Switchgears and substations with voltages above 1 kV. Internal surge protection

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Section 4. Switchgears and substations

Switchgears and substations with voltages above 1 kV. Internal surge protection

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Encyclopedia of radio electronics and electrical engineering / Rules for the installation of electrical installations (PUE)

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4.2.166. Electrical networks 3-35 kV must operate with an isolated neutral grounded through a resistor or an arcing reactor. In electrical networks 3-35 kV with compensation of the capacitive current of a single-phase earth fault, the degree of asymmetry of the phase capacitances relative to the earth should not exceed 0,75%. Alignment of the phase capacitances relative to the ground must be carried out by the transposition of wires and the distribution of high-frequency coupling capacitors. The number of arc extinguishing reactors and their installation locations should be determined for the normal operation of the network, taking into account possible divisions of its part and probable emergency modes.

Arc suppression reactors can be installed at all substations, except for dead-end ones connected to the electrical network by at least two power lines. Installation of reactors at dead-end substations is not allowed. Arcing reactors are not allowed to be included in the neutral of transformers connected to the busbars through fuses. The power of the arcing reactors is selected according to the value of the total capacitive earth fault current, taking into account the development of the network in the next 10 years. The use of self-adjusting capacitive earth fault current compensation is recommended.

4.2.167. In electrical networks of 3-35 kV, measures should be taken to prevent ferroresonance processes and spontaneous displacements of the neutral.

In electrical circuits of 3-35 kV, in which there are generators (synchronous compensators) with direct water cooling of the stator winding, due to the significant active conductivity of the generator insulation to the ground, protection against ferroresonant processes is not required.

4.2.168. The windings of transformers (autotransformers) must be protected from switching overvoltages with the help of RT or surge arresters installed in accordance with the requirements of 4.2.153.

4.2.169. In networks of 330, 500 and 750 kV, depending on the network layout, the number of lines and transformers, measures should be taken to limit long-term voltage increases and internal overvoltages. The need to limit quasi-steady and internal overvoltages and the parameters of protection against them are determined on the basis of overvoltage calculations.

4.2.170. In order to limit switching overvoltages dangerous for equipment, combined RV or surge arresters, circuit breakers with pre-switched resistors, electromagnetic voltage transformers or other means should be used, as well as their combination with measures to limit long-term voltage increases (installation of shunt and compensation reactors, circuit measures, system and anti-emergency automatics, in particular automatics from overvoltage).

Switching overvoltages on the buses of SS 330, 500 and 750 kV should be limited depending on the level of equipment insulation.

4.2.171. For 110-500 kV switchgear, technical solutions should be provided that exclude the occurrence of ferroresonant overvoltages that occur during series switching on of electromagnetic voltage transformers and capacitive voltage dividers of switches.

These solutions include in particular:

use of switches without capacitive voltage dividers;
use instead of electromagnetic capacitive transformers;
application of antiresonant voltage transformers;
1,5-2 times increase in the busbar capacity of the switchgear by installing additional capacitors on the buses, for example, communication.

See other articles Section Rules for the installation of electrical installations (PUE).

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