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:
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.