1. System Characteristics Analysis
- Voltage level: Check the nominal voltage (Un) and maximum operating voltage (Uc) of the DC system being designed. The maximum continuous operating voltage (Uc) of the SPD must be higher than the system voltage.
- Example: For a 48 V DC system, the Uc of the SPD must be 48 V or higher.
- Surge current capacity: Determines the appropriate impulse current (Iimp, Type 1) or nominal discharge current (In, Type 2) depending on the type of SPD.
- Type 1: Direct lightning strike (10/350μs waveform, e.g. Iimp 10kA or more).
- Type 2: Indirect surge (8/20μs waveform, e.g. In 5kA~20kA).
- Short-circuit current rating (Isccr): Consider the expected short-circuit current of the system and check whether the SPD can withstand it.
2. Selecting SPD type and location
- Type 1 SPD: Installed at the main distribution board (e.g. power input terminal), handles high lightning current.
- Type 2 SPD: Installed near the sub-distribution board or load, indirect surge protection.
- Type 3 SPD: Installed near sensitive electronic equipment, provides micro-surge protection.
- The installation location must be connected to an equipotential grounding system and the grounding resistance must be low (e.g., less than 10Ω is recommended).
3. Linkage with OCPD
- OCPD Selection: Fuses or circuit breakers to be used with SPDs must comply with the maximum rating specified by the SPD manufacturer (e.g. 315A gG fuse).
- In DC systems, use DC-only OCPDs (e.g. DC fuses or MCBs, MCCBs, SCBs).
- The rating of OCPD is set to approximately 50% of the upper OCPD (within the maximum rating).
- Protection coordination: SPD and OCPD must cooperate so that only SPD is isolated in case of short circuit, and power supply to the upper system must be maintained.
- Some SPDs may have internal short-circuit protection and may not require a separate OCPD (check manufacturer datasheet).
4. Voltage protection level (Up)
- The voltage protection level (Up) of the SPD must be lower than the impulse withstand voltage (Uw) of the protected equipment.
- Example: If the equipment Uw is 2.0kV, the SPD Up is designed to be 1.8kV or less.
- Up is measured in surge current waveform (8/20μs or 10/350μs) test.
5. Environment and installation conditions
- Environmental resistance: SPDs must be suitable for the installation environment (temperature, humidity, dust, corrosion, etc.). For example, IP rating (e.g. IP20 indoors, IP43, IP65 outdoors).
- Cable length: Keep the connection cable between the SPD and the grounding system as short as possible (0.5 m or less recommended) to minimize inductance effects.
- Terminal connection: The polarity (+, -) of the DC system must be strictly observed, and the terminal connection must be solid.
6. Testing and Certification
- SPDs must be tested according to IEC 61643-41 (e.g. impulse current test, thermal stability test).
- The manufacturer must provide a technical data sheet specifying the performance data of the SPD (e.g. Iimp, In, Up, Uc).
- In the case of Korea, review compliance with KSC IEC 61643-41 and Electrical Installation Technology Standards (KEC).
7. Maintenance and condition monitoring
- SPDs must include indicators and IoT (e.g. visual indication or remote communication) to detect deterioration status.
- Establish a surge monitoring system and scientifically maintain and manage surge data using AI-based Big Data.
- Establish a regular inspection plan to check for any deterioration in SPD functionality.
Key Design Considerations
- Manufacturer Specifications*: Refer to datasheets from manufacturers such as Raycap, Hakel, Saltek, Phoenix Contact, DEHN, etc. to verify compatibility of SPD and OCPD.
- System integration: SPD design should be considered in an integrated manner with the entire electrical system (e.g. solar power system, communication facilities, railway system).
- Local regulations: Reflects the Korean Electrical Code (KEC) and regional lightning risk (e.g. KMA lightning data).
- Simulation: Verify SPD performance during the design phase using surge simulation software (e.g. PSpice, MATLAB).
Specific requirements
If you provide us with your specific system (e.g. solar, data center), SPD model name, and voltage/current specifications, we can provide more specific design guidance.