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EP-4422010-B1 - METHOD AND CIRCUIT FOR SHORT-CIRCUIT PROTECTION OF DVR VOLTAGE VARIATION COMPENSATOR

EP4422010B1EP 4422010 B1EP4422010 B1EP 4422010B1EP-4422010-B1

Inventors

  • SAK, TOMASZ
  • MAZUREK, PIOTR
  • ZYMMER, KRZYSZTOF
  • PAWLACZYK, ANDRZEJ

Dates

Publication Date
20260506
Application Date
20230728

Claims (2)

  1. A method for short-circuit protection of a Dynamic Voltage Restorer (DVR) according to claim 2 against effects of short circuits in a load supplied from an electric 0,4kV power grid and against effects of short circuits in a booster voltage converter of the DVR voltage variation compensator, characterized in that a current in a load (Obc) circuit comprising a secondary winding (U2) of a booster transformer ( TD ) is measured and a current in a DC circuit of a booster voltage converter (P) is measured and compared with their threshold values, and when at least one threshold value of the measured currents is exceeded, a primary winding (U1) of the booster transformer ( TD ) is immediately short-circuited and the booster voltage converter ( P ) is disconnected from the primary winding (U1) of the booster transformer ( TD ) and from the 0.4 kV power grid on both sides.
  2. A system comprising a short-circuit protection system and a DVR voltage variation compensator, in which a primary winding of a booster transformer is connected in parallel with a semiconductor switch and with a shunt contactor short-circuiting it, and through contacts of a first cut-off contactor with two terminals of a booster voltage converter of the DVR voltage variation compensator, while contacts of a second cut-off contactor are connected on one side with terminals of a 0.4 kV power grid, and on the other side with the terminals of the booster voltage converter of the DVR voltage variation compensator, characterised in that an input (A1) of a protection control system (USZ) is connected via discriminator ( D1 ) to a current sensor ( I U2 ) in the load circuit (Obc) comprising a secondary winding current (U2) of the booster transformer ( TD) , an input ( A2 ) of the protection control system (USZ) is connected via discriminator ( D2 ) to a current sensor (I DC ) of a capacitor (C) of a DC circuit of a booster voltage converter (P) of a voltage variation compensator ( DVR ), furthermore an output (B1) of the protection control system (USZ) is connected to a control input (S) of a semiconductor switch (LP) , an output (B2) is connected to the shunt contactor( S1 ), an output ( B3 ) is connected to the first cut-off contactor (S2) , and an output (B4) is connected to the second cut-off contactor (S3) .

Description

The subject of the invention is a method and system for short-circuit protection of the DVR voltage variation compensator. The invention is used in LV power networks equipped with DVR voltage variation compensators, minimizing fluctuations in the voltage supplied to loads. Fluctuations in a rms value of a voltage of a power grid supplying loads can be caused by varying power demand throughout the day and connection to a low-voltage grid of a large number of distributed renewable RES energy sources with unpredictable, weather-dependent output. Power electronics DVR voltage variation compensators are being increasingly used to regulate the rms value of the grid voltage. The DVR compensator is equipped with a booster voltage converter (AC-DC-AC), which allows smooth, bidirectional regulation of line voltage by means of an booster transformer. Its secondary winding, with a voltage that is a fraction of the value of the mains voltage, is connected in series to a power line supplying sensitive loads. The voltage adjustment range is mostly within +/- 10% of the grid voltage. Such a range of regulation makes it possible to keep the voltage value at the DVR compensator connection point close to a rated value of the grid voltage. The power grid supplies many loads, including sensitive loads that require power continuously. Maintaining continuity of power supply to consumers, even under emergency conditions, places particularly high demands on the short-circuit protection systems of DVR voltage variation compensators. This is especially true for short circuits and long-term overloads in a distribution system and short circuits in DVR compensator converters. The booster voltage converter of the DVR compensator cannot be protected by circuit breakers or fuses because the booster transformer, during short-circuit in a mains-supplied load, behaves like a current transformer. For this reason, the connection of the booster voltage converter to the primary winding of the booster transformer, which constitutes its load in the emergency state, cannot be interrupted. The flow of short-circuit current through the secondary winding of the booster transformer forces the appearance of a high voltage on the primary winding and a sharp increase in the voltage on the DC circuit capacitor of the booster voltage converter. This voltage increase in the DC circuit leads to the breakthrough of transistors and damage to the booster voltage converter of the DVR variation compensator. Protection of the booster voltage converter requires the development of a suitable protection, specifically for this purpose. The superior problem is to maintain continuity of power supply to sensitive loads despite damages in the form of a short circuit in one of them or a short circuit in the DVR compensator's booster voltage converter. In the publication "Dynamic Voltage Restorer (DVR) System for Compensation of Voltage Sags, State -of-the-Art Review" International Journal of Computational Engineering Research (ijceronline.com) Vol. 3 Issue 1 (May 2014), the protection of the DVR compensator's booster voltage converter against the effects of a long-term overload of the power grid or a short circuit in the load is described. The protection method of the booster voltage converter, according to the disclosed study, consists in detecting a long-term overload or short circuit in a load supplied from the power grid, and then disconnecting the secondary winding of the booster transformer from the power grid on both sides, short-circuiting the resulting gap to form an alternative circuit conducting the load current. In the DVR compensator protection system, one end of the secondary winding of the booster transformer is connected through closed contact of a switch to a distribution transformer, and the other end through the closed contact of another switch to the loads supplied by the power grid. In parallel with this winding and the switch contacts connected to this winding, an open contact of a shunt switch is connected. The inconvenience of the above solution is that the DVR compensator is only protected against the effects of a large overload on a power grid or a short circuit in the load. Note also the cost of construction due to the need of using three apparatuses for the large currents flowing in the secondary winding of the booster transformer. Another inconvenience of this solution is duration of switching cycle of the DVR voltage variation compensator short-circuit protection contactors. This time is the sum of eigentimes of the bypass contactor of the cutoff contactors for the secondary winding of the booster transformer, plus the time to compensate for the spread of the eigentimes of these contactors. During switching cycle of the contactors, the peak voltage in DC circuit of the booster voltage converter increases, which exposes its transistors to damage. Reducing the duration of the contactors' switching cycle may cause a short-time interruption of the s