The selection of rated voltage and insulation voltage for control cables should be based on the working conditions, environmental requirements, and safety regulations of the circuit. The core principle is to "match the rated voltage with long-term working requirements, and ensure that the insulation voltage covers the risk of short-term overvoltage". The specific selection method is as follows:
The rated voltage is the "upper limit" of the long-term operation of the cable, which needs to be directly matched with the control circuitActual working voltageAnd the system grounding method, the steps are as follows:
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Clarify the working voltage of the circuit
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AC 220V control circuit: Select cables with rated voltage ≥ 220V (such as 0.3/0.5kV, where U=0.5kV ≥ 220V);
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AC 380V control circuit: Select cables with rated voltage ≥ 380V (such as 0.45/0.75kV, U=0.75kV ≥ 380V);
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DC control circuit (such as 110V, 220V): Select according to the peak value of DC voltage (equivalent to 1.414 times the rated AC voltage). For example, a 220V DC circuit needs to be matched with a cable with a rated voltage ≥ 311V (220 × 1.414), usually 0.3/0.5kV is sufficient.
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Consider the grounding method of the system
The "U ₀" parameter of rated voltage is related to the system grounding method:
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Neutral point grounding system (such as low-voltage distribution system): U ₀ needs to be ≥ phase voltage (for example, the phase voltage of a 380V system is 220V, corresponding to U ₀ ≥ 220V, that is, U ₀=450V in 0.45/0.75kV is satisfied);
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Non grounded systems or ungrounded circuits: U ₀ must be ≥ line voltage (such as 380V ungrounded circuits, U ₀ must be ≥ 380V).
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Recommended values based on industry standards
There are default selection criteria for different scenarios, such as:
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Industrial control circuits (such as PLC and relay circuits): commonly used 0.3/0.5kV or 0.45/0.75kV;
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Control circuit of high-voltage equipment (such as 10kV switchgear): Due to the possibility of induced voltage, 0.6/1kV and above should be selected.
The insulation voltage is the "short-time maximum test voltage" that the cable insulation layer can withstand, and it needs to cover any possible system issuestemporary overvoltageThe selection criteria for operating overvoltage and lightning induced voltage are as follows:
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According to the overvoltage level of the system
The insulation voltage should be greater than or equal to the possible occurrence of the systemMaximum short-time overvoltage(Usually 1.5-2 times the rated voltage):
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Ordinary low-voltage control circuit (220V/380V): The overvoltage generally does not exceed 1kV, so the insulation voltage can be selected as 1kV;
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Control circuits near high-voltage equipment (such as 10kV transformers): may be affected by induced overvoltage, and insulation voltage should be selected at 2kV or above.
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Meet the insulation test requirements
Before leaving the factory, the cable needs to undergo an insulation withstand voltage test (such as power frequency withstand voltage for 1 minute), and the insulation voltage needs to match the test standard:
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Cable with rated voltage of 0.3/0.5kV: The insulation voltage is usually 1kV and needs to pass a 1kV withstand voltage test;
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Cables with a rated voltage of 0.6/1kV: The insulation voltage is usually 2kV and must pass a 2kV withstand voltage test.
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Consider the impact of environmental factors
Adverse environments such as high temperature, humidity, and corrosive environments can reduce insulation performance, and it is necessary to increase the insulation voltage margin appropriately
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Prioritize meeting industry standards
There are specific regulations in different fields (such as electricity, chemical industry, and construction), for example:
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Power system control cables: follow the "GB 50217-2018 Design Standard for Power Engineering Cables", which requires the rated voltage to be not lower than the circuit working voltage, and the insulation voltage to meet the system overvoltage level;
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Building electrical: Following the "GB 50054-2011 Code for Design of Low Voltage Distribution", it emphasizes that the insulation voltage should cover the short-term voltage during grounding faults.
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Avoid "excessive selection" or "insufficient selection"
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If the rated voltage is too high, it will increase costs (such as 0.6/1kV cables being more expensive than 0.3/0.5kV), while if it is too low, insulation aging may occur due to long-term overvoltage;
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Insufficient insulation voltage can cause breakdown and short circuit during overvoltage, while excessive voltage may result in material waste.
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Combining cable model and insulation material
The voltage resistance performance of different insulation materials (such as PVC, cross-linked polyethylene XLPE) varies. For example, XLPE has higher insulation strength than PVC. Under the same rated voltage, XLPE cables have a larger insulation voltage margin and can be prioritized for high temperature or high overvoltage risk scenarios.
This article is generated by AI