Recently, many customers have been consulting Denor Customer Service about the key parameters of Surge Protective Devices (SPDs) and want to review the specific metrics for easily manufactured SPDs. It appears that people may still have limited understanding of the parameters marked on surge protectors. Today, a Denor technician will introduce some key parameters of easily manufactured Surge Protective Devices in this article.
1. Definition of Surge Protective Devices
A Surge Protective Device (SPD) is designed to limit transient overvoltage and to discharge surge current. It typically contains at least one nonlinear component.
2. Explanation of Key Parameters for Surge Protective Devices
- Single-Phase SPD: An SPD that is connected in parallel with the protected circuit. A single-phase SPD can separate the input and output ends, without special series impedance between these terminals.
- Two-Phase SPD: An SPD with two sets of input and output terminal connections that contain special series impedance between these terminals.
Figure 1-1: Interpretation of the Key Parameters of Easily Manufactured Surge Protective Devices
- Maximum Discharge Current (Imax): The peak value of current flowing through the SPD, based on an 8/20 microsecond waveform. This value is determined according to the second class load test procedure, ensuring that Imax is greater than the nominal discharge current (In).
- Nominal Discharge Current (In): The nominal discharge current characteristic defined during the second class test, represented by the peak value of current flowing through the SPD with an 8/20 waveform.
- Impulse Current (Iimp): Defined by three parameters: peak current (Ipeak), charge quantity (Q), and specific energy (W/R). Testing should follow the load action test procedures, aligned with SPD classification testing in the first level.
- Voltage Protection Level (Up): This parameter indicates the SPD’s performance in limiting voltage between its connection terminals. The value should be chosen from a priority value list and must exceed the maximum limiting voltage.
- Limiting Voltage (Um): The maximum voltage peak measured between SPD terminals when an impulse of a specified waveform and magnitude is applied.
- Maximum Continuous Operative Voltage (Uc): The maximum AC effective voltage or DC voltage that can continually be applied in the SPD protection mode. This value should significantly exceed the rated voltage (Un).
- Nominal System Voltage (Un): The nominal voltage relative to ground for the system.
- Transient Overvoltage Test Value (UT): This simulates the stress under TOV conditions, where a test voltage that adheres to the specified input is applied to the SPD for a defined duration (tT).
- Ingress Protection Rating (IP): The IP rating characterizes the degree of protection provided against the intrusion of solid foreign objects and water, especially concerning hazardous parts.
- Residual Voltage (Ures): The peak voltage across the SPD terminals when discharge current flows through it.
- Rated Short-circuit Current (ISCCR): Assesses the maximum expected short-circuit current rating for the SPD and the specified disconnection device in the power system.
- Follow Current (If): The current flowing into the SPD from the power system following an impulse discharge current.
As mentioned in IEC 61643-11, the following information should either be located directly on the SPD or permanently labeled on the body of the SPD:
- Manufacturer’s name or trademark and model.
- Maximum continuous operational voltage (Uc) for each protection mode.
- Type of current: AC or “~” and/or frequency.
- Voltage protection level (Up) for each protection mode.
- Ingress protection rating (when IP > 20).
- Manufacturer-declared test results for each protection mode:
- Class I Test: “Class I Test” and “Iimp” along with the value in kA, and/or “T1” (within a box) and “Imp” in kA.
- Class II Test: “Class II Test” and “In” in kA, and/or “T2” (within a box) and “In” in kA.
- Class III Test: “Class III Test” and “Uoc” in kV, and/or “T3” (within a box) and “Uoc” in kV.
By reading this, you should now have a better understanding of the parameters related to Surge Protective Devices. When selecting an SPD, it’s essential to grasp these key parameters to better match it with the circuit devices.
