Webinar "Surge protection for power lines 230/400 V 50 Hz, part 1", page 2

The second Webinar from the series "Surge protection"

Webinar text. Page 2

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Pole-mounted transformer substation protection

Газоразрядные элементы- Gas discharge elements
Искровой воздушный промежуток – Spark air gap
Защита от перенаряжений столбвой ТП – Pole-mounted transformer substation surge protection

- If we look at the electrical network, when there is overvoltage somewhere in the city or in the suburbs and look at the air transformer stations, which are located in Poland and in your country, I think they are identical or similar.

6 kV line arresters

Газоразрядные элементы- Gas discharge elements
Искровой воздушный промежуток – Spark air gap
Защита от перенаряжений столбвой ТП – Pole-mounted transformer substation surge protection
Газоразрядники линии 6 кв – Gas arresters of 6 kV line

- We can see that such a station today has a range of surge protective elements. For example, we see that on the high side, there are gas arresters and 6 kV lines

Structure of gas arresters

Газоразрядные элементы- Gas discharge elements
Искровой воздушный промежуток – Spark air gap
Защита от перенаряжений столбвой ТП – Pole-mounted transformer substation surge protection
Газоразрядники линии 6 кв – Gas arresters of 6 kV line

- If we look at such a arrester closely, we see that its structure is very simple. The question of pickup parameters stability is open to question. I don't think anyone can define the network of pickup voltage.

Additional protection element

Газоразрядные элементы- Gas discharge elements
Искровой воздушный промежуток – Spark air gap
Защита от перенаряжений столбвой ТП – Pole-mounted transformer substation surge protection
Газоразрядники линии 6 кв – Gas arresters of 6 kV line

- If we look at the next protection element, we will see an additional protection element on the transformer lead terminals.

Characteristics of the protection element

Газоразрядные элементы- Gas discharge elements
Искровой воздушный промежуток – Spark air gap
Защита от перенаряжений столбвой ТП – Pole-mounted transformer substation surge protection
Газоразрядники линии 6 кв – Gas arresters of 6 kV line

- If we look at the catalogue map of such an element, it is seen that there are only two electrodes, separated by the insulator. And here the distance is more precisely chosen. Question: who determined it and why such a length remains open for me, because according to my knowledge, these distances should be smaller. But simple methods to protect electro transmission and electric supply in order to make our systems work continuously.

Advantages of gas discharge elements

Газоразрядные элементы- Gas discharge elements
Искровой воздушный промежуток – Spark air gap
Positive traits:
- there are no problems with coal dust
Disadvantages:
-mechanic and electric instability
- possible formation of bridge networks due to accumulation of particles and grains in the electric field between the electrodes
Application:
- Only as a reserve when all the main surge protection elements are out of service

- What are the traits of such an element which deals with an air gap? There won't be any problem with coal dust, about which we've just spoken. But the disadvantages, as I've already said - are mechanical and electrical instability due to the impact of environment that is temperature, humidity, pressure. Possibility of formation of bridge circuits due to the accumulation of particles and fibre in the electric field between the electrodes in closed premises. And the use only as a reserve, activated when all the main surge protection elements fail.

Gas-filled arresters

Газоразрядные элементы- Gas discharge elements
Газонаполненные разрядники – gas filled dischargers
Gas filled dischargers are devices in which a pair of electrodes are placed in a hermetic case, the inner space of which is filled with the mixture of inert gases compressed to a certain pressure value.
Such a solution gave a chance to isolate from the influence of atmosphere conditions change and modern technology guarantees satisfactory repetition of such electric parameters as OP.

- In order to separate from the influence of environment it is necessary to terminate such electrodes in the body. And the next stages appear, it was appearing of gas-filled arresters in which a pair of electrodes is placed in a hermetic package. And inside the package there is a mixture of noble gases, compressed to a certain pressure value. That is, this device is more precise, with which we control the level of pickup voltage.

Arresters at railroads

Газоразрядные элементы- Gas discharge elements
Газонаполненные разрядники – gas filled dischargers

- If we look at the old elements still used. These are elements, which I made photo of on a railroad in the points, where there is automation.

Construction of gas-filled arresters 

Газоразрядные элементы- Gas discharge elements
Газонаполненные разрядники – gas filled dischargers

- If we look closely, I hope you see that the elements fixed the same pickup voltage. The distance between the electrodes is twice larger in the right arrester. It is seen, that such an element doesn't give us good protection, because its source parameters are not controlled and they are set only to comply with the requirements fixed on paper. In practice, such elements do not protect anything. If we look well, we will see that the electrodes are not connected on the other side. That means such elements are out-of-date.

