Utilizing Surge Generator and Testing Equipment for Electrical System Protection

Lightning is a serious natural disaster, which can seriously endanger the normal operation of communication equipment, computer network systems, and power systems, causing direct and indirect economic losses to enterprises. For example, buildings are damaged, important equipment is severely damaged, and personnel safety is endangered. Equipment damage, communication network interruption, and loss of important information will affect the normal production and work, causing great impact on production and life.Then Lightning Surge Generator is of great importance in our life.

1. Principles for Wiring and Setting Up Surge Generator
Surge Generators, also known as overvoltage protectors, surge testing equipment, or lightning protection protectors, abbreviated as “SPD”, have a basic principle. In the moment of transient overvoltage (lightning wave) occurrence (millisecond or nanosecond level), all protected objects (equipment, lines, etc.) in the protected area shall be connected to isopotential system. Thus, the amplitude of transient overvoltage in the circuit can be limited within the range of equipment bearing. This circuit includes the active line of power supply system and signal transmission line. SPD components are divided into voltage switch type and voltage limit type. Voltage switch type SPD, such as spark gap, gas discharge tube, and thyristor circuit, have high impedance when there is no surge, but their impedance changes to low value during voltage surge response; Voltage limit type SPD, such as varistor, suppression diode, have high impedance when there is no surge, but their impedance will gradually reduce with the increase of surge current and voltage. Various types of SPD use the characteristics of each component to form hybrid SPD with voltage switch, voltage limit or both characteristics.

Surge Generator SG61000 5 AL7

2. The Importance of Select the Correct Power SPD for a Surge Generator
For the protection of lightning wave intrusion into general low-voltage power distribution system, according to the importance of protected object, 1-2 levels of SPND should be installed. For the protection of lightning wave intrusion into low-voltage power distribution system of information system, the risk of lightning strike should be comprehensively evaluated according to the environmental factors of information system, the importance of information system equipment and the severity after lightning strike. The protection of transient overvoltage wave of lightning in information systems is divided into a, b, c and d four levels:
a. Level should install 3-4 level SPD in low-voltage system;
b. Level should install 2-3 level SPD in low-voltage system;
c. Level should install 2 level SPD in low-voltage system;
d. Level should install 1 level or above SPD in low-voltage system.

The first level should be installed in front of the distribution box of main incoming line, the second level should be installed in front of the distribution box, the third level should be installed in front of the distribution system of important equipment, and the fourth level should be installed in front of the working power supply of electronic equipment. Since the first lightning strike is a current wave of 10/350μs, the first level SPD should choose a voltage switch SPD (Surge generator) with test wave of 10/350μs, and the SPD of level 2 and above can choose the voltage limit SPD or hybrid SPD with test wave of 8/20μs.

3. Number and Setting of Surge generator SPD
In TN-C-S and TN-C systems, there are phase wires and PEN wires in the power inlet circuit, and the PEN wires need to be connected to the grounding busbar with the same potential level, so SPD should not be installed on these two systems. In TN-S and TT systems, the N-wires are not grounded at the inlet, and SPD should be installed on the N-wires in the same way as the phase wires.

It should be noted that the grounding system of 10kv networks of some cities in China has begun to adopt grounding system with small resistance. The grounding fault current of this network is not the capacitive current of 10-20 amps, but hundreds or thousands of amps of large grounding fault current. Due to the fact that the substations in China’s 10kv distribution do not have protective grounding of exterior of equipment and system grounding of 220/380v N-systems separated as foreign substation, the above large grounding fault current will cause 1-2kv fault voltage on the substation grounding resistance, and the fault voltage lasting time shall be the sum of the action time of 10kv grounding short circuit relays and circuit breakers, approximately from 0.5s to 1s. This transient overvoltage on the ground will bring electric shock hazard within the TN-systems, and may trigger electrical short circuit accidents within the aged surge testing equipment and lines in the TT-systems. It may also burn SPD in surge protective devices, causing persistent grounding short circuit, since the heat capacity of SPD can only bear transient surge in μs, but not transient overvoltage and current in ms. Therefore, for TT-systems powered by 10kv network grounding systems, the setting of surge protection should not be done in a usual manner, but rather should be done by connecting the phase wire through SPD to the N-wire, which is connected to the ground through spark gaps. By adjusting the spark gap discharge voltage to 3kv-3.5kv, it can avoid the accidents caused by 10kv network grounding faults, which may burn the SPD due to transient overvoltage on the ground.

4.Precautionary measures for surge generator
Surge-protective devices (SPDs) may be damaged by a lightning strike, or their lifespan may be over due to their long-term use and increased leakage current. When the leakage current increases to a certain value, the light-emitting diode above it will no longer be lit, or in other ways show its failure, and a spare should be replaced in time. If the replacement is not timely, the SPD will be completely damaged and a short circuit in the phase line will become a ground fault. Like other ground faults, it may cause overcurrent on the line. Some SPD products are equipped with overcurrent circuit breakers. If the product does not have this component, the line should be provided with overcurrent protection devices (fuses, circuit breakers). It can be installed on the connection line of SPD, or the overcurrent protection device on the power line can be used. The latter way is more economical, but it will cause the power line to be cut off due to the failure of the SPD, and this way is not suitable for the power line with important load.

If the SPD is protecting a Class I anti-electrocution device (device with metal casing and PE line), the failure of the SPD may cause electroshock accidents when the ground fault current Id is generated on the PEN line and PE1 line. This voltage drop is transmitted along the PE2 line to the outer shell of the surge testing equipment. If uf is greater than the safe voltage limit (50V for dry places and 25V for damp places), there is a possibility of electroshock accident. Therefore, a leakage protector RCD should be installed on the power side of the SPD as shown in the dashed line in the figure to prevent the occurrence of electroshock accident. When a large capacity spark gap SPD is installed in the power line, it may eject hot free gas when it releases the surge current, which is easy to cause explosion or fire. Such SPDs should not be installed in explosive or fire-dangerous places and should be kept away from combustibles.

With the increasing number of smart community projects, it is essential to take measures to prevent building disasters caused by lightning. Surge protectors are gaining more and more attention due to their unique protective functions.