Several hot issues in the present surge protective device SPD

Several hot issues in the present surge protective device SPD

1. Classification of test waveforms

For the surge protective device SPD test, there is fierce debate at home and abroad about the testing categories of Class I (Class B, Type 1), mainly on the method of simulating direct lightning impulse discharge, the dispute between the IEC and IEEE committees:

(1) IEC 61643-1, in Class I (Class B, Type 1) surge current test of the surge protective device, the 10/350µs waveform is a test waveform.

(2) IEEE C62.45 ‘IEEE Low-voltage surge protective devices – Part 11 Surge protective devices connected to low-voltage power systems – Requirements and test methods’ defines the 8/20µs waveform as the test waveform.

Approvers of the 10/350µs waveform believe that in order to ensure 100% protection during lightning strikes, the most severe lightning parameters must be used to test lightning protection equipment. Use 10/350µs waveform to detect LPS (Lightning Protection System) to ensure that it is not physically damaged by lightning. And the proponents of the 8/20µs waveform believe that after more than 50 years of use, the waveform shows a very high success rate.

In October 2006, relevant representatives of IEC and IEEE coordinated and listed several topics for research.

GB18802.1 power supply SPD has test waveforms of Class I, II, and III classifications, see Table 1.

Table 1: Level I, II and III testing categories

The United States has considered two situations in the following three latest standards:
IEEE C62.41. 1 ‘IEEE Guide on the Surges Environment in Low-Voltage (1000V and Less) AC Power Circuits’, 2002
IEEE C62.41. 2 ‘IEEE on Recommended Practice Characterization of Surges in Low-Voltage (1000V and Less) AC Power Circuits’, 2002
IEEE C62.41. 2 ‘IEEE on Recommended Practice on Surge Testing for Equipment Connected to Low-Voltage (1000V and Less) AC Power Circuits’, 2002

Situation 1: Lightning is not directly stroke the building.
Situation 2: It is a rare occurrence: lightning strikes on a building directly or the ground next to a building is struck by lightning.

Table 2 recommends applicable representative waveforms, and Table 3 gives the intensity values corresponding to each category.
Table 2: Location A. B. C (Case 1) Applicable Standard and Additional Impact Test Waveforms and Case 2 Parameter Summary.

Table 3: SPD situation at the exit 2 Test content ^{A, B}

Note:
A. This test is limited to the SPD installed at the exit, which is different from the standards and additional waveforms mentioned in this recommendation, except for SPD.
B. The above values apply to each phase test of multi-phase SPD.
C. The successful field operation experience of SPD with C lower than exposure level 1 indicates that lower parameters can be selected.

“There is no specific waveform that can represent all surge environments, so the complex real-world needs to be simplified into some easy-to-handle standard test waveforms. To achieve this, the surge environments are classified to provide surge voltage and current The waveform and amplitude are selected so as to be suitable for evaluating the different endurance capabilities of the equipment connected to the low-voltage AC power supply, and the equipment endurance and the surge environment need to be properly coordinated.”

“The purpose of specifying classification test waveforms is to provide equipment designers and users with standard and additional surge test waveforms and corresponding surge environment levels. The recommended values ​​for standard waveforms are simplified results obtained from the analysis of a large amount of measurement data. The simplification will allow a repeatable and effective specification for the surge resistance of equipment connected to low-voltage AC power supplies.”

The voltage and current waves used for the SPD impulse limit voltage test of telecommunications and signal networks are shown in Table 4.

Table 4: Voltage and the current wave of impact test (Table 3 of GB18802-1)

Note: Impact is applied between the line terminal and the common terminal. Whether to test between line terminals is determined according to suitability. The SPD for power supply and the SPD for telecommunications and signal networks should formulate a unified standard test waveform that can be matched with the withstand voltage of the equipment.

2.Voltage switch type and voltage limit type

In the long-term history, the voltage switching type and voltage limiting type are development, competition, complementation, innovation, and redevelopment. The air gap type of the voltage switch type has been widely used in the past decades, but it also exposes several defects. They are:

(1) The first level (level B) using 10/350µs spark gap type SPD caused a large number of base station communications equipment records of massive lightning damage.

(2) Due to the long response time of the spark gap SPD to lightning, when the base station has only spark gap SPD, and no other SPD is used for the second level (level C) protection, the lightning current may cause lightning sensitive devices in the device damage.

(3) When the base station uses B and C two-level protection, the spark gap SDP’s slow response time to lightning may cause all lightning currents to pass through the C-level voltage-limiting protector, causing the C-level protector to be damaged by lightning.

(4) There may be a blind spot of spark discharge between the energy cooperation between the gap type and the pressure-limiting type (blind point means that there is no spark discharge in the discharge spark gap), resulting in the spark gap type SPD not acting, and the second level (level C) protector needs to withstand higher. The lightning current caused the C-level protector to be damaged by lightning (limited by the area of ​​the base station, the decoupling distance between the two poles SPD requires about 15 meters). Therefore, it is impossible for the first level to adopt gap type SPD to effectively cooperate with the C level SPD.

(5) The inductance is connected in series between the two levels of protection to form a decoupling device to solve the problem of the protection distance between the two levels of SPD. There may be a blind spot or reflection problem between the two. According to the introduction: “Inductance is used as a depletion component and waveform The shape has a close relationship. For long half-value waveforms (such as 10/350µs), the inductor decoupling effect is not very effective (the spark gap type plus inductor cannot meet the protection requirements of different lightning spectrums when lightning strikes). When consuming components, the rise time and peak value of the surge voltage must be considered.” Moreover, even if the inductance is added, the problem of the gap type SPD voltage up to about 4kV cannot be solved, and the field operation shows that after the gap type SPD and the gap combination type SPD are connected in series, the C-level 40kA module installed inside the switching power supply loses the SPD There are numerous records of being destroyed by lightning.

