 Open Access
 Total Downloads : 219
 Authors : Quyen Huy Anh, Le Quang Trung
 Paper ID : IJERTV6IS100026
 Volume & Issue : Volume 06, Issue 10 (October 2017)
 Published (First Online): 10102017
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
Selection Guide for Low Voltage Surge Protector
,
Quyen Huy Anp Le Quang Trung2
Faculty of Electrical and Electronics Engineering HCM University of Technology and Education Ho Chi Minh city, VietNam
AbstractProper sizing the low voltage surge protective device (SPD), fabricated by metal oxide varistor (MOV) technology, will guarantee protection efficiency, so this paper focused on researching and developing indeep study of some main points as follows: The coefficient of conversion between the surge rated current of 8/20Âµs waveform and of 10/350Âµs waveform, based on the equivalent of energy absorption; the ageing characteristic of MOV for 8/20Âµs waveform (instead of 2ms square waveform); determining the surge rated current of low voltage SPD, fabricated by multi block MOV technology, based on the attenuation coefficient of surge dissipation ability between metal oxide varistors, connected in parallel with different tolerance of threshold voltage.
KeywordsMetal oxide varistor; the coefficient of conversion; the ageing characteristic; 8/20Âµs waveform;10/350Âµs waveform; multi block MOV technology.

INTRODUCTION
Vietnam is located in the center of East Asia, one of the three centers in the world with strong thunderstorms with about 120 days of thunderstorm per year. Therefore, the overvoltage protection for low voltage electrical and electronic devices by SPD is always concerned.
Fig. 1. Standard lightning impulses corresponding to the different installation locations of SPD.
B. The Conversion Method
The conversion of the surge current of 8/20s waveform into 10/350s waveform of the lowvoltage SPD is carried out by the principle of equation absorptive energy of MOV [3, 4]:
t1
There are many researches on SPD, fabricated by MOV technology before. However, some problems, related to properly size this type of lowvoltage SPD, have not been fully
W v(t)i(t)dt
t 0
(1)
studied, such as: the conversion between the lightning current amplitude surge rated current of 8/20Âµs waveform and 10/350Âµs waveform, the building of aged characteristic of MOV for 8/20Âµs waveform and the determine attenuation coefficient when manufacturing the lowvoltage SPD by multi layer MOV technology.

THE AMPLITUDE CONVERSION OF LIGHTNING SURGE CURRENT FROM 8/20ÂµS
WAVEFORM TO 10/350ÂµS WAVEFORM
A. The Problem
Currently, due to the promotion of their products, the low voltage SPD manufacturers usually provide products with 8/20s waveform. It is difficult for user when the lowvoltage SPD is installed in direct lightning strike areas on the power line. This means that it will withstand 10/350s waveform (Cat D, E in Fig. 1) [1]. Therefore, it is necessary to find the amplitude conversion of lightning surge from 8/20Âµs waveform to 10/350Âµs waveform.
Where: v(t) is the voltage across MOV, i(t) is the current going through the MOV.
To simplify integration, the conversion method is carried out by modeling and simulation by Matlab software. Then, record the results by making simulation results table for MOVs and find the conversion factor equivalent surge rated current of 8/20Âµs waveform into 10/350Âµs waveform.

Calculation Model
To simplify integration, the conversion method is carried out by modeling and simulation techniques with the functional block diagram shown in Fig .2.
Fig. 2. Calculation model the absorption energy of MOV with 8/20s waveform and 10/350s waveform surge rated current.

Make conversion for MOV S20K275
Step 1: Select MOV B60K320 of Siemens with Imax (8/20s) is 70kA [5].
Step 2: Set the amplitude value of the standard surge current I1 = 50kA,
8/20s.
Step 3: The absorption energy of the MOV B60K320 displayed on scope VI MOV is 1600J.
Step 4: I2 = 3kA, 10/350s, corresponding to the absorption energy of
MOV is 1600J.

