Surge Protector Parameter Selection

Publish Time: 12/02 2024 Author: Site Editor Visit: 86

2.1 Protection mode
SPD can be connected between L (phase line), N (neutral line), and PE (protective line), such as L 2L, L 2N, L 2PE, and N 2PE. These connection methods are related to the grounding type of the power supply system.
2.2 Maximum continuous working voltage Uc
The maximum root mean square voltage or DC voltage that may be continuously applied to both ends of the SPD is equal to the rated voltage of the SPD itself.
IEC6036452534 proposes that in the TT system, when the SPD is located on the power supply side of the residual current protector (RCD), U c≥1.1Uo; when the SPD is located on the load side of the residual current protector, U c≥1.5U o.
In TN and IT systems, U c≥1.1U o. The selection of Uc should take into account the horizontal fluctuation of the local power grid and the specific situation of the user's electricity consumption. It is not good to take a large value blindly, because if U c is large, the starting voltage of the entire varistor will also be high, and the surge voltage will cause damage to the equipment. International standards have a series of preferred values, which are related to the level of local power grids.
2.3 Lightning current Imax
Generally, a 10/350u s waveform and a current flow of ≥10KA per phase are selected at the junction of L PZ0 and L PZ1, and an 8/2 0u s waveform and a current flow of ≥5KA per phase are selected at the junction of L PZ1 and L PZ2. Since the energy of the 10/350u s waveform is 20 times greater than that of the 8/20u s, its current is 5 times greater. If an SPD with an 8/20u s waveform is used instead, its lightning current should be 5 times greater.
2.4 Protection level Up
This value should be greater than the maximum limiting voltage measured at the SPD terminal and consistent with the withstand voltage Uw of the equipment (1.2U p≤Uw). It can be selected from a series of reference values (such as 0108, 0109, ... 1, 1.2, 1.5, 1.8, 2, ... 8, 10KV, etc.). The better U p in the national standard is 800V and 900V.
2.5 Leakage current
Parallel SPD requires leakage current ≤30uA (Ministry of Public Security requires ≤20uA), and series SPD requires leakage current ≤01.mA.
2.6 Starting voltage Uas
In the past, it was believed that the starting voltage was the nominal varistor voltage. In fact, the current passing through the SPD may be much greater than the test current 1mA. At this time, the impact of the already elevated residual voltage on the equipment protection cannot be ignored. The time from varistor voltage to starting voltage (i.e., the response time of SPD) is relatively long, about 100ns. The higher the starting voltage, the higher the residual voltage, and the lower the voltage, the easier it is for the varistor to age. Its value should not be greater than the insulation level of the protected equipment.
2.7 Residual voltage Ures
It is the voltage actually applied to the port of the protected equipment. The lower the residual voltage, the better, and it should be less than the rated value of the impulse overvoltage withstand of the protected equipment. See Table 1:
Table 1220/380V three-phase system various equipment impulse overvoltage withstand rating Uw
2.8 Nominal discharge current In
It is used to classify SPD levels, with a discharge current of 8/20us or 10/350us simulating lightning current shock waves. Imax= 2~ 3 In.
2.9 Continuous working current Ic
The current flowing in the protection mode under the maximum continuous working voltage Uc is actually the sum of the currents flowing through each protection element and the internal auxiliary circuit connected in parallel with it. In order to avoid unnecessary action of overcurrent protection equipment or other protection equipment (such as RCD), the selection of Ic value is very useful. Under normal conditions, Ic should not cause any personal safety hazards (non-direct contact) or equipment failures (such as RCD). Generally, for RCD, Ic should be less than 1/3 of the rated residual voltage current value (I△n).
2.10 The above are several main parameters to consider when selecting SPD