Valve arrester RVO-6

The RVO-6 U1 arrester is designed to protect against atmospheric surges in the insulation of AC electrical equipment with a frequency of 50 and 60 Hz. Overvoltages are any kind of voltage increase that poses a threat to the integrity of the insulation of the electrical installation.

The protective effect of the arrester RVO-6 is to reduce the amplitude of the overvoltage wave to a value that is safe for isolating the protected electrical installation. When the voltage rises to certain limits, the spark gaps of the arrester break through and the overvoltage energy is discharged to the ground through a grounding conductor connected to the arrester.

Specifications:
Mains voltage class, effective value, kV: 6;
Rated voltage (Unr), effective value, kV: 7.5;
Pulse breakdown voltage at pre-discharge time from 2 to 20 µs, kV, not more than: 32;
Leakage current at rectified voltage equal to the rated voltage, mA, not more than: 0.6;
The length of the leakage path of the outer insulation, cm, not less than: 447;

The design and principle of operation of the arrester RVO
When a surge arrester is exposed to surges exceeding its breakdown voltage, a breakdown of the IP occurs and the operating resistances are connected to the network. In this case, the overvoltage at the installation point of the device is determined mainly by the voltage drop across the operating resistances. This is sometimes referred to as the remaining voltage across the arrester (Vres). This voltage must be 30% less than the permissible voltage on the protected insulation.

The current flowing through the arrester behind the impulse breakdown of the IP under the influence of a voltage of 50 Hz is called the follow current. This current is limited by the operating resistance of the device, the value of which increases sharply with a decrease in the voltage across the arrester. When the current passes through zero, the arc in the MT goes out, and the arrester returns to its original state. Thus, in the absence of overvoltages, the SP of valve-type arresters separate the operating resistances from the network and connect them at the time of the appearance of overvoltages dangerous for isolation.

Spark gaps, if possible, should have a horizontal volt-second characteristic, that is, a small change in the breakdown voltage Upr in a wide range of pre-discharge times (from μs to ms) and a small spread Upr. In addition, Upr should not change after repeated passage of normalized pulse and follow currents, as well as with temperature fluctuations and exposure to shaking, shock and vibration. The power supply must extinguish the arc of the follow current, as a rule, at its first transition through zero. In case 8, there are working resistors 5, spark gaps 4, spring 3 and seals 2 and 6. The RVO-6 valve arrester is connected to the current-carrying parts and to the ground through terminals 1 and 7.

In normal operation, the current from the operating resistor is isolated by gaps in the spark gaps. This is due to the fact that when the voltage is applied to the resistor for a long time, it loses its properties and will not work as it should. With a short-term exposure to current, its current-voltage characteristic does not change. When an internal or lightning overvoltage nevertheless appears in the network, the spark gaps pass it through themselves and a working resistor comes into play after them, which instantly reduces its resistance and passes the overvoltage through itself to the ground.

Maintenance
During operation of the RVO-6 valve arrester, it is necessary to monitor its porcelain insulation for signs of cracks or chips. It is also necessary to monitor the cleanliness of its porcelain cover and regularly clean it of dirt and dust to prevent current from passing through the surface of the external insulation. Moisture ingress is unacceptable inside the housing, because this directly affects the characteristics of the RVO-6 valve arrester. Preventive tests are carried out and during them leakage current and breakdown voltage are measured. One of the signs of a faulty arrester may be crackling inside its case, which is not normal, since in normal operation its operation is silent.

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