis Satapathy

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FAULT DETECTION AND CLEARANCE IN DC DISTRIBUTED SYSTEM
INTRODUCTION
Personally safety and prevention of property damage are important factors of conventional AC power systems.
For the investigated DC power system the star point of the sources loads is ungrounded.
Even though the AC sides of DC distributed system is ungrounded, short circuit and ground faults should be detected and cleared.
INTRODUCTION
GROUNDING AND FUSING
Each converter is connected to the DC ring bus through a cable node.
This cable node contains ground connection, fuses, circuit breakers and current transducers needed for protection.
The protection capacitors are selected so that the time constant of ground fault currents is sufficiently long for proper detection.
Here voltage dividing resistors are connected in parallel with the grounding capacitors.
CABLE NODE WITH TWO CABLE SEGMENTS AND ONE CONVERTER
FAULT SITUATION
Different fault situations are
Ground fault on DC side.
For a ground fault, all the protection capacitors contribute to the transient fault current.
If the fault is of the middle of the cable segment, half the fault current flows from each side.
Ground fault on AC side.
Here ground fault is more complicated due to the sinusoidal nature of the quantities giving initial condition.
Due to the high impedance between the star point of the AC side transformer, the main contribution of fault current flows from the DC side through converter to fault location.
EQUIVALENT CIRCUIT FOR GROUND FAULT ON THE DC SIDE
The current transducers in the cable node
DETECTION AND SELECTIVITY
When a ground fault appears, the fault current at the cable and converter interfaces flow in the sane direction which results in a common mode current.
According to the fault resistance value, high or low common mode current will flow.
FAULT CURRENTS FOR CONVERTER 1 AND 2 FOR GROUND FAULT ON
DC SIDE
INTEGRATED FAULT CURRENT FOR CONVERTER 1 AND 2 IN CASE OFGROUND FAULT ON DC SIDE
SIMULATION OF A GROUND FAULT ON AC SIDE
INTEGRATED FAULT CURRENT FOR CONVERTER 1 AND 2 FOR GROUND FAULT ON AC SIDE
CONCLUSION
• This paper presents a scheme and an algorithm for detection of ground faults and short circuits in a DC distributed power system, where the sources have high impedance or no connection to ground.
• A grounded system is preferably due to reasons of personal safety and protection of equipment.