Selection of Surge Protective Device (SPD)- (Part 4)


Typical System Voltage & MCOV rating (As per IEEE):

 

Typical IEEE System Voltages
Normal (Line to Line) Voltage (KV rms) Maximum ( Line to Line ) Voltage (KV rms) Maximum (Line to Ground) Voltage (KV rms) Min MCOV
kV rms kV rms kV rms kV rms
2.40 2.52 1.46 1.46
4.16 4.37 2.52 2.52
4.80 5.04 2.91 2.91
6.90 7.25 4.19 4.19
8.32 8.74 5.05 5.05
12.0 12.6 7.28 7.28
12.5 13.1 7.57 7.57
13.2 13.9 8.01 8.01
13.8 14.5 8.38 8.38
20.8 21.8 12.6 12.6
22.9 24.0 13.9 13.9
23.0 24.2 14.0 14.0
24.9 26.2 15.1 15.1
27.6 29.0 16.8 16.8
34.5 36.2 20.9 20.9
46.0 48.3 27.9 27.9
69.0 72.5 41.9 41.9
115.0 121 69.8 69.8
138.0 145 83.8 83.8
161.0 169 98 97.7
230.0 242 140 140
345.0 362 209 209
500.0 525 303 303
765.0 800 462 462

 

Typical System Voltage & MCOV rating (As per IEC):

 

Typical IEC System Voltages
Normal (Line to Line) Voltage (KV rms) Maximum ( Line to Line ) Voltage (KV rms) Maximum (Line to Ground) Voltage (KV rms) Minimum Uc
kV rms kV rms kV rms kV rms
3.3 3.7 2.1 2.1
6.6 7.3 4.2 4.2
10.0 11.5 6.6 6.6
11.0 12.0 6.9 6.9
16.4 18.0 10.4 10.4
22.0 24.0 13.9 13.9
33.0 36.3 21.0 21.0
47.0 52 30.1 30.1
66.0 72 41.6 41.6
91.0 100 57.8 57.8
110.0 123 71.1 71.1
132.0 145 83.8 83.8
155.0 170 98.3 98.3
220.0 245 142 142
275.0 300 173 173
330.0 362 209 209
400.0 420 243 243

 

SPD and Fuse / CB co-ordination chart:

Fuse/CB co-ordination chart
Incoming feeder fuse rating (A) Incoming feeder CB Rating (A) SPD fuse rating (A) SPD CB rating (A)
16 6 10 4
25 10 16 6
32 16 20 10
40 20 25 16
63 32 40 20
80 40 50 25
125 63 80 40
160 80 100 50
250 125 160 80
500 250 320 160
       

 

Sample Specifications of SPD for 277/480V Supply System

  • Voltage :277/480V 3Ø WYE, 480V 3Ø Delta
  • Frequency: 50/60Hz
  • Surge Technology: 40mm MOV
  • Nominal Discharge Rating (IN):20kA
  • Maximum Continuous Operating Voltage (MCOV): 320V
  • L-L=640V
  • L-N=320A
  • L-G=320A
  • G-N=320A
  • Maximum Surge Current, Per Mode (Per Phase) : 200kA (400kA
  • Voltage Protection Rating (VPR) (Clamping) : 800V(L-N)/700V(L-L)
  • Short Circuit Current Rating (SCCR): 10kA
  • Connection Type: Parallel Connection

  Reason for Failure of SPD :

Most SPDs will last for many years. The things that cause sudden failure are

  • External supply faults such as overvoltage -faulty transformer, MV lines
  • Local supply faults -broken or ungrounded neutral.
  • Wrongly-selected SPD voltage.
  • A surge in excess of the SPD’s rating.

 

Classes’ of surge arrestors according to impulse current:

Untitled

 1 = Test impulse current for lightning current arresters

2 = Test impulse current for surge arresters

  •  There are 3 x main categories of lightning surge arresters.
  • Class 1/A – (10/350) lightning current arresters, which can withstand direct lightning
  • Class 2/B – (8/20) surge arresters, to protect against induced surge currents
  • Class 3/C – (8/20) surge arresters, to protect against induced surge currents

 Meaning of 20kA (8/20μS) impulse current.

  • In 8/20μ The first value (8) is the rise time (from 10% to 90% of peak). The second value (20) is the duration for the test transient to decrease to half its peak value.

Standard for SPD:

  • Underwriter laboratories—UL 1449 (3rd Edition 2009)
  • IEEE C62.45 (2002)
  • NECT National Electrical Code Articles 245, 680 and 800.
  • NFPAT 780 Lightning protection code recommendations for the use of surge protection devices at a facility service entrance.
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