Result Table and Analysis
Do the same with other MOVs of Siemens, the simulation results are shown in Table I. Analyze this result, we find that to convert surges rated current of 8/20s waveform into 10/350s waveform, it is necessary to divide the value of surges current amplitude for the coefficient 16.6 17, and the error of absorption energy is from 0% to 15%.
TABLE I. SIMULATION RESULTS OF ENERGY ABSORPTION OF LOWVOLTAGE MOVS
Types of MOV
8/20s waveform
10/350s
waveform
Error of energy absorption (%)
Coefficient of surge current (I2/I1)
Imax (kA)
I1 (kA)
Energy absorption (J)
I2 (kA)
Energy absorption (J)
S20k230
8
8
180
0,5
152
15
16
S20K275
8
8
150
0,5
140
6
16
S20K320
8
8
210
0,5
178
15
16
B32K230
25
10
178
0,6
172
3
16,6
B60K230
70
50
1130
3
1150
2
16,6
B32K275
25
10
213
0,6
198
7
16,6
B60K275
70
50
1330
3
1345
1
16,6
B32K320
25
10
260
0,6
225
13
16,6
B60K320
70
50
1600
3
1600
0
16,6


THE AGEING OF LOWVOLTAGE SURGE PROTECTIVE DEVICE MOV

The Problem
The ageing of the lowvoltage SPD depends on the surge current amplitude and the number of times the lightning impulse going through. Currently, manufacturers usually provide the number of times of repeated lightning dissipation that SPD can withstand in the form of 2ms square impulse. However, the parameters of given impulse current are usually corresponding to 8/20s waveform. Therefore, it is need to buildup the lifespan characteristic of lowvoltage SPD according to the amplitude and the number of times of repeated the 8/20s waveform.

Determining Method [5, 6, 7]
r
The maximum allowable current impulse of MOV depends on the time of the lightning impulse going through and the number of repeated times has been defined. These parameters can be read from the attenuation characteristic of lowvoltage surge protective devices MOV, provided by the manufacturer. To identify the number of repeated times corresponding to the intensity of actual surge current (for all waveform), it is necessary to convert the actual waveform into equivalent square impulse. This method is called "rectangular method". If
i*dt
is known, t * is calculated according to the formula:
i*dt
t* (2)
Step : Calculate the pulse width:
*
t
r i*
t* i dt 414 21s
Where:
* is the pulse width on the characteristic line;
r i* 20
r
i*dt is the current integral depending on t and i* is the
Step 3: From Fig. 6, with t* 21s and i* =20kA, we
r
maximum current amplitude.

Determine the Allowable Repeated Times of Low Voltage SPD Device Siemens B40K275
Step 1: Build the simulation circuit for MOV B40K275 [5] and carry out simulation on Matlab (Fig. 3).
Fig. 3. Simulation circuit for determine the allowable repeated times of lowvoltage SPD device Siemens B40K275.
From the simulation result in Fig. 4, we can determine the
can find out the number of impulse repeated times that MOV B40K275 can withstand is n = 1.
Fig. 6. The number of impulse repeated times of MOV B40K275.
Do the same for current impulses 5kA, 40kA, the results are shown in Table II.
maximum current amplitude values
i* =20kA and from the
TABLE II. RESULTS OF REPEATED TIMES OF CURRENT IMPULSE THAT
simulated result in Fig. 5 we can calculate i*dt =414mAs.
Fig. 4. Current waveform of MOV B40K275.
Fig. 5. i*dt of MOV B40K275.
MOV CAN WITHSTAND.
Current impulses (kA)
i* (kA)
i* dt
(mAs)
t * (s)
r
The number of times of repeated current impulse n (times)
5
4.842
104.5
21
100
20
20
414
21
10
40
40.35
845
21
1
Thus, with the method of determining allowable repeated times of lightning impulse as above, users can define the potential of repeated lightning dissipation (the repeated times of lightning impulse ) corresponding to the 8/20s standard impulse, but with not the 2ms square impulse.

The Summary Table for the Number of Impulse Repeated Times of SIEMENS Low Voltage SPD
r
From the result of pulse width is t* 21s and Fig. 6, we build a summary table for the number of impulse repeated times that MOV B40K275 can withstand (Table III).
TABLE III. RESULTS OF IMPULSE REPEATED TIMES CORRESPONDING TO THE IMPULSE CURRENT THAT MOV CAN WITHSTAND.
I(A)
20
90
200
500
2000
7000
20000
40000
n
(times)
106
105
104
1000
100
10
1
From the results in Table III, we build the ageing characteristic of MOV B40K275 according to the amplitude and the number of repeated times of the 8/20s waveform (Fig. 7).
Fig. 7. Characteristic line for checking the number of impulse repeated
times of MOV.
Similarly, we can build the summary table as Table IV and the ageing characteristic (Fig. 8) of MOV B32K230.
TABLE IV. RESULTS OF THE NUMBER OF IMPULSE REPEATED TIMES CORRESPONDING TO THE IMPULSE CURRENT
THAT MOV CAN WITHSTAND.
I(A)
20
70
200
400
2000
5000
20000
25000
n (times)
106
105
104
1000
100
10
1
Fig. 8. Characteristic line for checking the number of impulse repeated times of MOV B40K23.