(6) The di/dt and du/dt values ​​of gap-type SPD are very large. The impact on the semiconductor components inside the protected equipment behind the first-level SPD is particularly noticeable.

(7) Spark gap SPD without deterioration indication function

(8) The spark gap type SPD cannot realize the functions of damage alarm and fault remote signaling (currently it can only be realized by LED to indicate the working status of its auxiliary circuit, and does not reflect the deterioration and damage of the lightning surge protector), so it is For unattended base stations, intermittent SPD cannot be effectively applied.

In summary: from the perspective of parameters, indicators, and functional factors such as residual pressure, decoupling distance, spark gas, response time, no damage alarm, and no-fault remote signaling, the use of spark gap SPD in the base station threatens the safe operation of the communication system Issues.

However, with the continuous development of technology, the spark gap-type SPD continues to overcome its own shortcomings, the use of this type of SPD also highlights the greater advantages. In the past 15 years, a lot of research and development has been carried out on the air gap type (see Table 5):

In terms of performance, the new generation of products has the advantages of low residual voltage, large flow capacity, and small size. Through the application of micro-gap trigger technology, it can realize the “0” distance matching with the pressure-limiting SPD and the combination of the pressure-limiting SPD. It also compensates for its lack of responsiveness and greatly optimizes the establishment of lightning protection systems. In terms of function, the new generation of products can guarantee the safe operation of the entire product by monitoring the operation of the trigger circuit. A thermal disengagement device is installed inside the product to avoid the burning of the outer shell; a large opening distance technology is adopted in the electrode set to avoid the continuous flow after zero crossings. At the same time, it can also provide a remote signal alarm function to select the equivalent size of lightning pulses, and extend the service life.

Table 5: Typical development of spark gap

S/N	Years	Main features	Remarks
1	1993	Establish a “V” shaped gap that changes from small to large, and set up a thin discharge insulator along the valley end as isolation to help obtain a low operating voltage and discharge until the gap, using electrodes and space structure and material properties in 1993. Lead the arc to the outside, forming an intermittent condition and extinguishing the arc. Early gap type dischargers had high breakdown voltage and great dispersion.
2	1998	The use of an electronic trigger circuit, especially the use of a transformer, realizes the auxiliary trigger function. It belongs to the active triggered discharge gap, which is an upgrade of the passive triggered discharge gap. Effectively reduces the breakdown voltage. It belongs to the pulse trigger and is not stable enough.
3	1999	The gap discharge is stimulated by a sparking piece (actively triggered by a transformer), the structure is designed as a semi-closed structure, and the horn-shaped circular or arc-shaped gap is changed from small to large, and the air guide groove is provided on the side to facilitate drawing and being elongated The electric arc is extinguished and the closed structure can be filled with arc extinguishing gas. It is the development of the early discharge gap electrode. Compared with the traditional closed discharge gap, the arc-shaped or circular groove optimizes the space and electrode, which is conducive to a smaller volume. The electrode gap is small, the intermittent ability is insufficient,
4	2004	Cooperate with the micro-gap triggering technology, adopt the large distance electrode setting and spiral channel cooling arc extinguishing technology, Greatly improve the trigger technology and intermittent ability, the use of energy trigger technology is more stable and reliable.
5	2004	Optimize the lightning protection device to form a composite surge protector device that meets the requirements of Class B and Class C protection. Modules made of discharge gaps, modules made of voltage limiting elements, bases and deterioration devices are combined in various ways to form overvoltage protection devices

Development track map

3. Similarities and differences between telecommunication SPD and power supply SPD

Table 6: Similarities and differences between telecommunication SPD and power supply SPD

Table 7: Common working voltage of communication SPD

4. Cooperation between external over-current protection and SPD

Requirements for over-current protection (circuit breaker or fuse) in the disconnector:

(1) Comply with GB/T18802.12:2006 “Surge Protection Device (SPD) Part 12: Selection and Use Guidelines of Low Voltage Distribution System”, “When SPD and over-current protection device cooperate, the nominal Under the discharge current In, it is recommended that the over-current protector does not operate; when the current is greater than In, the over-current protector can operate. For a resettable over-current protector, such as a circuit breaker, it should not be damaged by this surge .”

(2) The rated current value of the over-current protection appliance should be selected according to the maximum short-circuit current that may be generated at the SPD installation and the short-circuit current withstand capability of the SPD (provided by the SPD manufacturer), that is, “SPD and the over-current protection connected to it. The short-circuit current (produced when the SPD fails) of the device is equal to or greater than the maximum short-circuits current expected at the installation.”

(3) The selective relationship must be satisfied between the over-current protection device F1 and the SPD external disconnector F2 at the power inlet. The wiring diagram of the test is as follows:

The research results are as follows:
(a) The voltage on circuit breakers and fuses
U (circuit breaker) ≥ 1.1U (fuse)
U (SPD+over-current protector) is the vector sum of U1 (over-current protector) and U2 (SPD).

(b) The surge current capacity that the fuse or circuit breaker can withstand

Under the condition that the over-current protector does not operate, find the maximum surge current that the fuse and circuit breaker with different rated currents can withstand. The test circuit is as shown in the figure above. The test method is as follows: the applied inrush current is I, and the fuse or circuit breaker does not operate. When 1.1 times the inrush current I is applied, it operates. Through experiments, we found some minimum rated current values required for over-current protectors not to operate under inrush current (8/20µs wave current or 10/350µs wave current). See table:

Table 8: The minimum value of the fuse and circuit breaker under the inrush current with a waveform of 8/20µs

Table 9: The minimum value of the fuse and circuit breaker does not operate under the surge current of 10/350µs