Surge Protective Device Parameter Introduce
Basic Parameters
| Parameter name | Parameter symbol | Noun interpretation |
| Maximum continuous operating voltage | UC | The maximum AC voltage RMS or DC voltage that can be safely and continuously applied to the SPD. |
| Voltage protection level | UP | A performance parameter that characterizes the voltage between SPD limit terminals, whose value can be selected from a list of priority values. This value should be greater than the maximum limit voltage. |
| Transient overvoltage | UT | Test voltage applied to SPD for a specified time [ 5s and 120min ] without failure or abnormality, UT > UC. The TT distribution system requires an additional test to simulate a transient " high" over voltage between the neutral and PE ( TOV)(, 1200 Vac applied at 300 A for 200 ms ): compliance with this test requires the use of a CT2 mounting system ( special high energy withstand gas discharge tubes between N and PE ). |
| Maximum discharge current | In | In is the peak 8 / 20 μ s pulse current that the T1 or T2 SPD can withstand repeatedly ( 15 shocks ) without damaging it. |
| Nominal discharge current | Imax | Imax applies to the T2 test SPD and is the peak of 8 / 20 μ s pulse current flowing through the SPD without damaging it. |
| Impulse current | Iimp | Iimp is suitable for T1 SPD test and is the maximum impulse current ( 10 / 350 μ s ) that surge protection device can withstand without damaging it. This test simulates the impact on an AC power surge protector after a facility is directly struck by lightning. |
Figure 1 SPD Parameter Explanation
Selection of UC and UT
The maximum continuous working voltage UC of SPD depends on the nominal voltage ( UO ) of AC network and distribution system ( TN, TT, IT ); The level of transient overvoltage UT is related to UC. Also, resistance to " high pressure" TOV ( 1200 Vac, 300 A, 200 ms ) is required between the neutral point of TT system and PE.
| AC system | 230/400Vac | ||
| Power distribution system | TT | TN | IT |
| UC Required Minimum | 255 | 255 | 440 |
| Transient overvoltage UT | 335/440 | 335/440 | - |
| Transient overvoltage N / PE | 1200 | - | - |
Figure 2
Selection of Iimp
The impulse current Iimp is defined for Class T1 SPD. According to IEC 60364 - 5 - 534, the minimum value of single stage Iimp is required to be 12.5 kA, which is defined according to actual application conditions. For T1 SPD, our company can provide 3 impulse current values Iimp: 12.5 kA, 25 Ka and 50 Ka.
| Condition | Iimp | Model |
| Very high risk areas | 50kA | MYCH50-AC T1 |
| Severe thunderstorm area | 25kA | MYCH25-AC T1 |
| High and low thunderstorm areas | 12.5kA | MYCH12.5-AC T1+T2 |
Figure 3
Selection of In
According to the standard requirements, the minimum In value of SPD at the facility inlet ( LPZ interface or equipment front end ) is 5kA ( 8 / 20 μ s waveform ), but higher nominal discharge current is recommended in high thunderstorm area, which can prolong the service life of SPD. Imax ( maximum discharge current ) is related to the In value.
| Condition | In | Model |
| Very high risk areas | >20kA | MYN60-AC T2 |
| Severe thunderstorm area | 10-20kA | MYN40-AC T2 MYN20-AC T2T3 |
| High and low thunderstorm areas | <5kA | - |
Figure 4
Selection of UP
The user must select the UP of the SPD that matches the rated impulse voltage withstand value (UW ) of the equipment. In general, the lower the UP, the better the protection.
According to IEC 60364, the voltage protection level of SPD at 230 / 400 Vac grid incoming line shall not be greater than 2.5 kV: this value also meets the requirements of rated impulse voltage tolerance ( UW ) of electromechanical equipment.
The interface of the electronic equipment has lower shock resistance and requires finer protection: SPD with UP not greater than 1.5kV is usually configured.
| Location | Recommended UP | |
| 230/400V AC network | 120/208VAC network | |
| Incoming line of main distribution | ≤2.5Kv max | ≤1.5Kv |
| Electrical equipment ( switchboards, etc. ) | 2.5Kv | 1.5Kv |
| Protected electronic equipment | 1.5Kv | 0.8kV |
Figure 5
SPD coordination
If the line distance between the protected equipment and the first stage SPD is long ( more than 10m ) or the protected instrument is too precise, the two-stage coordinated SPD can reduce the oscillation overvoltage generated during surge transmission. However, the minimum distance between two SPDs shall be greater than 5 m or a decoupling device shall be installed in the middle.
