Máy biến áp trung thế loại trong nhà AK24

1. When the secondary terminals are connected to the measuring or protection devices, one of the terminals should be earthed for safety as seen in FIGURE VT-1. 2. The base plate must be earthed. 3. The secondary circuits must not be short-circuited during operation. Otherwise the voltage transformers will be thermally destroyed. 4. If any of the secondary windings of a voltage transformer, used for the purpose of measuring, will not be used then it must be left open with one terminal connected to earth as seen in FIGURE VT-2. However, even if the open-delta windings are not to be used for detection of earth faults, they must be connected in an open delta circuit and an appropriate resistor (depending on the voltage and thermal power rating of the secondary) must be connected and open-delta circuit must be earthed only at one point as seen on FIGURE VT-4. Please refer to the technical recommendations below. 5. For single phase transformers, the neutral terminal of the primary “ N ” must be earthed in the earthed (neutral) systems as seen in FIGURE VT-3. Other important points and notes; When using single pole insulated inductive voltage transformers, it is very important to be aware that, if a circuit is being closed or during the decaying period of an earth fault,ferroresonance may occur. Ferroresonance can lead to the overheating and thermal destruction of the voltage transformer or high levels of voltages may be induced. In general, ferroresonance can be eliminated by the use of an appropriate resistor. The resistor is placed as a burden in open-delta circuit formed by three voltage transformers delta windings. The open-delta circuit must always be earthed only at one point as seen in FIGURE VT-4.The open-delta connection can also be used for earth-fault monitoring with appropriate devices. As the number of cable systems is increasing in the energy distribution systems, the protection of voltage transformers have become very important for the uninterrupted operation of the system without any failure and/or down time. For that reason, ALCE is always recommending the use of open-delta windings in single phase inductive voltage transformers. The use of open-delta windings may not be sufficient for the protection of voltagetransformers by itself in some cases. An energy systems design engineer shall always use proper surge arresters, avalanche diodes, limiters and/or their combinations for the survivability of the distribution system after a fault or disturbance