Gas-filled arresters of minor energy

Газоразрядные элементы- Gas discharge elements
Газонаполненные разрядники – gas filled dischargers

- Due to the experience of the previous arresters, we now have new modern arresters. I am showing you arresters of minor energy in comparison to those which function on electric network, but such elements act in electric networks as the last protection stage, set by the electricity consumer inside the object. And we see that there are many different structures. Two and three-electrode elements give us the base for building protection circuits for different areas.

Cross-section of an arrester

Газоразрядные элементы- Gas discharge elements
Газонаполненные разрядники – gas filled dischargers
Электроды - electrodes
Межэлектродное пространство – inter-electrode space
Изолятор - insulator
Стекло или керамика – glass or ceramics
Радиоактивная масса – radioactive mass
Облегчение зажигания – breakdown lightening
Поперечное сечение миниатюрного газонаполненного разрядника – cross-section of a miniature gas filled discharger

- If we look at the section of such an element, we will see that in a ceramic or glass case. Ceramic case cover is of a higher quality. Two electrodes are mounted. One below another and the space between them is filled with noble gas. First steps, because gas ignition is characterized by some delay. There was an effort to ionize this interelectrode space with radio-active mass, but it was good when we dealt with one element. When there was a lorry with such elements, there were thousands of them, but then the radioactive mass gave a certain level of radiance and this radioactive mass was started to be used. And today good manufacturers have specially exited electrodes. Under the microscope we can see some spikes on them, which really ionize the interelectrode space and ease the ignition of such an interval between the electrodes.

Arrester in a DC circuit

Газоразрядные элементы- Gas discharge elements
Газонаполненные разрядники – gas filled dischargers
Разрядник в схеме постоянного тока – Arrester in a DC circuit
Дуговой разряд – arc discharge
Тлеющий разряд – glow discharge
Область гашения – blow-out area
Вольт-амперная характеристика типичного разрядного промежутка – volt-ampere characteristics of a typical discharge gap

- It is very important to understand, how separate elements used in SPD schemes at the DC and high frequencies function. But today we will only talk about elements, which function in AC circuits. In order to ease the understanding of the next webinars, let's discuss the operation of a gas filled arrester at the direct current. We see that its volt-ampere characteristic is symmetrical. This is critical because we use one element from the protection of positive and negative pulses. We see that there appears some hysteresis in the operation of our element. That is, when it is activated, it operates in one way, when we turn the current off, it returns in another way. But if we see the operation principle in general, we will see that the first pickup moment, which we call static pickup voltage. I named it this way in order to ease understanding. There are other notions in the catalogues. That is, as some voltage, the element is activated, and there happens the so-called glow discharge. And when we increase the current, which goes through the element, we go through an arc charge.

Arrester in AC circuit

Газоразрядные элементы- Gas discharge elements
Газонаполненные разрядники – gas filled dischargers
Разрядник в схеме переменного тока – Arrester in an AC circuit
Напряжение зажигания – Ignition voltage
Напряжение тления – glow voltage
Напряжение погашения – blow-out voltage
Напряжение дуги – arc voltage
Воздействие синусоидального напряжения на разрядник – impact of sine-curve voltage on the arrester

- If we look at the AC circuit, we can notice, that in this situation we deal with a slightly simplified environment, because the situation in which our voltage goes through zero and achieves maximal value and again in every half-sinusoid we go through zero doesn't always happen here. It means that the element is activated. The element is activated; we go to the glow discharge, the voltage increases, the current increases, the arc initiates, and the voltage drops to these 20-30 V. And when the voltage reduces, the current was not very high and interelectrode space is deionized and our element can extinguish the arc in AC. But it isn’t that easy. You see on these slides the elements, which I showed you on pictures, these are "LEUTRON" company elements, on which we will concentrate in our reports. We will talk about such elements and we will study their examples. We see, that different types of elements, even with an element which is fused and nails these electrodes up, when a too great continuous current flows through the element.

Sinusoidal voltage impact on the arrester

Газоразрядные элементы- Gas discharge elements
Газонаполненные разрядники – gas filled dischargers
Разрядник в схеме переменного тока – Arrester in an AC circuit
Воздействие синусоидального напряжения на разрядник при наличии перенапряжения – impact of sine-curve voltage on the arrester if there is a surge

- The outcome is as follows: environment on AC for a gas-filled arrester is much easier. We can be sure, that our element will be activated at the occurrence of overvoltage. It will restrict, cutting the half-sinusoids, and will turn off itself, but it is not that simple.

Arrester- pulse dialling

Газоразрядные элементы- Gas discharge elements
Газонаполненные разрядники – gas filled dischargers
Разрядник – импульсный пробой – arrester – pulse puncture
Вольт-секундная характеристика  - volt-second characteristics

- If we look at the impact of overvoltage on an arrester, we can always remember, that its pickup time, connect time and ignition time depend on the speed of pulse rise.

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