DETERMINE THE RATE LIGHTNING CURRENT IMPULSE OF SPD MULTILAYER VARISTOR MLV

The Problem
When manufacturing the lowvoltage SPD by MLV technology, connection parallel MLV is necessary in order to increase the rated current impulse. In this case, the rated current impulse of SPD by MLV is not equal to the sum of the rated surge current of the MOVs due to the uneven current distribution in these of MOVs. Therefore, it is necessary to determine the attenuation coefficient of the surge rated current [2].

Multiblock MOV Test Model
Determine attenuation coefficients is carried out by simulation on Matlab with parallel lowvoltage MOVs. This single MOV has a maximum surge rated current of 8kA 8/20s and tolerance of threshold voltage is Â± 10% (Fig. 9).
Fig. 9. Simulation of the current impulse going through elements of MOV 8kA and residual voltage respectively.
Simulate the current impulse 8/20s waveform going through elements of paralleled MOV with amplitudes includes: 10kA, 15kA, 20kA, 25kA, 40kA, 70kA and 100kA. The simulation results are shown in Fig. 10 and Fig. 11. The attenuation coefficient is presented in Table V.
Fig. 10. Current and voltage of SPD model using two MOVs, 8kA (TOL = 10% and 10%), 10kA 8/20s.
Fig. 11. Current going through MOV1 and MOV2, 8kA (TOL = 10% and – 10%), 10kA 8/20s.
TABLE V. SUMMARY TABLE THE LOWVOLTAGE SPD CONSISTS MULTIPLE MOV, 8KA CONNECTS IN PARALLEL.
Amplitude of test impulse (kA)
Types of MOV
Voltage tolerance of MOV
(%)
Number of MOV
Current impulse going through MOVs
(kA)
Residual voltage of MOV
(V)
Attenuation coefficient
10
2Ã—MOV8kA
+10
1Ã—MOV8kA
2.8
988
1.6
10
1Ã—MOV8kA
7.2
5
4Ã—MOV8kA
+10
3Ã—MOV8kA
3Ã—2.63
982
2.13
10
1Ã—MOV8kA
7.1
20
5Ã—MOV8kA
+10
4Ã—MOV8kA
4Ã—3.05
1005
2.0
10
1Ã—MOV8kA
7.8
25
7Ã—MOV8kA
+10
6Ã—MOV8kA
6Ã—2.9
1010
2.24
10
1Ã—MOV8kA
7.6
40
12Ã—MOV8kA
+10
11Ã—MOV8kA
11Ã—2.93
1025
2.4
10
1Ã—MOV8kA
7.7
70
23Ã—MOV8kA
+10
22Ã—MOV8kA
22Ã—2.83
1085
2.62
10
1Ã—MOV8kA
7.7
100
32Ã—MOV8kA
+10
31Ã—MOV8kA
31Ã—2.99
1185
2.56


CONCLUSION
Proper sizing the low voltage surge protective device (SPD), fabricated by metal oxide varistor (MOV) technology, will guarantee protection efficiency, so this paper focused on researching and developing indeep study of some main points as follows: The coefficient of conversion between the surge rated current of 8/20Âµs waveform and of 10/350Âµs waveform, based on the equivalent of energy absorption; the ageing characteristic of MOV for 8/20Âµs waveform (instead of 2ms square wveform); determining the surge rated current of low voltage SPD, fabricated by multi block MOV technology, based on the attenuation coefficient of surge dissipation ability between metal oxide varistors, connected in parallel with different tolerance of threshold voltage.

ACKNOWLEDGEMENTS
This research was supported by Ho Chi Minh City University of Technology and Education under a research at the Electrical Power System and Renewable Lab.
REFERENCES

Quyen Huy Anh, Electrical safety, Vietnam National University Publishing House – Ho Chi Minh City, Vietnam, 2012, pp.110111

Nguyen Ha Giang, Master thesis: Research and develop the model of surge protective devices on low voltage distribution network,
University of Technical Education Ho Chi Minh City, 2016

Young Sun Kim, Failure prediction of metal oxide varistor using nonlinear surge lookup table based on experimental. 2015.

Credson de Salles and Manuel L. B. Martinez, Surge Ageing of Metal Oxide Varistors., 2015.

Epcoss data book, Siov Metal oxide Varistor, Siemens, 2015, pp.5052.

Dawood Talebi Khanmiri, Degradation of low voltage metal oxide varistors in power supplies, 2016.

Dawood Talebi Khanmiri, Surge withstand capability of metal oxide varistors for 10/350Âµs waveform, 2016.